Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2000-04-24
2001-07-10
Doerrler, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
Reexamination Certificate
active
06256998
ABSTRACT:
BACKGROUND OF THE INVENTION
Pulse tube refrigeration without moving parts, operating at cryogenic temperature, is one attractive method for providing a reliable, vibration-free, long life, and simple cryocooler that can meet the requirements for cryogenic cooling in many applications. In order to produce cooling effect at a pulse tube cold end, it is necessary to cause a time-phasing [shifting] between gas pressure fluctuations and gas displacement inside the pulse tube. Such phase shift between the gas pressure fluctuation and the gas displacement inside the pulse tube is obtained by controlling the mass flow rate with a phase shifter located at the pulse tube warm end.
Several types of phase shifters have been developed for improvement in performance of the pulse tube refrigerator, such as double inlet, four valve, and active buffer type phase shifters. However, there are several disadvantages in present phase shifters for multiple stage pulse tube refrigerators.
In the double inlet type and four valve pulse tube refrigerator for producing large cooling capacity at relatively high temperature, a large amount of additional compressor work is expended due to mass flow in and out of a bypass line and valves. This added workload decreases overall efficiency of the machine. In multiple stage double inlet and four valve pulse tube refrigerators, phase interaction between each stage produces thermal losses and makes the refrigeration temperature unstable at each stage.
In the active buffer type pulse tube refrigerator producing small cooling capacity at very low temperature, regenerator inefficiency is very high due to larger mass flow rate through the regenerator cold end and poor phase shift effect at a higher ratio of regenerator void volume to pulse tube volume.
SUMMARY OF THE INVENTION
The present invention addresses these problems in the conventional pulse tube refrigerators. An objective of the present invention is to provide an improved two-stage pulse tube refrigerator which has higher overall efficiency at a higher temperature stage, and higher regenerator performance at a lower temperature stage, and less phase interaction losses.
In order to meet the above and other objectives, a two-stage pulse tube refrigerator in accordance with the invention comprises a pressure wave generator-compressor, first stage and second stage regenerators, first stage and second stage pulse tubes, heat exchangers, and a hybrid phase shift mechanism for the first and second stage pulse tubes. The second stage phase shift mechanism utilizes at least one fixed orifice. The fixed orifice phase shifter is either located at room temperature or thermally connected with the first stage cold end. The first stage phase shifter includes any one of a) 4 valves, b) 5 valves, c) 2 active buffers, or d) 3 active buffers.
In a pulse tube refrigerator with two active phase shifting valves, the valves are positioned at room temperature between the warm end of the first stage pulse tube and the compressor return and supply line. One orifice is positioned at room temperature between the warm end of the second stage pulse tube and one buffer where there is a moderate gas pressure. Another orifice is positioned at room temperature between the warm end of the first regenerator and the warm end of the second stage pulse tube.
In another pulse tube refrigerator with three active valves, the valves are positioned at room temperature between the warm end of the first stage pulse tube and the compressor return and supply line, and one active valve is positioned between the warm end of the first stage pulse tube and one buffer. One orifice is positioned at room temperature between the warm end of the second stage pulse tube and one buffer where there is a moderate gas pressure. Another orifice is positioned at room temperature between the warm end of the first regenerator and the warm end of the second stage pulse tube.
Still another pulse tube refrigerator has a hybrid phase shift mechanism with three buffers, three active valves and two orifices. The three active valves are positioned at room temperature between three buffers and the warm end of the first stage pulse tube. One orifice is positioned at room temperature between the warm end of the second stage pulse tube and one buffer where there is a moderate gas pressure. Another orifice is positioned at room temperature between the warm end of the first regenerator and the warm end of the second stage pulse tube.
A fourth embodiment of a pulse tube refrigerator in accordance with the invention has a double fixed orifice phase shifter for a second stage thermally connected with the first stage cold end. The warm end of the second stage pulse tube is thermally connected with the first stage cold end. One orifice is positioned between the first stage cold end and the second stage pulse tube warm end, and another orifice is positioned between the warm end of the second stage pulse tube and one buffer at the first stage cold end.
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Doerrler William
Helfgott & Karas P.C.
IGCAPD Cryogenics, Inc.
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