Patent Grant
9175884
The embodiments generally relate to systems, apparatus and methods for thermal management devices, and more specifically, to pulse tube cryocoolers.
Small cryogenic cooling systems are employed in various demanding applications including military and civilian active and remote sensing, superconducting, and general electronics cooling. Such applications often demand efficient, reliable, and cost-effective cooling systems that can achieve extremely cold temperatures below 80 degrees Kelvin.
Efficient cryogenic cooling systems are particularly important in sensing applications involving high-sensitivity infrared focal plane arrays of electromagnetic energy detectors (FPA's). Generally, an FPA may detect electromagnetic energy radiated or reflected from a scene and convert the detected electromagnetic energy into electrical signals corresponding to an image of the scene. To optimize FPA imaging performance, any FPA detector nonuniformities, such as differences in individual detector offsets, gains, or frequency responses, are corrected. Any spatial or temporal variations in temperature across the FPA may cause prohibitive FPA nonuniformities.
FPA's are often employed in avionics applications, particularly missile targeting and satellite applications, where weight, size, and spatial and temporal uniformity of cryogenic cooling systems are important design considerations. An FPA should operate at stable cryogenic temperatures for maximum performance and sensitivity.
Generally, two types of cryocooling systems exist and have been incorporated into FPA's, recuperative cryocoolers and regenerative cryocoolers. In recuperative cryocoolers, a cooling fluid is cycled in a continuous flow. Typical recuperative flow cycles are Brayton or Joule-Thomson processes. Disadvantageously, the cooling fluid typically requires a heavy and bulky FPA cooling interface and heat exchanger, which is attached to the FPA mounting assembly. Consequently, the FPA assembly requires additional mechanical support to secure the interface, heat exchanger, and cooling fluid. The bulky components and additional support hardware oftentimes requires additional cooling, which increases demands placed on the cooling system. In some instances, the bulky support structure, conventionally thought to improve temperature stability, actually reduces system cooling efficiency. Furthermore, the additional bulky mechanical FPA support hardware may cause alignment problems with an on board optical or infrared system during installation and operation, thereby increasing installation and operating costs.
In contrast to recuperative cryocoolers, regenerative cryocoolers have increasingly been employed. Typical regenerative cryocoolers include the Stirling, Gifford-McMahon and pulse tube types, all of which provide cooling through oscillating pressures and masses flows (e.g., the alternating compression and expansion of a working fluid), with a consequent reduction of its temperature. Conventional Stirling and Gifford-McMahon regenerative cryocoolers use displacers to move a working fluid (usually helium or another ideal gas) through their respective regenerators. The noise and vibration induced by the displacer creates problems, and the wear of the seals on the displacer requires periodic maintenance and replacement. Further, the displacer undesirably contributes to axial heat conduction and shuttles heat loss.
Therefore, it may be desirable for cryocooler devices to generate less vibration and less acoustic noise. It may also be desirable to decrease the number of moving parts used in cryocooler devices and to significantly increase the required maintenance intervals and reliability. Pulse tube cryocoolers are a known alternative to the Stirling and Gifford-McMahon cryocooler types; differing from them by the elimination of the mechanical displacer.
A pulse tube is essentially an adiabatic space wherein the temperature of the working fluid is stratified, such that one end of the tube is warmer than the other. A pulse tube cryocooler typically includes a regenerator comprised of a metallic alloy mesh, balls, granules, or shots and a pulse tube, the regenerator and pulse being connected via a cold heat exchanger. Conventional pulse tube cryocoolers operate by cyclically compressing and expanding a working fluid in conjunction with its movement through heat exchangers. Heat is removed from the system upon the expansion of the working fluid in the gas phase. Pulse tube cryocoolers can be divided into two types based on their drivers. The first type is usually referred to as “Stirling-type”, because this type employs a linear compressor with a piston or a plunger to linearly move the working gas, just as conventional Stirling cryocoolers usually do. In these Stirling-type pulse tube cryocoolers, the frequency of the compressors is identical with the oscillation frequency of the working fluid in the tube. Stirling pulse tube cryocoolers are usually operated at frequencies above 30 Hz.
At temperatures below 10 K, pulse tube cryocoolers typically work with frequencies as low as 1 to 2 Hz. For avionic applications pulse tube cryocoolers typically operate at 35K and have been used as low as 4.5K with cooling usually less than 0.1 W. In order to keep the volume of the compressor small, it is advantageous to decouple the compressor from the pulse tube such that both systems can be optimized independently of each other. The compressor can then be operated at a higher frequency of e.g. 50 Hz to provide a constant high and low pressure region. The compressor then utilizes a valve system that alternately connects the hot side of the regenerator with low and high pressure. The frequency of valve switching can be adjusted to the desired operation frequency of the pulse tube cryocooler and can be chosen to be much smaller than the frequency of the compressor. Since this valve switching is similar to the construction of the above mentioned Gifford-McMahon-refrigerater (G-M-refrigerator), pulse tube cryocoolers with such valve compressors are usually called G-M-pulse tube cryocoolers.
Stirling-type pulse tube cryocoolers, which mainly aim at miniaturization, reliability, long life and high efficiency, are gradually replacing Stirling cryocoolers, especially in military and space fields (such as infrared sensors for missile guidance, satellite based surveillance, atmospheric studies of ozone hole and greenhouse effects). However, it remains desirable to provide improved cryocoolers of this type which decrease the overall cost of manufacture without sacrificing the reliability, life and efficiency of the system.
The embodiments are designed to overcome the noted shortcomings associated with conventional systems, apparatus, and methods. In example embodiments, a glass substrate having a substantially plate or flat wafer shape is provided and configured to form a pulse tube cryocooler (hereinafter “PTC”) having one or multiple stages. Advantageously, the embodiments, as designed, provide a low cost, long life, reliable and efficient PTC. Further, the PTC of the example embodiments, may generate less vibration and less acoustic noise than conventional cryocoolers.
Example embodiments provide a PTC comprised of an etched glass substrate bonded to a glass plate or wafer and defining one or multiple stages. The etched glass substrate includes a plurality of channels etched into a surface thereof to define a first heat exchanger, a pulse tube, a cold heat exchanger or cold head, a regenerator and a second heat exchanger or aftercooler. The pulse tube is disposed between the cold head and the first heat exchanger and is operable for receiving a fluid which has a temperature above ambient. In example embodiments, the first heat exchanger is connected to a valve or inertance tube which, in turn, is connected to a buffer tank or reservoir. The regenerator is disposed between the cold head and the aftercooler, the aftercooler being connected to an external compressor. The bonding of the etched glass substrate to the glass plate or wafer encloses the etched channels to form capillaries operable for conducting and distributing fluid.
In an example embodiment, a PTC is provided that is manufactured by the method of providing and etching a surface of a glass substrate with a plurality of channels to form a first heat exchanger region, a pulse tube region, a cold head region, a regenerator region and a second heat exchanger or aftercooler region. Once the glass substrate is etched with the desired number of channels a blank glass plate or wafer is bonded thereon for hermetic sealing (i.e., to enclose the channels thereby forming capillaries for conducting and distributing a gas or fluid). Thereafter, an inlet port is made through a defined location at the first heat exchanger region for connection to an inertance tube. An outlet port is made through a defined location at the aftercooler region for connection to a compressor.
In an example embodiment, an operation of the PTC includes having a gas or fluid enter through an inlet port and through the pulse tube. The PTC is configured to insulate the heat exchange process at its respective ends. That is, the heat exchanger is configured to be large enough such that gas/fluid flowing from the inlet port traverses through the first heat exchanger and only part way through the pulse tube before flow is reversed. Likewise, fluid flow from the compressor side traverses through the aftercooler and only part way through the regenerator before flow is reversed. Gas/fluid in the middle portion of the PTC (i.e., the cold head) is sealed in, remains in the PTC during operation, and forms a temperature gradient that insulates the two ends of the PTC. Roughly speaking, the gas/fluid in the PTC is divided into three segments, with the cold head portion acting as a displacer but consisting of gas as opposed to a solid materials. Functionally, the PTC transmits hydrodynamic or acoustic power in the oscillating gas cryo-system from one end to the other across a temperature gradient with a minimum power dissipation and entropy generation.
In other example embodiments, a folded or manifold configuration may be provided. In such configurations, two glass substrates are etched and bonded such that one substrate forms a pulse tube layer and the other forms a regenerator layer. The two layers are then bonded together in a stacked form with a third blank layer disposed between the two, warm at one end and cold at the other. Each layer is provided with a plurality of through holes or fluid flow passages such that fluid can translate from layer to the other. In such configurations, the warm end may be provided with a first connection from the compressor and into the regenerator and a second connection from the inertance tube and into the pulse tube.
In other example embodiments, a multiple stage PTC is provided. In such configurations, multiple glass substrates are etched and bonded such that one substrate forms a pulse tube layer having at least one pulse located thereon and the other forms a regenerator layer having at least one regenerator located thereon. The layers are then bonded together in a stacked form, with the combination and stacking varying depending on the intended use and geometric boundaries. Each layer is provided with a plurality of through holes or passageways such that fluid can translate from one layer to the other. In such configurations, a first connection from the compressor and into the regenerator and a second connection from the inertance tube and into the pulse tube is provided. In example embodiments, a second inertance tube connection is provided. Advantageously, cryocooler capacity can be increased by adding additional identical layers.
Additional features and advantages of the disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the disclosure as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present example embodiments of the disclosure, and are intended to provide an overview or framework for understanding the nature and character of the disclosure as it is claimed. The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure, and together with the detailed description, serve to explain the principles and operations thereof.
The embodiments may take form in various components and arrangements of components, and in various steps and arrangements of steps. The appended drawings are only for purposes of illustrating example embodiments and are not to be construed as limiting the subject matter.
The embodiments will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These example embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numbers refer to like elements throughout the various drawings. Further, as used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The embodiments are designed, provide a low cost, reliable, long-life, and efficient pulse tube cryocooler (hereinafter “PTC”) operable for use with military and civilian active and remote sensing, superconducting, and general electronics cooling applications. Example embodiments presented herein disclose systems, apparatus and methods for a glass slide pulse tube cryocooler operable for use with avionics applications, and more particularly, missile targeting and satellite applications, where weight, size, and spatial and temporal uniformity of cryogenic cooling systems are important design considerations. Advantageously, the PTCs provided herein may be used for cooling an infrared (IR) focal plane array (FPA) disposed in an integrated detector cooler assembly (IDCA).
Referring now to the
In example embodiments, the glass substrate 50 may be a silica glass material, such as fused silica glass, soda-lime-glass, Sodium borosilicate glass, Pyrex, crystal glass, or Oxide glass. Further, in example embodiments, the glass substrate 50 may be a solid that possesses a non-crystalline (i.e. amorphous) structure and that exhibits a glass transition when heated towards the liquid state. Further, in example embodiments, the glass substrate 50 may be composed of ionic melts, aqueous solutions, molecular liquids, and polymers. Still further, in example embodiments, a polymeric glass substrate may be used such as, for example, acrylic glass, polycarbonate, polyethylene terephthalate.
In example embodiments, disposed at the hot end 25 of the pulse tube 12 is an inlet port 22 for receiving a valve connection or an inertance tube 1. In example embodiments, the inertance tube 1 is connected or connectable via an orifice 4 to a buffer or reservoir 2 configured for maintaining a fluid. In example embodiments, the hot end 29 nearest the aftercooler 18 is provided with an outlet port 24 and is connected or connectable to a compressor or moveable piston 3. The bonding of the etched glass substrate 50 to the glass plate or wafer 52 encloses the etched channels 11, 13 to form capillaries operable for conducting and distributing fluid. In example embodiments, the fluid may be helium, nitrogen, argon, methane, ethane, or other gas components, or mixtures thereof.
In example embodiments, the heat exchanger channels 11 are approximately 50 to 100 microns wide and 0.5-2 mm deep. In other example embodiments, the regenerator channels 13 are 15-30 microns wide and 0.5-2 mm deep. In still other example embodiments, the pulse tube 12 is approximately 1-4 mm deep. In still other example embodiments, the spacing between the heat exchanger and regenerator channels is equal to the respective channel width.
In example embodiments, an operation of the PTC 10 includes having a fluid first enter the PTC 10 through the inlet port 22 and through the pulse tube 12. The compressor 3 moves periodically back and forth or from left to right and back to generate high and low pressures. More specifically, as a result of the movement of the compressor 3, the fluid moves from left to right and back while the pressure within the PTC 10 increases and decreases. As the pressure increases, the fluid is compressed thereby increasing the temperature to above the ambient temperature. Conversely, as the pressure decreases, the fluid expands and the temperature decreases. If the fluid is compressed it enters the regenerator 14 with an elevated temperature and leaves the regenerator 14 at the cold head 20 with decreased temperature, hence heat is transferred into the regenerator 14. On its return, the heat stored within the regenerator 14 is transferred back into the fluid. The thermal environment of a fluid near the cold head 20, that moves back and forth in the PTC 10, changes when it passes through the aftercooler 18. In the regenerator 14 and in the aftercooler 18 the heat contact between the fluid and its surrounding material is optimal for the desired operation. The temperature of the fluid is substantially the same as of the surrounding medium. However, in the pulse tube 12 the fluid is thermally isolated (adiabatic), so, in the pulse tube 12, the temperature of the fluid vary with the pressure.
Stated another way, the PTC 10 is configured to insulate the heat exchange process at it two ends 17, 19. The PTC 10 is sized to be larger enough so that fluid flowing from the inlet port 22 traverses through the first heat exchanger 16 and only part way through the pulse tube 12 before flow is reversed. Likewise, fluid flow from the compressor 3 traverses through the aftercooler 18 and only part way through the regenerator 14 before flow is reversed. In the illustrated configuration, gas/fluid in the middle portion of the PTC 10 (i.e., the cold head 20) is sealed in by the competing flows from the pulse tube 12 and the regenerator 14 and remains in the cold head 20 region during operation. Advantageously, the result is that a temperature gradient is formed which insulates the PTC 10 at its two ends 17, 19. The fluid in the PTC 10 is divided into three segments, with the cold head 20 acting as a displacer but consisting of fluid as opposed to a solid materials. Advantageously, the overall function of the PTC 10 is that is transmits hydrodynamic or acoustic power in the oscillating fluid cryo-system from one end to the other across a temperature gradient with a minimum power dissipation and entropy generation.
Referring now to
Referring now to
Referring now to
In example embodiments, the PTC 10 may be used for cooling and maintaining at an operating temperature an infrared (IR) focal plane array (FPA) (not shown) disposed in an integrated detector cooler assembly (IDCA) (not shown). In such example embodiments, cooling the FPA to a desired operating temperature may be performed by providing a glass slide pulse tube cryocooler that is connected or connectable to the FPA. The glass tube cryocooler may include first and second ends and a plurality of channels etched into a surface between said ends. The plurality of channels are configured to define a heat exchanger positioned at the first end, an aftercooler positioned at the second end, a cold head disposed between the heat exchanger and the aftercooler, a pulse tube disposed between and in fluid communication with the heat exchanger and the cold head, and a regenerator disposed between and in fluid communication with the cold head and the aftercooler. In such example embodiments, the etched surface of the glass substrate is bonded with a glass plate to enclose the plurality of channels to form capillaries for conducting and distributing a fluid. Further, the regenerator is connected or connectable with an oscillating compressor which compresses or permits expansion of the fluid such that a temperature gradient is formed at the cold head to insulate the first and second ends and maintain the FPA at the desired operating temperature. In example embodiments, the use of the PTC permits cooling of the FPA within 5 to 10 seconds.
Referring now to
At step 130, the glass substrate 50 may have inlet and outlet ports 22, 24 bored therein. The inlet port 22 may be in fluid communication with an inertajnce tube, said inlet port 22 being operable for conducting and distributing a fluid from a inertance tube to the pulse tube 12. The outlet port 24 may be in fluid communication with a compressor, said outlet port 24 being operable for conducting and distributing a fluid from the aftercooler 18 to the compressor.
At step 140, a determination is made as to whether more than one stage or layers are required for the application. If more than one stage/layer is required, then through holes or fluid flow passages 28 are bored into a glass plate 52 along defined locations at the distal ends (Step 150). Thereafter, at Step 160, the glass substrate 50 is bonded with the glass plate 52 such that the plurality of channels 11, 13 are enclosed and hermetically sealed, thereby forming capillaries. In example embodiments, the glass substrate 50 may have partially, pre-bored through holes 28 which correspond to those bored into the glass plate 52. Alternatively, the glass plate 52 may first be bonded to the glass substrate 50 and then have the through holes 28 bored, it being understood that the through holes 28 are operable for connecting, conducting and distributing a fluid in a stacked, multi-stage configuration. At Step 170, the layers are bonded together such that the through holes 28 permit the flow of fluid from one to another. If a multi-stage, stacked PTC 10 is to be manufactured, the pulse tube layer(s) and regenerator layer(s) are bonded to together in a folded or manifold type configuration.
If, however, only one stage or layer is required, then the glass substrate 50 is bonded with a glass plate 52 such that the plurality of channels 11, 13 are enclosed and hermetically sealed, thereby forming capillaries (Step 180).
In example embodiments, the glass plate 52 is bonded to the etched glass substrate 50 by using glass frit material to coat bond surfaces and then heating the glass to the softening point such that the frit material melts and makes a hermetic seal. In other example embodiments, a KOH/NaOH solution may be used to bond the glass plate 52 to the etched glass substrate 50.
At Step 190, the bonded PTC 10 is inspected for both fidelity and precision. Thereafter, the PTC 10 is incorporated into and connected to the specified application (Step 200), such as an IDCA, and the PTC 10 is then filled with a fluid having the desired physical properties (Step 210).
Advantageously, the disclosed systems, apparatus and methods for a glass slide PTC offers low-cost manufacturing with precision control over the generation of the capillary passages which can be tailored to specific cooling requirements, and offers the capability to incorporate high-performance materials such as carbon fibers for excellent thermal characteristics.
The embodiments described above provide advantages over conventional devices and associated systems and methods. It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments without departing from the spirit and scope of the disclosure. Thus, it is intended that the disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents. Furthermore, the foregoing description of the embodiments and best mode for practicing the disclosure are provided for the purpose of illustration only and not for the purpose of limitation—the disclosure being defined by the claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6865894 | Olson | Mar 2005 | B1 |
| 7363767 | Wang | Apr 2008 | B2 |
| 20050022540 | Kim et al. | Feb 2005 | A1 |
| 20050198970 | Acharya et al. | Sep 2005 | A1 |
| 20130283823 | Yuan et al. | Oct 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2008125139 | Oct 2008 | WO |
| Entry |
|---|
| S.W.K. Yuan et al., A Non-tube Inertance Device for Pulse Tube Cryocoolers, IEEE/CSC 7 ESAS European Superconductivity News Forum (ESNF), No. 10, Oct. 2009, pp. 143-148. |
| S. Sobol et al., A Study of a Miniature In-Line Pulse Tube Cryocooler, International Cryocooler Conference, Inc., 2011, pp. 87-95. |
| Ray Radebaugh, Pulse Tube Cryocoolers for Cooling Infrared Sensors, Proceedings of SPIE, The International Society for Optical Engineering, Infrared Technology and Applications XXVI, vol. 4130, 2000, pp. 363-379. |
| J.L. Hall et al., A Contaminant Ice Visualization Experiment in a Glass Pulse Tube, Proceedings of the 1999 Cryogenic Engineering Conference, Jul. 1999, pp. 1-8. |
| Number | Date | Country | |
|---|---|---|---|
| 20150013348 A1 | Jan 2015 | US |
