We have developed pulse tube cryocoolers for high temperature superconducting (HTS) filter subsystems used in the base stations of mobile telecommunication systems. The demands for a smaller-sized cryocooler with higher efficiency and with 5-year reliability prompted us to develop such a cryocooler with U-type expanders and flexure-bearing-supported linear compressor opposed pistons. We have developed an HTS filter and a long-life Stirling pulse tube cryocooler to cool the filter whose cooling capacity is 1W at 80K class. For a compressor input power of 60W at an operating frequency of 50 Hz, this cryocooler achieved a cooling capacity of 1.05W at 80K (0.63W at 70K), 5.5% Carnot (3.9% Carnot at 70K), with a minimum temperature of 57K in an ambient 23℃. The HTS filter has a fractional bandwidth below 1.2% at 2GHz and has a minimum insertion loss at 0.3dB. We integrated them with the cryocooler into a subsystem and the external dimensions of this system are a total volume of 8.7L.

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The needs for reliable refrigerators for High Temperature Superconducting (HTS) filter subsystems employed in the base stations of mobile telecommunication systems has been becoming apparent in the past several years. We have developed a long life ST (Stirling) type pulse tube refrigerator, named SPR-05,for the application. In this paper, the construction and endurance test results of the refrigerator are described. The pulse tube refrigerator is a ST type with opposing compressor pistons that is driven by liner motors. Much effort was made to improve the reliability of flexure bearings and to avoid the gas contamination. The refrigerator has been successfully tested for over 16000 hours. The results prove that our refrigerator is a powerful candidate for use of HTS filter cooling.

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LG Electronics(LGE) has developed a Pulse Tube Cryocooler (PTC) for High Temperature Superconductor(HTS) Applications. An inertance tube is used as for phase shifter and moving magnet type linear motor is used for making pressure wave. The performance of the air-cooled PTC is 5.5W@65K under 25℃ ambient temperature condition and the electric input power of a single acting linear compressor is 280 watts. However, the performance of PTC is affected by an ambient temperature significantly and as the ambient temperature higher, the cooling capacity lower. Therefore a PTC used in commercial fields such as the cooling element of HTS RF filter of wireless moving communication has to overcome the circumstance of wide-range ambient temperatures. This paper reports the test results on the basic performance of the PTC and the influence of performance with respect to the ambient temperatures.

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This paper describes the numerical simulation of a 4K-GM refrigerator. The simulation model is composed of a regenerator, a cooling stage, and an expansion space, whose volumetric change are considered. The basic equations are made up of one-dimensional fluid equations and an energy equation of the regenerator material and the cooling stage. The fluid equations are expressed in the general coordinate system of which a coordinate axis moves with time to take account of the volumetric change of the expansion space. The validity of the calculation model was confirmed through comparing the calculation results with results of experiments. The developed calculation model was used to study the effect of the specific heat and the diameter of regenerator material and the porosity of a regenerator on the refrigeration capacity.

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A Stirling cycle machine is a closed regenerative cycle machine realized as external-combustion machines in various applications including engines and coolers, using refrigerants, such as helium, which have no impact on the depletion of the ozone layer and global warming. Stirling coolers are much suitable for use at ultra-low temperatures from -180℃ to -50℃ in the field of refrigeration. The authors have developed a prototype Stirling cooler and cooling unit (Stirling unit) which consists of the Stirling cooler, a secondary heat transfer fluid circuit and a radiator to reject heat from the Stirling cooler. The paper describes results of evaluation for cooling method of cylinder block including piston rings and influence of driving frequency on the Stirling unit performance.

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KUBOTA has been developing a gas engine-driven Stirling heat pump using both engine shaft power and engine exhaust heat. This machine is a heat-assisted Stirling heat pump and is constructed as two sets of three-cylinder machines, each a combination of two Stirling subsystems; one a power producer and one a heat pump. This paper describes the performances of the heat pump composed of 6 cylinders. The cylinder arrangement is symmetric with respect to the shaft and the pistons are connecting by Scotch-yoke mechanism with linear bearings for improving mechanical efficiency. The phase of hot-side piston to absorb heat can be set to suit the engine heat balance. It was shown by the performance tests that the heat pump had high COP and could construct a high performance heat supply system.

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A low temperature difference Stirling engine "YA-2" has excellent performance than any other similar engine. This come from unique structure of the engine, such as liner arrangement of working space, wide phase angle, high efficiency plate fin and tube heat exchanger, one way piston rings, and so on. We regard that this construction is applicable to Low temperature difference reverse cycle machines like air conditioners, etc. In this paper, we investigate Heat pump operation analytically and experimentally in terms of differences between regular and reverse cycle. By experiment, we obtain 2.6kW of capacity and about 3.3 of COP for Heat pump operation of YA-2 for 17K temperature difference.

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KUBOTA has been developing a gas engine-driven Stirling heat pump using both engine shaft power and engine exhaust heat. Since Stirling heat pumps work at small temperature difference, comparing with Stirling engines, COP is much influenced by the regenerator performances such as flow loss and heat transfer. The performances of three kinds of wire mesh regenerators made of stainless steel were investigated by numerical simulations. From the experimental results, the wire mesh of which wire diameter was 45 μ m showed the best regenerator performances in our operating conditions. And the results of the numerical simulations were well fitted for the experimental results. Finally, from the loss relations, the best regenerator specifications in Stirling heat pumps could be found.

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The Stirling refrigerator is being developed for a home-use refrigerator now, but generally the temperature range is becoming lower and the refrigerating capacity is becoming bigger. As a result, the potential of high efficiency of Stirling cycle is being lost. The purpose of this research is to develop the highly effective micro Stirling refrigerator. Owing to the micro, irreversibility in the heat transfer is highly reduced. In this paper, the heat and mass transfer characteristics of a layered-plates type regenerator, which is promising as the regenerator of a highly effective refrigerator, in reciprocation oscillatory flow field were investigated. Consequently, it was experimentally confirmed that the influences of operating parameters on temperature distribution and pressure drop.

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This paper presents pressrue loss through a hybrid matrix. Hybrid matrix is mixed nylon and copper mesh. A parts of matrix are copper mesh. It is original matrix. Nylon mesh is light weight. But, it has some weak points. copper mesh make up for weak points of nylon mesh matrix. Hybrid matrix has lower pressure loss than nylon matrix.

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A regenerator matrix of a Stirling-cycle cryocooler ususally consists of stacked wire-gauze. Recently a plastic regenerator matrix is investigated. It is expected to decrease its weight and cost. A free-piston type Stirling-cycle cryocooler for an IR sensor, which can generate cooling capacity of 1W max at 80K level, is commercialized. We measured the performance characteristics of the cooler employing a plastic regenerator matrix. The regenerator matrix all replaced by plastic screens lowered COP to about 2/3 times that of stainless steel wire-gauze. In case the regenerator matrix is partly replaced by plastic screens, COP depended on the ratio. The proper stacking method resulted in COP almost equal to that of the wire-gauze.

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