US 3793846 A
Cryogenic refrigerator system is provided with a contaminant adsorber in the cold region of the refrigerator which can be selectively connected into the cryogen gas circuit in such a position as to receive warm gas passing out of the regenerator to purge the regenerator into the adsorber.
Description (OCR text may contain errors)
United States Patent [191 Dehne [451 Feb. 26, 1974 DECONTAMINATION METHOD AND APPARATUS FOR CRYOGENIC REFRIGERATORS  Inventor: Axel G. Dehne, Los Angeles, Calif.
 Assignee: Hughes Aircraft Company, Culver City, Calif.
 Filed: Nov. 28, 1972  Appl. No.: 310,199
 US. Cl 62/6, 62/85, 62/474  Int. Cl. F25b 9/00  Field of Search 62/6, 85, 475, 474
 References Cited 7 UNITED STATES PATENTS 3,200,581 8/1965 Weiland 62/6 3,205,679 9/1965 Geist 62/474 3,360,955 l/l968 Witler..... 62/6 3,421,331 l/l969 Webb 62/6 3,656,313 4/1972 Low 62/6 Primary Examiner-William J. Wye Attorney, Agent, or Firm-W. H. MacAllister, Jr.; Allen A. Dicke, Jr.
[5 7] ABSTRACT Cryogenic refrigerator system is provided with a contaminant adsorber in the cold region of the refrigerator which can be selectively connected into the cryogen gas circuit in 'such a position as to receive warm gas passing out of the regenerator to purge the regenerator into the adsorber.
13 Claims, 4 Drawing Figures PATENTED FEB 2 6 I974 sum 2 OF 4 DECONTAMINATION METHOD AND APPARATUS FOR CRYOGENIC REFRIGERATORS BACKGROUND This invention is directed to a cryogenic refrigerator system which includes a contaminant adsorber in the cold part of the system.
The efficiency of cryogenic refrigerators is very critical, because small losses at cryogenic temperature levels cause cycle inefficiency which results in a reduction in refrigeration capability. When the refrigeration system is designed for a particular load, this means that the temperature at the load will increase. In miniaturized equipment, over-design for providing excess capacity to overcome efficiency losses is undesirable.
Regenerators have temperature gradients and, as the cryogen carrying contaminants passes therethrough, the contaminants settle out as liquids or solids along the length of the regenerator. This contamination adversely effects regenerator performance, because it clogs flow passages. The clogged flow passages cause increase in pressure drop and cause reduced heat exchange with the regenerator matrix material. Both degrade efficiency. Furthermore, is some cases the contaminants coat the surfaces of the regenerator matrix to degrade heat exchange. With continually reversing regenerator cycles, the contaminants tend to move toward the cold end where they finally remain located, because the temperature does not sufficiently rise to purge them. During the portion of the cycle where warm gas is leaving the warm end of the regenerator, the contaminants in the regenerator are not swept out, because they are located at a point in the regenerator where the partial pressure thereof is substantially zero.
K. W. Cowans et al., US. Pat. No. 3,282,064 illustrates the-prior art where a bypass adsorber is connected between the crankcase and warm end of a Stirling cycle refrigerator.
SUMMARY In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a decontamination method and apparatus for cryogenic refrigerators. It comprises a cryogenic refrigerator system which includes a contaminant adsorber positioned in the cold portion of the refrigerator and connected to selectively transmit gas to the cold side of the refrigerator so that the regenerator is purged with relatively warm gas from the adsorber.
Accordingly, it is an object of this invention to provide a decontamination method which includes selectively directing, relatively warm cryogen gas through a regenerator to at least partially purge the regenerator and then through a contaminant adsorber which is at sub-atmospherictemperature. It is another object to provide a refrigerator apparatus wherein a contaminant adsorber is positioned within the apparatus so that, when the refrigeration apparatus is operating, the contaminant adsorber is at the sub-atmospheric temperature. It is a further object to provide a contaminant adsorber which is connectable to receive relatively warm gas passing it out of a regenerator to collect the contaminants. It is yet another object to provide a refrigeration apparatus which includes an adsorber for collecting contaminants from the refrigerator system, including contaminants in the refrigeration-producing portion of the cryogen gas cycle. Other objects and advantages of this invention will become apparent from the study of the following portion of this specification, the claims, and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a Stirling refrigerator system having a contaminant adsorber connected thereto, in accordance with the preferred embodiment of my invention.
FIG. 2 is a second embodiment thereof.
FIG. 3 is a third embodiment thereof.
FIG. 4 is a schematic illustration of a Vuilleumier refrigerator system showing a contaminant adsorber connected therein, in accordance with my invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically illustrates a refrigerator system 10 which includes a refrigerator mechanism 12. In the embodiment illustrated, the refrigerator mechanism 12 is a unitary structure which has a cold cylinder 14 and a compression cylinder 16 secured to a crankcase I8. Crankcase 18 has a rotary crankshaft 20 therein which is driven by a power source which provides the motive power to the refrigerator. Crank pin 22 on the crankshaft has a connecting rod 24 which connects to cold piston 26. Cold piston 26 reciprocates in the bore of cold cylinder 14, as controlled by the rotation of crankshaft 20. Similarly, connecting rod 28 is interconnected between crankpin 22 and compressor piston 30. Compressor piston 30 reciprocates in compression cylinder 16 under the control of crankshaft 20. Seal rings 32 and 34 are respectively mounted upon pistons 26 and 30 and respectively engage within cylinders 14 and 16 to minimize flow of gas from the working chamber so that pressure changes due to piston operation are not degraded. Any flow of oxygen gas from the working chamber into the crankcase volume can be permitted to build up until the crankcase has a mean pressure therein, or the gas in the crankcase can be returned to the working part of the system by means of a return line, as taught in K. W. Cowans et al. Pat. No. 3,282,064. On the other hand, crankcase pressure can be treated in accordance with A. G. Dehne Pat. No. 3,640,082.
The structure thus described comprises the refrigerator mechanism of a Stirling cycle refrigerator. Gas passage 36 in the cold cylinder is connected to gas passage 38 in the compressor cylinder. Line 40 is connected from cold gas passage 36 through cold point 42, where useful refrigeration is produced. Line 40 is connected to regenerator 44. The other end of regenerator 44 is connected by line 46 through heat rejection point 48 to hot gas passage 39. It is at heat rejection point 48 that the heat received at cold point 42 and the heat of compression from system operation is discharged, for example to the ambient. Regenerator 44 is of conventional configuration and, as is appropriate in a miniatured cryogenic systems, may contain metal washers, perforated discs, wire coils, or metal balls.
As described in S. F. Malaker et al. Pat. No. 3,074,244, the system is operated on the Stirling cycle to produce refrigeration. This cycle causes reciprocation of the cryogen gas through regenerator 44, with a consequent deposition of impurities from the cryogen gas into the regenerator. While the impurities tend to liquefy or solidify at a particular temperature, which suggests that they move in and out of the warm end of the regenerator, with deposition at a particular cold point in the regenerator, in practice they continually migrate toward the cold end until they are no longer removed by the flow of gas toward the warm end. Thus, the contaminants tend to remain in the regenerator, clog the passages to increase pressure drop, and deposit on the surface, all of which reduce heat transfer. Of course, it is necessary to provide insulation for the cold portions of the system. The dotted box 50 represents the insulated zone which contains the parts at subatmospheric temperature. The insulated zone represented by this box can be in the form of a cold box, dewar, or the like.
The described structure represents a complete Stirling cycle refrigerator which, when operated, produces refrigeration at cold point 42. Operation is in accordance with the well-known Stirling cycle, as described in Malaker et al. Pat. No. 3,074,244. This includes increase and decrease in gas pressure in the circulating system between passages 36 and 38 and through regenerator 44. In order to remove contaminants from the system, a contaminant adsorber vessel 52 is provided. It contains adsorber 54 which is a dessicant, molecular sieve, or the like. There are many commercial brands available, such as Linde X13.
Vessel 52 is located within insulated zone 50 so that it is held at cryogenic temperature. At cryogenic temperature, the adsorber material 54 is much more efficient. Vessel 52 is serially connected, with shutoff valve 56 located at ambient temperature and connected to line 46. Above shutoff valve 56, in the series connection, is check valve 58, vessel 52 and check valve 60 connected to line 40. Shutoff valve 56 can be manually, remotely, or automatically operated. During normal operation of the refrigeration system 10, valve 56 is closed. The short line 62 between lines 40 and to the check ball in checkvalve 60 and the short line 64 between line 46 and the close valve 56 provide a very small additional volume, with the result that there is little degradation of refrigerator performance, due to additional non-working volume in the system.
Periodically during the normal operation of the refrigerator, when decontamination is desirable, valve 56 is opened. Thereupon, upon the rising pressure portion of the Stirling cycle, checkvalve 56 opens so that vessel 52 receives cryogen therein for adsorption of the contaminants into adsorber 54. During the decreasing pressure portion of the cycle, the gas in vessel 52 moves through checkvalve 60 and down through regenerator 44. During the next compression portion of the cycle, gas again moves from line 45 up into the adsorber vessel, with some of the cryogen which has flowed downwardly through the regenerator now passing upwardly through the adsorber. Thus, contaminant adsorption takes place. Furthermore, the gas passing through checkvalve 60 and downward through regenerator 44 during the expansion part of the cycle is relatively warm, as compared to that gas which passes at substantially constant temperature from the cold point 42 into regenerator 44 after the expansion quadrant. Thus, more contaminants are swept downwardly out of the regenerator 44 during this decontamination cycle of operation. While valve 56 is open, refrigeration capability of the refrigerator is degraded, so that the regenerator warms up somewhat to permit purge of the contaminants out of the regenerator into the adsorber.
When as much loss of refrigeration has been caused by the contamination removal cycle as can be tolerated, valve 56 is closed, and the refrigeration system returns to the normal Stirling cycle. Thereupon, it again cools down to the normal operating temperature. Depending upon the thermal mass of the heat load at cold point 42 and its maximum permissible operating temperature, the contaminant removal cycle is periodically actuated for a short time. Operation of the decontaminant removal cycle for not more than 5 seconds does not adversely interfere with the heat load capacity at the cold point, provided that the thermal inertia of the load is sufficiently large. Operation not oftener than once every day is adequate is continuous duty to keep the cryogen gas and the regenerator adequately free of contaminants. Cleanup of the adsorber can be accomplished by purge of hot gas through separate connections when the refrigerator is shut down for other reasons.
FIG. 2 illustrates a refrigerator system 66 which includes a refrigerator mechanism 68. The mechanism 68 is identical to mechanism 12 and is connected within the refrigeration system to operate on the Stirling cycle. The cold cylinder of the refrigeration mechanism is closed in insulation illustrated by the dotted line box 72. The cold gas passage 74 is connected by line 76 to cold point 78, at which point the refrigeration load occurs. The cold point 78 is illustrated as a heat exchanger, but the cold point, like the cold point in refrigerator 10, can appear as a mounting plate on the end of the cold cylinder, or other convenient refrigeration location. Line 76 passes through tee 80 and is connected to regenerator 82. Again, the regenerator is the same as regenerator 44. Line 84 out of the warm side of the regenerator is connected through a three-way valve 86 through tee 88 and heat rejection point 90 to the hot gas passage 92 in the hot cylinder of the refrigerator mechanism 68. This system works as a Stirling refrigerator, as previously described with respect to re frigeration system 10 and refrigerator mechanism 12.
With respect to the embodiment of FIG. 1, it was noted that not all gas passing out of the regenerator passes through the adsorber. To provide a full flow contaminant removal system, the structure of the embodiment of FIG. 2 is provided. Warm gas flow line 94 is connected from tee 88 through tee 96 and through checkvalve 98 to tee 80. The spring loading of the ball on its seat in checkvalve 98 is sufficiently high to prevent flow through hot gas glow line 94 during normal refrigerator operation, when the valve 86 is turned in the direction illustrated in FIG. 2. Contaminated adsorber vessel 100, containing adsorber 102, the same as adsorber 54, is connected to the side port of three-way valve 86 and through checkvalve 104 to tee 96. Vessel 100 is within the cold zone within the insulated zone 72 and preferably has a long outlet pipe to provide a low temperature gradient between the adsorber vessel and the ambient at the three-way valve 86.
When three-way valve 86 is turned to the vertical position, line 84 is connected through three-way valve 86 to the adsorber vessel 100 and is cut off from tee 88. When the differential pressure of the hot cylinder, as compared to the cold cylinder, is rising, gas flow proceeds up the line 94 and through checkvalve 98 into regenerator 82. Flow continues from the regenerator through line 84 and through three-way valve 86 into adsorber 100. When the pressure in line 94 decreases below that in adsorber vessel 100, flow from the adsorber goes upoward through checkvalve 104 and back down through line 94. With the next pressure increasing part of the cycle, gas in line 94 passes through checkvalve 98 and through regenerator 82 into the adsorber vessel. Thus, upon repetition of this cycle, all gas passing through the regenerator 82 passes into and through the adsorber vessel 100. The same criteria for operation of the refrigerater system 66 in the contaminant removal mode that are applicable to the embodiment in FIG. 1 are applicable to the embodiment of FIG. 2. Similarly, adsorber purging has the same criteria. Thus, an advantage of the embodiment of FIG. 2 is that all of the relatively warm gas flowing downward through regenerator 82 passes through the contaminant removal vessel. A disadvantage lies in the fact that the volume of line 84 is added to the system during normal operation, thus reducing cycle efficiency for a particular set of machine-operating criteria. However, the volume of line 94 can be kept minimized.
Refrigeration system 106 is also a Stirling cycle refrigerator having a refrigeration mechanism 108, the same as refrigeration mechanism 12. It has a cold gas passage 110 to which is connected line 112 which is connected to the cold point 114 at which the net refrigeration is produced. Line 112 passes through tee 116 to regenerator 118. The regenerator 118 is the same as regenerator 44. Line 120 passes out of the warm end of regenerator 118 through tee 122 and into three-way valve 124. The other side of three-way valve is connected by line 126 through heat rejection exchanger 128 to hot gas passage 130. The cold end of the cold cylinder and the regenerator are enclosed within the insulated zone illustrated by dotted line box 132.
Adsorber vessel 134 contains adsorber 136 and is located outside of the insulated zone. Vessel 134 is connected on one side by a self-sealing coupling 138 and through checkvalve 140 to tee 122. The other end of vessel 134 is connected through coupling 142 to tee 144 in line 146. Line 146 connects the tee to one side of three-way valve 124. Line 146 is connected through shut-off valve 148 to adsorber vessel 150 positioned within the insulated zone and cryogenically cooled by the refrigeration of the refrigeration system. The adsorber vessel 150 contains adsorber 152. Vessel 150 is connected through checkvalve 154 to tee 116.
In normal Stirling cycle refrigeration operation, valve 148 is closed, and three-way valve 124 connects line 120 to line 126, as shown on FIG. 3. When the contam inant removal operating cycle is desired, the shut-off valve 148 is opened, and three-way valve 124 is changed to position where it connects line 126 with line 146. Now, with an increase in differential pressure in line 126, as compared to line 112, warm gas flows up line 146 through adsorber 150, checkwise 154, and into regenerator 118. Now, with a decrease in pressure in line 146 due to the operation of the pistons in the refrigerator mechanism, gas flows from regenerator 118 through line 120 and regenerator vessel 134 out into line 146 and 126. With the next increase in pressure, warm gas flows upward through line 146, carrying with it the gas which flowed out of regenerator vessel 134. The upoward flow again passes through adsorber vessel 150 and checkvalve 154 back into regenerator 118.
With continuous repetition of this cycle, warming gas flows downward through regenerator 118 and successively through contaminant adsorber vessels 134 and 150. The principle amount of contaminant is removed in vessel 134, and much of the remainder is removed in vessel 150, because that second contaminant removal has its adsorber at cryogenic temperatures.
The advantage of a two-adsorber system of this nature is that the major portion of the contaminants can be physically removed by opening couplings 138 and 142 and removal of vessel 134. A new, clean, prepressurized contaminant adsorber vessel can replace it, or the adsorbent in vessel 134 can be renewed by purging with hot, clean gas.
The refrigeration system 154 of FIG. 4 has some physical resemblance to the Stirling cycle refrigerator described above, by its mechanical structure, interrelationship of parts, and its thermodynamic cycle are quite different. The refrigeration system 154 operates on the Vuilleumier cycle, as taught in Pat. No. 1,275,507. In such a cycle, the refrigeration system has a portion which is at cryogenic temperatures to receive heat from the load to be refrigerated, a portion at temperature above the ambient which serves as the power input to the system, and a portion substantially at am bient, but slightly above ambient to serve as heat rejection to the ambient from both the refrigeration load and the power input heat. A description of the Vuilleumier cycle, as adapted for miniaturized refrigeration equipment, is given in K. W. Cowans reissue Pat. No. RE 27,338.
Referring to FIG. 4, refrigeration system 154 has a refrigerator mechanism 156 which comprises a cold cylinder 158 and a hot cylinder 160 mounted on a crankcase 162. Cold displacer 164 is reciprocably mounted in cold cylinder 158 and preferably has a seal ring riding in the cylinder to minimize passage of gas past the displacer. Similarly, hot displacer 166 is reciprocably mounted in hot cylinder 160 with an appropriate seal ring. The displacers divide the volume in the mechanism between cold volume 168, crankcase volume 170, and hot volume 172. Crank 174 has connecting rods 176 and 178 connected to the displacers, in order to maintain their phase relationship. While no power input is required at the crank 174 in a theoretical Vuilleumier machine, a motor is often connected thereto for maintaining the cycle timing and for small amounts of power input or output.
Cold line 180 is connected from cold volume 168 through cold point 182, which furnishes the refrigeration heat load through tee 184, regenerator 186, tee 188, and heat exchanger which rejects heat to ambient to crankcase volume 170. On the other side of the machine, hot line 192 connects hot volume 172 through heat input heat exchanger 194, hot regenerator 196, and through tee 198 to tee 188. It is seen that all three volumes are connected together so that, no matter how the displacers are moved, the absolute volume in which the gases are located remains constant. However, increase in pressure is caused by increasing the average temperature of the gas, and this is accomplished by moving the gas through the regenerators into the warmer direction. Similarly, reduction in pressure with a consequent gas expansion and cooling is occasioned by the reduction in temperature caused by moving the gas through the regenerators in the colder direction. As taught in the referenced patents, displacer cycling causes refrigeration. The cold end of the machine is enclosed in cold insulation, represented by the dotted line insulation box 200, while the hot end of the machine is enclosed in hot insulation, represented by the dotted line insulation box 202.
Adsorber vessel 204 contains adsorbent 206. Vessel 204 is serially connected from tee 198 at ambient temperature through shut-off valve 208 and checkvalve 210. The other end of adsorber vessel 204 is connected through checkvalve 212 to tee 184. With valve 208 shut off, displacer operation causes flow through cold regenerator 180 and causes increases and decreases in pressure in the system. With valve 208 open, increases in pressure cause flow upward through checkvalve 210 into the adsorber vessel 208. Following reductions in pressure in the system cause flow from the adsorber vessel 204 and through checkvalve 212 and through tee 184. Part of this passes downward through regenerator 180 toward tee 190. On the next pressure increase portion of the cycle, some of this gas moves into vessel 204. Thus, this is a continuing cycling of cryogen gas downward through cold regenerator 180 and upward through cryogen vessel 204. By this means, the relatively warm purged gas is supplied to regenerator 180, and this gas subsequently passes through the adsorber. This system is similar to the system of FIG. 1, but applied to a different refrigerator cycle. If desired, the systems of FIGS. 2 and 3 could be applied to the refrigerator of FIG. 4, in similar manner to which they are applied to the Stirling cycle refrigerator of FIGS. 2 and 3.
This invention having been described in its preferred embodiment, it is clear that it is susceptible to numerous modifications and embodiments within the scope of the invention and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.
What is claimed is:
1. An apparatus for decontamination of a cryogenic refrigerator in combination with a cryogenic refrigerator, said cryogenic refrigerator comprising:
a cold cylinder in which refrigerant gas is expanded to produce refrigeration;
a regenerator connected to receive in its cold end cold refrigerant gas from said cold cylinder, said regenerator having a warm refrigerant gas connection on its warm end opposite said cold end;
a refrigerated insulated zone, the improvement comprising:
an adsorber vessel containing an adsorbent for adsorbing contaminants from the refrigerant gas at cryogenic temperatures, a control valve serially connected with said adsorber vessel, said adsorber vessel and control valve combination being connected in parallel to said regenerator, said adsorber vessel being positioned within said insulated zone so that, when said control valve is opened, refrigerant gas flowing from the warm end of said regenerator passes into said refrigerated adsorber vessel.
2. The apparatus of claim 1 wherein said control valve is outside of said insulated zone so that said control valve is substantially unrefrigerated.
3. The apparatus of claim 2 wherein said control valve is a shut-off valve and further including a checkvalve in series with said adsorber vessel and connected to said regenerator.
4. The apparatus of claim 3 wherein said checkvalve is connected between the adsorber vessel and the cold end of said regenerator and is positioned so that refrigerant gas flow can proceed from said adsorber vessel toward the cold end of said regenerator.
5. The apparatus of claim 4 wherein said adsorber vessel is connected to be refrigerated by said cold cylinder.
6. The apparatus of claim 4 wherein there is a second checkvalve in series with said shut-off valve connected therebetween, said adsorber vessel and the warm end of said regenerator, said second checkvalve being positioned to pass refrigerant flow from the warm end of said regenerator into said adsorber vessel.
7. The apparatus of claim 4 wherein said refrigerator apparatus includes a warm cylinder, said control valve being a three-way valve, said three-way valve being connected to the warm end of said regenerator, being connected to said adsorber vessel and being connected to said warm cylinder.
8. The apparatus of claim 7 further including a refrigerant gas line connected between said warm cylinder in parallel to said adsorber vessel and to said checkvalve so that, upon switching said three-way valve from a connection between said warm cylinder and the warm end of said regenerator to a connection between said adsorber vessel and the warm end of said regenerator, warm gas flows said warm cylinder through said by-pass line and through said checkvalve into the cold end of said regenerator and thence into said regenerator vessel.
9. The apparatus of claim 8 wherein said checkvalve is a first checkvalve and there is a second checkvalve, said second checkvalve being positioned between said adsorber vessel and said first checkvalve.
10. The apparatus of claim 4 wherein said adsorber vessel is a first adsorber vessel and wherein there is a second adsorber vessel positioned outside of said insulated zone, said second adsorber vessel being connected between the warm end of said regenerator and said first adsorber so that adsorption of contaminants from the refrigerant gas first occurs into the second adsorber vessel at ambient temperature and then the refrigerant gas flows through said first adsorber vessel or adsorption at cryogenic temperature.
11. The apparatus of claim 4 wherein said refrigerator apparatus is a Stirling refrigerator.
12. The apparatus of claim 4 wherein said refrigerator apparatus is a Vuilleumier cycle refrigerator.
13. The method of removing contaminants from the refrigerant gas in a cryogen refrigerator where the refrigerator includes a cold cylinder, a regenerator connected on one end to the cold cylinder to receive cold refrigerant gas from the cold cylinder and thereby define a cold end on the regenerator, the regenerator also having a warm end connected to ambient temperature, an adsorber vessel serially connected with a control valve and connected in parallel to the regenerator and connected to be refrigerated by the cold cylinder, the process comprising the steps of:
maintaining the control valve closed so that refrigeration is produced at the cold end of the cold cylinder and the adjacent end of the regenerator is cooled, together with reciprocation of refrigerant gas through the regenerator with heat exchange between the refrigerant gas and the regenerator resulting in deposition of contaminants from the rewarm end thereof so that the regenerator has its contaminants flushed out by relatively warm refrigerant gas passing from the cold end to the warm end of the regenerator and then into the contaminant adsorber vessel.