U.S. patent application number 12/700966 was filed with the patent office on 2010-10-21 for thermal regulation passive device with micro capillary pumped fluid loop.
This patent application is currently assigned to Astrium SAS. Invention is credited to Christophe Figus.
Application Number | 20100263836 12/700966 |
Document ID | / |
Family ID | 39030875 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100263836 |
Kind Code |
A1 |
Figus; Christophe |
October 21, 2010 |
Thermal Regulation Passive Device with Micro Capillary Pumped Fluid
Loop
Abstract
The device includes an evaporator and a condenser connected by
an outer tube in which extends at least one inner tube having one
end leading into the condenser and another end connected to an end
of a central duct for collecting the vapours of a heat-carrier
fluid, in a microporous mass provided in the outer tube and pumping
by capillarity the liquid-phase fluid flowing in at least one outer
duct between the outer and inner tubes from the condenser to the
evaporator, while the vapour-phase fluid flows from the evaporator
to the condenser in at least one inner duct inside said at least
one inner tube. The invention can be used for the thermal energy
transfer from an electronic component or circuit in relation with
the evaporator to a cold source in relation with the condenser.
Inventors: |
Figus; Christophe; (Dremil
Lafage, FR) |
Correspondence
Address: |
MILLER, MATTHIAS & HULL
ONE NORTH FRANKLIN STREET, SUITE 2350
CHICAGO
IL
60606
US
|
Assignee: |
Astrium SAS
Paris
FR
|
Family ID: |
39030875 |
Appl. No.: |
12/700966 |
Filed: |
February 5, 2010 |
Current U.S.
Class: |
165/104.26 |
Current CPC
Class: |
F28D 15/043
20130101 |
Class at
Publication: |
165/104.26 |
International
Class: |
F28D 15/04 20060101
F28D015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2007 |
FR |
07 05769 |
Claims
1. A passive thermal regulation device, comprising at least one
heat transfer loop with capillary pumping of a heat-carrier fluid,
said loop comprising an evaporator having a microporous mass, and a
condenser, for being in heat exchange relationship with a heat
source and a cold source respectively, and tubing connecting said
evaporator to said the condenser and transporting said heat-carrier
fluid essentially in vapour phase from said evaporator to said
condenser and essentially in liquid phase from said condenser to
said evaporator, said tubing comprising an outer tube, housing said
microporous mass having a substantially elongated shape and,
ensuring a flow of said liquid-phase heat-carrier fluid by
capillary pumping, wherein said liquid phase of said fluid is
pumped by at least one end of said microporous mass which is facing
said condenser, and flows in at least one outer duct delimited
between said outer tube and at least one inner tube extending
within said outer tube, and said vapour phase of said fluid heated
in said microporous mass of said evaporator is collected in a
longitudinal central duct made in said microporous mass and
discharged by at least one inner duct delimited within said at
least one inner tube, said at least one inner tube being connected
by one end to an end of said central duct, while said vapour phase
is discharged at an other end of said at least one inner tube, at
said condenser.
2. The device according to claim 1, wherein said outer tube is
closed on itself, forming a continuous loop, two substantially
opposite portions of said outer tube, in relation to a centre of
said loop, are in heat exchange relationship, one portion with said
condenser and the other portion with said evaporator and with said
microporous mass housed in said other portion of said outer tube,
and passed through over an entire length of said microporous mass
by said central duct, two inner tubes extending within said outer
tube, each of said two inner tubes being connected, by a first end,
with one of two ends of said central duct of said microporous mass
respectively, while a second end of each inner tube opens out into
said condenser opposite said second end of the other inner tube so
as to connect an inner vapour-phase fluid duct delimited within
each inner tube to said at least one outer duct of liquid-phase
fluid flowing from said condenser towards a corresponding end face
of said microporous mass.
3. The device according to claim 1, wherein said outer tube is
closed at both ends which are in a heat exchange relationship, one
with said condenser, and the other with said evaporator (22) and
with said microporous mass housed in said other end of said outer
tube, said liquid phase of said fluid is pumped by said one end of
said microporous mass facing said condenser, and flows in said
outer duct delimited between said outer tube and said inner tube
extending within said outer tube, and said vapour phase of said
fluid heated in said microporous mass of said evaporator is
collected in a longitudinal central duct made in said microporous
mass and discharged by said the inner duct delimited within said
inner tube, said inner tube being connected by one end to one end
of said central duct, while said vapour phase is discharged at said
other end of said inner tube, at said condenser.
4. The device according to claim 1, wherein said other end of said
at least one inner tube located at the level of said condenser is
fitted into an annular microporous mass filling a space delimited
within said condenser between said other end of said inner tube and
said outer tube.
5. The device according to claim 4, wherein liquid condensing in
said condenser is drained to said annular microporous mass, by at
least one of a capillary drain and a microporous mass located along
a wall of said outer tube at said condenser.
6. The device according to claim 1, wherein each of said evaporator
and condenser comprises at least one outer sleeve made from a good
heat conducting material, said at least one sleeve of said
evaporator surrounding at least partially, a portion of said outer
tube that houses said microporous mass and said at least one sleeve
of said condenser surrounding a portion of said outer tube in which
said at least one inner duct releases said vapour-phase fluid
towards said at least one outer duct.
7. The device according to claim 6, wherein said at least one outer
sleeves comprises at least one base plate made from a good heat
conducting material whereby said sleeve is intended to be placed in
heat exchange relationship with one of a hot and cold source.
8. The device according to claim 1, wherein said at least one inner
tube has walls made from at least one thermally insulating
material.
9. The device according to claim 1, wherein said at least one inner
tube for discharging said vapour extends into said microporous
mass.
10. The device according to claim 9, wherein said at least one
inner tube has an outer wall comprising at least one capillary
drain defined by at least one groove, arranged at least on a
portion of said inner tube that extends into said microporous mass,
so as to convey said liquid phase deep within said microporous mass
by capillarity.
11. The device according to claim 1, wherein said at least one
inner tube has an outer wall comprising capillary drains defined
for example by grooves, said capillary drains extending over the
entire length of said tube.
12. The device according to claim 1, wherein apart from said
microporous mass, an outer wall of said at least one inner tube is
in contact with an inner wall of said outer tube, except at the
level of at least one capillary drain defining at least one outer
duct conveying said liquid phase of said fluid.
13. The device according to claim 1, wherein said microporous mass
has a substantially cylindrical outer shape, together with a
portion of said outer tube that houses said microporous mass
without radial play.
14. The device according to claim 1, wherein said evaporator has an
area intended to be in heat exchange contact with said heat source
and one dimension of said area along an axis of said outer tube is
significantly smaller than a length of said microporous mass.
15. The device according to claim 14, wherein said microporous mass
has a diameter and a length that is substantially 2 to 15 times
greater than said diameter.
16. The device according to claim 1, wherein said outer tube is in
heat exchange contact with said microporous mass over an outer
surface of said mass apart from at least one of longitudinal end
surfaces of said mass.
17. The device according to claim 1, wherein said outer tube has a
cross-section with a constant diameter.
18. The device according to claim 1, wherein said outer tube is
made from a good heat conducting material, at least in a first
portion of said outer tube that is in heat exchange relationship
with said microporous mass, and in a second portion of said outer
tube in heat exchange relationship with said condenser or
constituting said condenser.
19. The device according to claim 18, wherein said outer tube is
metal, preferably stainless steel.
20. The device according to claim 1, wherein said outer tube and
said at least one inner tube are cylindrical with a circular
cross-section, said at least one inner tube having a diameter which
is substantially half of a diameter of said outer tube.
21. The application of a passive thermal regulation device with at
least one heat transfer loop according to claim 1, to the transfer
of thermal energy from a heat source, such as an electronic
component or set of components, in heat exchange relationship with
the evaporator, to a cold source, in heat exchange relationship
with the condenser.
22. A method for transferring thermal energy from a heat source to
a cold source with a passive thermal regulation device having at
least one heat transfer loop, including a step of using a heat
transfer loop with capillary pumping of a heat-carrier fluid, said
loop comprising an evaporator having a microporous mass, and a
condenser, and arranging said evaporator and condenser in heat
exchange relationship with a heat source and a cold source
respectively, and tubing connecting said evaporator to said
condenser and transporting said heat-carrier fluid essentially in
vapour phase from said evaporator to said condenser and essentially
in liquid phase from said condenser to said evaporator, said tubing
comprising an outer tube, housing said microporous mass having a
substantially elongated shape and, ensuring a flow of said
liquid-phase heat-carrier fluid by capillary pumping, wherein said
liquid phase of said fluid is pumped by at least one end of said
microporous mass which is facing said condenser, and flows in at
least one outer duct delimited between said outer tube and at least
one inner tube extending within said outer tube, and said vapour
phase of said fluid heated in said microporous mass of said
evaporator is collected in a longitudinal central duct made in said
microporous mass and discharged by at least one inner duct
delimited within said at least one inner tube, said at least one
inner tube being connected by one end to an end of said central
duct, while said vapour phase is discharged at an other end of said
at least one inner tube, at said condenser.
Description
[0001] The present invention relates to a purely passive thermal
regulation device, comprising at least one heat transfer loop with
the flow of a heat-carrier fluid by capillary pumping, of the type
also known as a micro capillary pumped fluid loop, and used for
cooling heat sources, such as electronic components or sets of
components (circuits).
[0002] According to the prior art, a heat transfer loop comprises
an evaporator intended to extract heat from a heat source and a
condenser intended to return the heat to a cold source. The
evaporator and the condenser are connected by tubing in which a
heat-carrier fluid flows in a liquid state in the cold part of the
loop, and in a gaseous state in the hot part of the loop. The
device of the invention relates more particularly to fluid loops in
which the pumping of heat-carrier fluid is carried out by
capillarity (capillary loop). In this type of loop, the evaporator
is associated with a fluid reserve in a liquid state, and comprises
a microporous mass (also called a wick) carrying out the pumping of
the fluid by capillarity. The liquid-phase fluid contained in the
reserve associated with the evaporator evaporates in the
microporous mass under the effect of the heat originating from the
heat source. The gas created in this way is discharged to the
condenser, in heat exchange contact with the cold source, where it
condenses and returns in liquid phase to the evaporator, in order
to thus create a heat transfer cycle.
[0003] One of the limitations of such a heat transfer loop in
operation lies in the more or less significant quantity of thermal
energy that is transferred to the liquid reserve via the
evaporator.
[0004] A first effect of this parasitic phenomenon is the heating
of the liquid flowing in the loop or contained in the reserve of
the evaporator. A second parasitic effect is the reduction of the
thermal performance of the transfer loop, which is very sensitive
to the temperature of the liquid. Such a transfer loop transports
almost all of the energy by phase change of the heat-carrier fluid,
and requires, in order to operate, several kilogram calories to
keep the fluid flowing from the condenser to the evaporator in a
liquid state. Even partial heating of the liquid by any means thus
very considerably reduces the heat transfer performance of the
loop, and can even result in its complete stoppage.
[0005] The object of the present invention relates to passive
thermal regulation devices with micro capillary pumped fluid loops,
intended for the cooling of heat sources such as electronic
components and/or circuits. According to the state of the art, such
electronic components or circuits are characterized by a small size
(thickness of 1 to 2 mm, area of 10 to 100 mm.sup.2, for example),
and high discharge power densities (over 50 W/cm.sup.2, for
example). Furthermore, the temperature variation between the
junction of the electronic component or circuit and the housing of
said component or circuit is very large (by a factor of 2 to 3)
compared with the temperature variation of the housing of the
component or circuit and the temperature of a base plate of a board
on which the component or circuit is installed.
[0006] The use of a heat transfer loop with capillary pumping to
fit the size of the component or circuit, known as a micro loop,
allows for the temperature difference between the junction of the
component or circuit and the base plate of the board on which it is
installed to be reduced advantageously, and thus for the
reliability of the component or circuit to be increased, by
increasing the power dissipated by the component or circuit.
[0007] Such a micro capillary pumped fluid loop is characterized in
that it has small dimensions (typical thickness of 1 to 2 mm,
typical area of 10 to 100 mm.sup.2), in order to allow for it to be
installed as close as possible to, or even inside, the component or
circuit.
[0008] A first drawback of the state of the art for producing such
a device lies in the fact that the small size of said micro loop
promotes the parasitic transfer of heat to the liquid reserve,
which significantly reduces the performance of the loop. This
drawback is one of the main limitations for the small size of the
evaporator of a micro loop according to the state of the art.
[0009] For example, a fluid loop device representative of the state
of the art is described in U.S. Pat. No. 7,111,394. In this device,
as shown diagrammatically in longitudinal cross-section in FIG. 1
and in cross-section in FIG. 2, which are attached, and arranged in
a tube 10 sealed closed at both ends, the evaporator 11 is
connected to a liquid reservoir 15, and comprises a microporous
mass 12 having a generally cylindrical shape, pierced through by a
central artery 14 within which flows the liquid phase 19 of the
fluid returning from the condenser 16 towards the reservoir 15.
Around the artery 14, on the periphery of the microporous mass 12,
ducts 13 are pierced, in which is collected vapour 18, resulting
from the heat exchange taking place in the evaporator 11, between
the mass 12 and the liquid-phase fluid in the reservoir 15, and
pumped by capillarity by the microporous mass 12. It is notable
that the vapour phase 18 is confined to the periphery of the mass
12, closest to the area where heat exchange occurs between the heat
source (for example an electronic component in contact against the
outer surface of the tube 10 at the evaporator 11) and the
evaporator 11. The vapour phase is thus maintained at a sufficient
distance from the central liquid phase, preventing the parasitic
heat flows inevitably present in the mass 12 from heating the
liquid phase too much and having a negative effect on the
efficiency of the loop. The vapour phase collected in the ducts 13
of the mass 12 is guided towards the condenser 16 by the annular
gap between the outer tube 10 and an inner tube 17, in one or more
portions, connected by one end to the end of the central artery 14
of the mass 12, while its opposite end opens into the condenser 16
and communicates with the annular volume between the tubes 10 and
17, in order to collect the condensates and recycle the liquid
phase towards the reservoir 15.
[0010] However, if the miniaturization of the device is sought, to
an outer diameter of the evaporator 11 of typically 1 to 2 mm, the
peripheral ducts 13 will be very close to the inner artery 14
conveying the liquid, even more so as the diameters of the ducts 13
and the artery 14 must be of a sufficient size to ensure a fluid
flow rate allowing for efficient transfer of the heat to be
discharged. Significant parasitic heat flows from the vapour to the
liquid will then inevitably occur, the liquid will heat up and the
efficiency of the loop will collapse.
[0011] Another drawback of this device representative of the state
of the art also arises from the complexity of production, as soon
as the miniaturization of the device is desired.
[0012] In order to overcome the drawbacks of the state of the art,
the invention proposes a device having at least one micro loop that
is very simple to produce, limiting these parasitic effects and
thus improving the thermal performance of each micro loop. The
device according to the invention is also advantageous for fluid
loops with larger dimensions and heat transfer capacity.
[0013] In order to overcome the above-mentioned drawbacks, the
invention proposes a passive thermal regulation device, comprising
at least one heat transfer loop with capillary pumping of a
heat-carrier fluid, said loop comprising an evaporator having a
microporous mass, and a condenser, intended to be in heat exchange
relationship with a heat source and a cold source respectively, and
tubing connecting the evaporator to the condenser and transporting
the heat-carrier fluid essentially in vapour phase from the
evaporator to the condenser and essentially in liquid phase from
the condenser to the evaporator, the tubing comprising an outer
tube, housing the substantially elongated microporous mass, which
ensures the flow of the liquid-phase heat-carrier fluid by
capillary pumping, which is characterized in that said liquid phase
of said fluid is pumped by a least one end of the microporous mass
that is facing the condenser, and flows in at least one outer duct
delimited between said outer tube and at least one inner tube
extending within said outer tube, and the vapour phase of said
fluid heated in the microporous mass of the evaporator is collected
in a longitudinal central duct made in said microporous mass and
discharged by at least one inner duct delimited within said at
least one inner tube, said at least one inner tube being connected
by one end to an end of said central duct, while the vapour phase
is discharged at the other end of said at least one inner tube, at
the condenser.
[0014] According to a first advantageous embodiment of the device,
said outer tube is closed on itself, forming a continuous loop, of
which two substantially opposite portions in relation to the centre
of said loop are in heat exchange relationship, one with said
condenser, and the other with said evaporator and with said
microporous mass, housed in said other portion of the outer tube,
and passed through over its entire length by said central duct, two
inner tubes extending within said outer tube, each of the two inner
tubes being connected, by a first end, to one of the two ends of
the central duct of said microporous mass respectively, while the
second end of each inner tube opens out into said condenser,
opposite the second end of the other inner tube so as to connect
the inner vapour-phase fluid duct delimited within each inner tube
to said at least one outer duct of liquid-phase fluid flowing from
the condenser towards the corresponding end surface of said
microporous mass.
[0015] According to a second particular embodiment, advantageous in
terms of simplicity, said outer tube is closed at both ends and
both ends are in heat exchange relationship, one with said
condenser, and the other with said evaporator and with said
microporous mass housed in this end of the outer tube, said liquid
phase of said fluid is pumped by the end of the microporous mass
facing the condenser, and flows in an outer duct delimited between
said outer tube and an inner tube extending within said outer tube
and the vapour phase of said fluid heated in the microporous mass
of the evaporator is collected in a longitudinal central duct made
in said microporous mass and discharged by the inner duct delimited
within said inner tube, said inner tube being connected by one end
to an end of said central duct, while the vapour phase is
discharged at the other end of said inner tube, at the
condenser.
[0016] In all cases, to facilitate the pumping of the liquid
condensed in the condenser and to separate the vapour and liquid
phases at this point, it is advantageous that said other end of
said a least one inner tube located at the condenser is fitted into
an annular microporous mass filling a space delimited within said
condenser between said other end of said inner tube and said outer
tube.
[0017] Moreover, preferably, the liquid condensing in the condenser
is drained to said annular microporous mass, preferably along the
wall of said outer tube for example by a capillary drain or a
microporous mass located along the wall of said outer tube at said
condenser.
[0018] If the space constraints of the device allow,
advantageously, each of the evaporator and the condenser comprises
at least one outer sleeve made from a good heat conducting
material, said at least one sleeve of the evaporator surrounding,
at least partially, a portion of the outer tube housing said
microporous mass, and said at least one sleeve of the condenser
surrounding a portion of the outer tube in which at least one inner
duct releases the vapour-phase fluid towards said at least one
outer duct.
[0019] In these cases, at least one of the outer sleeves of the
evaporator and the condenser comprises at least one base plate made
from a good heat conducting material whereby said sleeve is
intended to be placed in heat exchange relationship with a source
that is respectively hot or cold.
[0020] In these different embodiments, the walls of said at least
one inner tube are made from at least one thermally insulating
material, preferably a synthetic material known as plastic, in
order to ensure good thermal insulation between the vapour phase
flowing in the inner tube and the liquid phase flowing in the
duct(s) located between the inner and the outer tubes.
[0021] In an advantageous embodiment, said at least one inner tube
for discharge of the vapour extends into said microporous mass in
order to provide greater sealing between the vapour and liquid
phases of the fluid at the microporous mass.
[0022] Advantageously, said inner tube comprises in its outer wall
at least one capillary drain defined for example by at least one
substantially longitudinal groove, at least on that portion of said
inner tube that extends into the microporous mass, so as to convey
the liquid phase deep within said microporous mass by
capillarity.
[0023] Advantageously in all cases, the outer wall of said at least
one inner tube comprises capillary drains defined for example by
substantially longitudinal grooves extending preferably over the
entire length of said tube.
[0024] According to another advantageous variant embodiment, in
addition to said microporous mass, the outer wall of said at least
one inner tube is in contact with the inner wall of said outer
tube, except at the at least one capillary drain defined by at
least one substantially longitudinal groove made in the outer
surface of said inner tube and defining at least one outer duct
conveying the liquid phase of said fluid.
[0025] Said microporous mass advantageously has a substantially
cylindrical outer shape, together with the portion of said outer
tube that houses it without radial play.
[0026] In order to retain good efficiency of the loop while
avoiding parasitic phenomena, said evaporator has an area intended
to be in heat exchange contact with said heat source, a dimension
of which along the axis of said outer tube is significantly smaller
than the length of said microporous mass, preferably of the order
of half of said length of said mass.
[0027] Moreover, said microporous mass has a length that is
approximately 2 to 15 times greater than its diameter so as to
create a significant reserve of liquid distant from the area of
heat exchange with the heat source.
[0028] Advantageously moreover, said outer tube is in heat exchange
contact with said microporous mass over the entire outer surface of
said mass apart from one or both of its longitudinal end
surfaces.
[0029] In a simple embodiment, said outer tube has a
constant-diameter cross-section.
[0030] Moreover, the outer tube is advantageously made from a good
heat conducting material, at least in one portion in heat exchange
relationship with said microporous mass, and in another portion in
heat exchange relationship with said condenser or constituting the
latter.
[0031] In practice, said outer tube is metal, preferably stainless
steel.
[0032] According to a simplified structure, said outer tube and
said at least one inner tube are cylindrical with a circular
cross-section, the diameter of said at least one inner tube being
approximately half of the diameter of the outer tube.
[0033] The invention also relates to the application of a passive
thermal regulation device with at least one heat transfer loop
according to the invention as defined above, to the transfer of
thermal energy from a heat source, such as an electronic component
or set of components, in heat exchange relationship with the
evaporator, to a cold source in heat exchange relationship with the
condenser.
[0034] Further characteristics and advantages of the invention will
become apparent from the non-limitative description given below of
specific examples of embodiments described with reference to the
attached drawings, in which:
[0035] FIG. 1 is a longitudinal cross-sectional view of an example
fluid loop device according to U.S. Pat. No. 7,111,394;
[0036] FIG. 2 is a cross-sectional view at the microporous mass of
the example in FIG. 1, according to U.S. Pat. No. 7,111,394, FIGS.
1 and 2 having already been described above,
[0037] FIG. 3 is a diagrammatic longitudinal cross-sectional view
of a fluid micro loop device according to the invention;
[0038] FIG. 4 is a longitudinal cross-sectional view on a larger
scale of a detail of the device in FIG. 3 around the microporous
mass;
[0039] FIG. 5 is a cross-sectional view along V-V in FIG. 4 at the
evaporator;
[0040] FIG. 6 is a view similar to FIG. 3 of a simplified micro
loop fluid device variant according to the invention;
[0041] FIG. 7 is a diagrammatic longitudinal cross-sectional view,
on a smaller scale than FIG. 3 and limited to the portions of the
device including the evaporator and the condenser, of a variant
embodiment of the device in FIG. 3;
[0042] FIG. 8 is a cross-sectional view along VIII-VIII in FIG.
7,
[0043] FIG. 9 is a diagrammatic longitudinal cross-section at the
evaporator, of another variant embodiment of the device of the
invention; and
[0044] FIG. 10 is a cross-sectional view along X-X in FIG. 9.
[0045] A first embodiment of the passive thermal regulation device
of the invention is illustrated in FIG. 3, showing a longitudinal
cross-section of an entire double micro loop, FIG. 4 showing a
longitudinal cross-section of the area of the loop encompassing the
evaporator and FIG. 5 showing a cross-section of the centre of the
evaporator. All of the numerical values and technical
characteristics relating to the materials and fluids given below
are for information only. This information is compatible with the
industrial production of the invention with the existing equipment
of the state of the art.
[0046] In this embodiment, the device with micro capillary pumped
fluid loop 20 comprises an outer tube 21 having walls made from a
good heat conducting material, advantageously metal, for example
made from stainless steel, that is for example a cylindrical tube
with a circular cross-section, with a constant outer diameter of 2
mm and a wall thickness of 0.2 mm. This tube 21 is closed on itself
in a continuous loop to form a closed circuit, in which flows a
heat-carrier fluid, which can typically be ammonia, water, or any
other diphasic fluid. A filling tube of the micro loop connected to
the main tube 21 is not shown in FIG. 3 in order to simplify the
diagram.
[0047] In an evaporator 22, a microporous mass or wick 23, having a
cylindrical shape with a circular cross-section, is positioned
without radial play inside a section of the tube 21. The outer
diameter of the microporous mass 23 is therefore 1.6 mm and its
length is for example 20 mm. The microporous mass can be a single
block of the same composition, with pores the diameter or principal
dimension of which is of the order of 1 to 10 .mu.m. In a variant
embodiment, the pores can optionally have variable dimensions, for
example ranging from large pores in the axial end areas 23b of the
wick 23 to promote the capillary pumping of the liquid and its
insulation vis-a-vis parasitic heat flows originating from the heat
source 27 and the central area 23a of the wick 23, to small pores
in the central area 23a of the wick 23, where the vaporization of
the pumped liquid fluid takes place, as explained below.
[0048] The evaporator 22 also comprises a cylindrical sleeve 24,
also with a circular cross-section, that is passed through axially
and without significant radial play by the portion of the outer
tube 21, which surrounds the microporous mass 23, the sleeve 24
being made from a good heat conducting material, preferably metal,
and, optionally, of the same type as the outer tube 21, i.e.
stainless steel, the length of the sleeve 24 along its axis, which
is also that of this section of the tube 21 and the microporous
mass 23 (as these three components are substantially coaxial) being
about half the length of the mass 23.
[0049] Thus, the sleeve 24 is in a good heat exchange relationship
with the outer tube 21, which is also in a good heat exchange
relationship with the microporous mass 23 over the entire outer
surface of the latter apart from its two longitudinal end faces 23c
connected to each other by a cylindrical central duct 25 with a
circular cross-section, which passes right through the mass 23.
[0050] Moreover, as shown in FIG. 5, the sleeve 24 of the
evaporator 22 is secured to a base plate 26, and preferably of a
single piece with the latter, the axial dimension of which can
preferably be the same as that of the sleeve 24, and which
constitutes an area via which the evaporator 22 can be placed in
heat exchange relationship with a heat source 27, shown
diagrammatically in dotted lines in FIGS. 3, 4 and 5 by a
parallelepipedal body, which can be an electronic circuit or
component to be cooled, and against which the base plate 26 is in
plane contact promoting heat transfers by conduction from the heat
source 27 to the base plate 26 and therefore to the sleeve 24,
itself in a good heat exchange relationship, as already mentioned
above, with the microporous mass 23, as a result of the coaxial
mounting without radial play of the mass 23 in a section of the
tube 21, and of the latter in the sleeve 24 of the evaporator
22.
[0051] The base plate 26 of the evaporator 22 in thermal contact
with the heat source 27 thus has a dimension of approximately 10 mm
along the axis of the outer tube 21, and the base plate 26 is
centred in relation to the microporous mass 23, such that both the
areas and end faces 23b and 23c of the microporous mass 23 are
separated from the central area 23a of heat exchange with the heat
source 27.
[0052] To improve the heat exchanges at the contact surfaces, the
microporous mass 23 is attached to the inner cylindrical wall of
the tube 21 and the outer cylindrical wall of the tube 21 is itself
attached to the inner cylindrical wall of the sleeve 24 of the
evaporator 22 by any means that ensures the best thermal contact
possible, for example by gluing, sintering or any other means.
[0053] The device also comprises a condenser 28 mounted, in this
example, on a straight section of the outer tube 21 that is
opposite the straight section of tube 21 passing through the
evaporator 22, in the loop formed by the outer tube 21 and in
relation to the centre of the loop. As for the evaporator 22, the
condenser 28 comprises a cylindrical sleeve 29, made from a good
heat conducting material, preferably metal, which is in good heat
exchange contact with the section of tube 21 that passes through
it, on the one hand, and on the other hand, with a cold source 30,
shown diagrammatically in FIG. 3 by a dotted rectangle, and which
can be a heat sink, for example a metal component of a supporting
structure.
[0054] As for the evaporator 22, the sleeve 29 of the condenser can
optionally comprise a base plate (not shown) promoting heat
exchange contact with the cold source 30 and, as in the evaporator
22, steps can be taken to promote thermal contact between the
sleeve 29 of the condenser 28 and the portion of outer tube 21
passing through it.
[0055] The device also comprises two inner tubes 31, which in this
example, are substantially identical to each other, cylindrical
with a circular cross-section, with a constant diameter that is
approximately half that of the outer tube 21, and which are made
from a thermally insulating material, for example a synthetic
material known as plastic.
[0056] For example, their outer diameter is 1 mm and their wall
thickness is 0.1 mm.
[0057] Each of these inner tubes 31 has a first end 32, by which it
is fitted and fixed into one respectively of the two longitudinal
ends of the longitudinal central duct 25, for example having a
diameter of 0.8 mm, of the microporous mass 23, as shown in more
detail in FIG. 4, so that each of the inner tubes 31 is connected
to the microporous mass 23 by fitting its first end 32 into one
respectively of the two longitudinal end areas 23b of the mass 23.
The connection of the inner tubes 31 with the microporous mass 23
must be sealed in order to prevent the liquid and vapour phases
from coming into contact at this point.
[0058] The second end 33 of each of the two inner tubes 31 extends
into the section of the outer tube 21 passing through the sleeve 29
of condenser 28, into which each second end 33 opens out freely
opposite the second end 33 of the other inner tube 31, so that the
outer tube 21 and the two inner tubes 31 delimit an annular outer
duct 34, inside the outer tube 21 and outside the inner tubes 31,
and two inner ducts 35 each inside one respectively of the two
inner tubes 31.
[0059] In order to separate the vapour phase from the liquid phase
generated by condensation in the condenser 28, it can be
advantageous to tightly fit the end 33 of each of the inner tubes
31 into one of the two annular microporous masses 38 respectively,
each filling an annular space delimited between a portion of the
corresponding end 33 and a radially peripheral portion of the outer
tube 21 in the condenser 28, the function of which is to capture
the liquid phase by capillarity at the condenser 28, while
preventing the vapour phase from returning in the outer duct 34.
Advantageously, it is possible to extend these annular microporous
masses 38 along the inner wall of the outer tube 21 at the
condenser 28 in order to pump the liquid more efficiently at this
point. This capillary drain can be produced by a cylindrical sleeve
39 of microporous mass, having a radial thickness less than that of
the masses 38, and connecting them to each other, and optionally of
a single piece with the two masses 38 in a microporous monolithic
component 40. As a variant, the cylindrical sleeve 39 can be
replaced by a metal sleeve with grooves extending from one to the
other of its axial ends, on its inner surface, each groove forming
a capillary drain.
[0060] This device operates as follows. The base plate 26 of the
evaporator 22 collects heat generated by the heat source 27 and
transmits it, by conduction, to the section of outer tube 21 in
contact with the microporous mass 23.
[0061] The microporous mass 23, heated in this way by the section
of outer tube 21 surrounding it, heats essentially in its central
area 23a the liquid-phase fluid originating from the outer duct 34,
which has been sucked up and pumped by capillarity by the
microporous mass 23, at its longitudinal end areas 23b which are
sufficiently long axially to thermally insulate the liquid in the
outer duct 34, which can thus contain a liquid reserve close to the
wick 23. Each axial end face 23c of the wick 23 where the liquid
phase arrives is also separated from the central area 23a of the
wick which is in heat exchange with the heat source 27. In other
words, each end area 23b of the microporous mass 23 keeps the
liquid away from the hot central area 23a where vaporization takes
place. The liquid-phase fluid pumped into the microporous mass 23
is vaporized in the central area 23a and the vapour is collected in
the central duct of the mass 23, whence the vapour-phase fluid is
discharged towards each of the two inner ducts 35, which guide the
vapour-phase fluid to the ends 33 of the inner tubes 31 into the
condenser 28, where the vapour of this fluid condenses, and the
liquid condensates are pumped by the microporous masses 38, 39 and
guided by the outer duct 34 from the condenser 28 towards the
evaporator 22, to ensure the liquid-phase fluid supply of the
microporous mass 23, via its two longitudinal end faces and areas
23b and 23c, as already mentioned above.
[0062] Thus, the liquid-phase fluid moves along the arrows 36 in
FIG. 3, in the outer duct 34, from the condenser towards the two
longitudinal ends 23c of the microporous mass 23 of the evaporator
22, while the vapour generated by the evaporator 22 during the
operation of the loop is collected in the central duct 25 of the
mass 23, in the central area 23a of the latter, and discharged by
the two longitudinal end areas 23b of the mass 23 in the inner
ducts 35, in which the vapour-phase fluid moves along the arrows 37
in FIG. 3, from the evaporator 22 to the condenser 28, where the
ducts 35 communicate with the outer duct 34 providing the return of
liquid-phase fluid to the evaporator 22 via the microporous
component 40. The thermally insulating material of the inner tubes
31, which separate the vapour phase from the liquid phase, has the
advantage of limiting the heat exchanges between the two fluid
phases flowing in the double loop.
[0063] Due to the considerable length of the microporous mass 23
relative to its diameter and relative to the dimensions of the heat
collecting area in the evaporator 22, the liquid-phase fluid
reserve contained in the outer duct 34, inside the outer tube 21
and on each side of the microporous mass 23, is sufficiently far
away from the heat source 27, despite the small size of the
evaporator 22, to minimize the parasitic flow of thermal energy
towards the liquid reserve, which allows for the improvement of the
thermal performance of the device.
[0064] It must be noted that, in the device as presented above, the
evaporator 22 and the condenser 28 each comprise a thermally
conductive sleeve 24 or 29, but, as variants, as described below
with reference to FIGS. 7 to 10, the sleeve can be constituted
directly by a section of the outer tube 21 made of a good heat
conducting material, and which, also as a variant, can be made from
such a good heat conducting material only on the two sections of
the outer tube 21 that, for one, surrounds the microporous mass 23
and for the other, is surrounded by the sleeve of the condenser 28
or itself constitutes the sleeve.
[0065] FIG. 6 shows a simplified variant of the device of the
invention, comprising an elementary micro capillary pumped fluid
loop, in which is located an outer tube 21 that connects an
evaporator 22 to a condenser 28, while being engaged and fixed by
its two closed longitudinal ends in sleeves 24 and 29 respectively
of the evaporator 22 and the condenser 28. The axial end portion of
outer tube 21 engaged in the sleeve 24 of the evaporator 22
surrounds the cylindrical microporous mass 23 which, in this
example, has a longitudinal central duct 25 for collecting vapour,
which only opens out by the longitudinal end 23c of the mass 23
that is facing the condenser 28, and into which is fitted and fixed
one end of a thermally insulating inner tube 31, extending within
the thermally conductive outer tube 21. The other end 33 of the
inner tube 31 is fitted into an annular mass 38 of another
monolithic microporous element 40' making it possible to separate
the liquid phase from the vapour phase at the condenser 28, and
opens out inside the end portion of the outer tube 21 housed in the
sleeve 29 of the condenser 28 and lined with the microporous
component 40', in order to connect the duct 35, within the inner
tube 31 and guiding the vapour-phase fluid from the output of the
duct 25 of the mass 23 to the condenser 28, to the annular outer
duct 36 guiding the condensed liquid-phase fluid from the condenser
28 to the microporous mass 23 of the evaporator 22, which pumps the
liquid by capillarity and vaporizes it under the effect of the heat
received from the heat source 27, in a heat exchange relationship
with the evaporator 22, the heat discharged from the heat source 27
being transferred by the condenser 28 to the cold source 30, when
the fluid loop is operating, in the same conditions as described
above for the example in FIGS. 3 to 5.
[0066] The microporous element 40' comprises the annular mass 38,
similar to one of the two annular masses 38 in FIG. 3 and occupying
the radial space between the end 33 and the outer tube 21, and
extended towards the closed end of the outer tube 21 by an axial
thin microporous tube 39' and a radial thin microporous disc 41
against the base closing the end of the tube 21, the microporous
tube 39' and disc 41 constituting a capillary drain that
facilitates the supply to the mass 38, of liquid condensed in the
condenser 28 within the component 40', and thus guided by capillary
pumping into the outer duct 31.
[0067] In FIG. 6, the tubes 21 and 31 are straight, but they can be
bent in their central portions between the evaporator 22 and the
condenser 28, in order to adapt the device to the volume available
in the immediate environment of the heat source 27 and/or cold
source 30.
[0068] FIGS. 7 and 8 show a variant embodiment of the device
according to FIGS. 3 to 5, in which the outer sleeves of the
evaporator 22 and the condenser 28 are removed and each replaced by
a respective section of the outer tube 21, having constant outer
and inner diameters over its entire length. Similarly, the outer
and inner diameters of the inner tubes 31 are constant over their
entire length, the inner diameters of the inner tubes 31 and of the
central duct 25 of the microporous mass 23 being equal. For the
rest, the arrangement of the evaporator 22 and of the condenser 28
is essentially the same as in FIGS. 3 and 4, so that the same
references denote the same components. However, in this variant,
capillary drains 42 in the form of grooves are made in the outer
surface of each inner tube 31 at least at the end portion 32 of the
inner tube 31 which is fitted into the microporous mass 23 so as to
convey the liquid deep into said mass 23. A large number of grooves
42 can be made on the entire outer periphery of each inner tube 31,
so as to optimize the fluid pumping flow rate (see FIG. 8). These
capillary drains 42, in the form of grooves that narrow at their
opening on the outer surface of the inner tube 31, thus having a
cross-section promoting the capillary pumping of the liquid used in
the loop, can extend over the entire length of the corresponding
inner tube 31 up to the condenser 28, in the end 33 of the tube 31,
as shown in the upper half cross-sections in FIGS. 7 and 8.
However, the grooves do not penetrate deeper than half the
thickness of the wall of the inner tube 31, so as to maintain good
thermal insulation between the vapour and liquid phases of the
fluid. In this example in FIGS. 7 and 8, the end 32 of each inner
tube 31 extends into the microporous mass 23 over an axial distance
of one to several times the diameter of the outer tube 21, so that
the grooves defining the capillary drains 42 guide the liquid deep
within the mass 23 by capillarity.
[0069] As a variant, the grooves of the drains 42, which can be
parallel to the axis of the tube 31 or helical, are filled with a
microporous material, the pores of which have dimensions greater
than those of the pores of the microporous mass 23, and
substantially equal to or greater than the pores of the microporous
mass 40.
[0070] In a further variant shown in the lower half cross-sections
in FIGS. 7 and 8, the capillary drains 42 in the form of grooves
can be replaced, at least at the evaporator 22, but preferably over
the entire length of each inner tube 31, by another annular
microporous mass 43 surrounding the inner tube 31, this other
microporous mass 43 being capable of having a different composition
from the main microporous mass 23 used for the evaporation of the
fluid, for example having pores with a significantly larger average
diameter, typically by a factor of 2 to 10, than the average
diameter of the pores of the main microporous mass 23 and
substantially equal to or slightly greater than that of the pores
of the microporous mass 40. Microporous capillary drains 43 are
thus produced.
[0071] FIGS. 9 and 10 show respectively, in a longitudinal
cross-section at the evaporator 22 and a transverse cross-section
between the latter and the condenser 28, two further variant
embodiments of the device according to the invention. As a variant
according to the upper half cross-sections in FIGS. 9 and 10, the
outer wall of each inner tube 31 is in contact with the inner wall
of the outer tube 21, from the longitudinal ends of the microporous
mass 23 of the evaporator 22 to the condenser 28, except at the
narrowed openings of a number of outer ducts 34', each of which has
a small cross-section, in this example in the shape of a droplet,
made in the outer surface of the inner tubes 31 in which numerous
grooves 42' are made over the entire periphery of each tube 31.
These longitudinal or helical grooves 42', or others, each defining
an outer duct 34', are only made in substantially the outer radial
half of the thickness of the wall of each inner tube 31, so that
the liquid phase flowing in these grooves 42'--outer ducts 34'
remains well insulated thermally from the vapour phase flowing in
the inner ducts 35 inside the tubes 31.
[0072] For the rest, the evaporator 22 exhibits substantially the
same arrangement of the wick 23 as in FIG. 7, with however, a
stepped cut-out in the ends 33 of the inner tubes 31 where they are
fitted into the microporous mass 23, when the capillary drains
formed by the outer ducts 34' extend into the microporous mass in
order to supply liquid to the end surfaces 23c of the end areas 23b
of the mass 23, while the massive inner radial annular half of each
inner tube 31 abuts an axial end surface of the central area 23a of
the mass 23. At the condenser (not shown) substantially the same
arrangements as in FIG. 7 are present, with the ends of the grooves
34' of the tubes 31 that open out against the annular microporous
mass 38, another cylindrical central microporous mass optionally
being capable of being mounted between the two annular masses
38.
[0073] As a variant, it is possible to fill the outer ducts 34'
with a microporous material having pores with average dimensions
greater than those of the pores of the mass 23, at least in the end
portions 32 and optionally 33, of the tubes 31, at the evaporator
and the condenser, or even over the entire length of the tubes
31.
[0074] Also as a variant, as shown in the lower half cross-sections
in FIGS. 9 and 10, the outer ducts 34' forming capillary drains can
be replaced by another annular microporous mass 43', surrounding
the ends 32 and/or 33, or even each tube 31 in its entirety, the
radial thickness of which is reduced to substantially its inner
radial half, the average dimensions of the pores of the annular
mass 43' being greater than those of the pores of the mass 23 and
substantially equal to or slightly greater than that of the
microporous mass of the condenser. Outer ducts arranged in
capillary drains 43' are thus produced. It is also possible to
produce a single-loop device having a single inner tube 31
according to FIG. 6 with outer ducts 34' being produced, acting as
capillary drains and defined by grooves 42' in the outer surface of
the inner tube 31 in contact with the inner surface of the outer
tube 21 as in FIGS. 9 and 10, it then being possible to provide a
tube for filling with liquid fluid in the axial extension of the
condenser 28, on the side opposite the evaporator 22.
[0075] In embodiments having double loops, as in FIGS. 3, 7 and 9,
the filling tube opens out "radially" or perpendicularly into a
portion of the outer tube 21 located between condenser and
evaporator 22.
[0076] Given the small dimensions of a device with at least one
fluid micro loop according to the invention, such a device can be
advantageously applied to the transfer of thermal energy from a
heat source 27 with a high thermal power density but small
dimensions, such as an electronic component or circuit, placed in
heat exchange relationship with the evaporator of the device of the
invention, to a cold source 30 placed in heat exchange relationship
with the condenser of said device.
* * * * *