U.S. patent application number 16/094328 was filed with the patent office on 2019-04-25 for cryogenic device with compact exchanger.
The applicant listed for this patent is SOCIETE FRANCAISE DE DETECTEURS INFRAROUGES- SOFRADIR. Invention is credited to Ahmad Sultan, Jean-Christophe Terme.
Application Number | 20190120529 16/094328 |
Document ID | / |
Family ID | 57233543 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190120529 |
Kind Code |
A1 |
Terme; Jean-Christophe ; et
al. |
April 25, 2019 |
CRYOGENIC DEVICE WITH COMPACT EXCHANGER
Abstract
This cold generation device implements the "Joule-Thomson"
expansion principle. It includes a heat exchanger having a fluid
under high pressure and under low pressure circulating in
counterflow therethrough. The heat exchanger is formed of the stack
of pellets (5) made of a porous material, and particularly a
sintered material, forming a cylindrical mandrel, having a
capillary (10) wound at the periphery thereof and in contact
therewith, the capillary having the high-pressure fluid circulating
therethrough, the low-pressure fluid circulating in counterflow
inside of the porous mandrel thus formed.
Inventors: |
Terme; Jean-Christophe;
(Lans en Vercors, FR) ; Sultan; Ahmad;
(Saint-Egreve, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOCIETE FRANCAISE DE DETECTEURS INFRAROUGES- SOFRADIR |
Palaiseau |
|
FR |
|
|
Family ID: |
57233543 |
Appl. No.: |
16/094328 |
Filed: |
June 2, 2017 |
PCT Filed: |
June 2, 2017 |
PCT NO: |
PCT/FR2017/051390 |
371 Date: |
October 17, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 9/02 20130101; F25B
2341/062 20130101; F25B 41/067 20130101; F25B 2400/052 20130101;
F28D 7/024 20130101; F28F 13/003 20130101; F25B 2309/022
20130101 |
International
Class: |
F25B 9/02 20060101
F25B009/02; F25B 41/06 20060101 F25B041/06; F28D 7/02 20060101
F28D007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2016 |
FR |
1655128 |
Claims
1. A cold generation device implementing the "Joule-Thomson"
expansion principle, comprising a heat exchanger having a fluid
under high pressure and under low pressure circulating in
counterflow therein, wherein the heat exchanger is formed of the
stack of pellets made of a porous material, and particularly a
sintered material, forming a cylindrical mandrel, having a
capillary wound at the periphery thereof and in contact therewith,
the capillary having the high-pressure fluid circulating
therethrough, the low-pressure fluid circulating in counterflow
inside of the porous mandrel thus formed; and wherein a
thermally-insulating porous element is interposed between each of
the pellets.
2. The cold generation device of claim 1, wherein the porous
thermally-insulating element is formed of a fabric, particularly
made of fiber glass.
3. The cold generation device of claim 1, wherein the pellets have
a cylindrical shape, wherein the thermally-insulating intercalary
elements have a circular shape, and wherein the diameter of the
intercalary elements is smaller than or equal to the external
diameter of the pellets.
4. The cold generation device of claim 1, wherein the pellets are
made up of sintered silver or copper.
5. The cold generation device of claim 1, wherein the capillary is
made of metal, particularly of copper, of stainless steel, or of
cupronickel alloy.
6. The cold generation device of claim 5, wherein the capillary
receives a silver deposit, which is a function of the nature of the
material forming the pellets, said deposit being realized before
the winding of the capillary on the mandrel formed by the stack of
pellets.
7. The cold generation device of claim 1, wherein the spirals
defined by the winding of the capillary around the mandrel formed
by the stack of pellets are not in contact with one another.
8. The cold generation device of claim 7, wherein a
thermally-insulating yarn is wound on the intervals separating the
spirals, said yarn being particularly made up of fiber glass.
Description
TECHNOLOGICAL FIELD
[0001] The disclosure pertains to the general field of
refrigerating machines, and more particularly to cold generation
devices intended to allow the operation of certain types of
detectors, and more particularly of infrared detectors of cooled
type, also called quantum infrared detectors. It more particularly
targets devices of the type in question implementing as a cold
source the principle of the so-called "Joule-Thomson"
expansion.
BACKGROUND
[0002] In the specific context of infrared detectors, it is
desired, for obvious bulk reasons, to limit the volume of the
cryogenic source. Actually, miniature cryogenic machines frequently
use the "Joule-Thomson" expansion principle, thus enabling to have
a high cryogenic power, and accordingly a fast cooling,
particularly of infrared detectors or of electronic components
requiring, for their operation, operating at relatively low
temperatures.
[0003] The performance of such cryogenic machines is known to
depend on the efficiency of the heat exchange which occurs between
the high-pressure fluid and the low-pressure fluid before the
expansion of the fluid occurs. The efficiency of the heat exchange
is thus essential.
[0004] For this purpose, prior art devices use a Hampson-type
counterflow exchanger, where the high-pressure fluid flows in a
capillary surrounding a cylindrical sleeve or mandrel, closed by
insulating foam. The heat exchange takes place at the periphery of
the sleeve, at the level of which the low-pressure fluid circulates
in counterflow.
[0005] To optimize such a heat exchange, it has been provided to
increase the surface area of exchange between the high-pressure
fluid and the low-pressure fluid, by providing the capillary with
radial fins. If, indeed, the heat exchange surface area is thereby
increased, however, the presence of fins, due to their thickness,
increases the spacing between two consecutive spirals, and thereby
decreases the number of spirals of the capillary for a given length
of the mandrel, at least partially neutralizing the desired
optimization of the exchange.
[0006] For the same purpose, it has already been provided to
increase the length of the exchanger, and more particularly the
length of the capillary. The issue of the bulk of said exchanger,
and thus of the refrigerating machine, then arises.
[0007] It has already been provided to decrease the axial
conduction in the exchanger, which is inherent to the use of the
mandrel and a source of loss of efficiency.
SUMMARY OF THE DISCLOSURE
[0008] The disclosed embodiments aim at a device of the type in
question enabling both to increase the efficiency of such a device,
particularly by decreasing the cooling time of the installation,
without altering the bulk of existing devices or, on the contrary,
with a constant cooling time, to decrease the bulk of such
devices.
[0009] For this purpose, the disclosed embodiments provide a cold
generation device implementing the "Joule-Thomson" expansion
principle, comprising an exchanger having a fluid under high
pressure and under low pressure circulating in counterflow
therein.
[0010] According to the disclosed embodiments, the heat exchanger
is formed of the stack of pellets made of a porous material, and
particularly a sintered material, forming a cylindrical mandrel
having a capillary wound in contact therewith, the capillary having
the high-pressure fluid circulating therethrough, the low-pressure
fluid circulating in counterflow inside of the porous mandrel thus
formed.
[0011] Further, a thermally insulating porous fabric, typically
made of fiber glass, is interposed between each of the pellets made
of sintered material.
[0012] In other words, the disclosed embodiments basically comprise
replacing the mandrel and the fins of prior art with a stack of
porous sintered material, favoring the heat exchange of the
low-pressure fluid with the high-pressure fluid circulating in the
peripheral capillary in contact with said material.
[0013] Such an optimization of the exchange results from the nature
of the material forming the mandrel, and further enables to do away
with the fins optimizing the heat exchange of prior art, and
accordingly enables to optimize the spiral concentration of the
capillary having the high-pressure fluid circulating therethrough,
and accordingly enables to optimize the compactness of the cold
generation device.
[0014] Further, due to the interposition, between the pellets of
sintered material, of thermally-insulating grids, typically made of
fiber glass, which thus do not conduct heat, the axial conduction
is decreased and the operation of the cold generation device is
accordingly optimized.
[0015] Advantageously, the pellets are made up of sintered silver
or of sintered copper.
[0016] The capillary is made of a metal, typically of copper, of
stainless steel, or even of a cupronickel alloy.
[0017] According to an advantageous feature, the spirals of the
capillary are not in contact with one another. To achieve this, a
thermally-insulating yarn, typically made of fiber glass and used
as a spacer, is wound together with said capillary. Such a yarn
ensures different functions:
[0018] thermally insulating two consecutive spirals of the
capillary;
[0019] thermally insulating said spirals of the external tube or
well into which the device is likely to be introduced;
[0020] ensuring a tightness of the device with such an external
tube or well, forcing the low-pressure fluid to pass through the
sintered material pellets, inducing an optimization of the
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The way in which the embodiments may be implemented and the
resulting advantages will better appear from the following
non-limiting description, in relation with the accompanying
drawings, among which:
[0022] FIG. 1 is a diagram illustrating the principle of the
"Joule-Thomson" expansion implemented at the level of the cold
generation device.
[0023] FIG. 2 is a simplified representation of the device.
[0024] FIG. 3 is a view similar to FIG. 2 illustrating the
respective circuit of the high-pressure and low-pressure fluid;
[0025] FIG. 4 is a simplified representation of a cryostat;
[0026] FIG. 5 is a simplified representation in partial sagittal
cross-section view of one of the portions of the cryostat of FIG.
4.
DETAILED DESCRIPTION
[0027] The operating diagram of a device implementing the
"Joule-Thomson" expansion has thus been shown in relation with FIG.
1. The diagram shows the source of high-pressure fluid HP, which
fluid may be a gas, typically argon, nitrogen or air, and the
return of said fluid after the expansion.
[0028] The counterflow heat exchanger between the high-pressure
fluid originating from high-pressure source HP and the low-pressure
fluid, after expansion at the level of the evaporator (2), an
expansion valve (3) being mounted before the evaporator, has been
shown by double coil (1). The assembly is integrated within a
vacuum enclosure (4).
[0029] The core of the exchanger has been shown in FIG. 2. It is
formed by the stack of pellets (5), made of porous material, and
particularly of a sintered material made up of silver. Silver is
indeed a very fine heat conductor and is further easy to sinter. It
may also be envisaged to use copper to replace silver.
[0030] Typically, the porosity of such pellets is close to 100
nanometers. In other words, the orifices generated by the sintering
of the pellets have a typical diameter of 100 nanometers.
[0031] Such pellets (5), of generally cylindrical shape, are for
example assembled to one another by means of securing rods (6),
starting from the high-pressure connector (7), and provided with
nuts (8) at their lower base. As a variation, the pellets may be
glued together.
[0032] According to the contemplated embodiments, the pellets (5)
are separated from one another by an intercalary or grid (9) made
of a non-conductive porous material, typically formed of a fiber
glass woven material. Such intercalaries have a typically
0.3-millimeter thickness. The use of such intercalaries tends to
oppose any axial heat conduction, optimizing the surface area of
heat exchange between the two flows, respectively at low pressure
and high pressure.
[0033] The assembly thus formed by the pellets and the
intercalaries forms a cylindrical mandrel, having a capillary (10)
wound in contact therewith, the high-pressure fluid flowing through
the capillary. The capillary is for example made of copper, of
stainless steel or of a cupronickel alloy. It typically has an
outer diameter of 0.5 millimeter and an inner diameter of 0.3
millimeter.
[0034] Due to the porous character of the pellets (5), the
low-pressure fluid crosses them and cools them. In turn, due to
their good heat conductivity, the pellets cool down the
high-pressure fluid which flows through the capillary. Actually, a
good thermal contact is necessary between the capillary and the
pellets.
[0035] The manufacturing of such a device may be carried out as
follows.
[0036] First, the pellets (5) are formed by means of a mould shaped
according to the desired shape of said pellets. The silver powder
is poured into the mould, and the temperature of the mould is
raised to a temperature lower than the melting temperature of
silver, to obtain a simple sintering without causing a melting of
the powder.
[0037] After having been manufactured, the pellets are stacked by
interposing the thermally-insulating elements (9), the latter
having an external diameter smaller than or equal to that of the
pellets (5), so that they cannot come into contact with the
capillary (10).
[0038] The pellets and the intercalaries are slipped on the
securing rods (6), for example, threaded, and locked by means of
the nuts (8). A mandrel is thus formed de facto.
[0039] The capillary, for example, made of a cupronickel alloy, is
submitted to a treatment comprised of a silver deposition, for
example, by electrolysis, if the pellets are made of sintered
silver. Such a deposition aims at favoring the subsequent contact
with the pellets (5), particularly when said capillary is secured
by welding or by soldering. Thus, after the winding of the
capillary (10) around the mandrel, the assembly is placed in a
furnace to generate the soldering phenomenon.
[0040] As a variation, it may be envisaged to consolidate the
assembly thus formed by means of a thermally-conductive binder, for
example formed of a "solgel"-type glue film filled with metal
powder, applied in the capillary/pellet area.
[0041] According to an advantageous feature, it is desired to avoid
any contact between the consecutive spirals of the capillary, to
avoid any thermal bridge between them.
[0042] For this purpose, it should be reminded that the device aims
at being integrated in a cylindrical well of a cryostat, such as
illustrated in FIG. 4. Such a cryostat (11) is conventionally
maintained in vacuum. It receives in the enclosure that it defines
an infrared detector (12), positioned vertically in line with a
window (13) transparent to the radiation to be detected. Finally,
it comprises two wells (14) having a device inserted in each of
them to generate the cold necessary to the operation of said
detector.
[0043] FIG. 5 shows a simplified view in partial sagittal
cross-section view of one of the wells (14) provided with the
device.
[0044] Thus, to force the low-pressure fluid, and particularly the
low-pressure gas, to cross the porous pellets (5), a yarn (15) made
of an insulating material, for example, made of fiber glass or of
polyester fibers such as commercialize under trademark
Terylene.RTM., bearing between two consecutive spirals of the
capillary (10), that is, in the interval separating said spirals,
and against the inner wall (16) of the cylindrical well (14), is
positioned. The yarn (15) is thus wound along the mandrel, and then
secured at its two ends, typically by gluing.
[0045] Thus, with the arranging of the yarn (15), it is done away
with any thermal bridge between spirals on the one hand, and
between the spirals and the well (14).
[0046] The consecutive spirals of the capillary (10) are thus
thermally insulated from one another. Further, the spirals of the
capillary (10) are thermally insulated from the bridge (14).
[0047] Finally, the presence of the yarn (15) provides a tightness
of the device with respect to said well, forcing the low-pressure
fluid to cross the pellets (5) and thus contributing to optimizing
the efficiency of the device.
[0048] In the specific case of the implementation of the device for
an infrared detector, the operating temperature thereof is
typically in the range from 77 K to 250 K.
[0049] The pressure of the high-pressure fluid is typically in the
range from a few tens to a few hundreds of bars.
[0050] The device enables to considerably increase the heat
exchange surface area as compared with prior art devices, of the
type comprising a capillary with fins, typically 1,000 times at
constant bulk. It can then easily be understood that the efficiency
of such a refrigerating machine is itself increased, or that the
bulk of such a refrigerating machine may be significantly
decreased, while keeping the same performance as prior art devices.
Such results are particularly advantageous in the context of cooled
infrared detectors.
* * * * *