US3314244A

US3314244A - Pulse tube refrigeration with a fluid switching means

Info

Publication number: US3314244A
Application number: US545444A
Authority: US
Inventors: Frederick H Green
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1966-04-26
Filing date: 1966-04-26
Publication date: 1967-04-18
Anticipated expiration: 1984-04-18

Description

April 13, 1967 F. H. GREEN I 3,314,244

PULSE TUBE REFRIGERATION WITH A FLUID SWITCHING MEANS Filed April 26, 1966 1'6: 5 fizf ae/a /7. 6266/1/ INVENTOR.

United States Patent 0 3,314,244 PULSE TUBE REFRIGERATION WITH A FLUID SWITCHING MEANS Frederick H. Green, Palos Verdes Estates, Calif., assignor to The Garrett Corporation, Los Angeles, Calif a corporation of California Filed Apr. 26, 1966, Ser. No. 545,444 11 Claims. (Cl. 62-88) This invention relates to an improved laminar flow cooling device in which very low temperature refrigeration is achieved by means of an oscillating pressure exerted in a gas filled tubular enclosure and, more particularly, to a means for oscillating the pressure which means contains no moving parts.

In a United States Patent No. 3,237,421 there is disclosed a Pulse Tube Refrigerator wherein the pressure of the gas in a tubular enclosure is oscillated and the flow of gas within the enclosure is restricted to laminar flow, i.e., parallel to the axis of the enclosure. At one end of the enclosure there is a heat exchanger that removes heat from the compressed gas. Then, after a few pressure oscillations, a significant temperature gradient is induced along the axis within the tubular enclosure. The pulse tube refrigerator requires no moving parts in the refrigeration section but only requires means to oscillate the pressure therein. In the prior art, two mechanical valves are provided to control the oscillation of gas pressure within the enclosure. The valves are actuated by an operator whenever his judgment determines that the first valve should be open and the second closed to compress the gas or that the second valve should be opened and the first one closed to exhaust the gas. In another embodiment, the above mentioned patent suggests that a reciprocating piston may be used to compress and expand the gas within the system. Although this scheme eliminates the judgment of an operator, the timing of the compression and expansion cycle of the gas is done independently of the refrigerating requirements.

Therefore, one object of this invention is to provide means with no moving parts to control the movement of gas into and out of the pulse tube refrigerator.

Another object of this invention is to use the pulse tube refrigerator to control the period of oscillation of the gas moving into and out of the pulse tube refrigerator.

Briefly, this invention includes a fluid device that has one fluid inlet communicating with two diverging outlet legs. One of the legs is coupled to the regenerator for the pulse tube refrigerator. At the point of junction of the two legs, there is a pressure or vacuum lateral control arrangement by which the flow of fluid to one or the other leg can be controlled. The control arrangement senses the pressure in the regenerator. Thus, when a compressable fluid such as air is fed into the fluid device, the air exits through the leg coupled to the regenerator. This causes the pressure within the regenerator and pulse tube refrigerator to build up. When the pressure builds up to a predetermined value, the control arrangement, since it senses the pressure in the regenerator, switches the flow of air to the other leg. The pressure in the regenerator and pulse tube refrigerator drops as the air therein is able to exit through the fluid device. When the pressure in the regenerator reaches a predetermined lower limit, the control arrangement has insufficient pressure applied thereto and the flow of air switches back to the first leg to again compress the air within the regenerator and pulse tube refrigerator. The cycle is repeated auto matically. 7

These and other objects, features and advantages will become more apparent from the following description of a preferred embodiment of the invention selected for pur- 3,314,244 Patented Apr. 18, 1967 poses of illustration and shown in the accompanying drawing, in which FIG. 1 shows schematically the pulse tube refrigerator and regenerator in combination with a fluid switching device;

FIG. 2 is a graph showing the temperature at various positions along the refrigerator and regenerator when the system is in equilibrium; and

FIG. 3 shows schematically an enlarged sectional view of the fluid switching device shown in FIG. 1.

Although a pulse tube refrigerator is part of the prior art, first will be explained the method of operation of the pulse tube refrigerator since it is a relatively new art. In general, the method is based upon the concept of a heat exchange mechanism which operates to provide both a cooling effect in a first part of a confined space and a heating effect in a second part of the confined space in such a manner that heat is pumped from the first part to the second part.

Referring to FIG. 1, the pulse tube refrigerator achieves this result by having an oscillating pressure exerted on a gas confined within a tubular enclosure 10. A pressurized volume of gas is caused to move into and out of the tubular enclosure 10 by a compressed air supply means 22 in a novel manner to be hereinafter described. The pressurized volume enters the enclosure 10 through a conduit 11 provided at one end thereof and then exits out of the same conduit 11. However, a laminar flow pattern parallel to the axis of the tubular enclosure 10 is maintained by an element 12 preferably made of a porous metallic material such as sintered bronze. The compressed air, entering through conduit 11, disperses within a chamber 13 disposed between the sintered element 12 and the base of the enclosure 1%). The compressed air then passes through the element 12 compressing the molecules within enclosure 10 causing the temperature to rise. At the other end of the enclosure 10 is disposed a heat exchanger 14 which is cooled by, for example, water flowing through tubes 16 and 17. The heat exchanger 14 removes heat from the compressed air. After the heat is removed the air within the enclosure 10 is allowed to expand by removing the pressure from conduit 11. In expanding, the gas within the enclosure is cooled. This cycle is repeatable and each time heat is absorbed by the gas from the sintered element 12 and heat is given up by the gas to the heat exchanger 14. To produce refrigeration more efficiently and at much lower temperatures, a regenerator 18 is provided between conduit 11 and the compressed air supply means 22. After the system reaches equilibrium a temperature gradient is produced along the regenerator and the pulse tube refrigerator such as shown in FIG. 2. The compressed pair enters the regenerator 18 through a conduit 19 and the air is cooled as it passes through the regenerator as shown by the curve between points A and B on the graph. The temperature of the gas is constant between the time it leaves the regenerator (point B on the graph) and the time it exits through the sintered element 12 (point C). The temperature of the gas within the enclosure 10 follows the curve from points C to D during compression. After the gas is compressed, the gas is cooled by the heat exchanger 14 to point B (approximately the temperature of the water entering and leaving tubes 16 and 17). The gas is allowed to expand and as the gas expands the temperature follows the curve from points E to F. It is noted that the gas approaches the sintered element 12 during expansion at a lower temperature than the gas which left the sintered element during compression. As the gas passes through the sintered element 12 it absorbs heat from a cold plate 21 disposed in heat conducting contact with the sintered element 12, as shown by the temperature curve from points F to G.

As mentioned previously, the prior art uses moving mechanisms to cause compression and expansion of the gas within enclosure 10. However, the means 22 in this invention for causing compression and expansion of the gas in enclosure has no moving parts. Referring to FIG. 3, the means 22 is shown in cross-section and enlarged. The means 22 is a fluid device having an inlet 23 and two

outlet legs

19 and 26 that branch from the inlet to assume a Y shape. The inlet 23 and the leg 19 are preferably disposed substantially on a straight line to provide the fluid device with memory. In the general area of the junction of the two

legs

19 and 26, there is a side pressure or vacuum control arrangement in the form of a relatively small bore 27. The bore 27 is disposed on the same side as leg 19 and is coupled to and communicates Withthe regenerator by a tube 28. As mentioned before, the leg 19 is also coupled to the regenerator 18.

The fluid device operates as follows: Compressed air is coupled to inlet 23. The inlet 23 is so shaped to ensure that air at subsonic velocities passes through a throat section 29. Since the fluid device has been constructed with memory, i.e., the stream of air has a tendency to pass through leg 19 into the regenerator 18. The pressure in the regenerator 18 increases and, when the pressure rises to predetermined value, the pressure, being fed to the bore 27 by tube 28, causes the stream of air to switch to the other leg 26. This causes the pressure in the regenerator 18 to drop. The air in the regenerator 18 is able to exhaust out of leg 19 and turn around within the fluid device due to reaction of the main stream of air therein leaving the throat section 29. The air from the regenerator and the main stream of air exit through leg 26. Leg 26 is made sufficiently large to conduct both the main stream of air and the air from the regenerator. When the pressure in the regenerator 18 drops to a predetermined level, the pressure at bore 27 is insuflicient to hold the stream of air so that the stream exits through leg 26 and the stream of air switches back to leg 19. The air in the regenerator is again compressed and the cycle is repeated.

It is to be noted that the slope, that a section of an interior wall 31 to the right of the throat section 29 makes with the axis of the inlet 23, determines the maximum pressure that the regenerator would be subjected to before the stream of air is switched to flow out of leg 26. Then, when the stream of air has switched, it tends to stick to an interior wall 32 and less pressure through bore 27 is required to hold the stream than to switch the stream. The slope, that the section of the wall 32 to the right of the throat section 29 makes with the axis of the inlet 23, determines what predetermined minimum pressure that the regenerator would be subject to before the pressure therein is caused to rise by the means 22 switching.

Thus, the novel combination of the fluid device and the pulse tube refrigerator enhances the results achieved in the system, because the compression cycle is continued until the pressure in the system rises to the predetermined level before the stream of air is switched. This ensures maximum compression during each cycle. Then, the expansion cycle continues until the predetermined minimum pressure is attained. Thus, when more or less refrigeration is required, the timing of the refrigeration cycle adjusts itself automatically to the needs. This is accomplished without the use of moving mechanism, i.e., having no moving parts. This is a desirable feature because a relatively inexpensive system is able to operate reliably at extreme ambient temperatures.

With the present disclosure in view, modification of the invention will appear to those skilled in the art. Accordingly, the invention not to be limited to the exact details of the illustrated preferred embodiment but includes all such modification and variations coming within :he scope of the invention as defined in the appended :laims.

What is claimed is: I

1 In combination, a pulse tube refrigerator comprisa tubular enclosure disposed to receive gas under pressure at one end thereof,

a flow smoothing heat exchanger disposed at said one end of said enclosure for smoothing the flow of gas entering said enclosure,

means for removing heat at the other end of said en closure, and

means for cyclically increasing and decreasing the pressure of the gas within said enclosure;

said means for cyclically increasing and decreasing the pressure of the gas including conduit means for supplying gas under pressure;

a fluid switching means having an inlet connected to said conduit means, and two outlets communicating with said inlet, and one of said outlets communicating with said one end of said enclosure; and

fluid control means disposed on said fluid switching means for controlling the exit of the gas from the switching means into one or the other outlet.

2. In the combination of claim 1 wherein:

said fluid control means includes at least one bore formed in said switching means and communicating with one of said outlets substantially adjacent to the junction of said two outlets to cause the gas to be deflected to said other outlet when pressure is applied to said bore and to allow the gas to deflect back to said one outlet when no pressure is applied to said bore.

3. In the combination of claim 2 wherein:

said bore communicates with said tubular enclosure to cause the pressure within said tubular enclosure to be fed to said bore to deflect the gas to said other outlet when the pressure rises to a predetermined level.

4. In the combination of claim 3 wherein:

said inlet and said one outlet of said switching means are substantially aligned to provide memory for said switching means to tend to direct the flow of gas to said one outlet rather than to said other outlet.

5. In the combination of claim 1 wherein:

a regenerator is disposed between said fluid switching means and said tubular enclosure and said one outlet communicates with said regenerator which in turn communicates with said enclosure.

6. In the combination of claim 5 wherein:

7. In the combination of claim 6 wherein:

said bore communicates with said regenerator to cause the pressure within said regenerator to be fed to said bore to deflect the gas to said other outlet when the pressure therein rises to a predetermined level.

8. In the combination of claim 7 wherein:

9. In the combination of claim 8 wherein:

said inlet is shaped to cause the gas to pass therethrough at subsonic velocities.

10. In the combination of claim 8 wherein:

said one outlet has a smaller cross-section than said other outlet.

11. In combination, a pulse tube refrigerator comprismg:

a tubular enclosure disposed to receive gas under pressure at one end thereof,

means for removing heat at the other end of said enclosure,

means for cyclically increasing and decreasing the pressure of the gas Within said enclosure, and

means for sensing the pressure Within said enclcsure pressure should be increased and decreased in response to the pressure within said enclosure.

References Qited by the Examiner UNITED STATES PATENTS 1,321,343 11/1919 Vllilleurnier 6Z33 1,459,270 6/1923 Vuilleurnier 62-88 3,237,421 3/1966 Gifiord 6288 and for controlling said second means as to when the 1 WILLIAM J. VVYE, Primary Examiner.

Claims

1. IN COMBINATION, A PULSE TUBE REFRIGERATOR COMPRISING: A TUBULAR ENCLOSURE DISPOSED TO RECEIVE GAS UNDER PRESSURE AT ONE END THEREOF, A FLOW SMOOTHING HEAT EXCHANGER DISPOSED AT SAID ONE END OF SAID ENCLOSURE FOR SMOOTHING THE FLOW OF GAS ENTERING SAID ENCLOSURE, MEANS FOR REMOVING HEAT AT THE OTHER END OF SAID ENCLOSURE, AND MEANS FOR CYCLICALLY INCREASING AND DECREASING THE PRESSURE OF THE GAS WITHIN SAID ENCLOSURE; SAID MEANS FOR CYCLICALLY INCREASING AND DECREASING THE PRESSURE OF THE GAS INCLUDING CONDUIT MEANS FOR SUPPLYING GAS UNDER PRESSURE; A FLUID SWITCHING MEANS HAVING AN INLET CONNECTED TO SAID CONDUIT MEANS, AND TWO OUTLETS COMMUNICATING WITH SAID INLET, AND ONE OF SAID OUTLETS COMMUNICATING WITH SAID ONE END OF SAID ENCLOSURE; AND FLUID CONTROL MEANS DISPOSED ON SAID FLUID SWITCHING MEANS FOR CONTROLLING THE EXIT OF THE GAS FROM THE SWITCHING MEANS INTO ONE OR THE OTHER OUTLET.