U.S. patent application number 12/403668 was filed with the patent office on 2009-09-17 for cylindrical bernoulli heat pumps.
Invention is credited to Charles Agosta, Arthur R. Williams.
Application Number | 20090229796 12/403668 |
Document ID | / |
Family ID | 40933998 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090229796 |
Kind Code |
A1 |
Williams; Arthur R. ; et
al. |
September 17, 2009 |
CYLINDRICAL BERNOULLI HEAT PUMPS
Abstract
Embodiments of a heat transfer apparatus, and related methods,
involve a first flow path through a neck portion of a venturi
defined by at least one boundary wall, a first heat source external
to and in thermal communication with the boundary wall, and a drive
system for driving a first fluid through the neck portion, whereby
heat is transferred from the first heat source to the first fluid
through the boundary wall.
Inventors: |
Williams; Arthur R.;
(Holden, MA) ; Agosta; Charles; (Harvard,
MA) |
Correspondence
Address: |
GOODWIN PROCTER LLP;PATENT ADMINISTRATOR
53 STATE STREET, EXCHANGE PLACE
BOSTON
MA
02109-2881
US
|
Family ID: |
40933998 |
Appl. No.: |
12/403668 |
Filed: |
March 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61069274 |
Mar 13, 2008 |
|
|
|
Current U.S.
Class: |
165/121 ;
62/401 |
Current CPC
Class: |
F28F 13/125 20130101;
F25B 9/08 20130101; F25B 2341/0011 20130101; F28F 13/08
20130101 |
Class at
Publication: |
165/121 ;
62/401 |
International
Class: |
F28F 13/12 20060101
F28F013/12; F25D 9/00 20060101 F25D009/00 |
Claims
1. A heat transfer apparatus, comprising: means defining a first
flow path through a neck portion of a venturi defined by at least
one boundary wall; a first heat source external to and in thermal
communication with the boundary wall; and a drive system for
driving a first fluid through the neck portion, whereby heat is
transferred from the first heat source to the first fluid through
the boundary wall.
2. The apparatus of claim 1, wherein the drive system comprises: at
least one first radial array of blades positioned within the neck
portion; and at least one second radial array of blades axially
displaced from the neck portion, rotation of the first radial array
of blades providing a driving force for the second radial array of
blades.
3. The apparatus of claim 2, wherein the drive system further
comprises a gear box linking the first radial array of blades to
the second radial array of blades, a rotation of the first radial
array of blades providing a driving force for the second radial
array of blades.
4. The apparatus of claim 1, wherein the first heat source
comprises means defining a second flow path external to the
boundary wall.
5. The apparatus of claim 1, wherein the second flow path is
substantially perpendicular to the first flow path through the neck
portion.
6. The apparatus of claim 1, further comprising means defining a
return flow path from an exit of the neck portion back to an
entrance of the neck portion.
7. The apparatus of claim 6, wherein the first flow path and return
flow path define a closed loop.
8. The apparatus of claim 6, further comprising a heat exchanger
along the return flow path.
9. The apparatus of claim 8, wherein the heat exchanger removes
heat from a fluid flowing through the return flow path.
10. The apparatus of claim 2, wherein at least one of the first
radial array of blades or the second radial array of blades extend
substantially radially to the boundary wall of the first flow
path.
11. The apparatus of claim 2, wherein a cross-sectional area of the
first radial array of blades is smaller than a cross-sectional area
of the second radial array of blades.
12. The apparatus of claim 1, wherein the neck portion has a
central elongate axis and further comprising a flow deflector
positioned substantially centrally thereabout.
13. The apparatus of claim 12, wherein the second radial array of
blades comprises a plurality of blades extending substantially
radially between the boundary wall and an outer wall of the flow
deflector.
14. The apparatus of claim 1, further comprising a source for
providing the first fluid, the first fluid comprising a high-gamma
gas.
15. The apparatus of claim 1, wherein the boundary wall at an apex
of the neck portion exhibits a high thermal conductivity.
16. A method of transferring heat, comprising: providing a first
flow path through a neck portion of a venturi defined by at least
one boundary wall; providing a first heat source external to and in
thermal communication with the boundary wall; and driving a first
fluid through the neck portion to transfer heat from the first heat
source to the first fluid through the boundary wall.
17. The method of claim 16, wherein the first fluid is at least
partially driven by a drive system comprising: at least one first
radial array of blades positioned within the neck portion; and at
least one second radial array of blades axially displaced from the
neck portion, wherein a rotation of the first radial array of
blades drives the second radial array of blades.
18. The method of claim 16, wherein the first heat source comprises
a second flow path external to the boundary wall.
19. The method of claim 16, wherein the second flow path is
substantially perpendicular to the first flow path through the neck
portion.
20. The method of claim 16, wherein the neck portion comprises a
venturi shape.
21. The method of claim 16, further comprising transporting the
fluid exiting the neck portion back to an entrance of the neck
portion through a flow return path.
22. The method of claim 21, further comprising removing heat from a
fluid flowing through the return path.
23. The method of claim 22, wherein the heat is removed by a heat
exchanger in thermal communication with the return flow path.
24. The method of claim 22, wherein at least one of the first
radial array of blades or the second radial array of blades extend
substantially radially to the boundary wall of the first flow
path.
25. The method of claim 16, wherein a cross-sectional area of the
second radial array of blades is smaller than a cross-sectional
area of the first radial array of blades.
26. The method of claim 16, further comprising deflecting the first
fluid about a flow deflector positioned substantially centrally
about a central elongate axis of the neck portion.
27. The method of claim 26, wherein the second radial array of
blades comprises a plurality of blades extending radially between
the boundary wall and an outer wall of the flow defector.
28. The method of claim 16, wherein the first fluid comprises a
high-gamma gas.
29. The method of claim 16, wherein the boundary wall at an apex of
the neck portion exhibits a high thermal conductivity.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to, and the benefit of,
U.S. Provisional Patent Application No. 61/069,274, filed on Mar.
13, 2008, the entire disclosure of which is hereby incorporated by
reference.
TECHNICAL FIELD
[0002] In various embodiments, the invention relates to heat
transfer systems, and more particularly to systems and methods for
the transfer of heat between a heat source and a fluid passing a
boundary wall in thermal communication with the heat source.
BACKGROUND
[0003] Heat transfer systems such as heat pumps may be used to move
heat from a source to a sink, and may underlie, for example, the
operation of air-conditioning systems and/or heating systems for
buildings.
[0004] Heat transfer systems can be divided into two fundamental
classes distinguished by the direction in which heat moves. In one
class of heat transfer system, heat flows from higher temperatures
to lower temperatures. This heat flow may, for example, be
harnessed to produce mechanical work, as in internal-combustion
engines. A second class of heat transfer device includes systems
that move heat from lower temperatures to higher temperatures. Such
systems are commonly called "heat pumps." Refrigerators and air
conditioners, for example, are heat pumps.
[0005] Heat pumps necessarily consume power. In general, commonly
used heat pumps employ a working fluid (gaseous or liquid) whose
temperature is varied over a range extending from below that of the
source to above that of the sink to which heat is pumped. The
temperature of the working fluid is often varied by compression of
the fluid. While conventional heat pumps may be effective in
transferring or pumping heat, substantial power (in the form of
mechanical work) is necessary to compress the fluid and facilitate
heat transfer, making these systems inefficient.
SUMMARY OF THE INVENTION
[0006] In various embodiments, the present invention relates to
improved systems and methods for transferring heat between a heat
source and a fluid. More particularly, embodiments of the invention
include heat transfer systems (i.e., systems for moving heat from
one location to another), such as, but not limited to heat pumps
(i.e., systems that consume power to move heat from one location (a
"source") to another, higher temperature location (a "sink" or
"heat sink")), that utilize the "Bernoulli principle" to enable
heat transfer between a heat source and a working fluid, whereby
microscopic random molecular motion (temperature and pressure) is
converted into directed motion (macroscopic fluid flow) while
leaving the total kinetic energy unchanged. Whereas compression
consumes power, Bernoulli conversion does not. Exploitation of the
Bernoulli effect, therefore, substantially improves system
efficiency relative to conventional, compression-based systems.
[0007] In addition, the present invention relates to improved
systems and methods for minimizing the creation of entropy during
the fluid flow process, thereby further improving the system
efficiency relative to conventional, compression-based systems.
[0008] One aspect of the invention pertains to a heat transfer
apparatus, embodiments of which include means defining a first flow
path through a neck portion of a venturi defined by at least one
boundary wall, a first heat source external to and in thermal
communication with the boundary wall, and a drive system for
driving a first fluid through the neck portion, whereby heat is
transferred from the first heat source to the first fluid through
the boundary wall. The drive system may include at least one first
radial array of blades positioned within the neck portion and at
least one second radial array of blades axially displaced from the
neck portion. Rotation of the first radial array of blades provides
a driving force for the second radial array of blades. The drive
system may also include a gear box linking the first radial array
of blades to the second radial array of blades, so that rotation of
the first radial array of blades provides a driving force for the
second radial array of blades. As used herein, the term "radial
array of blades" is intended to encompass arrangements that behave
as a turbine or as a blower, depending on whether energy is
absorbed from or imparted to a fluid flow. The blades need not be
separate members but may instead correspond to openings in a rotary
cage or similar arrangement, or to baffles or other structures in
turbine or blower configurations known in the art.
[0009] In one embodiment, the first heat source includes means
defining a second flow path external to the boundary wall. The
second flow path may be substantially perpendicular to the first
flow path through the neck portion. The apparatus may include means
defining a return flow path from an exit of the neck portion back
to an entrance of the neck portion. In some embodiments, the first
flow path and return flow path define a closed loop. The apparatus
may include a heat exchanger along at least a portion of the return
flow path, e.g., to remove heat from a fluid flowing through the
return flow path.
[0010] The first radial array of blades and/or the second radial
array of blades may extend substantially radially to the boundary
wall of the first flow path. The cross-sectional area of the first
radial array of blades may be smaller than the cross-sectional area
of the second radial array of blades. In one embodiment, the neck
portion has a central elongate axis and a flow deflector positioned
substantially centrally thereabout. The second radial array of
blades may include a plurality of blades extending substantially
radially between the boundary wall and an outer wall of the flow
deflector. The apparatus may include a source for providing the
first fluid, the first fluid including, or consisting essentially
of, air and/or a high-gamma gas. The boundary wall within the neck
portion and, for example, at or near an apex of the neck portion
(i.e., a local minimum in the cross-sectional area of the flow),
may exhibit a high thermal conductivity.
[0011] Another aspect of the invention includes a method of
transferring heat. Embodiments of the method include providing a
first flow path through a neck portion of a venturi defined by at
least one boundary wall, providing a first heat source external to
and in thermal communication with the boundary wall, and driving a
first fluid through the neck portion to transfer heat from the
first heat source to the first fluid through the boundary wall. In
one embodiment, the first fluid is at least partially driven by a
drive system. The drive system may include at least one first
radial array of blades positioned within the neck portion and at
least one second radial array of blades axially displaced from the
neck portion (i.e., by being positioned either upstream or
downstream of the neck portion). Rotation of the first radial array
of blades drives the second radial array of blades.
[0012] The first heat source may include a second flow path
external to the boundary wall. The second flow path may be
substantially perpendicular to the first flow path through the neck
portion. In some embodiments, the neck portion is venturi shaped.
The method may further include transporting the fluid exiting the
neck portion back to an entrance of the neck portion through a flow
return path. Heat may be removed from a fluid flowing through the
return path, for example, by a heat exchanger in thermal
communication with the return flow path.
[0013] In one embodiment, the first radial array of blades and/or
the second radial array of blades extend substantially radially to
the boundary wall of the first flow path. The cross-sectional area
of the second radial array of blades may be smaller than a
cross-sectional area of the first radial array of blades. The first
fluid may be deflected about a flow deflector positioned
substantially centrally about a central elongate axis of the neck
portion. The second radial array of blades may include a plurality
of blades extending radially between the boundary wall and an outer
wall of the flow defector. The boundary wall at or near an apex of
the neck portion may exhibit a high thermal conductivity. The first
fluid may include, or consist essentially of, air and/or a
high-gamma gas.
[0014] These and other objects, along with advantages and features
of the present invention herein disclosed, will become more
apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be
understood that the features of the various embodiments described
herein are not mutually exclusive and can exist in various
combinations and permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0016] FIG. 1A shows a schematic side view of a venturi shaped
flow, in accordance with one embodiment of the invention;
[0017] FIG. 1B shows a schematic perspective view of a cylindrical
venturi nozzle, in accordance with one embodiment of the
invention;
[0018] FIG. 1C shows a schematic perspective view of a
two-dimensional venturi nozzle, in accordance with one embodiment
of the invention;
[0019] FIG. 2 shows a schematic side view of a heat transfer system
including a venturi flow, in accordance with one embodiment of the
invention;
[0020] FIG. 3 shows a schematic front view of a grid structure for
a heat transfer system including a venturi flow, in accordance with
one embodiment of the invention;
[0021] FIG. 4A shows a schematic view of a closed-loop heat
transfer system including a venturi flow, in accordance with one
embodiment of the invention;
[0022] FIG. 4B shows a schematic view of the closed-loop heat
transfer system of FIG. 4A, further including a control system;
[0023] FIG. 5 is a graph showing the relationship between velocity
and temperature across a width of a neck portion of a heat transfer
system including a venturi flow, in accordance with one embodiment
of the invention;
[0024] FIG. 6A shows a schematic side view of a heat transfer
system including a drive system, in accordance with one embodiment
of the invention;
[0025] FIG. 6B shows a schematic side view of another heat transfer
system including a drive system, in accordance with one embodiment
of the invention;
[0026] FIG. 7A shows a schematic side view of a single venturi, in
accordance with one embodiment of the invention;
[0027] FIG. 7B shows a schematic side view of a planar venturi
array, in accordance with one embodiment of the invention;
[0028] FIG. 7C shows a schematic side view of a cylindrical venturi
array, in accordance with one embodiment of the invention;
[0029] FIG. 8A shows a schematic plan view of a squirrel-cage heat
transfer system, in accordance with one embodiment of the
invention;
[0030] FIG. 8B shows a schematic plan view of another squirrel-cage
heat transfer system, in accordance with one embodiment of the
invention;
[0031] FIG. 9 shows a schematic end view of a cylindrical blade
array including a plurality of curved blades, in accordance with
one embodiment of the invention;
[0032] FIG. 10 shows a schematic end view of a cylindrical blade
array including a plurality of stators surrounded by a plurality of
rotors, in accordance with one embodiment of the invention;
[0033] FIG. 11A shows a schematic side view of the flow paths
through a cylindrically arranged heat transfer system, in
accordance with one embodiment of the invention;
[0034] FIG. 11B shows a schematic end view of the heat transfer
system of FIG. 11A;
[0035] FIG. 12A shows a schematic front view of another
cylindrically arranged heat transfer system, in accordance with one
embodiment of the invention;
[0036] FIG. 12B shows a schematic top plan view of the heat
transfer system of FIG. 12A;
[0037] FIG. 12C shows a schematic bottom plan view of the heat
transfer system of FIG. 12A;
[0038] FIG. 13 shows a schematic side view of another cylindrically
arranged heat transfer system, in accordance with one embodiment of
the invention;
[0039] FIG. 14 shows a schematic side view of a stacked
cylindrically arranged heat transfer system, in accordance with one
embodiment of the invention;
[0040] FIG. 15 shows a schematic view of a plurality of flow paths
through a cylindrically arranged heat transfer system, in
accordance with one embodiment of the invention;
[0041] FIG. 16 shows another schematic representation of the fluid
flow paths of FIG. 15;
[0042] FIG. 17 shows a plan view of a fin arrangement within an
open central portion of a cylindrically arranged heat transfer
system, in accordance with one embodiment of the invention;
[0043] FIG. 18 shows a plan view of a first fluid flow path for a
"no-touch" condition flow through a cylindrically arranged blade
array, in accordance with one embodiment of the invention; and
[0044] FIG. 19 shows a plan view of a cylindrically arranged blade
array for use in a "no-touch" condition flow, in accordance with
one embodiment of the invention.
DESCRIPTION
[0045] In general, the present invention relates to heat transfer
systems, and more particularly to Bernoulli heat pumps for use in
transferring heat from a heat source to a working fluid.
[0046] One embodiment of the invention includes a venturi-shaped
channel through which a working fluid can flow in accordance with
the Bernoulli principle. An exemplary venturi 100 is shown in FIG.
1A. The venturi 100 includes an inlet portion 110, a neck portion
120 (e.g., a region of the flow-path with a heat exchanging
boundary, 120 and/or 140, connecting the region of decreasing
cross-sectional area to the region of increasing cross-sectional
area), and a diffuser or outlet portion 130, with the
cross-sectional area of the venturi 100 decreasing from the inlet
portion 110 to the neck portion 120 and increasing, after passing
an apex 140 of the neck portion 120, in the outlet portion 130. The
venturi 100 may have any appropriate cross-sectional shape such as,
but is not limited to, a circular, oval, square, or rectangular
cross-section. The cross-sectional shape may be constant along the
length of the venturi 100. Alternatively, depending on the
application, the cross-sectional shape may vary along the length of
the venturi 100. For example, the cross-section of the venturi 100
may be substantially circular at an apex 140 of the neck portion
120 while being substantially square at an outer edge 150 of the
inlet portion 110 and/or an outer edge 160 of the outlet portion
130. An example venturi nozzle 100 with a cylindrical cross-section
(e.g. a venturi nozzle with a cross-sectional area varying along a
length thereof) is shown in FIG. 1B, while an example venturi
nozzle 100 with a rectangular cross-section (e.g. a venturi nozzle
with a cross-sectional area varying along a length thereof due to a
variation of only one dimension of the cross-section) is shown in
FIG. 1C. In operation, a working fluid enters the venturi 100
through the inlet portion 110. As the cross-sectional area of the
venturi 100 decreases towards the neck portion 120, the directed
motion of particles within the working fluid must increase in order
to maintain a constant mass flux. Such conversion occurs, without
the addition of energy, by the local reduction of the random
molecular motion of the particles. As a result, as the
cross-sectional area decreases, the temperature and pressure of the
working fluid decrease, while the velocity of the working fluid
increases. Whereas compression consumes power, Bernoulli conversion
does not. Though Bernoulli conversion itself consumes no power, the
fluid nozzling may result in relatively strong velocity gradients
within the working-fluid flow, which may result in some viscous
loss. After passing through the neck portion 120, the
cross-sectional area of the venturi 100 increases, resulting in a
reduction in fluid velocity and a corresponding increase in
pressure and temperature.
[0047] Therefore, as the working-fluid flows through the central
neck portion 120 of the venturi 100, the velocity of the fluid
increases while the temperature decreases. After the working fluid
has substantially passed the apex 140 of the central neck portion
120, the velocity of the working fluid decreases while the
temperature increases. As a result, a venturi 100 may be used to
quickly and efficiently reduce the temperature of a working fluid
in the vicinity of the neck portion 120. Placing a heat source at
or near the neck portion 120 allows the venturi 100 to act as a
heat transfer system, with heat being passed from the heat source
to the working fluid at the neck portion 120 as long as the
temperature of the working fluid at the neck portion 120 is lower
than that of the heat source (regardless of whether the temperature
of the working fluid entering the inlet portion 110 is higher than
that of the heat source). In various embodiments, the heat source
is located within the neck portion 120, in the outlet portion 130
downstream of the neck portion 120, or extending between both the
neck portion 120 and the outlet portion 130.
[0048] In one embodiment, the venturi 100 is operated by driving
the working fluid through a flow path defined by at least one
boundary wall 170. The boundary wall 170 may be formed from any
appropriate material including, but not limited to, a metal, a
ceramic, a plastic, or a composite material. In an alternative
embodiment, the flow path including the venturi 100 may be
self-forming, for example, by directing gas through a small
aperture.
[0049] An exemplary venturi 100 including a heat source in thermal
communication with a neck portion 120 of the venturi 100 is shown
in FIG. 2. In this embodiment, a working fluid is driven from an
inlet portion 100, through the neck portion 120, and out through an
outlet portion 130. A heat source 210 is positioned within the neck
portion 120. The heat source 210 may be a source of air to be
cooled, such as an interior air flow in a building, for an air
conditioning system. Alternatively, the heat source may include a
recirculating cooling fluid for a mechanical device, a pipe flow in
a fluid transport system (such as, for example, an oil or gas
piping system), a mixed-phase fluid flow, or any other appropriate
fluid flow or solid heated material requiring cooling. Example heat
sources may include components for electrical systems and/or
vehicles, such as aircraft or ground transportation.
[0050] In the illustrated embodiment, the heat source 210 includes
a channel 220 through which a heated fluid 230 is flowed. The
channel 220 may include a material selected to provide a high
thermal conductivity between the heat source 210 and the working
fluid within the venturi 100. A high thermal conductivity material
may include any material having a thermal conductivity that is
higher than that of one or more surrounding materials in thermal
communication with the high thermal conductivity material. Example
materials include, but are not limited to, metals (such as, but not
limited to, copper or aluminum), graphite-based materials, textured
surfaces, including nano-textured surfaces, and/or carbon nano-tube
based materials. In one embodiment, the channel 220 may include or
consist essentially of a material such as, but not limited to, a
metal such as copper, steel, aluminum, a ceramic, a composite
material, or combinations thereof.
[0051] The channel 220 may be constructed from a single material or
from a plurality of materials. For example, one embodiment of the
invention includes a channel 220 having a high thermal conductivity
in contact with the neck portion 120 of the venturi 100; elsewhere,
the flow path has a lower thermal conductivity, or even a high
thermal insulation.
[0052] In an alternative embodiment, the heat source 210 is a solid
block of material, without a channel defined therethrough, such as,
but not limited to, a metal such as copper, steel, aluminum, a
ceramic, a composite material, or combinations thereof. The
material is selected to provide a high thermal conductivity between
the heat source 210 and the working fluid within the venturi 100.
The solid block heat source 210 relies on conduction through the
material to transport heat from a source to the neck portion 120 of
the venturi 100.
[0053] In one embodiment, a portion 240 of the channel 220 is
embedded within the boundary wall 170 of the venturi 100, such that
the channel is in direct physical contact with the working fluid
within a portion of the venturi 100, e.g., within the neck portion
120. In an alternative embodiment, the heat source 210 is placed
against a sealed boundary wall 170 of the venturi 100, such that
any heat transferred between the heat source 220 and the working
fluid must pass through the boundary wall 170.
[0054] The heat source 210 may have any appropriate cross-sectional
shape. For example, as shown in FIG. 2, the heat source 210 may
conform to the boundary wall 170 of the venturi 100 along a portion
thereof. Alternatively, the heat source 210 may have any desired
cross-sectional shape such as, for example, a circular, oval,
square, or rectangular cross-section.
[0055] In operation, heat is transferred from the heat source 210
to the working fluid as it passes through the neck portion 120 of
the venturi 100 (i.e., the portion of the venturi 100 where the
velocity is at or near a maximum and the temperature is at or near
a minimum). Because convection is orders of magnitude more
effective than conduction in transferring heat, the surface area of
the channel portion 240 exposed to the working-fluid flow can be
much smaller than that exposed to the heat-source flow. As a
result, the entire channel 220 may be formed from a material
exhibiting a high thermal conductivity (e.g., a metal), thereby
allowing heat to be conducted from the heat-source fluid 230 to the
channel 220 over the entire cross-section of the channel 220, after
which the heat is transferred from the channel 220 to the working
fluid within the venturi 100 through the exposed channel portion
240.
[0056] One or more fins may extend from the channel portion 240
into either the working fluid within the venturi 100 and/or into
the heat-source fluid 230 to provide additional surface area over
which heat transfer can take place. These fins may have any
appropriate size and shape, and may be formed from any of the
thermally conducting materials described herein. An exemplary fin
structure for placement within the neck portion 120 of a venturi
100 is shown in FIG. 3. In this embodiment, fins 310 extend from
the boundary wall 170 of the venturi 100 and are arranged in a grid
pattern. The fins may, for example, be formed from the same
material as the heat source channel 220 (in the case of a fluid
flow based heat source) or of the same material as the heat source
210 itself (for a solid heat source). In one embodiment, the fins
310 extend from the exposed channel portion 240 at an apex 140 of
the venturi 100. In alternative embodiments, any appropriate
number, arrangement and placement of fins may be used. The fins may
be hollow to allow the heated fluid to be cooled 230 within the
heat source channel 220 to flow through the fins.
[0057] The height 250 of the apex 140 of the neck portion 120 may
be substantially smaller than the width of the cross-section at the
apex 140, thereby allowing heat to be transferred between the heat
source 210 and the working fluid within the venturi 100 over a
substantial area.
[0058] In one embodiment, the venturi 100 is constructed as an
open-loop system, such that the working fluid is entrained from the
surrounding atmosphere and exhausted to the surrounding atmosphere
after being driven through the venturi 100. In this embodiment, the
working fluid may include, or consist essentially of, air, one or
more high-gamma (heat capacity ratio) and/or low-c.sub.p (specific
heat at a constant pressure) gases, one or more rare gases,
particles of one or more solid materials, or mixtures thereof. A
high-gamma gas is one having a value of gamma greater than that of
air, while a low-c.sub.p gas is one having a value of c.sub.p lower
than that of air. In another embodiment (for example, an
implementation designed for underwater heat transfer), the working
fluid may include, or consist essentially of, water, one or more
high-gamma and/or low-Cp gases, one or more rare gases, particles
of one or more solid materials, or mixtures thereof. But more
generally, any suitable gaseous or liquid working fluid may be
utilized. The suitability of a working fluid may be determined by
factors including, but not limited to, the thermal properties of
the material, viscosity, toxicity, expense, and/or scarcity. In one
embodiment, working fluids having lower values for specific heat
are advantageous, at least because the specific heat determines how
big a temperature drop is produced by a given flow speed. Suitable
fluids include, but are not limited to, those having high thermal
conductivity, low viscosity, appropriate gas-liquid transition
temperatures, low cost (e.g. to manufacture and handle), and/or
meeting required environmental standards. The working fluid may be
driven through the venturi 100 by a fan, pump, blower, or other
appropriate fluid drive system, placed either upstream of the
venturi 100 (i.e. before the inlet portion 110) or downstream of
the venturi 100 (i.e. after the outlet portion 130).
[0059] In an alternative embodiment, the venturi 100 is part of a
closed-loop system wherein, upon exiting the outlet portion 130 of
the venturi 100, the working fluid is recirculated back to the
inlet portion 110. As the working fluid in a closed-loop system is
not exhausted to the surrounding atmosphere, fluids which may be
environmentally damaging, but which provide improved heat transfer
characteristics over air, may be utilized. In order to remove the
heat transferred to the working fluid from the heat source 210, one
or more heat exchangers may be incorporated into a return leg of a
closed-loop system.
[0060] FIG. 4A illustrates an exemplary closed-loop heat transfer
system incorporating a return leg including a heat exchanger. In
this embodiment, the heat transfer system 400 includes a venturi
100 through which a working fluid is driven, as described above. A
heat source 210 is placed in thermal contact with the neck portion
120 of the venturi 100; heat is transferred from the heat source
210 to the working fluid as it is driven through the venturi 100.
Upon exiting the outlet portion 130 of the venturi 100, a fluid
return path 410 carries the working fluid back to the inlet portion
100 of the venturi 100. This fluid return path 310 may include, for
example, a closed duct system through which the fluid is free to
travel. One or more means of driving the working fluid around the
fluid return path 410 and through the venturi 100 may be placed at
any appropriate location within the system 400. For example, the
embodiment shown in FIG. 4A includes a blower fan 420 located
downstream of the venturi 100. More generally, any suitable fluid
driving system may be used including, but not limited to, blowers,
fans, pumps, turbines, and/or jets. Indeed, multiple fluid driving
means--e.g., a plurality of blower fans 420 positioned at various
locations around the closed fluid return flow path 410--may be
used.
[0061] One or more heat exchangers 430 may be placed along the
fluid return path 410 to remove the heat transferred to the working
fluid from the heat source 210. The form of heat exchanger 430 is
not critical to the present invention. Suitable configurations
include, but are not limited to, parallel-flow heat exchangers,
cross-flow heat exchangers, counter-flow heat exchangers, shell and
tube heat exchangers, plate heat exchangers, regenerative heat
exchangers, adiabatic wheel heat exchangers, plate fin heat
exchangers, multi-phase heat exchangers, spiral heat exchangers, or
combinations thereof. This heat exchanger 430 may, for example,
take heat from the working fluid and vent it to the surrounding
atmosphere.
[0062] The heat transfer system 430 may be used, for example, in an
air-conditioning system, where heat is to be removed from the
interior of a building and vented to the exterior of the building.
In this embodiment, the heat source may include a flow of interior
building air which is driven passed one or more venturis 100. Heat
from the interior air is transferred to the working fluid, after
which the interior air is exhausted back into the building. The
heat that is transferred to the working fluid can then be removed
from the working fluid by the heat exchanger 430, which vents the
heat to the atmosphere outside the building. Alternatively, the
heat from the working fluid may be utilized for other purposes,
e.g., local or special-purpose heating, or power generation.
[0063] In alternative embodiments, heat transfer systems according
to the invention include a plurality of venturis 100, heat sources
210, heat exchangers 430, and/or flow paths 410. Heat transfer
systems according to the invention may also include both open-loop
flow paths and closed-loop flow paths for either the working fluid
and/or a heat-source fluid flow.
[0064] In one embodiment, additional (and conventional) control
devices are incorporated into the system to control elements of the
working-fluid flow including, but not limited to, the velocity, the
pressure, the temperature, the humidity, and the volume and/or
proportions of individual components of the working fluid.
Measurement devices may also be incorporated into the system to
monitor performance characteristics of the system including, but
not limited to, the temperature, velocity, pressure, and properties
and/or proportions of the individual components of the working
fluid. In one embodiment, a control system receives data from the
measurement device(s) and utilizes these to operate the control
devices in order to optimize the performance of the system,
continuously and in real-time. The control system may also respond
to user inputs.
[0065] An exemplary heat transfer system 400 including a control
system 440 is shown in FIG. 4B. The control system 440 includes a
controller 450 (e.g., an electronic controller such as a computer,
and/or a mechanical controller) that controls the functionality of
a humidity controller 460 and/or a fan 420. The humidity controller
460, or other appropriate flow-control element, controls the
injection of a second fluid component into the working-fluid flow.
In one embodiment, no humidity controller is required. The control
system 440 also includes at least one sensor 470 for sensing at
least one parameter of the working-fluid flow (such as, but not
limited to, temperature, flow rate, pressure, density, humidity,
and/or chemical composition). The sensor(s) 470 may be place at any
appropriate location within the heat transfer system 400 such as in
the return flow path 410 upstream of the venturi 100. The sensor
470 is coupled to a measurement device 480 which communicates with
the sensor 470 and sends a measured reading from the sensor 470 to
the controller 450. In an alternative embodiment, the sensor 470
may communicate directly with the controller 450, without the need
for a measurement device 480 therebetween. In operation, the
control system 440 controls at least one parameter of the
working-fluid flow to assist in controlling the transfer of heat
between the working fluid and the heat-source flow (from a
heat-generation source 490 such as, for example, the interior air
flow of a building).
[0066] In one embodiment, a pressure-control system may be used in
a closed-loop system to control the pressure of the working fluid
within the system. For example, a pressure-control system may
pressurize the working fluid within the system to either above or
below atmospheric pressure. In one embodiment, the working fluid is
pressurized to a pressure of between 1.2 and 1.8 atmospheres, and
more typically to a pressure of between 1.4 and 1.6 atmospheres. In
an exemplary embodiment, the working fluid is pressurized to a
pressure of approximately 1.5 atmospheres. In one embodiment, a
heat transfer system includes a plurality of venturis 100, which
may, for example, be stacked together to form the heat transfer
system. This system may be used, for example in an automobile
radiator.
[0067] The efficiency of a Bernoulli heat pump is, in general,
limited by factors such as the entropy increase associated with the
exhaust of heat at a temperature above that at which the heat was
acquired and/or the entropy increase due to the variation of the
flow speed across the boundary layer at the venturi wall (which, in
turn, is related to the viscosity multiplied by the square of the
velocity gradient).
[0068] More particularly, due to the effects of viscosity,
Bernoulli conversion is not fully reversible. That is, that after
passing through the neck of the venturi, the flow does not simply
return to the same flow conditions that it had upstream of the neck
portion. Rather, the fluid dynamics of flow upstream and downstream
of the neck of the venturi are quite different, especially with
regard to the sign of the pressure gradient and the stability of
the flow with respect to turbulence.
[0069] If the flow remains laminar downstream of the neck, then its
cross-sectional area does not spontaneously increase. The result is
called a "laminar jet." The "unfavorable" sign (>0) of the
longitudinal pressure gradient downstream of the neck renders
laminar flow unstable. If any condition (e.g., surface roughness)
triggers the transition, the flow becomes turbulent, and its
cross-sectional area increases. While the dramatic increase in
effective viscosity that accompanies the transition to turbulent
flow increases the cross-sectional area of the flow, it also
increases the irreversible dissipation. For example, experimental
data for so-called "critical flow venturis" (CFVs) suggests that
the pressure recovery for Mach-1 venturis is limited to
approximately 90%. That is, a pressure drop of 10% across the
venturi is required to maintain the flow, even if the venturi
surface is very smooth. The power consumed maintaining the flow is
proportional to this pressure drop; the coefficient of
proportionality is the volume flow rate.
[0070] Bernoulli heat pumps may be either open-loop or closed-loop.
In general, both open and closed systems require a venturi and a
source of shaft work to maintain flow through the venturi. The
shaft work may be provided, for example, by an axial blower. Open
and closed systems differ in the disposition of the heat
transferred to the working fluid in the venturi neck. In open
systems, the working fluid emerging from the venturi and the heat
that has been transferred to it are simply exhausted into the
environment. In closed systems, the working fluid is not
discharged, but rather is returned to the entrance of the venturi
for repeated use. While closed systems offer greater choice with
regard to the fluids used, they may require removal of the heat
transferred to the working fluid (e.g., by a heat exchanger), as
discussed, for example, with respect to FIGS. 4A and 4B. The heat
transferred into and out of the working fluid by the heat source
and sink are commonly delivered by independent fluid flows.
Similarly, the source and sink fluid flows are maintained by fluid
drive devices such as, but not limited to, pumps, blowers or fans.
These propulsion devices, whatever their character, generally
require power consuming motors. The heat delivered by the heat
source need not be carried by a fluid flow, but can, in certain
embodiments, be delivered directly through a thermal conductor
exposed directly to whatever is to be cooled.
[0071] In addition, due to the effects of viscosity, the
working-fluid flowing through a venturi will include boundary-layer
regions extending from the boundary walls of the venturi. More
particularly, thermal equilibrium at the boundary wall implies the
so-called "no-slip" boundary condition, wherein the mean velocity
of the working fluid at the surface of the boundary wall is zero.
The no-slip condition, in turn, implies a sharp variation of the
macroscopic flow speed across (i.e., transverse to) the flow. The
thin region in which this sharp variation occurs is called the
boundary layer. Sharp speed variation causes the viscous generation
of heat. The interplay among the viscous generation of heat, the
conduction of heat by the slowly moving fluid near the boundary
wall, and the convection of heat by the rapid axial flow away from
the venturi wall determines the variation of the fluid temperature
across the boundary layer.
[0072] This interplay may limit the transfer of heat into the
working-fluid flow. The flow of heat between the boundary wall and
the working-fluid flow is affected by the transverse temperature
gradient at the venturi wall. In particular, viscous heating causes
the sign of this gradient to change as the wall temperature is
varied. As the wall temperature is reduced, a temperature is
reached for which the transverse temperature gradient vanishes.
Further reduction of the wall temperature results in heat transfer
from the working fluid into the venturi wall. The temperature at
which the transverse temperature gradient changes sign is called
the adiabatic or recovery temperature. Temperature recovery across
the boundary layer may, in some embodiments, limit the
effectiveness of cooling based on the Bernoulli effect.
[0073] The relative change in velocity and temperature of the
working fluid near the boundary wall of a venturi is shown
graphically in FIG. 5. More particularly, FIG. 5 shows the
magnitude 530 of the velocity 510 of the working fluid decreasing
from its free-stream value (in the venturi core 550 above the edge
of the boundary layer 520) down to zero at the boundary wall 560 of
the venturi. Simultaneously, the graph shows the temperature 540 of
the working fluid increasing as it approaches the boundary wall 560
of the venturi.
[0074] In various embodiments of the invention, the working fluid
may consist essentially of a single fluid component. This fluid
component may be a gas such as, for example, air, oxygen, a
high-gamma gas, a rare gas, and/or mixtures thereof. In one
embodiment the fluid component is a liquid, such as, for example,
water. Alternatively, the working fluid may include a plurality of
fluid components. In such cases, a heat transfer system
incorporating a venturi can achieve a greater level of heat
transfer than may be achieved using a single, unitary working
fluid. In one embodiment, the working fluid includes two separate
fluid components. In an alternative embodiment, three or more fluid
components are used. By using a working fluid including a plurality
of fluid components, the effect of the boundary layer on the
transfer of heat from the heat source (in thermal communication
with the boundary layer) to the working fluid may be substantially
reduced. For example, in one embodiment of the invention, the
working fluid includes air as the first fluid component. A second
fluid component such as water is entrained into the fluid flow.
Upon passing through the neck portion of a venturi, the second
fluid component is separated from the mean flow path of the working
fluid, passing through the boundary layer in the fluid near the
wall, and striking the surface of the boundary wall. When
lower-temperature particles of the second fluid component impinge
against the boundary wall, heat transfer therebetween
increases.
[0075] The first and second working fluid components may be
segregated within the venturi by any suitable means. More
particularly, to achieve increased heat transfer, particles of a
second fluid component--whatever their composition or thermodynamic
state--after coming into thermal equilibrium with the working-fluid
flow in the free-stream portion of the flow, are segregated from
the first fluid component and impinge upon a boundary wall of the
venturi. Segregating the first and second fluid may be accomplished
by, for example, filtering, dehumidification and/or exhaust
scrubbing.
[0076] Embodiments of the invention may include systems and/or
methods to increase the efficiency of a heat transfer system by
using kinetic energy generated within a high-flow-rate portion of
the system to power a drive system for the working fluid. For
example, in one embodiment, kinetic energy in the working fluid
through the neck portion of the venturi is removed from the flow by
a first radial array of blades, and transferred to a second radial
array of blades (e.g. a blower) which is used to drive the
working-fluid flow. This may compensate, at least in part, for any
viscous losses generated within the venturi. The first radial array
of blades may be positioned at or near an apex of the venturi, or
may instead be placed at another location within or near the neck
portion of the venturi. The second radial array of blades may be
axially displaced from the neck portion, and may, for example, be
placed either upstream or downstream of the neck portion. For
example, the second radial array of blades may be placed either in
an inlet and/or outlet portion of the venturi. Alternatively, the
second radial array of blades may be placed at any point in the
return flow path of a closed loop system. In one embodiment, the
energy generated by the first radial array of blades is used to
drive a single second radial array of blades. In alternative
embodiments, the energy generated by the first radial array of
blades is used to at least partially power multiple second radial
arrays of blades.
[0077] One or more first radial arrays of blades may be coupled to
one or more second radial arrays of blades through a mechanical or
electrical coupling system. For example, the first radial array(s)
may be mechanically connected to the second radial array(s) through
one or more mechanical linkages. The mechanical linkage may include
a gear box to account for the difference in flow speed between the
first radial array of blades (operating within the fast-flowing
working fluid in the neck portion) and the slow-moving working
fluid away from the neck portion. The first radial array(s) may
also be coupled to the second radial array(s) through an electrical
coupling system, with the energy captured by the first radial
array(s) being converted into electrical energy which can then be
sent to the second radial array(s), located at any position within
the system, to drive the working fluid.
[0078] In operation, as a working fluid passes through the neck
portion of a venturi, the velocity of the working fluid increases.
Placing the first radial array(s) within the neck portion means
that it is driven by the accelerated working fluid. The energy
captured by the first radial array(s) as it is (or they are) driven
by the working fluid may then be used to drive the second radial
array(s) located elsewhere in the system and, for example, either
upstream or downstream of the neck portion. This second radial
array(s) may then drive the working fluid through the neck portion.
As a result, kinetic energy within the neck portion can be
harnessed to assist in driving the working fluid, thereby reducing
the amount of energy required to drive the system.
[0079] FIG. 6A illustrates an exemplary heat transfer system 600
including a first radial array of blades 610 within a neck portion
120 of a venturi 100. The first radial array of blades 610 is
coupled through a mechanical linkage 620 to a second radial array
of blades 630 located in an inlet portion 110 of the venturi 100.
The mechanical linkage 620 may include a gearing mechanism (not
shown). The first radial array of blades 610 and second radial
array of blades 630 may be unitary or may include multiple radial
arrays of blades. In operation, the working fluid is driven through
the venturi 100 by the second radial array of blades 630. As the
working fluid accelerates and passes through the neck portion 120,
the fluid drives the first radial array of blades 610 located
therein. The energy extracted by the first radial array of blades
610 is fed back into the second radial array of blades 630 through
the mechanical linkage 620 to provide energy to drive the second
radial array of blades 630. Any additional energy required to drive
the second radial array of blades 630 may be provided by an
electrical motor or other suitable driving mechanism. As discussed
hereinabove, a heat source may be located within the neck portion,
allowing heat to be transferred from the heat source to the working
fluid.
[0080] In an alternative embodiment, a heat transfer system 650
includes a cylindrical flow channel 660 with a flow deflector 670
located substantially centrally therein to change the
cross-sectional area from an inlet portion 675 to a neck portion
680 of a heat transfer system 650. In this embodiment, a first
radial array of blades 685 is housed within a portion of the flow
deflector 670 and driven by the working fluid as it flows around
the flow deflector 670 and through the reduced cross-sectional area
between the wall of the flow deflector 670 and the wall of the
cylindrical flow channel 660. The energy extracted by this first
radial array of blades 685 is then used to drive at least one
second radial array of blades (not shown), as described
hereinabove. In one implementation, the second radial array(s) 630
are located at or near a leading edge 690 of the flow deflector
670. In an alternative implementation, the second radial array(s)
630 are located elsewhere within the system, e.g., upstream of the
neck portion 680, downstream of the neck portion 680, and/or within
a flow return portion of a closed loop system. One or more heat
sources may be placed in thermal communication with the cylindrical
flow channel 660 and/or the flow deflector 670 within the neck
portion 680, allowing heat to be transferred from the heat source
to the working fluid within the neck portion 680. A flow diffuser
may be positioned downstream of the neck portion 680 to assist in
smoothly transitioning the working-fluid flow from a fast and cold
state to a slow and hotter state downstream of the neck portion
680. This flow diffuser may, for example, be shaped similarly to,
but oriented in an axially opposite direction from, the flow
deflector 670.
[0081] In various embodiments of the invention, the flow path
through a neck portion of a heat transfer system and, for example,
a neck portion of a venturi, may be arranged in a number of
different configurations. Exemplary configurations are shown in
FIG. 7A through 7C. In FIG. 7A, the first flow path 710, i.e., the
working-fluid flow path, includes a flow path through a neck
portion 720 of a single venturi 100, as described hereinabove. In
FIG. 7B, the first flow path 725, includes a flow path through a
plurality of neck portions 120 formed by a plurality of blades 730
arranged as a planar venturi array 740.
[0082] In FIG. 7C, the first flow path 750 includes a flow path
through a plurality of neck portions 120 formed by a plurality of
blades 730 arranged radially about a central portion 760 as a
cylindrical venturi array 770. In this embodiment, the working
fluid is driven into the central portion 760 through an entrance
flow path, and the fluid flows radially outward between the blades
730. Locating one or more heat sources at or near the neck portion
720 of the first flow path 750 between the adjacent blades 730
allows heat to be transferred from the heat source to the working
fluid, as described hereinabove.
[0083] FIG. 8A illustrates exemplary heat transfer systems 800 that
include a radial array of blades having a plurality of blades 810
arranged about a central portion 820. The heat transfer system 800
is formed as a squirrel-cage-type system with a working fluid
entering the central portion 820 along an entrance flow path
substantially along the radial axis 830 of the system 800. The
working fluid flows radially out through a first flow path 840
between adjacent blades 810 and exits the squirrel-cage through an
exit flow path defined by a channel 850 extending from the casing
860 of the squirrel-cage. In operation, the blades 810 rotate about
the central radial axis, thereby drawing the working fluid into the
central portion 820 through the entrance flow path and forcing the
working fluid through the first flow path 840 between the adjacent
blades 810. The working fluid is then forced out through the
channel 850 defining the exit flow path. The blades 810 may be
driven at any rotational velocity adequate to provide the
appropriate flow speed through the first flow path 840 between
adjacent blades 810.
[0084] Placing a heat source in thermal communication with the
blades 810, or at least a portion thereof, causes the first flow
path 840 between the adjacent blades 810 to act as a working-fluid
flow path for a Bernoulli-type heat transfer system, with heat
being transferred from the heat source through the blades 810 and
into the fast moving, and therefore cooled, working fluid. The
blades may be of any appropriate shape to provide the required
fluid flow conditions in the first flow path 840. In the embodiment
of FIG. 8A, the blades 810 have a unitary shape and are formed of a
solid thermally conductive material such as, but not limited to,
copper or aluminum. In other embodiments, the blades may have
different shapes.
[0085] FIG. 8B illustrates an exemplary cylindrical
squirrel-cage-type heat transfer system 800 with hollow blades 870.
In this embodiment, each blade 870 includes an outer wall 880
defining a channel 890 through which a second fluid (i.e., a fluid
transporting a heated fluid from one or more heat sources) flows.
Each blade 870 is shaped such that the first flow path 840 (i.e.,
the working-fluid flow path) between adjacent blades has a venturi
shape. As a result, as the working fluid is driven through the
first flow path 840, heat is transferred through the outer walls
880 of the blades 870 from the heat-source fluid flow to the
working-fluid flow. As with the other venturis described herein,
the outer wall 880, or a portion thereof, may include, or consist
essentially of, a material having a high thermal conductivity
relative to the surrounding structure. For example, the outer wall
880 may have a high-thermal-conductivity material (e.g., a metal)
placed at and/or near the apex of the venturi-shaped first flow
path 840, with a lower-thermal-conductivity material making up the
remainder of the outer wall 880. As a result, heat transfer between
the heat-source flow and the working-fluid flow will take place
primarily at the apex of the venturi, where the working fluid is at
or near its highest velocity and lowest temperature, thereby
maximizing the heat-transfer rate.
[0086] The heat transfer system 800 may be a closed loop system or
an open loop system. For an open loop system, the working fluid,
such as air or water, is drawn into the entrance flow path from the
surrounding atmosphere and driven through the first flow path 840
between adjacent blades 810 by the rotation of the blades 810. The
working fluid is then vented back out to the surrounding atmosphere
through the channel 850 defining the exit flow path. For a closed
loop system, the channel 850 defining the exit flow path is coupled
to a return flow path that returns the working fluid back to the
entrance flow path, as shown, for example, in FIGS. 4A and 4B. The
closed-loop system may provide a substantially constant mass flux
for the working fluid though the system.
[0087] The number, size, and geometry of the blades may vary
depending on the application. The configuration of the blades
dictates the shape of the first flow path between adjacent blades.
For example, in one embodiment, the first flow path between
adjacent blades is substantially straight. In another embodiment,
the first flow path between adjacent blades is, at least in part,
substantially curved. An exemplary cylindrical blade array 900 for
use, for example, in a squirrel-cage-type heat transfer system, is
shown in FIG. 9.
[0088] In this embodiment, the cylindrical blade array 900 includes
a plurality of blades 910 arranged around a central portion 920 and
configured to rotate about a central axis 930, with a first flow
path 940 defined by the gap between the adjacent blades 910. Each
blade 910 includes an outer wall 950 defining a flow channel 960
through which a second fluid (i.e., a fluid transporting a heated
fluid from one or more heat sources) flows. The outer wall 950
includes a portion exhibiting a high thermal conductivity, with
respect the remainder of the outer wall 950, located at and/or near
an apex portion 970. The blades 910 are shaped such that the first
flow path 940 follows a curved path, with the apex of the curve at
an apex portion (i.e. a portion having a minimum cross-sectional
area) of the first flow path 940. In alternative embodiments,
differently shaped blade arrays and/or flow paths may be used, as
appropriate.
[0089] In operation, a heat-source fluid flow is driven through at
least one of the blades 910, allowing heat to be transferred from
the heat source to the working fluid at the apex portion 970 as the
working fluid is driven through the first flow path 940 by the
rotation of the blades 910 about the central rotational axis 930.
In one embodiment, the flow channels 960 for two or more adjacent
blades 910 are connected at a distal end of the blades 910, such
that the heat-source flow within the second flow path defined by
the channels 960 flows in one direction along the length of one
blade 910 before flowing back along the length of an adjacent blade
910 in the opposite direction. As a result, the heat-source flow
need only fluidly communicate with the blades 910 at one end of the
system 900.
[0090] With reference to FIG. 10, a cylindrical blade array 1000
may include a plurality of stator portions 1010 surrounded by a
plurality of rotor portions 1020. As before, the plurality of
stators 1010 and rotors 1020 are arranged around a central portion
1030 and configured to rotate about a central axis 1040, with a
first flow path 1050 defined by the gap between the adjacent
stators 1010 and adjacent rotors 1020. Each rotor 1010 includes an
outer wall 1060 defining a flow channel 1070 through which a second
fluid (i.e., a fluid transporting a heated fluid from one or more
heat sources) flows. The outer wall 1060 may include a portion
exhibiting a high thermal conductivity with respect the remainder
of the outer wall 1060, and located at and/or near an apex portion
1080 of the stators 1010. In operation, the stators 1010 remain
stationary while the rotors 1020 rotate around an outer radial wall
of the stators 1010. The rotation of the rotors 1020 drives a
working fluid through an entrance flow path into the central
portion 1030 and out through the first flow path 1050 defined by
the gap between the adjacent stators 1010 and adjacent rotors
1020.
[0091] An exemplary heat-transfer-system flow arrangement 1100
through a cylindrically oriented blade array for a
squirrel-cage-type heat transfer system is shown in FIGS. 11A and
11B. This flow arrangement 1100 may be utilized with any of the
rotor blades and/or stator arrays described herein, or with any
other suitably configured blade arrangement. As described
hereinabove, a squirrel-cage-type heat transfer system 1110
includes a plurality of hollow blades 1120 configured to rotate
about a central portion 1130, with a first flow path 1140 defined
between adjacent blades 1120. A housing 1150 is located outside the
blade array and guides the working fluid exiting the first flow
path 1140 into a return flow path 1160 that returns the working
fluid through an entrance flow path 1165 to the central portion
1130. A second fluid flow path 1170 (i.e., a heat-source fluid flow
path) extends through a sealed central bearing 1175 and through a
plurality of the blades 1120. In one embodiment, two or more
adjacent blades 1120 are connected at a distal end thereof, such
that the heat-source flow path 1170 flows in one direction along
the length of one blade 1120 before flowing back along the length
of an adjacent blade 1120 in the opposite direction. As a result,
the heat-source flow 1170 need only be fluidly connected to the
blades 1120 at one end of the system 1110, with the sealed central
bearing 1175 housing both a heat source entrance flow and a heat
source exit flow.
[0092] The system 1110 operates as a closed-loop heat transfer
system, with the working fluid being driven through the first flow
path 1140 by the rotation of the blades 1120, and then being
returned through a return flow path 1160 and an entrance flow path
1165 to the central portion 1130 to repeat the process.
Simultaneously, a fluid flow from a heat source is driven through
the second fluid flow path 1170 within the hollow blades 1120
through the sealed bearing 1175. As a result, as the working fluid
is driven through the first fluid flow path 1140, heat is
transferred through a high-thermal-conductivity portion of the
walls of the blades 1120 from the heat-source flow to the working
fluid. As described above, one or more heat exchangers may be
positioned along the return flow path 1160 to remove the heat added
to the working fluid from the heat source.
[0093] In one embodiment, the blades 1120 are rotated at a
sufficient rotation rate to cause a mean flow direction of the
first flow path to point at least partially towards a rear surface
of the blades 1120, thereby causing the working-fluid flow to
impinge on the rear of each blade 1120 and provide kinetic energy
to the blades 1120, increasing the efficiency of the system.
[0094] A heat transfer system including a first flow path through a
cylindrically arranged blade array may include a wall separating
the blade array from the return flow path. For example, FIG. 12
shows a closed-loop heat transfer system 1200 including a wall or
plate 1210 with an open central portion 1220. The plate 1210 may be
of any suitable cross-sectional thickness and geometry. For
example, in one embodiment, the plate 1210 is substantially
cylindrical in form and of sufficient thickness to allow one of
more flow channels (used to carry a heat source flow through the
plate) to be embedded therein. The plate or housing 1210 may be
formed as a single structure or may include a plurality of
interconnected structures. The plate 1210 can be used to house
elements including, but not limited to, one or more heat-source
flow channels, one or more heat exchanger elements, one or more
measurement devices, one or more control devices, and/or a power
source and/or controller for a working fluid and/or heat source
fluid drive system. A housing 1230 encloses the system 1200. The
plate may include structure or structural elements, such as
baffles, walls, and/or strengthening elements, separating the
radially diverging and radially converging flows.
[0095] The system 1200 includes a radially diverging flow 1240
extending out from the open central portion 1220 on one side of the
plate 1210, with a radially converging flow 1250 extending towards
the open central portion 1220 on the other side of the plate 1210.
In operation, the flow path for a working fluid extends through the
open central portion 1220, out along the radially diverging flow
path 1240 on one side of the plate 1210, up through an outer flow
return path 1260 extending around an outer radial edge of the plate
1210, and back towards the open central portion 1220 along the
radially converging flow path 1250. The flow may be driven, for
example, by a plurality of rotor blades located within the radially
diverging flow path 1240 on one side of the plate 1210 and rotating
about the open central portion 1220.
[0096] In operation, the working-fluid flow velocity diminishes as
the cross-sectional area of the flow increases with radial distance
from the open central portion 1220 along the radially diverging
flow path 1240 (due to the increase in cross-sectional area of the
flow as the radius from the open central portion 1220 increases).
The working fluid then flows along the outer radial wall of the
plate 1210 along the outer flow return path 1260 before travelling
back to the open central portion 1220 along the radially converging
return flow path 1250. The working-fluid flow velocity increases,
and the temperature drops, as it converges towards the open central
portion 1220 (due to the decrease in cross-sectional area of the
flow as the radius from the open central portion 1220 decreases).
The maximum working-fluid flow velocity, and therefore the minimum
working fluid temperature, occurs where the working fluid passes
through the open central portion 1220 of the plate 1210 (i.e.,
where the cross-sectional area that the working fluid must traverse
is at a minimum). As a result, the central open portion 1220 of the
plate 1210 effectively acts as a neck or venturi. The minimum
working-fluid flow velocity, and therefore the maximum working
fluid temperature, occurs where the working fluid passes axially
along the outer flow return path 1260.
[0097] In this embodiment, a heat source may be placed in thermal
communication with at least a portion of a boundary wall of the
open central portion 1220. As a result, the system 1200 produces a
flow equivalent to other venturi-flow heat transfer systems
described herein, with a working fluid being accelerated through a
first flow path (in this case the open central portion 1220) and
with heat being transferred to the working fluid from a heat source
in thermal communication with the boundary wall of the first flow
path. One or more heat exchangers may be placed at any appropriate
location along the return flow path (e.g., within the outer flow
return path 1260 and/or the radially converging return flow path
1250) within the closed loop flow to remove heat from the working
fluid. In one embodiment, a heat exchanger is located at or near
the outer flow return path 1260 (i.e., where the flow passes
axially along the outer radial edge of the plate 1210 and
transitions from a radially diverging to radially converging flow)
where the working fluid flow has its slowest velocity and highest
temperature.
[0098] In one embodiment, the heat source includes a solid material
that conducts heat to the boundary wall of the open central portion
1220. In an alternative embodiment, the heat source includes a
heat-source fluid flow in addition to, or in place of, the solid
material. The boundary wall of the open central portion 1220, or at
least a portion thereof, may include a portion having a higher
thermal conductivity than the surrounding wall, thereby encouraging
heat transfer only through the portion of the flow where the
temperature differential between the working fluid and the heat
source is at a maximum.
[0099] An exemplary heat transfer system 1300 with a heat-source
fluid flow carrying heat to the boundary wall 1305 of the open
central portion 1220 is shown in FIG. 13. In this embodiment, the
heat-source flow enters into a hollow section of the wall 1210 via
an entrance portion 1310, and the flow exits via an exit portion
1320 after passing the boundary wall 1305 of the open central
portion 1220. The wall 1210 may be entirely hollow, thereby
allowing the heat-source flow to flow freely through the entire
hollow inner chamber of the wall 1210, or the wall 1210 may instead
be substantially solid with flow paths embedded therein to
transport the heat-source fluid from the entrance portion 1310,
past the boundary wall 1305 of the open central portion 1220, and
out through the exit portion 1320. These flow paths may take any
form that ensures the heat-source flow is capable of passing heat
through the boundary wall 1305 of the open central portion 1220 and
into the working fluid. The boundary wall 1305 may be curved or
flat. In one embodiment, the boundary wall 1305 of the open central
portion 1220 is curved to form a venturi within the open central
portion 1220. A rotor blade array 1330 is positioned within the
radially diverging flow path 1240 to drive the flow.
[0100] One embodiment of the invention, shown in FIG. 14, includes
a plurality of separate closed-loop heat transfer systems 1300
connected together. In this embodiment, a single driving mechanism
may be used to drive the flow within a plurality of heat transfer
systems 1300, for example, by having a rotor blade array 1330 for
each closed-loop system coupled to a single rotor axle 1410. In
this embodiment, two closed-loop flows are placed back-to-back. In
an alternative embodiment, three or more closed loop flows are
placed back-to-back to form an array of heat transfer systems.
These heat transfer systems may be in thermal communication with
the same and/or different heat sources.
[0101] The configuration of FIGS. 12-14 may be used with any of the
embodiments described herein, including arrays of rotor blades
having heat sources therein, rotor/stator blade arrays, and/or
"no-touch" blade arrays. In each of these embodiments, heat may be
pumped from a heat source to a working fluid through the open
central portion 1220 (i.e. the open flow path through the central
portion of the plate 1210) and/or through one or more neck portions
defined between adjacent blades. In each of these embodiments, the
plate 1210 may be of any arbitrary thickness.
[0102] The cylindrical heat transfer systems described herein may
transfer heat to a working fluid from a heat source in thermal
communication with the boundary wall of the open central portion,
from a heat source in thermal communication with one or more of a
plurality of rotor blades driving the working-fluid flow, and/or at
any other appropriate location around the system. In addition, the
cylindrical heat transfer systems may include any of the
measurement and/or control systems described herein.
[0103] In one embodiment, heat is transferred from the heat-source
flow to the cold portion of the working fluid (e.g., the portion of
the working fluid traveling through the neck portion of a
venturi-shaped first fluid flow path), and from the hot portion of
the working fluid (e.g., the slow-moving portion of the working
fluid within the return flow path) to a sink flow (e.g., a fluid
flow within a heat exchanger located along at least a portion of
the return flow path). The system may include multiple
working-flow, sink-flow pairs. An exemplary system 1500, including
four such working-flow, sink-flow pairs is shown in FIG. 15. This
embodiment includes three flows: a heat-source flow 1510, a
heat-sink flow 1520 (for example, in a heat exchanger) and a
working-fluid flow 1530. As with other cylindrically arranged
systems described herein, the system is driven by a blade array
that rotates about a central rotor axle 1540.
[0104] In alternative embodiments, a greater number of
working-flow, sink-flow pairs may be utilized. Increasing the
number of working-flow, sink-flow pairs may, for example, increase
the area of shared wall available for heat transfer, thereby
increasing the efficiency of the system. A schematic representation
of the relative fluid flow paths is shown in FIG. 16.
[0105] In one embodiment, shown in FIG. 17, one or more fins 1710
are located within the open central portion 1720 of a heat transfer
system and extend from the boundary wall 1730 of the open central
portion 1720. The system depicted in FIG. 17 has a plurality of
fins 1710 or thermal conductors. In this embodiment, the fins 1710
advantageously increase heat transfer between the heat source and
the working fluid due to the increase in surface area therebetween.
In alternative embodiments, any appropriate number and/or geometry
of thermal conductor may be placed within the open central portion
1720. The size, shape, and number of fins 1710 may, for example, be
selected to maximize the heat transfer between the heat source (in
thermal communication with the fins 1710) and the working fluid
while minimizing the effect of the fins 1710 on the working-fluid
flow (i.e., minimizing the reduction in fluid flow efficiency due
to the addition of the fins 1710). The flow through the open
central portion 1720 may also be affected by the size and shape of
the rotor axle 1740 extending through the open central portion 1720
to drive the rotor blade array.
[0106] Various embodiments of the invention may include cylindrical
heat transfer systems wherein rotor blades specifically shaped and
driven at a set rotation rate to minimize the interaction between
the working-fluid flow between adjacent blades and the walls of the
blades themselves. Minimizing the interaction between the blades
and the working fluid may be achieved by configuring the system
such that the first flow path extends through the space between
adjacent blades substantially parallel to the surfaces of those
blades, such that the working fluid does not impinge upon (or
"touch") the blades as it travels therebetween. Systems that
satisfy this "no touch" condition exhibit increased efficiency due
to, for example, reduced energy required to drive the system.
[0107] In one embodiment, in order to minimize the extent to which
the rotor blades "touch" the flow, the shape of each blade is
determined by the requirement that the vector addition of the
desired radius-dependent radial velocity and the local rotational
velocity of the rotor blades is substantially equal to purely
radial motion in a stationary coordinate system. In this
embodiment, the motion of each point on the rotor blade is purely
rotational, dictated by the rotation rate and the local radius.
[0108] The radial variation in the local speed of the working-fluid
flow may be utilized to improve the efficiency of the system. For
example, in one embodiment, a "no touch" flow condition is
generated by ensuring that the decline of the local flow speed is
directly related to the inverse of the radius. This is simply the
conservation of the mass flux through a cross-sectional area that
increases linearly with increasing radius, ignoring the fact that
the density of the gas may vary with the speed of the flow. In more
complex flow models, the effects of density variation as the flow
speed decreases may be accounted for. In a further embodiment, a
one-dimensional compressible flow model of the flow through a blade
array allows for the inclusion of shaftwork, i.e., the energy added
to or removed from the flow by turbines or blowers through
interaction of the blades with the working fluid. Because, in
certain embodiments, viscous losses are unavoidable, and because
the no-touch rotor acts as either a blower or turbine when rotated
at rates other than its design rotation rate, the no-touch rotor
also provides the required driving force. In certain embodiments,
the effects of viscous losses may be accounted for either
phenomenologically with a quasi-one-dimensional model or
multidimensional (computational fluid dynamics) analysis, or
empirically using experimental data.
[0109] In one embodiment, the shape of each blade in a blade array
is determined based on two parameters: (i) a function v(r)
describing the velocity of the working fluid flow as a function of
radius, if the flow were perfectly radial (that is, no rotational
motion), and (i) a design rotation speed. In one embodiment, the
function v(r) may be determined by a relationship v(r).about.1/r.
In an alternative embodiment, the function v(r) may depend on
additional factors to account, for example, for compressible flow.
In one embodiment, the function v(r) may be simply proportional to
1/r. Such a choice reflects the conservation of mass in a
constant-density flow through a cross-sectional surface area that
is increasing as a function of radius. In an alternative
embodiment, different functions for v(r) may be utilized. These
functions may address factors such as, but are not limited to,
compressible flow, compressible flow with viscous losses, and/or
empirical data from experimental results. For example, in one
embodiment the function v(r) can be varied until the design
rotation rate and measured "diffuser rotation rate" become
substantially equal.
[0110] In one embodiment, at a specific rotation rate the no-touch
rotor neither substantially consumes nor substantially produces
work/power and, as such, acts simply as a diffuser. In one
embodiment, the blade array will produce some entropy that in turn
produces a pressure drop across the diffuser. That pressure drop
may be restored, for example, by rotating the blade array slightly
faster than its diffuser, or no-touch, rate, to compensate for any
entropy in the system, thereby making it serve as an integrated
diffuser and blower. In one embodiment, the blade array is rotated
at its diffuser or no-touch rate, with another blade array such as,
but not limited to, an axial blower located within an outer flow
return path, providing a driving mechanism for the flow, for
example to compensate for entropy.
[0111] The effect of turbulence within the system may be reduced
through the use of a "no-touch" condition by, for example,
minimizing the interaction within a boundary layer on the surface
of the blades due to impingement of the working fluid on the
blades. This may be achieved, for example, through blade shaping
and/or rotational speed selection such that the mean flow path of
the working-fluid flow through the blades matches the shape of the
blades themselves, thereby minimizing the interaction between the
working-fluid flow and the blade walls as the working-fluid flows
radially out through the blade array. FIG. 18 illustrates an
exemplary working-fluid flow-path pattern flowing out from an open
central portion 1810 through a blade array (not shown) in a
rotational frame. In this embodiment, to provide for a
substantially "no-touch" fluid flow, the blades in the rotor blade
array conform to the shape of the working-fluid flow paths 1820. An
exemplary blade array 1900, including a plurality of shaped blades
1910 located around an open central portion 1920, is shown in FIG.
19. In this embodiment, the blades drive the fluid flow (at least
to the extent that rotating the rotor faster than a zero-torque
value compensates for pressure loss due to viscous friction in the
rotor) while minimizing the interaction between the fluid and the
blade walls. One or more of the blades 1910 may also be in thermal
communication with one or more heat source, thereby allowing heat
to be transferred from the heat source to the working fluid through
the wall of the blades 1910 as the working fluid is driven through
the blade array. Through appropriate blade shaping and/or
rotational speed selection, the "no-touch" flow condition may be
utilized with any of the cylindrical heat transfer systems
described herein.
[0112] The radial array of blades may be rotated clockwise or
counterclockwise, depending on the orientation of the blades. In
the embodiment of FIG. 19, the blades are oriented such that a
counterclockwise rotation of the blade array will produce the
required radially diverging working fluid flow therethrough.
[0113] In one embodiment, to the extent that the working-fluid
flows radially at a speed necessary to ensure the "no-touch"
condition, the flow is parallel to the blades. If the local speed
in a region within the flow is slower than desired, the advancing
face of the rotor blade catches up with it, and imparts energy by
pumping or blowing action. If, on the other hand, a portion of the
flow moves faster than desired, it encounters the receding
(suction) side of the rotor blade and pushes the receding blade,
slowing the flow and providing turbine action. For a given rotation
rate, the relative amounts of blower and turbine action within the
blades determine whether the rotor array is behaving as a net
turbine or as a net blower. At one particular rotation rate the two
effects cancel, providing a substantially "no touch" flow through
the rotor blade array. As a result, the blades may correct for any
local non-uniformities within the first fluid flow path of the
working fluid by providing a force to the working fluid to minimize
deviations from the "no touch" condition.
[0114] In operation, the fluid drive system (e.g., the rotating
radial array of blades that interact with the working fluid flow)
may act as a blower, a turbine, and/or a pure diffuser (for the
"no-touch" flow). For a fluid drive system acting primarily as a
blower, the advancing surface of each blade pushes on the working
fluid flow as it passes through the flow path between the adjacent
blades to drive the fluid through the system. For a fluid drive
system acting primarily as a turbine, the working fluid flow pushes
on the receding surface of the blades of the blade array, thereby
driving the rotation of the blades. The net action of the fluid
drive system is the combined effect of both the locally acting
blower and turbine action over the full blade array. If the
rotation rate is below a certain value, the net effect of the
rotation of the blade array is to act as a turbine. If the rotation
rate is above a certain value, the net effect of the rotation of
the blade array is to act as a blower. By appropriate selection of
the rotation rate, blade geometry, and/or working fluid, the net
effect of the rotation of the blade array may provide a diffuser
action with no net blower or turbine action on the working fluid
(i.e., the "no-touch" condition).
[0115] Because of viscous losses associated with the no-slip
boundary condition at the surfaces of the rotor blades, the
pressure of the working fluid as it exits the first fluid flow path
rotating at a turbine rate is not sufficient to maintain the
closed-loop flow throughout the entire system. In such
circumstances, to provide the pressure required to sustain the
flow, the rotor blade array rotates at a blower rotation rate. As a
result, the no-touch configuration for the rotor blade array is
efficient as, for example, the stagnation-pressure drop across the
rotor is significantly smaller than that found with traditional
diffusers. The power required to provide the required blower action
is less than required by a traditional blower operating on slowly
moving input gas. Thus, less pressure increase is required and it
is cheaper (in power) to provide what is required.
[0116] Having described certain embodiments of the invention, it
will be apparent to those of ordinary skill in the art that other
embodiments incorporating the concepts disclosed herein may be used
without departing from the spirit and scope of the invention.
Accordingly, the described embodiments are to be considered in all
respects as only illustrative and not restrictive.
* * * * *