U.S. patent application number 14/443891 was filed with the patent office on 2015-10-15 for system and method for geothermal heat harvesting.
The applicant listed for this patent is AAVID THERMALLOY, LLC. Invention is credited to Randolph H. Cook, Jonathan James Hall, Sukhvinder S. Kang, Joseph Edward Nicolato.
Application Number | 20150292774 14/443891 |
Document ID | / |
Family ID | 49681245 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150292774 |
Kind Code |
A1 |
Kang; Sukhvinder S. ; et
al. |
October 15, 2015 |
System and method for geothermal heat harvesting
Abstract
A system and method for deploying a heat harvesting system and
for harvesting heat from a geothermal well using one or more heat
pipes. A heat exchanger may receive heat from one or more heat
pipes for transfer to a heat receiving component. The heat pipes
may be thermally coupled to the heat exchanger via a thermal gap
material having a relatively low thermal conductivity. A mounting
component may engage heat pipes and define a thermal gap between
the heat pipes and heat exchanger. A heat spreader, having a
relatively high thermal conductivity, may be used to transfer heat
from the heat pipes to the thermal gap material and help define a
working temperature for the heat pipes. A heat pipe deployment
system may include anti-buckling supports and/or a guide to help
keep the heat pipes from buckling and to guide the heat pipes into
corresponding well bores during deployment.
Inventors: |
Kang; Sukhvinder S.;
(Concord, NH) ; Cook; Randolph H.; (Gilford,
NH) ; Nicolato; Joseph Edward; (Virginia Beach,
VA) ; Hall; Jonathan James; (Gilmanton, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AAVID THERMALLOY, LLC |
Laconia |
NH |
US |
|
|
Family ID: |
49681245 |
Appl. No.: |
14/443891 |
Filed: |
November 21, 2013 |
PCT Filed: |
November 21, 2013 |
PCT NO: |
PCT/US2013/071149 |
371 Date: |
May 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61788074 |
Mar 15, 2013 |
|
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|
61728849 |
Nov 21, 2012 |
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Current U.S.
Class: |
165/45 ;
165/104.21 |
Current CPC
Class: |
F24T 10/40 20180501;
F24T 10/17 20180501; F24T 2010/53 20180501; Y02E 10/10 20130101;
F24T 10/30 20180501 |
International
Class: |
F24J 3/08 20060101
F24J003/08 |
Claims
1. A geothermal heat harvesting system, comprising: a heat
exchanger arranged to receive heat from a geothermal well for
transfer to a heat receiving component; and one or more heat pipes
arranged in the well to transfer heat from the well to the heat
exchanger, the one or more heat pipes each having an evaporator
section positioned within the geothermal well and distant from the
heat exchanger and a condenser section positioned adjacent the heat
exchanger.
2. The system of claim 1, further comprising: a thermal gap
material positioned in a thermal gap between the condenser section
of the one or more heat pipes and the heat exchanger, the thermal
gap material providing a thermal coupling between the one or more
heat pipes and the heat exchanger such that a desired temperature
drop is achieved between the one or more heat pipes and the heat
exchanger when heat is transferred via the thermal gap material,
the thermal gap material having a thermal conductivity less than
about 12 W/m-K.
3. The system of claim 2, wherein a conduction length of the
thermal gap and the thermal conductivity of the thermal gap
material are arranged to define a working temperature for the at
least one heat pipe.
4. The system of claim 2, wherein the thermal gap material includes
liquid water or geothermal brine and has a thermal conductivity of
about 0.6 W/m-K.
5. The system of claim 2, further comprising a heat spreader
between the one or more heat pipes and the thermal gap material and
that is in direct thermal contact with the one or more heat pipes
and the thermal gap material.
6. The system of claim 5, wherein the heat spreader is metal and/or
has thermal conductivity over 12 W/m-K.
7. The system of claim 5, wherein the heat spreader includes a
sleeve positioned over the heat pipe.
8. The system of claim 5, wherein the heat spreader has a
cylindrical shape, a partial cylindrical shell configuration, is a
sleeve and/or is a plate.
9. The system of claim 1, wherein the one or more heat pipes
includes a plurality of heat pipes that are arranged around the
heat exchanger at a vertical level in the well.
10. The system of claim 9, wherein the one or more heat pipes
includes a plurality of heat pipes that are arranged around the
heat exchanger at multiple vertical levels in the well.
11. The system of claim 1, wherein the one or more heat pipes each
have a length of 40 to 300 feet.
12. The system of claim 1, wherein the condenser section of the
heat pipes is aligned along a length of the heat exchanger.
13. The system of claim 1, wherein the condenser section of the
heat pipes is uniformly spaced from the heat exchanger along a
length of the condenser section of 2 to 20 feet.
14. The system of claim 1, wherein the evaporator section of the
one or more heat pipes extends radially away from the heat
exchanger from 20 to 300 feet.
15. The system of claim 1, further comprising a collar engaged to
the one or more heat pipes, the collar configured to receive the
heat exchanger at an inner side of the collar and to position the
one or more heat pipes from the heat exchanger so as to define a
thermal gap between the one or more heat pipes and the heat
exchanger.
16. The system of claim 1, further comprising a heat receiving
component that includes a heat exchange fluid, one or more conduits
to conduct a heat exchange fluid, a thermal storage device, a
thermal storage medium, and/or one or more thermoelectric or other
power conversion devices.
17. The system of claim 1, wherein the one or more heat pipes
includes a thermosiphon, a loop thermosiphon, a pulsating heat
pipe, and/or an osmotic heat pipe.
18. A heat pipe and mounting component apparatus for use with a
heat exchanger in harvesting geothermal heat, comprising: one or
more heat pipes each having two end portions and an elongated
central portion; and a mounting component arranged and dimensioned
to engage with an end portion of the one or more heat pipes and to
position the end portion within a specified distance of a perimeter
of the heat exchanger to define a thermal gap between the one or
more heat pipes and the heat exchanger to be filled by a thermal
gap material that thermally couples the one or more heat pipes to
the heat exchanger.
19. The apparatus of claim 18, further comprising the thermal gap
material positioned in the gap between, and thermally coupling, the
heat exchanger and the one or more heat pipes.
20. The apparatus of claim 19, wherein a size of the gap and a
thermal resistance of the thermal gap material are configured to
permit the one or more heat pipes to operate at an optimal heat
pipe working temperature for use in harvesting geothermal
energy.
21. The apparatus of claim 20, wherein the optimal heat pipe
working temperature is higher than the temperature of the heat
exchanger by an amount between 10% and 40% of the temperature
difference from the heat exchanger to the geothermal resource.
22. The apparatus of claim 18, wherein the thermal gap material has
a thermal conductivity of 0.5 to 12 W/m-K that is less than a
thermal conductivity of the mounting component.
23. The apparatus of claim 18, wherein the mounting component has a
contact area with the one or more heat pipes and a thermal
conductivity selected to promote heat spreading from the one or
more heat pipes that are thermally coupled to the mounting
component.
24. The apparatus of claim 23, further comprising the thermal gap
material which includes water.
25. The apparatus of claim 18, wherein the mounting component has a
surface area facing the heat exchanger that is larger than a
surface area presented by the at least one heat pipe to the heat
exchanger.
26. The apparatus of claim 25, wherein the surface area of the
mounting component facing the heat exchanger is at least 1 to 10
times the surface area presented by the at least one heat pipe to
the heat exchanger.
27. The apparatus of claim 18, wherein the mounting component
includes a collar arranged to extend around the perimeter of the
heat exchanger, the collar including a plurality of spacer elements
extending radially inwardly from the collar to define, at least in
part, the gap between the one or more heat pipes and the heat
exchanger.
28. The apparatus of claim 18, wherein the mounting component
includes an upper collar and a lower collar, the upper and lower
collars being spaced from each other and having the one or more
heat pipes fixed to the upper and lower collar and arranged to
define a gap between the one or more heat pipes and the heat
exchanger in areas between the upper and lower collars.
29. The apparatus of claim 28, further comprising an anti-buckling
support engaged with the one or more heat pipes below the lower
collar and arranged to move relative to the one or more heat pipes
in the presence of a force over a threshold.
30. The apparatus of claim 18, wherein the one or more heat pipes
each include an evaporator section and a condenser section, the one
or more heat pipes being thermally coupled with the mounting
component at the condenser section.
31. The apparatus of claim 18, further comprising a heat exchanger
positioned adjacent the mounting component, wherein the thermal gap
is present between the heat exchanger and the mounting
component.
32. The apparatus of claim 31, further comprising a thermal gap
material positioned between the mounting component and the heat
exchanger, the thermal gap material having a thermal conductivity
that is less than a thermal conductivity of the mounting
component.
33. The apparatus of claim 32, wherein the thermal gap material
includes liquid water.
34. The apparatus of claim 18, further comprising a heat pipe guide
including a guide channel to guide movement of a heat pipe into a
bore in a geothermal well.
35. A geothermal heat harvesting system, comprising: a heat
exchanger arranged to transfer heat from a geothermal well to a
heat receiving component; one or more heat pipes arranged in the
well to transfer heat from the well to the heat exchanger, the one
or more heat pipes having an evaporator section and a condenser
section; and a thermal gap material positioned in a thermal gap
between the one or more heat pipes and the heat exchanger, the
thermal gap material providing a thermal coupling between the one
or more heat pipes and the heat exchanger such that more than 60%
of heat transferred between the one or more heat pipes and the heat
exchanger is transferred via the thermal gap material, the thermal
gap material having a thermal conductivity less than about 12
W/m-K.
36. The system of claim 35, wherein a conduction length of the
thermal gap and the thermal conductivity of the thermal gap
material are arranged to define a working temperature for the at
least one heat pipe.
37. The system of claim 36, wherein the thermal gap material
includes liquid water and has a thermal conductivity of about 0.6
W/m-K.
38. The system of claim 35, further comprising a heat spreader
between the at least one heat pipe and the thermal gap material and
that is in direct thermal contact with the at least one heat pipe
and the thermal gap material.
39. The system of claim 38, wherein the heat spreader is metal
and/or has thermal conductivity over 12 W/m-K.
40. The system of claim 39, wherein the heat spreader includes a
sleeve positioned over the heat pipe.
41. The system of claim 38, wherein the heat spreader has a
cylindrical shape, a partial cylindrical shell configuration, is a
sleeve and/or is a plate.
42. The system of claim 35, wherein the heat receiving component
includes a heat exchange fluid, one or more conduits to conduct a
heat exchange fluid, a thermal storage device, a thermal storage
medium, and/or one or more thermoelectric or other power conversion
devices.
43. The system of claim 35, wherein the heat pipe includes a
thermosiphon, a loop thermosiphon, a pulsating heat pipe, osmotic
heat pipe and/or other possible specific configurations driven by
other forces such as electro-osmotic, acoustic, electrical, and/or
magnetic.
44. A method for deploying a thermal coupling for a geothermal
device, comprising: providing a heat exchanger in a geothermal
well; providing one or more heat pipes in the geothermal well, each
of the heat pipes including a condenser section located nearer the
heat exchanger than an evaporator section of the heat pipe; and
providing a thermal gap material that extends between, and
thermally couples, the one or more heat pipes and the heat
exchanger such that more than 60% of heat transferred between the
one or more heat pipes and the heat exchanger is transferred via
the thermal gap material, the thermal gap material having a thermal
conductivity less than about 12 W/m-K.
45. The method of claim 44, wherein a conduction length of the
thermal gap and the thermal conductivity of the thermal gap
material are arranged to define a working temperature for the at
least one heat pipe.
46. The method of claim 44, wherein the thermal gap material
includes liquid water and has a thermal conductivity of about 0.6
W/m-K.
47. The method of claim 44, further comprising providing a heat
spreader between the at least one heat pipe and the thermal gap
material and that is in direct thermal contact with the at least
one heat pipe and the thermal gap material.
48. The method of claim 47, wherein the heat spreader is metal
and/or has thermal conductivity over 12 W/m-K.
49. The method of claim 48, wherein the heat spreader includes a
sleeve positioned over the heat pipe.
50. The method of claim 47, wherein the heat spreader has a
cylindrical shape, a partial cylindrical shell configuration, is a
sleeve and/or is a plate.
51. The method of claim 44, further comprising transferring heat
from the heat exchanger to a heat receiving component that includes
a heat exchange fluid, one or more conduits to conduct a heat
exchange fluid, a thermal storage device, a thermal storage medium,
and/or one or more thermoelectric or other power conversion
devices.
52. The method of claim 44, wherein the one or more heat pipes
includes a thermosiphon, a loop thermosiphon, a pulsating heat
pipe, and/or an osmotic heat pipe.
53. A heat pipe and mounting component apparatus for use with a
heat exchanger in harvesting geothermal heat, comprising: one or
more heat pipes each having two end portions and an elongated
central portion; an upper collar arranged and dimensioned to engage
with an end portion of the one or more heat pipes and to position
the end portion within a specified distance of a perimeter of the
heat exchanger located inside of the collar to define a thermal gap
between the one or more heat pipes and the heat exchanger; and an
anti-buckling portion separate from the upper collar and attached
to the one or more heat pipes at a location below and away from the
upper collar, the anti-buckling portion being releasably attached
to the one or more heat pipes to allow movement of the one or more
heat pipes relative to the anti-buckling portion in a direction
along a length of the one or more heat pipes.
54. The system of claim 53, wherein the anti-buckling portion is
attached to the one or more heat pipes by a frangible connection,
such as a metallurgical joint or adhesive, that fixes the heat
pipes relative to the anti-buckling portion until a force applied
to the one or more heat pipes exceeds a threshold value.
55. The system of claim 54, wherein the frangible connection fixes
the anti-buckling portion relative to the heat pipes and the upper
collar until a force moving the upper collar toward the
anti-buckling portion exceeds the threshold value.
56. The system of claim 53, wherein the upper collar and the
anti-buckling portion are movable toward each other so as to
contact each other.
57. The system of claim 56, further comprising a lower guide
portion that includes one or more heat pipe guides arranged to
guide the one or more heat pipes in deployment in the geothermal
well in directions away from the heat exchanger.
58. The system of claim 57, wherein the anti-buckling portion is
positioned between the upper collar and lower guide portion, and
the upper collar is movable toward the lower guide portion to
deploy the one or more heat pipes in the well.
59. The system of claim 58, further comprising a lower collar
engaged with the one or more heat pipes at a location below the
upper collar and above the anti-buckling portion.
60. The system of claim 53, wherein the upper collar and/or the
anti-buckling portion include two parts that are engagable with
each other so as to receive a drill string or a portion of the heat
exchanger between the two parts.
61. The system of claim 53, wherein the heat pipe includes a
thermosiphon, a loop thermosiphon, a pulsating heat pipe, and/or
osmotic heat pipe.
62. A method for deploying one or more heat pipes in a geothermal
well for use with a heat exchanger in harvesting geothermal heat,
comprising: providing one or more heat pipes each having a first
portion engaged with an upper collar and a second portion engaged
with an anti-buckling portion separate from the upper collar and
attached to the one or more heat pipes at a location below the
upper collar and above a distal end of the one or more heat pipes;
inserting the distal end of the one or more heat pipes into a
corresponding well bore; exerting a force on the one or more heat
pipes so as to disengage the one or more heat pipes from the
anti-buckling portion and allow the one or more heat pipes to move
in a direction along a length of the one or more heat pipes
relative to the anti-buckling portion; and arranging the upper
collar adjacent a heat exchanger in the geothermal well.
63. The method of claim 62, wherein the anti-buckling portion is
releasably attached to the one or more heat pipes by a frangible
connection.
64. The method of claim 62, wherein the step of arranging the upper
collar includes positioning a portion of the one or more heat pipes
within a specified distance of a perimeter of the heat exchanger to
define a thermal gap between the one or more heat pipes and the
heat exchanger.
65. The method of claim 62, further comprising providing a lower
guide portion that includes one or more heat pipe guides arranged
to guide the one or more heat pipes in deployment in the geothermal
well in directions away from the heat exchanger; and using the
lower guide to guide movement of the one or more heat pipes into
respective bores during the inserting step.
Description
BACKGROUND
[0001] Harvesting of heat energy from a geothermal well (i.e., an
underground region) can be useful for various purposes, including
electrical energy generation, transferring heat to above ground
systems for use in space heating, industrial or other processes, or
other uses.
SUMMARY OF INVENTION
[0002] Aspects of the invention provide for heat harvesting from a
geothermal well (i.e., an underground region) using one or more
heat pipes. In some embodiments, one or more heat pipes may be
arranged in a tree-type or other configuration and used to transfer
heat from portions of the geothermal well to a heat exchanger and a
heat receiving component, such as a heat exchange liquid, a
thermoelectric device, or other component that receives heat, e.g.,
for use in generating electricity.
[0003] In one aspect of the invention, a geothermal heat harvesting
system includes a heat exchanger arranged to receive heat from a
geothermal well for transfer to a heat receiving component. The
heat exchanger may include a cylindrical body or pipe that receives
heat at its outer wall and transfers that heat to a working fluid,
such as water or steam, in the heat exchanger. The heated fluid may
be conducted out of the heat exchanger to a heat receiving
component such as a thermal storage device, a thermal storage
medium, and/or one or more thermoelectric or other power conversion
devices, such as a steam turbine and generator.
[0004] One or more heat pipes may be arranged in the well to
transfer heat from the well to the heat exchanger, e.g., heat pipes
may be arranged around the heat exchanger and extend outwardly from
the heat exchanger into hot rock or other medium of the geothermal
well. The heat pipes may be arranged in one or more levels, e.g., a
plurality of heat pipes may be arranged around the heat exchanger
and extend radially into the geothermal well (e.g., 20 to 100 feet)
at one or more vertical positions in the well. The one or more heat
pipes may each have an evaporator section positioned within the
geothermal well and distant from the heat exchanger, and a
condenser section positioned adjacent the heat exchanger. Thus,
heat received at the evaporator section may be transferred to the
condenser section, which relays the heat to the heat exchanger. The
heat pipes may be arranged in any suitable way, and may include a
thermosiphon, a loop thermosiphon, a pulsating heat pipe, and/or an
osmotic heat pipe. The heat pipes may have a length of 40 to 120
feet (or other suitable length such as up to 300 feet), and may
have the condenser section aligned along a length of the heat
exchanger. For example, the condenser section of the heat pipes may
be uniformly spaced from the heat exchanger along a length of the
condenser section of 2 to 20 feet. Thus, portions of the condenser
section may be spaced from the heat exchanger to achieve a defined
thermal gap or thermal resistance which helps to control the heat
transfer rate between the heat pipes and the heat exchanger,
allowing the heat pipe to operate at an optimal or other designed
working temperature.
[0005] In some embodiments, a thermal gap material may be
positioned in a thermal gap between the condenser section of the
one or more heat pipes and the heat exchanger. The thermal gap
material may provide a thermal coupling between the one or more
heat pipes and the heat exchanger such that a desired temperature
drop is incurred when heat is transferred between the one or more
heat pipes and the heat exchanger via the thermal gap material. The
thermal gap material may have a relatively low thermal
conductivity, e.g., less than about 12 W/m-K or around 0.6 W/m-K,
so as to meter heat transferred to the heat exchanger in comparison
to a condition in which the heat pipe(s) are coupled to the heat
exchanger by a steel or other relatively highly thermally
conductive metal connection. A conduction length of the thermal gap
and the thermal conductivity of the thermal gap material may be
arranged to define a working temperature for the at least one heat
pipe, which may be elevated above the operating temperature of the
heat exchanger by 10 to 40% of the temperature difference between
the heat exchanger and the geothermal resource and may allow the
heat pipe(s) to harvest heat from the geothermal resource more
efficiently than at lower temperatures. A majority of heat
transferred between the heat pipe(s) and the heat exchanger may be
transferred through the thermal gap material, e.g., 60%, 70%, 90%,
95% or more of heat transferred between the two may be transmitted
through the thermal gap material.
[0006] In some embodiments, a heat spreader may be provided between
the at least one heat pipe and the thermal gap material to help
transfer heat from the heat pipe to the thermal gap material. Thus,
the heat spreader may have a relatively high thermal conductivity,
e.g., above 12 W/m-K, and be in direct thermal contact with the at
least one heat pipe and with the thermal gap material. While the
heat spreader may be arranged in different ways, the heat spreader
may generally present a relatively smaller surface area to the heat
pipe(s) for receiving heat and a relatively larger surface area to
the thermal gap material. For example, the heat spreader may
include a sleeve positioned over the heat pipe, and/or may include
a plate with a partial cylindrical shell configuration that
generally conforms to the outer periphery of a heat exchanger. The
heat spreader may therefore effectively increase a surface area of
the heat pipes for transferring heat to the thermal gap
material.
[0007] In some embodiments, the heat pipe(s) may be mechanically
coupled by a collar or other mounting component which also helps
define the thermal gap between the heat pipe(s) and the heat
exchanger. For example, a collar may engage with one or more heat
pipes and be configured to receive the heat exchanger at an inner
side of the collar, i.e., the collar may extend around the heat
exchanger. The collar may help to position the one or more heat
pipes from the heat exchanger so as to define a thermal gap, e.g.,
one or more spacer elements such as protrusions extending radially
inwardly from the collar inner side may help maintain a desired
distance between the heat pipe(s) and the heat exchanger. Two or
more relatively short collars (e.g., 1 to 2 feet long, or more or
less) may be employed, and may be spaced from each other along the
condenser section of one or more heat pipes, e.g., at a distance of
10 to 20 feet or more (or less), so that portions of the heat pipes
extending between the collars are suitably positioned from the heat
exchanger to define a thermal gap. Alternately, a collar may have a
relatively long length, e.g., of 10 to 20 feet or more (or less),
and be arranged as a solid cylindrical shell, e.g., to control
fluid flow in the thermal gap between the heat pipes and the heat
exchanger along the length of the shell. In some embodiments, the
collar may include one or more openings in the shell to permit
fluid flow, e.g., to allow relatively hot fluid in the geothermal
well to flow into the space between the collar and the heat
exchanger and allow relatively cool fluid to exit. A collar or
other mounting component may, or may not function as a heat
spreader.
[0008] In one aspect of the invention, a heat pipe and mounting
component apparatus for use with a heat exchanger in harvesting
geothermal heat includes one or more heat pipes each having two end
portions and an elongated central portion, and a mounting component
dimensioned to engage and thermally couple with at least one heat
pipe at or near one of the said end portions. The mounting
component may be dimensioned to extend at least partially around a
portion of a perimeter of the heat exchanger. For example, the
mounting component may include a collar or sleeve arranged to
receive a portion of a heat exchanger in the central opening of the
collar, and/or may include a shoe or plate that extends around only
a part of the heat exchanger. The portion of the mounting component
that faces the heat exchanger may be shaped to generally conform to
the shape of an adjacent portion of the heat exchanger, e.g., so
that a generally uniform gap may be present between the mounting
component and the heat exchanger. As will be understood by those of
skill in the art, a uniform gap may provide for a uniform
conduction length for heat passing between the mounting component
and the heat exchanger, and thus uniform and predictable heat
flow.
[0009] An interface material, or thermal gap material, may be
positioned between, and thermally couple, the heat exchanger and
the mounting component. The interface material may have a thermal
conductivity that is less than the mounting component, and thus may
provide a desired thermal gap or resistance to heat flow, e.g., to
allow the one or more heat pipes to operate within an optimal
working temperature range. As discussed in detail below, having a
heat pipe operate in an optimal working temperature range may allow
for more efficient heat harvesting. Thus, the thermal conductivity
of the interface material may be selected to define an optimal heat
pipe working temperature for use in harvesting geothermal energy,
e.g., may be 0.5 to 12 W/m-K. Other characteristics of the thermal
coupling of the heat pipe(s) to the heat exchanger, such as the
surface area of the mounting component that faces the heat
exchanger and the conduction length of the thermal gap, may be
similarly selected to define, or otherwise be consistent with, an
optimal heat pipe working temperature. In some embodiments, the
optimal heat pipe working temperature may be higher than the
temperature of the heat exchanger by an amount between 10% and 40%
of the temperature difference between the heat exchanger and the
geothermal resource. In contrast to the thermal gap material, the
mounting component may have a relatively high thermal conductivity
that is selected to promote heat spreading from the one or more
heat pipes for transfer to the thermal gap material. As a result, a
surface area of contact between the thermal gap material and the
mounting component, and the thermal conductivity and thickness of
the thermal gap material may be the primary controlling factors in
defining a working temperature of the one or more heat pipes
thermally coupled to the mounting component.
[0010] A surface area of the mounting component that faces the heat
exchanger may define the surface area of contact between the
thermal gap material and the mounting component, and so may help
define heat flow characteristics of the heat pipe/heat exchanger
thermal junction. In some embodiments, the mounting component may
have a surface area facing the heat exchanger (i.e., a surface area
that functions to transfer a majority of heat to the heat
exchanger) that is larger than a surface area presented by the at
least one heat pipe to the heat exchanger. That is, the mounting
component may present a larger surface area for heat transfer to
the heat exchanger than the heat pipe(s) would present in the
absence of the mounting component. Such an arrangement may allow
for higher heat flow rates, and/or better control over the heat
flow rate of the thermal junction. In one embodiment, the surface
area of the mounting component facing the heat exchanger may be at
least 1 to 10 times the surface area presented by the at least one
heat pipe to the heat exchanger.
[0011] The mounting component may also function to help deploy one
or more heat pipes in a well and/or perform other functions. For
example, the mounting component may include an upper collar portion
and a lower collar portion, with the upper collar portion having
one or more heat pipes fixed to the upper collar portion and the
lower collar portion defining a heat pipe guide feature to receive
at least one heat pipe that is fixed to the upper collar portion.
The heat pipe(s) may move in a sliding relationship in the guide
feature as the upper collar portion is moved toward the lower
collar portion, e.g., to help guide the heat pipe(s) into side
holes formed from a main well as the heat pipes are lowered into
the main well bore.
[0012] In another aspect of the invention, a heat pipe and mounting
component apparatus for use with a heat exchanger in harvesting
geothermal heat includes one or more heat pipes each having two end
portions and an elongated central portion, and a mounting component
arranged and dimensioned to engage with an end portion of the one
or more heat pipes and to position the end portion within a
specified distance of a perimeter of the heat exchanger to define a
thermal gap between the one or more heat pipes and the heat
exchanger. The thermal gap may be filled by a thermal gap material
that thermally couples the one or more heat pipes to the heat
exchanger. The thermal gap material may have a thermal conductivity
of 0.5 to 12 W/m-K that is less than the heat pipes, mounting
component or heat exchanger outer surface, e.g., the thermal gap
material may be water (including brine or water containing a
variety of dissolved minerals and other substances) or a thermal
grout, such as a cement-like substance with an engineered thermal
conductivity. The mounting component may, or may not assist in
transferring heat to the heat exchanger, e.g., may play a minor
role in actual heat transfer. For example, a majority of heat
transferred from a heat pipe to the heat exchanger may occur along
portions of the heat pipe where no mounting component, heat
spreader or other structure is located. In one embodiment, the
mounting component includes an upper collar and a lower collar
which are fixed to a set of heat pipes and are spaced from each
other. Thus, an exposed portion of the heat pipes may extend
between the collars and be spaced from the heat exchanger by a
desired thermal gap. A bulk of heat transferred from the heat pipes
to the heat exchanger may occur along the exposed heat pipe
sections extending between the collars. In some embodiments, a heat
spreader in the form of a sleeve may be arranged around the heat
pipes, e.g., the heat pipes may include two concentric tubes with
the outer tube functioning as a heat spreader.
[0013] In another aspect of the invention, a heat pipe deployment
system may include one or more anti-buckling supports to assist in
inserting one or more heat pipes in a geothermal well. For example,
a geothermal well may be prepared for deployment of heat pipes by
drilling or otherwise forming bores that extend radially outwardly
from a main well bore. These bores may each receive at least one
corresponding heat pipe, which is inserted into the bore from the
main well bore and may have a length of 100 feet or more. To assist
in inserting the heat pipe(s) into corresponding radial bores, one
or more anti-buckling supports may be engaged with the heat pipe(s)
to help keep the heat pipe(s) relatively straight when an axial
load is applied to the pipe(s) to push the pipe(s) into the
bore(s). The anti-buckling supports may disengage from the heat
pipe(s) under particular conditions, such as when an axial force on
the heat pipe(s) relative to the support exceeds a threshold. Thus,
the anti-buckling supports may release from the heat pipes to allow
their further insertion into a bore.
[0014] The system may additionally, or alternately include a heat
pipe guide, or "kicker," that helps to guide the heat pipe(s) into
their respective bore. For example, the heat pipe guide may be
arranged in the main well bore and include a flared or curved guide
channel for one or more heat pipes. The guide channel may engage a
heat pipe, e.g., at the distal end, and guide the heat pipe into a
radially extending bore. The heat pipe guide may also be used to
guide a tool that forms radially extending heat pipe bores, such as
a rotary drilling tool, high pressure jet device, etc.
[0015] Thus, in one aspect of the invention, a heat pipe and
mounting component apparatus for use with a heat exchanger in
harvesting geothermal heat may include one or more heat pipes each
having two end portions and an elongated central portion and an
upper collar engaged with an end portion of the one or more heat
pipes. An anti-buckling support, separate from the upper collar,
may be attached to the one or more heat pipes at a location below
and away from the upper collar. The anti-buckling support may be
releasably attached to the one or more heat pipes to allow movement
of the one or more heat pipes relative to the anti-buckling portion
in a direction along a length of the one or more heat pipes, e.g.,
in response to an axial force on the heat pipe(s) relative to the
anti-buckling support that exceeds a threshold.
[0016] In some embodiments, the anti-buckling support is attached
to the one or more heat pipes by a frangible connection, such as a
metallurgical joint or adhesive, that fixes the heat pipes relative
to the anti-buckling portion until a force applied to the one or
more heat pipes exceeds a threshold value. The frangible connection
may fix the anti-buckling support relative to the heat pipes and
the upper collar until a force moving the upper collar toward the
anti-buckling portion exceeds the threshold value. For example, as
a force is applied to the upper collar and/or heat pipes to push
the heat pipes downwardly and into respective radial bores, the
heat pipes and attached anti-buckling support may move downwardly
together. However, at a specified point, such as where the
anti-buckling support reaches the radial bores, the anti-buckling
support may disengage from the heat pipes. In some embodiments,
when the anti-buckling support disengages from the heat pipe(s),
the anti-buckling portion may slide along the heat pipes such that
the upper collar and anti-buckling portion move toward each other.
In other embodiments, the anti-buckling portion may completely
detach from the heat pipes.
[0017] In some embodiments, a lower heat pipe guide portion may
also be provided which includes one or more heat pipe guides
arranged to guide the one or more heat pipes in deployment in the
geothermal well in directions away from the heat exchanger. For
example, the anti-buckling portion may be positioned between the
upper collar and lower guide portion, and the upper collar may be
movable toward the lower guide portion to deploy the one or more
heat pipes in the well, e.g., into radially extending bores from a
main well bore. As noted above, two or more collars may be engaged
with the heat pipes at an upper end, e.g., a lower collar may be
engaged with the one or more heat pipes at a location below the
upper collar and above the anti-buckling support. In some
embodiments, the upper and/or lower collars, the anti-buckling
support and/or the lower heat pipe guide may include two or more
parts that are engagable with each other so as to receive a drill
string or a portion of the heat exchanger between the two parts.
For example, the components may be arranged in a clam shell or
other configuration so that the components can be assembled over
and around an existing drill string at the surface of the well.
[0018] In another aspect of the invention, a method for deploying
one or more heat pipes in a geothermal well for use with a heat
exchanger in harvesting geothermal heat includes providing one or
more heat pipes each having a first portion engaged with an upper
collar and a second portion engaged with an anti-buckling portion
separate from the upper collar and attached to the one or more heat
pipes at a location below the upper collar and above a distal end
of the one or more heat pipes. The distal end of the one or more
heat pipes may be inserted into a corresponding well bore, e.g., a
bore that extends radially from a main well bore, and a force may
be exerted on the one or more heat pipes so as to disengage the one
or more heat pipes from the anti-buckling support. For example, the
heat pipes may be forced downwardly into the main well bore such
that the distal ends of the heat pipes move into a radially
extending bore. The anti-buckling support may help keep the heat
pipes generally straight in the main well bore (e.g., prevent
buckling) until a certain point, such as when the anti-buckling
support reaches a point where the heat pipes exit the main well
bore and enter a radially extending bore. At this point, the heat
pipes may detach from the anti-buckling support, allowing the one
or more heat pipes to move in a direction along a length of the one
or more heat pipes relative to the anti-buckling portion. The upper
collar may be arranged adjacent a heat exchanger in the geothermal
well, e.g., to position a condenser portion of the one or more heat
pipes at a desired distance from the heat exchanger and thereby
establish a desired thermal gap.
[0019] In another aspect of the invention, a geothermal heat
harvesting system includes a heat exchanger arranged to transfer
heat from a geothermal well to a heat receiving component, one or
more heat pipes arranged in the well to transfer heat from the well
to the heat exchanger, the one or more heat pipes having an
evaporator section and a condenser section, a heat spreader in
direct thermal contact with the condenser section of at least one
heat pipe, and a thermal gap material positioned in a thermal gap
between the heat spreader and the heat exchanger. The heat spreader
may have a surface area and a first thermal conductivity, and the
thermal gap material may have a second thermal conductivity that is
less than the first thermal conductivity. As discussed above, a
surface area of the heat spreader that functions to transfer a
majority of heat to the heat exchanger, along with the thermal
conductivity of the thermal gap material and a thickness of the
thermal gap material (which defines the conduction length for heat
moving between the heat spreader and the heat exchanger) may define
a working temperature for the one or more heat pipes. In one
embodiment, the heat spreader is metal and/or has thermal
conductivity over 12 W/m-K, and the thermal gap material has a
thermal conductivity of 0.5 to 12 W/m-K. The heat spreader may have
a cylindrical shape, a partial cylindrical shell configuration,
include a sleeve and/or a plate, etc., and may have a surface
contour arranged to generally conform to a surface contour of a
heat exchanger portion with which the heat spreader is thermally
coupled. This arrangement may help define a uniform thermal gap
between the heat spreader and the heat exchanger.
[0020] The geothermal heat harvesting system may be employed for
any suitable purpose, e.g., the heat receiving component may
include a heat exchange fluid, one or more conduits to conduct a
heat exchange fluid, a thermal storage device, a thermal storage
medium, and/or one or more thermoelectric or other power conversion
devices. Also, heat pipes used in this or other embodiments may
include a thermosiphon, a loop thermosiphon, a pulsating heat pipe,
osmotic heat pipe and/or other possible specific configurations
driven by other forces such as electro-osmotic, acoustic,
electrical, and/or magnetic.
[0021] In another aspect of the invention, a method for deploying a
thermal coupling for a geothermal device includes providing a heat
exchanger in a geothermal well, providing one or more heat pipes in
the geothermal well, each of the heat pipes including a condenser
section located nearer the heat exchanger than an evaporator
section of the heat pipe, providing a heat spreader thermally
coupled to the condenser section of at least one heat pipe, the
heat spreader having a first thermal conductivity, and providing a
thermal gap material that extends between, and thermally couples,
the heat spreader and the heat exchanger, the thermal gap material
having a second thermal conductivity that is less than the first
thermal conductivity. Components of the system, such as the heat
spreader, thermal gap material, etc., may have any of those
features described herein.
[0022] In yet another aspect of the invention, a method for
designing a geothermal heat harvesting system includes determining
an optimal working temperature range for one or more heat pipes
used to transfer heat from portions of a geothermal well to a heat
exchanger, determining a first surface area of a heat spreader to
be thermally coupled to the heat exchanger based on the optimal
working temperature range, the heat spreader being designed to
provide heat to the heat exchanger via a thermal gap material
having a thermal conductivity that is less than the heat spreader,
and providing the heat spreader having the first surface area. The
thermal conductivity of the thermal gap material and/or the
thickness of the thermal gap material may also be determined based
on the optimal working temperature range. In one embodiment, an
optimal working temperature range may be determined by modeling
fluid flow in the geothermal well in response to heat removal by
the one or more heat pipes from portions of the geothermal
well.
[0023] These and other aspects of the invention will be apparent
from the following description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Aspects of the invention are described with reference to the
following drawings in which numerals reference like elements, and
wherein:
[0025] FIG. 1 shows a schematic drawing of a geothermal heat
harvesting system in an illustrative embodiment;
[0026] FIG. 2 shows a schematic drawing of a geothermal heat
harvesting system having multiple heat pipes arranged at multiple
levels in a well;
[0027] FIG. 3 shows a partial side view of a thermal transfer
arrangement for transferring heat from one or more heat pipes to a
heat exchanger in an illustrative embodiment;
[0028] FIG. 4 shows a cross sectional top view of the thermal
transfer arrangement of FIG. 1 along the line 4-4 in one
embodiment;
[0029] FIG. 5 shows a cross sectional top view of the thermal
transfer arrangement of FIG. 1 along the line 4-4 in another
embodiment;
[0030] FIG. 6 shows an arrangement for deploying thermal gap
material in an illustrative embodiment;
[0031] FIG. 7 shows an arrangement for deploying thermal gap
material in an embodiment in which one or more ports are used to
position thermal gap material in a gap;
[0032] FIG. 8 shows a perspective view of a heat pipe deployment
system prior to heat pipe deployment;
[0033] FIG. 9 shows a cross sectional view along the line 9-9 in
FIG. 8;
[0034] FIG. 10 shows an anti-buckling support in an illustrative
embodiment;
[0035] FIG. 11 shows a collar having a clam shell arrangement;
[0036] FIG. 12 shows a cross sectional view along the line 12-12 in
FIG. 8;
[0037] FIG. 13 shows a perspective view of a heat pipe deployment
system in an illustrative embodiment;
[0038] FIG. 14 shows a close up view of a heat pipe guide in the
FIG. 13 embodiment;
[0039] FIG. 15 shows an illustrative embodiment including a
multi-part mounting component in an assembled condition;
[0040] FIG. 16 shows the FIG. 15 embodiment in a pre-deployment
condition;
[0041] FIG. 17 shows the mounting component and heat pipes of the
FIG. 15 embodiment in a deployed condition;
[0042] FIG. 18 shows an illustrative embodiment of heat exchanger
portions including one or more alignment features;
[0043] FIG. 19 shows a top perspective view of an upper portion of
a mounting component in an illustrative embodiment;
[0044] FIG. 20 shows a cross sectional view of the FIG. 19
embodiment along the line 20-20 in FIG. 15;
[0045] FIG. 21 shows a cross sectional side view of the FIG. 19
embodiment;
[0046] FIGS. 22-25 show illustrative embodiments for saddles
useable for engaging one or more heat pipes; and
[0047] FIG. 26 shows a cross sectional side view of an arrangement
in which heat pipes extend into a heat exchanger space.
DETAILED DESCRIPTION
[0048] Aspects of the invention are not limited in application to
the details of construction and the arrangement of components set
forth in the following description or illustrated in the drawings.
Other embodiments may be employed and aspects of the invention may
be practiced or be carried out in various ways. Also, aspects of
the invention may be used alone or in any suitable combination with
each other. Thus, the phraseology and terminology used herein is
for the purpose of description and should not be regarded as
limiting.
[0049] FIG. 1 shows a schematic view of a geothermal heat
harvesting system 100 in an illustrative embodiment. It should be
appreciated, however, that this is only one example configuration
for a heat harvesting system 100 and that other system types or
configurations are possible for use with aspects of the invention.
For example, in this embodiment, a heat receiver 6 includes a steam
generator, turbine, and electricity generator coupled to the
turbine (along with other suitable components, such as control
systems, valves, heat and/or electricity storage systems, etc.)
that use heat harvested from the geothermal well 1 to generate
electricity. Heat may be delivered from the well 1 to the heat
receiver 6 in the form of steam or other heated fluid. However, the
heat receiver 6 may be arranged in other ways. For example,
harvested heat may be used to heat a building, to heat materials
used in an industrial process (such as oil shale heating to recover
petroleum), to generate electricity via one or more thermoelectric
devices, to provide heat for a heat pump system, and so on.
Moreover, the heat receiver 6 may include components below ground,
such as thermoelectric components (e.g., Peltier or similar
devices) located in the well 1 that generate electricity,
additional heat exchangers, and so on.
[0050] It should also be understood that a geothermal well 1, as
used herein, may include any underground region from which heat is
harvested. In this embodiment, the well 1 is accessed by drilling
using an above-surface drilling system, but the well 1 may be
accessed in other ways, such as by digging a hole, providing
below-ground system 100 components in the hole, and again filling
the hole, whether with soil originally dug from the hole or other
materials. Also, drilling to provide components in a well 1 may be
done by rotating bit, fluid jet injection and/or any other suitable
techniques, or combinations of such techniques.
[0051] In this embodiment, the geothermal well 1 includes fluid
(such as underground water) that has at least some ability to flow
in the well 1 (i.e., in a region around the below-ground components
of the system 100), and therefore move heat in the well 1 by
convection. However, embodiments described herein need not exchange
fluid in the well 1 (e.g., underground water or steam) with fluid
used by the heat harvesting system 100 to carry heat to the heat
receiver 6. Instead, any fluid used by the system 100 to transport
heat from the well 1 to the heat receiver 6 is generally isolated
from rock, underground water and/or other features of the well. It
should also be understood that aspects of the invention are not
limited to such applications, however, but may be used in "dry"
well 1 conditions in which fluid is not very free to flow in the
well 1, or other well conditions.
[0052] The system 100 in FIG. 1 includes a heat exchanger 2 that in
this embodiment transfers heat harvested from the well 1 to fluid
that flows between the heat exchanger 2 and the heat receiver 6.
The fluid may be gas and/or liquid (such as steam and/or water) or
any other material, such as a molten salt, glycol solution or other
material. In this embodiment, the heat exchange fluid flows in a
closed loop system, although open loop flow may be used in some
embodiments. Flow of the heat exchange fluid may be driven by pump,
gravity, capillary action and/or other driving forces. In one
embodiment, the heat exchanger may include one or more "hot" pipes
positioned at an outer periphery of the heat exchanger 2 that carry
heated fluid upwardly, and one or more "cold" pipes positioned at
an interior of the heat exchanger 2. In another arrangement, the
heat exchanger 2 includes a single outer pipe (e.g., used to
conduct heated fluid to the receiver 6), and a single inner pipe
(e.g., used to deliver relatively cool fluid to the well 1 for
heating). The heat exchanger 2 may include other features to
enhance heat transfer, such as serpentine flow tubes or other
pathways, finned tube segments, baffles, and other components to
assist in transferring heat to the working fluid, whether by
increasing a surface area of heated components presented to the
working fluid, slowing or diverting flow of the working fluid in
one or more sections of the heat exchanger, etc. Also, the heat
exchanger 2 may be arranged to transfer heat to the working fluid
over an extended length of the well 1, may be arranged to transfer
heat at multiple, distinct sections or levels of the well (e.g.,
which are vertically displaced), or may transfer heat to the
working fluid only in one well section (e.g., near a bottom of the
well 1). However, other arrangements are possible.
[0053] In accordance with an aspect of the invention, one or more
heat pipes 5 are coupled with a mounting component 3 (in this
example a collar or other support arranged to mount one or more
heat pipes) that is positioned around at least part of an outer
periphery of the heat exchanger 2 and that positions the heat pipes
5 for transfer of heat to the heat exchanger 2 via a thermal gap
material 4. Thus, in this example, heat is harvested by the heat
pipes 5 that extend radially from the mounting component 3 into
portions of the geothermal well 1 surrounding a well bore in which
the heat exchanger 2 is positioned. The harvested heat from the
heat pipes 5 is transmitted to the thermal gap material 4, e.g., by
conduction and/or convection, which in turn transfers heat to the
heat exchanger 2. In some embodiments, heat may be conducted from
the heat pipes 5 to the mounting component 3 which transfers heat
to the thermal gap material 4 and into an outer wall or other
suitable portion of the heat exchanger 2. Accordingly, a liquid or
other fluid flowing in the heat exchanger 2 picks up the heat and
transports it to the heat receiver 6. Although only two heat pipes
are shown, any suitable number of such heat pipes assemblies may be
arrayed along the length of the heat exchanger 2 to provide the
required heat harvesting rate for a particular geothermal energy
system 100. For example, FIG. 2 shows an arrangement in which the
heat exchanger 2 is located in a main well bore 11, and multiple
heat pipes 5 extend radially into corresponding bores 12 that
extend away from the main well bore 11. In this embodiment, the
heat pipes 5 are arranged at three levels, or distinct vertical
positions, relative to the main well bore 11, although more or
fewer levels may be employed. Also, multiple heat pipes 5 may be
deployed at each level, such as 3, 4, 6 or more heat pipes 5 per
level. Alternately, the heat pipes 5 may be arrayed around the main
well bore 12 in random or irregular ways, e.g., to accommodate
particular geologic features of the well 1.
[0054] The mounting component 3 may support portions of the heat
pipes 5 so that the heat pipes are spaced from the heat exchanger 2
by a thermal gap, i.e., a space of desired size and thickness to
create the thermal resistance through which heat is transferred
from the heat pipes 5 to the heat exchanger 2. In some embodiments,
the thermal gap may be about 1/4 inch to 2 inches, although other
suitable spacing may be employed. Thus, the heat pipes 5 may be out
of direct contact with the heat exchanger so that a majority of
heat transferred to the heat exchanger is through a thermal gap
material 4 located in the thermal gap, e.g., 60%, 70%, 80%, 90%,
95% or more of heat transfer may occur via the thermal gap material
4. The thermal gap material 4 may have a relatively low thermal
conductivity, e.g., 0.5 to 12 W/m-K, at least as compared to a
thermal conductivity of the material at the heat pipe 5 and/or heat
exchanger 2 outer surface. As such, the thermal gap material 4 may
meter heat transfer in a desired way, e.g., to allow the heat pipes
5 to operate at an optimal working temperature as discussed more
below. The thermal gap material 4 may be or include a thermal
grout, e.g., a cement-like material that is designed to have a
desired thermal conductivity, or other material such as water
(including water with dissolved minerals, salts and/or other
material). Thus, the thermal gap material 4 may be a solid, liquid,
semi-solid or other composite and may transfer heat by conduction
and/or by convection.
[0055] In some embodiments, to achieve meaningful heat harvesting
rates, the geothermal well should include a liquid pool or
liquid-permeated porous rock so as to allow circulation of liquid
within the volume of the geothermal well 1. Heat removal from the
geothermal resource by the heat exchanger 2, and particularly by
the heat pipes 5, cools the liquid of the well 1 and increases its
density. As the denser, cool liquid sinks downwardly in the
geothermal well 1, hotter liquid from below or elsewhere in or
around the well 1 may move outwards and upwards to create large
scale liquid circulation that may be necessary to deliver
sufficient heat to the heat pipes 5 and the heat exchanger 2 for
harvesting. This liquid already present in the geothermal well may
itself, at least in part, function as a thermal gap material. Of
course, other system 100 arrangements employing a lower heat
harvesting rate need not exploit a liquid or liquid-permeated
substrate and/or employ a large scale liquid circulation to operate
properly. Also, although this embodiment shows the heat pipes 5
extending away from the mounting component 3 in a downward, curving
arc, the heat pipes 5 may extend in a straight line and/or at any
suitable angle(s) to the horizontal, including extending
horizontally (or nearly so) in some embodiments.
[0056] FIG. 3 shows a cross sectional side view of the heat pipe
mounting assembly of the FIG. 1 embodiment. The mounting component
3 (which in this embodiment is shaped as a collar or sleeve)
extends around at least part of the outer periphery of the heat
exchanger 2 and positions the heat pipes 5 to define a gap between
the heat pipes 5 and the heat exchanger 2. Note that the mounting
component 3 may help establish a suitable gap between the heat
pipes 5 and the heat exchanger 2 in portions of the heat pipes 5
positioned below or otherwise away from the mounting component 3.
The heat exchanger 2 in this embodiment includes an outer pipe 22
which carries a working fluid flow in a downward direction and an
inner pipe 21 which carries an working fluid flow in an upward
direction, e.g., heated working fluid may travel upwardly in the
inner pipe 21 to the heat receiver 6. Thus, heat from the heat
pipes 5 may be transmitted to the working fluid flowing downwardly
in the outer pipe 22 in this embodiment. Of course, the flow
direction may be reversed, with relatively hot working fluid
flowing upwardly in the outer pipe 22 and cooler working fluid
flowing downwardly in the inner pipe 21.
[0057] In the gap between the mounting component 3/heat pipes 5 and
the heat exchanger 2 is a thermal gap material 4, such as a thermal
grout. As is explained in more detail below, the thermal
conductivity of the thermal gap material 4 may be lower than the
thermal conductivity of the mounting component 3 and heat pipes 5,
and generally speaking, "meters" the flow of heat from the mounting
component 3/heat pipes 5 to the heat exchanger 2 so that the heat
pipe(s) 5 operate at an appropriate working temperature. In some
embodiments, relatively little heat may be transmitted from the
heat pipes 5 to the mounting component 3, so that a bulk of heat
transfer from the heat pipes 5 to the heat exchanger 2 occurs
directly from the heat pipes 5 to the thermal gap material 4 and
then to the heat exchanger 2. However, in other embodiments, a
significant amount of heat may be transferred from the heat pipes 5
to the mounting component 3, which is then transferred from the
mounting component 3 to the thermal gap material 4. In this case,
the mounting component 3 may function as a heat spreader, i.e.,
assisting to transmit heat from a first surface area of a heat pipe
having a first size to a second surface area of the mounting
component 3 that has a second size greater than the first size. As
discussed more below, such heat spreading may assist in desired
heat transfer to the heat exchanger, and to do so, a heat spreader
may have a relatively high thermal conductivity, e.g., above 12
W/m-K. In some embodiments, a surface of the mounting component 3
that faces or otherwise thermally communicates with the heat
exchanger 2 may be configured to generally conform to the shape of
the heat exchanger portion that receives heat from the thermal gap
material 4, e.g., so that a conduction length across the thermal
gap material 4 may be maintained constant or otherwise
controlled.
[0058] Many heat pipes are closed systems that rely on the counter
flow of "liquid" and "vapor" phases of the "working fluid" within a
sealed interior volume of the pipe to transport heat along the
pipe. At the hot or "evaporator" end, heat is absorbed by
evaporating or boiling the liquid inside the heat pipe into its
vapor phase while at the cold or "condenser" end the vapor phase
condenses back into a liquid and releases heat into the walls of
the heat pipe. Vapor travels automatically from the hot end to the
cold end by the pressure difference caused by small temperature
differences between the hot and cold ends. Other forces, such as
gravity, are used to return the condensed liquid from the cold to
the hot end. Heat pipes that depend on gravity as the primary means
to return condensed liquid from the cold end to the hot end are
also called thermosiphons. Liquid and vapor flow in opposite
directions in the heat pipe.
[0059] Because heat transport in heat pipes is mediated by the
physical movement of liquid and vapor phases of the working fluid,
the heat transport rate that can be achieved in heat pipes is
limited by many mechanisms that apply to fluid flows. Some common
limiting mechanisms are entrainment limit, flooding limit, sonic
limit, boiling limit etc., but in short, the heat transport limit
of heat pipes is strongly dependent on the temperature of the
working fluid inside the heat pipe. (The liquid and vapor phases
inside a heat pipe exist in near thermodynamic equilibrium so, for
the purpose of this description, a single temperature is used to
refer to both phases.)
[0060] In accordance with an aspect of the invention, the thermal
gap (i.e., the conduction length or distance from the mounting
component 3 (or other heat spreader) and/or the heat pipe 5 to the
heat exchanger 2) and the thermal gap material 4 in the gap between
the heat spreader/heat pipe 5 and the heat exchanger 2 may be
arranged to conduct heat such that the heat pipe(s) 5 operate at a
desired working temperature, and enable substantial heat harvesting
from the geothermal resource via the heat pipe(s) 5. For example,
if the heat pipes 5 were to be placed in direct and very intimate
thermal contact with the heat exchanger 2, the operating
temperature of the heat pipes would be low, close to the cold fluid
temperature in the heat exchanger 2. Such cold heat pipes extending
into the hot rock or other well 1 substrate could create a "high
heat demand" from the well 1. However, at the "cold operating
temperature," the heat pipes 5 would have a "low heat transport
capability" and would not be able to carry the heat that would want
to flow into the heat pipe 5 from the hot rock or other well
substrate.
[0061] On the other hand, if the thermal connection between the
heat pipes 5 and the heat exchanger 2 is poor (such as if the heat
pipes 5 are simply inserted into the holes drilled into hot rock
around a main well bore and not thermally coupled to the heat
exchanger 2 in any particular way), the heat pipe temperature would
be high, closer to the high temperature of the hot rock. Such "hot
heat pipes" would create a "low heat demand" from the rock even
though the heat pipes 5 would have a "high heat transport
capability" due to their high operating temperature. In both the
above scenarios, the heat pipes 5 would not provide a suitably high
heat harvesting rate, at least for some applications. By providing
a suitable thermal gap characteristics (conduction length and
thermal conductivity) between the heat pipes 5/heat spreader and
the heat exchanger 2, the heat pipes 5 may operate at the desirable
"in between" temperature such that a "relatively high heat demand"
is placed on the hot rock and is well balanced against the
"relatively high heat transport capability" of the heat pipes
5.
[0062] A further benefit of the "balanced high heat harvesting"
rate of the heat pipes 5 is that more well fluid may be cooled to a
higher density to drive a larger total convective circulation in
the geothermal resource. In this way, embodiments configured in
accordance with an aspect of the invention may operate such that
the heat content of the geothermal well, or "reservoir," is
replenished at the same rate that heat is harvested for efficient
and cost effective energy production over long term operation.
Computer modeling of a geothermal well 1 having its heat harvested
using three thermal transfer components (i.e., heat pipe/heat
spreader/thermal gap material assemblies) positioned along the
length of a vertical heat exchanger arrangement like that in FIG. 2
have shown that the thermal transfer components are effective in
increasing convective flow in the geothermal well 1, and that
additional thermal transfer assemblies are expected to improve
convective flow over systems with fewer thermal transfer
assemblies.
[0063] FIG. 4 shows a top cross sectional view of the mounting
component 3 along the line 4-4 in FIG. 1 in an illustrative
embodiment. In this example, the mounting component 3 has the form
of a continuous annular collar or sleeve that extends around the
heat exchanger 2. Also, in this embodiment, four heat pipes 5 pass
through openings in the wall of the collar 3, thereby thermally
coupling the heat pipes 5 to the collar 3 and allowing the collar 3
to function as a heat spreader. Of course, fewer or more heat pipes
5 may thermally couple with the mounting component 3 if desired.
Other configurations for a mounting component 3 are possible, such
as that shown in FIG. 5 in which the mounting component 3 includes
four "shoes" or curved plates that each thermally couple with a
corresponding heat pipe 5. The shoes may be physically attached to
each other, or not, as desired, and may be thermally coupled with
each other, or not. Note also that the mounting component 3 need
not necessarily be thermally coupled with a heat pipe 5, but
instead may mechanically support the heat pipe 5 in a desired
orientation and distance from a heat exchanger 2, e.g., to define a
desired thermal gap. Thus, the mounting component 3 need not
function as a heat spreader or otherwise transmit significant heat
from the heat pipes 5 to the thermal gap material 4. Also, a heat
spreader may be used in conjunction with a mounting component 3
that serves to physically support the heat pipe(s) 5, but does not
function as a heat spreader.
[0064] While the surface area of the heat pipes 5 and/or heat
spreader is an important design consideration when arranging the
system to operate such that the coupled heat pipe(s) 5 function at
a desired working temperature, the distance between the heat pipes
5 and/or heat spreader and the heat exchanger 2 (or conduction
length) may be another important factor. As noted above, the
surface of the heat pipes 5 or heat spreader that faces the heat
exchanger 2 may be shaped or contoured to match or conform with a
counterpart surface of the heat exchanger 2. Thus, if the heat
exchanger 2 has a cylindrically-shaped outer surface, the mounting
component 3 or other heat spreader may include a corresponding
cylindrically-shaped inner surface that faces the heat exchanger 2.
Alternately, if the heat exchanger 2 includes a dimpled, grooved,
or other shaped surface, the mounting component 3 or other heat
spreader may have a corresponding shape. This arrangement may help
maintain a thermal gap between the heat spreader and the heat
exchanger 2 at a constant or otherwise known value, e.g., to help
ensure that a conduction length of the thermal gap material 4 is
constant or otherwise known across the thermal junction. In some
embodiments, the distance between the mounting component 3 and the
heat exchanger 2 may be defined in different ways, such as by
standoffs, tabs, pins, annular rings or other structures that
extend from the mounting component 3 toward the heat exchanger 2.
These gap-defining elements may help ensure that there is a minimum
(or maximum) distance between the mounting component 3/heat pipes 5
and the heat exchanger 2. The gap-defining elements may be made
small enough or otherwise configured to contribute minimally to
heat transfer between the heat spreader and the heat exchanger, or
alternately, these gap-defining spacer elements may function as a
non-trivial part of the heat transfer. If so, the gap between the
heat spreader and the heat exchanger (conduction length), the
thermal conductivity of the thermal gap material and/or the surface
area of the heat spreader (i.e., the surface area facing the heat
exchanger or that meaningfully contributes to heat transfer to the
heat exchanger) may be designed to provide the desired heat
transfer rate along with the gap-defining elements.
[0065] Deployment of a thermal gap material 4 in the space or gap
between the mounting component 3/heat pipes 5 and the heat
exchanger 2 may be done in a variety of ways. For example, the
thermal gap material 4 may take the form of a flowable grout that
can flow when deployed, and then may optionally harden after
deployment. The grout may be pumped into place after the mounting
component 3 and heat exchanger 2 are positioned relative to each
other in the well 1, or may be applied to the heat exchanger 2
and/or to the mounting component 3 prior to positioning of the
elements relative to each other. In other embodiments, the thermal
gap material 4 may be present in the well 1 at or after the time of
installing the heat exchanger 2 and/or heat pipes 5. For example,
the thermal gap material 4 may be or include water (such as brine)
in the well 1 that occurs naturally or is introduced, e.g., by
pumping the water into the well 1. Thus, in some embodiments, the
thermal gap material may include a liquid that can flow so as to
accommodate convective heat transfer, as well as conductive heat
transfer, between the heat pipes 5 and the heat exchanger 2.
[0066] FIG. 6 shows an illustrative embodiment in which thermal gap
material 4 is contained in one or more reservoirs 42 as introduced
into the well 1. In FIG. 6, the portion of the image to the left of
the heat exchanger 2 shows the thermal gap material 4 before
deployment, while the portion of the image on the right of the heat
exchanger 2 shows the thermal gap material 4 after deployment. A
shaped charge (e.g., an explosive device), a plunger or piston, a
clamp or other mechanism 41 may deform the reservoir 42, or
otherwise force the thermal gap material 4 to flow from the
reservoir 42 into the gap between the heat exchanger 2 and the heat
pipes 5 and/or heat spreader. FIG. 7 shows another illustrative
embodiment in which the mounting component 3 has an attached
thermal gap material reservoir 42 that includes one or more ports
43 arranged to expel thermal gap material 4 in the gap when the
thermal gap material is caused to flow. In this embodiment, the
reservoir 42 that is squeezed by a clamp 41 that includes a collar
or sleeve with a conical lower surface that bears on the reservoir
42 as the collar is moved downwardly toward the mounting component
3. (As in FIG. 6, the portion of the image to the left of the heat
exchanger 2 in FIG. 7 shows the thermal gap material 4 before
deployment, while the portion of the image on the right of the heat
exchanger 2 shows the thermal gap material 4 after deployment.) Of
course, other arrangements are possible for deploying a thermal gap
material 4, such as a pump that pumps thermal gap material 4 via a
conduit to the gap between a heat pipe and the heat exchanger.
Also, while in the FIGS. 6 and 7 embodiments the thermal gap
material 4 flows generally downwardly and radially inwardly, the
material 4 may flow in any suitable way, e.g., the material 4 may
flow only radially inwardly from one or more reservoirs to a
thermal gap between a heat spreader and/or heat pipe and the heat
exchanger.
[0067] In accordance with an aspect of the invention, one or more
heat pipes may be engaged with a mounting component so that the
assembled heat pipes and mounting component may be lowered into a
well bore and the heat pipes deployed into corresponding well
bores. For example, FIG. 8 shows an illustrative arrangement in
which four heat pipes 5 are attached to a mounting component 3 that
includes upper and lower collars 3a, although more collars 3a may
be used if desired. The upper and lower collars 3a may be spaced
from each other, e.g., at a distance of 5, 10, 20 or more feet
along the length of the heat pipes 5, which in this embodiment may
be up to 120 to 300 feet long or more. In other embodiments, the
upper and lower collars 3a may be replaced with a single collar
that spans along a desired length of the heat pipes 5, e.g., 5, 10
or 20 feet or more in length. The single collar 3a may be arranged
as a cylindrical shell, e.g., to prevent flow into/out of a space
within the collar 3a, or may have openings to permit flow. In the
illustrated embodiment, the portion of the heat pipes 5 between the
collars 3a are exposed and a gap between the heat pipes 5 and a
heat exchanger 2 positioned within the heat pipes (not shown) may
be defined by the collars 3a. Given the relatively long length of
the heat pipes 5 positioned adjacent the heat exchanger 2, a
majority of heat transferred from the heat pipes 5 to the heat
exchanger 2, e.g., 90%, 95% or more, may be transmitted directly
from the heat pipes 5 to the heat exchanger via a thermal gap
material 4. Thus, the collars 3a may play a minor role in heat
transfer in this embodiment, but in other embodiments may serve to
transfer a much larger amount of heat.
[0068] FIG. 9 shows a cross sectional view of a collar 3a along the
line 9-9 in FIG. 8. This embodiment is similar to that shown in
FIG. 4, with one difference being that the collar 3a (a mounting
component) engages the heat pipes 5 at an outer surface of the
collar 3a. Also, the collar 3a is shown including one or more
spacer elements 34, such as a protrusion, rib, pin, etc. that
extends radially inwardly from an inner side of the collar 3a. The
spacer elements 34 may assist in defining a suitable thermal gap
between the heat pipes 5 and the heat exchanger 2, not only in
areas at or near the collar 3a, but also for portions of the heat
pipes 5 between the upper and lower collars 3a. Note also that the
heat pipes 5 in this embodiment each include a heat spreader 51 in
the form of a sleeve 51 that is positioned over the outer surface
of the heat pipe 5. In one embodiment, the heat pipe 5 may be
formed by a copper tube or pipe, and the heat spreader 51 may be
arranged as a stainless steel sleeve that extends over a portion
of, or the entire, heat pipe 5. The heat spreader 51 may serve to
not only increase a surface area for heat transfer from the heat
pipe 5, but also may provide the heat pipe 5 with mechanical
support (e.g., to resist crushing and/or bursting of the pipe 5),
corrosion resistance, and/or other characteristics. The collars 3a
may engage the heat spreaders 51 by welding, an adhesive, clamping,
an interference fit or other suitable arrangement.
[0069] In accordance with an aspect of the invention, the assembly
may include one or more anti-buckling supports which may help
support the heat pipes before and/or during deployment in the well
1. For example, as shown in FIG. 8, anti-buckling supports 3c may
be attached to the heat pipes 5 below the collars 3a, e.g., to help
keep the heat pipes 5 from bending or buckling during deployment or
to otherwise support the heat pipes 5. A distance between each
anti-buckling supports 3c and an adjacent anti-buckling support 3c
or collar 3a may be arranged to be equal to or less than a maximum
unsupported length of heat pipe for loading in compression without
buckling. So, for example, if a particular force is needed to be
applied to the heat pipes 5 for deployment of the heat pipes into
the well 1, one or more anti-buckling supports 3c may be provided
at suitable locations along the length of the heat pipes 5 to help
prevent buckling of the pipes 5 during deployment. The heat pipes 5
may be attached to the anti-buckling supports 3c in a way that
maintains the anti-buckling supports 3c in place relative to the
heat pipes 5 during deployment of the heat pipes 5 into the well 1,
but that releases the heat pipes 5 relative to the anti-buckling
supports 3c once a force exerted on the heat pipes 5 relative to
the anti-buckling support 3c exceeds a threshold. For example, with
reference to FIG. 3, as the collars 3a and heat pipes 5 are moved
downwardly in the main well bore 11, the heat pipes 5 may be
deployed into their respective bores 12 of the well 1. As the
anti-buckling supports 3c reach the point where the heat pipes 5
exit the main well bore 11, the anti-buckling supports 3c may
disengage from the heat pipes 5, e.g., via a frangible or other
releasable connection.
[0070] For example, FIG. 10 shows one illustrative embodiment of an
anti-buckling support 3c. Heat pipes 5 may be engaged at openings
37 of heat pipe engagement portions 35, and the heat pipes may be
fixed to the portions 35 by welding, solder, an adhesive, a clamp,
or other arrangement. Frangible links 36 may permit the engagement
portions 35 and heat pipes 5 to disengage from a central portion 38
of the anti-buckling support 3c, e.g., when a suitable force is
applied to the heat pipes 5 relative to the support 3c whether in
shear and/or tension. As will be understood, and is discussed more
below, the heat pipes 5 may be releasably attached to the
anti-buckling support(s) 3c in other ways, such as by an adhesive
that breaks or fails in the presence of a suitable force, rubber
sleeves on the heat pipes 5 that hold the anti-buckling supports 3c
in place relative to the heat pipes 5, but allow the heat pipes 5
move along their length relative to the anti-buckling supports in
the presence of a suitable force, and others.
[0071] Another feature shown in FIG. 10 is that the anti-buckling
support 3c may be arranged with a clam shell or other suitable
configuration that allows the support 3c to be assembled around an
existing drill string and/or heat exchanger 2. That is, when
installing a thermal energy harvester in a well 1, a drill string
used to form one or more bores 11, 12 may be in place when the heat
pipes 5 and mounting component(s) 3 are installed. By making the
anti-buckling support 3c and/or the collars 3a in a clam shell
configuration (see FIG. 11 regarding a collar 3a having a clam
shell arrangement), the support 3c and/or collars 3a may be
assembled around a drill string or heat exchanger 2. That is, bolts
or other fasteners used to secure the support 3c and/or collar 3a
sections together may be removed so the sections can be placed
around the drill string or heat exchanger 2 and then fastened
together. FIG. 12 shows a cross sectional view along the line 12-12
in FIG. 8 and shows another illustrative embodiment for an
anti-buckling support 3c. In this embodiment, the heat pipes 5 are
engaged by sleeve-shaped engagement portions 35 of the
anti-buckling support 3c as opposed to a plate shaped element as in
FIG. 10. The frangible links 36 are formed as rib-shaped elements
that extend along a length of the heat pipes 5, although other
arrangements are possible. FIG. 12 also shows an embodiment of a
collar 3a like that in FIG. 9, except that in FIG. 12 the collar 3a
is formed in two sections. The sections may be joined together by
bolts or other fasteners, welding, etc. This embodiment also
incorporates a spacer element 34 at the joint between the two
collar sections.
[0072] In accordance with another aspect of the invention, a heat
pipe deployment system may include a heat pipe guide, or "kicker,"
that helps to guide the heat pipe(s) into their respective bore in
a well. For example, the heat pipe guide may be arranged in the
main well bore and include a flared or curved guide channel for one
or more heat pipes. The guide channel may engage a heat pipe, e.g.,
at the distal end, and guide the heat pipe into a radially
extending bore. The heat pipe guide may also be used to guide a
tool that forms radially extending heat pipe bores, such as a
rotary drilling tool, high pressure jet device, etc. For example,
FIG. 13 shows an assembly including four heat pipes 5, upper and
lower collars 3a, an anti-buckling support 3c and a heat pipe guide
3b. FIG. 14 shows a close up view of the heat pipe guide 3b. The
guide 3b may include a plurality of guide grooves 39, e.g., one for
each heat pipe 5, that is curved or otherwise arranged to guide
movement of the distal end of the heat pipes 5 into a corresponding
radial bore 12 as the heat pipes 5 are lowered into a well 1. The
radius of curvature of the grooves 39 may be any suitable distance,
such as 10-30 ft. Although in this embodiment, the guide 3c is
shown arranged as a solid part with no through hole, e.g., through
which a heat exchanger 2 may pass, the guide 3c may be arranged to
receive a drill string, heat exchanger 2 or other element in an
opening in the center of the guide 3c. Moreover, the guide 3b may
be made in a clam shell configuration or other multi-part
arrangement that permits assembly of the guide 3b around a drill
string. In some embodiments, the guide 3b may be used to guide a
drill bit or other device that is used to form the bores 12 for
heat pipes. This may help ensure that the grooves 39 are aligned
with corresponding bores 12 for insertion of the heat pipes 5.
Alternately, the bores 12 may be made without the use of the guide
3b, and the grooves 39 may be suitably aligned with the bores 12
prior to heat pipe insertion.
[0073] In accordance with another aspect of the invention, a
portion of a mounting component, anti-buckling support and/or heat
pipe guide may form part of the heat exchanger. That is, in the
embodiments above, a portion of the mounting component is adjacent
to, and spaced from, a portion of the heat exchanger and a thermal
gap material serves to conduct heat from the heat spreader to the
heat exchanger. However, in some embodiments, one or more portions
of the heat pipe deployment system may function as part of the heat
exchanger, and any thermal gap or other thermal link between heat
pipes and the heat exchanger may be provided as part of the system.
For example, FIG. 15 shows an embodiment in which a mounting
component 3a, heat pipe guide 3b, and anti-buckling support 3c
serve as part of the heat exchanger 2. In this embodiment, the heat
exchanger 2 includes an inner pipe 21 that extends downwardly
within an outer pipe 22. The inner pipe 21 carries cool working
fluid to near a bottom of the well 1, and heated working fluid is
conducted upwardly in the space between the inner and outer pipes
21, 22. Although the inner pipe 21 extends downwardly to near a
bottom of the well 1, the outer pipe 22 is connected to the
mounting component 3a, and from that point downward, the assembly
of the mounting component 3, anti-buckling support 3c and heat pipe
guide 3b defines the "outer pipe" of the heat exchanger 2. To
contain the working fluid in the heat exchanger 2, the portions 3a,
3b and 3c may be joined together to define a water tight conduit
around the inner pipe 21, e.g., by the use of o-rings, adhesives,
threaded connections, clamps and/or other components. Any thermal
gap provided between the heat pipes 5 and the working fluid in the
heat exchanger 2 may be provided as part of the portions 3a, 3b and
3c.
[0074] FIG. 16 shows the heat spreader arrangement of FIG. 15 in an
"expanded" state prior to deployment in the FIG. 12 configuration.
That is, the mounting component 3 may include an upper portion 3a
that is fixed to the heat pipes 5 and a lower portion 3b that
includes heat pipe guides to guide deployment of the heat pipes 5
into corresponding bores 12 in the well 1 as the upper portion 3a
is moved toward the lower portion 3b. However, this embodiment
additionally includes one or more middle portions 3c (e.g., an
anti-buckling portion) that may be attached to the heat pipes 5,
e.g., to help keep the heat pipes 5 from bending or buckling during
deployment or to otherwise support the heat pipes 5. A distance L
between each middle portion 3c and an adjacent middle portion 3c,
upper portion 3a or lower portion 3b may be arranged to be equal to
or less than a maximum unsupported length of heat pipe for loading
in compression without buckling. So, for example, if a particular
force is needed to be applied to the heat pipes 5 by the upper
portion 3a for deployment, one or more middle portions 3c may be
provided at a suitable length L along the heat pipes 5 to help
prevent buckling of the pipes 5 during deployment. The heat pipes 5
may be attached to the middle portions 3c in a way that maintains
the middle portions 3c in place relative to the heat pipes 5 during
deployment of the heat pipes 5 into the well 1, but that releases
the heat pipes 5 relative to the middle portion 3c once the middle
portion reaches the lower portion 3b or an adjacent middle portion
3c below. For example, as the upper portion 3a is moved toward the
lower portion 3b in the well 1, the heat pipes 5 will be deployed
into their respective bores 12 of the well 1 and the middle portion
3c will move downwardly toward the lower portion 3b. When the
middle portion 3c contacts the lower portion 3b, a connection
between the middle portion 3c and the heat pipes 5 will be released
so that the heat pipes 5 can slide relative to the middle portion
3c. For example, the heat pipes 5 may be joined to the middle
portion 3c by a frangible joint (e.g., a tin soldered connection,
an adhesive, etc.) that is capable of supporting the middle portion
3c on the heat pipes 5, but that breaks away once the middle
portion 3c contacts the lower portion 3b. This allows the upper
portion 3a to be moved downwardly, further deploying the heat pipes
5 in the well 1 until the upper portion 3a meets the middle portion
3c.
[0075] As a result, the portions 3a, 3b, 3c may be stacked onto
each other when the heat pipes 5 are fully deployed into the well
1. As mentioned above, the portions 3a, 3b, 3c may be joined
together, as shown in FIG. 17, to form a water tight seal at an
inner portion such that the portions 3a, 3b, 3c may define an outer
conduit of the heat exchanger 2. For example, as shown in FIG. 18,
the portions 3a, 3b, 3c may engage each other such that one portion
(the middle portion 3c in this example) includes a protruding
conical section that engages with a conical receiver opening in the
other portion (the lower portion 3b in this example). These conical
sections may be tightly forced together, forming a water tight
seal, by threaded engagement, one or more clamps, etc. The conical
engagement surfaces of the middle portion 3c and the lower portion
3b (a male conical engagement surface of the middle portion 3c, and
female engagement surface of the lower portion 3b) may also help
align the portions 3c, 3b relative to each other in a radial
direction. For example, if the heat pipes 5 and middle portion 3c
are lowered to the lower portion 3b as shown in FIG. 18, the middle
and lower portions 3c, 3b may need to be aligned with each other
radially to form a suitable water tight joint. In addition, or
alternately, the heat pipe 5 ends may need to be aligned with guide
grooves in the lower portion 3b, and the radial alignment feature
provided by the conical engagement surfaces may also serve to align
the heat pipes 5 with the guide grooves.
[0076] Furthermore, the middle and lower portions 3c, 3b may
include features that help align the portions in a rotational
direction. For example, the lower portion 3b may include two heat
pipe guide grooves located at 180 degrees from each other. To help
align the heat pipes 5 with their respective guide grooves, the
conical engagement surfaces may include complementary slots and
protrusions that interact to align the middle and lower portions
3c, 3b rotationally. For example, the lower portion 3b may include
one or more V-shaped slots in the conical engagement surface (with
the wide end of the "V" facing upwardly) that received
complementary V-shaped protrusions on the conical engagement
surface (with the narrow end of the "V" facing downwardly) of the
middle portion 3c. The complementary slots and protrusions may
engage with each other to rotate the middle and lower portions 3c,
3b relative to each other, as necessary, so that the heat pipe 5
ends are suitably located relative to the guide grooves of the
lower portion 3b. Those of skill in the art will appreciate that
other engagement surface arrangements are possible to provide
radial and/or rotational alignment of the middle and lower portions
3c, 3b. Moreover, such alignment features may be provided between
adjacent middle portions 3c, and/or between a middle portion 3c and
the upper portion 3a.
[0077] FIG. 19 shows a perspective view and FIG. 20 shows a cross
sectional view of the upper portion 3a along the line 20-20 in FIG.
15. As can be seen, the inner pipe 21 extends within an inner wall
31 of the upper portion 3a. The inner wall 31 is joined to the
outer pipe 21 of the heat exchanger 2, and so forms an outer
conduit of the heat exchanger 2 in this embodiment. An outer wall
32 is also provided, but may function only as a well bore liner
pipe. As such, the outer wall 32 may be made of a less robust or
corrosion resistant material than other parts of the upper portion
3a since the outer wall 32 may be needed only during installation
of the upper portion 3a, e.g., to prop up the walls of a well hole.
The upper portion 3a couples to four heat pipes 5 in this
embodiment, though more or fewer heat pipes 5 could be used. The
upper portion 3a includes saddles 33 that join to a respective heat
pipe 5, and may provide physical support for the pipe 5 relative to
the upper portion 3a. The saddles 33 may be arranged in different
ways, such as by a block of material having a hole formed in it, as
a two-part clamshell device that clamps onto the heat pipe outer
surface, a plate with a hole formed in it, etc. The saddles 33 may
be directly joined to the inner wall 31, and the joint may be
arranged (e.g., of suitable cross sectional area) to provide a
desired (e.g., to create a suitable thermal gap) thermal coupling
between the heat pipe 5 and the inner wall 31. For example, if the
heat pipe 5 is directly in contact with the saddle 33, a joint
between the saddle 33 and the inner wall 31 may be suitably sized
(e.g., of suitable cross sectional area and joint thermal
conductivity) to provide a suitable thermal coupling between the
heat pipe 5 and the inner wall 31 to balance the heat pipe
temperature and the heat harvesting rate as earlier described.
Alternately, the junction of the saddles 33 to the inner pipe 31
may be of such relatively small cross sectional area and/or low
thermal conductivity as to be ineffective in transferring heat to
the working fluid, and instead a thermal gap material 4, e.g.,
filling a space between the inner and outer walls 31, 32, provides
the bulk of thermal coupling between the heat pipe 5 and the inner
wall 31, similar to that in the FIG. 3 embodiment.
[0078] In another embodiment, if the saddles 33 are joined to the
inner wall 31 with higher than desired thermal transfer capacity, a
junction between the saddles 33 and the heat pipes 5 may be
arranged to provide the desired thermal junction. For example, as
shown in the close up view of the saddle 33 at the 9 o'clock
position in FIG. 20, a joint between the heat pipes 5 and the
saddles 33 may include a thermal gap material 4 that provides the
desired thermal coupling between the heat pipes 5 and the inner
wall 31. This arrangement may have the advantage of being
constructed outside of the well 1, e.g., a thermal gap material 4
such as a grout, polymer material, etc., may be provided between
the heat pipe 5 outer surface and the saddle 33 when the heat pipes
5 are attached to the saddle 33. This may allow for easier, less
expensive and possibly more accurate control of the thermal gap
thickness between the heat pipe 5 and the saddle 33.
[0079] FIG. 21 shows a cross sectional side view of the upper
section 3a of the FIG. 15 embodiment and illustrates that the inner
wall 31 of the upper section 3a may be joined to the outer pipe 22
of the heat exchanger 2. This joint may be formed in any suitable
way, such as by welding, a threaded connection, a clamp, etc. Also,
this view shows a saddle 33 arrangement in which the saddle 33 is
joined directly to the inner wall 31 only, e.g., by brazing,
welding, an adhesive, etc.
[0080] FIGS. 22-25 show different saddle arrangements for
connecting a heat pipe 5 to the inner wall 31 or other portion of a
mounting component 3. Note that all, or at least some, of these
saddle arrangements may be used with a middle portion (or
anti-buckling support) 3c of a mounting component 3. In FIG. 22,
the saddles 33 are arranged to have two parts 33a, 33b that are
joined together at a seam 33c that is oriented radially relative to
the inner wall 31. Thus, to mount a heat pipe 5 to the inner wall
31, a first part 33a or 33b may be attached to the inner wall 31,
e.g., via welding at a joint 33d. With the heat pipe 5 positioned
against the first part 33a or 33b, the other part may be positioned
adjacent the heat pipe 5 and attached to the inner wall 31 to
capture the heat pipe 5 in place. FIG. 23 shows a similar
arrangement to that of FIG. 22, except that the saddle portions
33a, 33b do not extend completely around the heat pipe 5. In fact,
the saddle 33 need not surround all or part of the heat pipe 5, but
may engage just a portion of the heat pipe, as shown for example in
FIG. 24. In an arrangement like that in FIG. 24, the heat pipe 5
may be attached to the saddle 33 by welding, brazing, an adhesive,
or other suitable arrangement. In fact, a heat pipe 5 may be
secured to any type of saddle, including those of FIGS. 22 and 23,
by welding, brazing, an adhesive or other arrangement, and the
connection of the heat pipe 5 to the saddle 33 may be made
permanent (e.g., so the heat pipe 5 will not detach from the saddle
33 without damage or deformation of the heat pipe 5 or saddle 33)
or made frangible or otherwise releasable. For example, a heat pipe
5 may be attached to a saddle 33 so that the heat pipe 5 can detach
from the saddle 33 in certain conditions, such as where more than a
threshold level of force is applied to the heat pipe 5 relative to
the saddle 33. However, one possible advantage of attaching a heat
pipe 5 to a saddle 33, yet allowing the heat pipe 5 to freely
slide, e.g., like that in FIGS. 22 and 23, is that the heat pipe 5
may be attached to the inner wall 31 yet allowed to slide along its
length relative to the saddle 31, which may be desirable in
circumstances where a temperature of the heat pipe may cycle
between high and low temperatures. This feature may also be
exploited when used with a middle portion (anti-buckling support)
3c of the mounting component 3. For example, the heat pipe 5 may be
passed through the opening of a saddle 33 so that the heat pipe 5
can slide freely relative to the saddle 33. To support the middle
portion 3c relative to the heat pipe 5, rubber sleeves may be
positioned on the heat pipe 5 above and below the saddle 5 that
engage the heat pipe 5 with a suitable amount of friction to
support the weight of the middle portion 3c, but allow the heat
pipe 5 to slide relative to the saddle 33 with forces over a
threshold level. Alternately, the rubber sleeves may be replaced
with a frangible or releasable connection (e.g., a brazed or solder
joint, adhesive, etc.), a break-away collar or other component that
releases the heat pipe 5 from the saddle 33 when the force on the
heat pipe 5 relative to the saddle 33 exceeds the threshold level.
Thus, the arrangement of FIG. 24 may also be used with a middle
portion 3c, and if so, a connection of the heat pipe 5 to the
saddle 33 may be made frangible so as to give way once force over a
threshold level is applied to the heat pipe 5 relative to the
saddle 33. One type of frangible connection may be provided by a
tin soldered joint, an adhesive of suitable bonding strength,
etc.
[0081] FIG. 25 shows another arrangement similar to that in FIG.
22, except that the seam 33c between the saddle portions 33a, 33b
is oriented circumferentially rather than radially as in FIG. 22.
This may allow a first portion 33a of the saddle 33 to be attached
to the inner wall 31, and the second portion 33b to be attached to
the first portion 33a to capture the heat pipe 5. The first and
second portions 33a, 33b may engage in any suitable way, such as by
welding, one or more screws or other fasteners, etc. In one
arrangement, the first and second portions 33a, 33b may be joined
by a hinge at one seam portion 33d, so that the second portion 33b
may be pivoted to an open position to allow a heat pipe 5 to be
positioned in a receiving groove of the first portion 33a.
Thereafter, the second portion may be pivoted to a closed position
and secured to the first portion 33a to capture the heat pipe 5. As
with other saddle embodiments, the heat pipe 5 may be secured to
the saddle via a permanent or frangible connection as well.
[0082] While in the embodiments above, a thermal gap material or
other component is provided to control (e.g., limit) heat transfer
between a heat pipe and a working fluid of the heat exchanger 2,
such material is not always required, especially when the well
temperature is low. For example, FIG. 26 shows an embodiment in
which a condensing portion of a heat pipe 5 extends through the
inner wall 31 to directly contact the working fluid in the heat
exchanger 2. (The opening in the inner wall 31 through which the
heat pipe 5 passes may be sealed closed, e.g., welded or brazed, to
prevent leakage of working fluid.) The condensing portion of the
heat pipes 5 may be a relatively long length, e.g., 5 meters or
more, and may extend from near a bottom end of the heat exchanger 2
upwardly. A similar result may be achieved as well by having the
heat pipes in direct thermal contact with the inner wall 31, such
as by having the heat pipes 5 in direct contact with saddles 33,
that are in direct contact with the inner wall 31, where the
saddles 33 and the wall 31 are formed of, or include, a highly
thermally conductive material, such as steel. As noted above, such
an arrangement may reduce the temperature and the heat transport
capability of the heat pipes, but such a result may be acceptable
for some applications.
[0083] The indefinite articles "a" and "an," as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to mean "at least one."
[0084] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Multiple elements listed with "and/or" should be construed in the
same fashion, i.e., "one or more" of the elements so conjoined.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified.
[0085] The use of "including," "comprising," "having,"
"containing," "involving," and/or variations thereof herein, is
meant to encompass the items listed thereafter and equivalents
thereof as well as additional items.
[0086] It should also be understood that, unless clearly indicated
to the contrary, in any methods claimed herein that include more
than one step or act, the order of the steps or acts of the method
is not necessarily limited to the order in which the steps or acts
of the method are recited.
[0087] While aspects of the invention have been described with
reference to various illustrative embodiments, such aspects are not
limited to the embodiments described. Thus, it is evident that many
alternatives, modifications, and variations of the embodiments
described will be apparent to those skilled in the art.
Accordingly, embodiments as set forth herein are intended to be
illustrative, not limiting. Various changes may be made without
departing from the spirit of aspects of the invention.
* * * * *