Since a piston does not exist in expansion space like the conventional cryocoolers, a pulse cryocooler cannot evaluate a performance in geometry. However, it becomes a very important factor to understand a motion of gas in expansion space, in order to raise a cooling performance. It considers as the simple method of understanding the cooling generating mechanism of a pulse tube cryocooler gas in a pulse tube is judged a solid piston (gas piston), and there is the equivalent PV method which computes work in expansion space. However, the work flow within an actual pulse tube of the ability of it to be able to express by the equivalent PV method is not certain. As the beginning, the compression machine (phase shifter) was installed at the pulse tube hot-end, and evaluation examination of the work flow in the boundary was measured and carried out at it, in this report.

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To predict the refrigeration capacity of a two-stage pulse tube cryocooler operating at less than 4K, a new numerical simulation is developed. Full one-dimensional governing equations for expander are solved using the finite difference method. It considers variable physical properties of real helium gas and regenerator materials. The calculation results show the pressure oscillation in one refrigeration cycle, the equivalent PV diagrams both at the hot end and at the cold end of the pulse tube, and the axial temperature distributions both of the pulse tube and the regenerator.

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A 4K pulse tube refrigerator with higher cooling power at first stage was manufactured and tested. The first stage cooling power of over 50W at 60 K and that of the second of over 0.7 W at 4.2 K were gotten with less than 7.5 kW compressor input power.

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We measured simultaneously the pressure and the velocity of the oscillating gas to determine the work flow and the phase difference between the pressure and velocity in a thermoacoustic traveling wave engine. We revealed that heat flow was converted into work flow through the Stirling cycle in the present engine. Moreover, we could determine a position where only the traveling wave is formed. An installation of a second regenerator at this particular position led us to construct a thermoacoustic Stirling cooler with low viscous losses.

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New types of thermoacoustic refrigerators have been developed. It has been reported that the pressure and velocity amplitudes and the heat transferred by sound waves are considerably improved when two thermoacoustic sound wave generators are joined together at their open ends, compared with those of independently operated generators. From a practical point of view, when two thermoacoustic refrigerators are joined together at their open ends, it is expected that the refrigeration performance will be improved compared with that of independently operated ones. The effects of temperature and the flow rate of cooling water in the heat exchanger of the refrigerator on the refrigeration performance are also confirmed.

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A new type of thermoacoustic sound wave generator utilizing the waste heat of a 4-cycle automobile gasoline engine is described. The exhaust-pipe-connected sound wave generator, in which the hot heat exchanger is set in the exhaust pipe in order to recover the waste heat of exhaust gas, is proposed. A temperature of 780℃ of exhaust gas in the exhaust is observed. In a conventional thermoacoustic sound wave generator, sound waves originate at a temperature of the hot heat exchanger, T_H, of 200〜300℃ and become sufficient at 700℃. It is confirmed that the new generator generates sufficient waves and its performance is almost equal to that of the electric-heater-driven generator at a thermal input of 300W, which corresponds to slightly more than 1% of the heat quantity of exhaust gas provided under the condition that the number of engine revolutions is 2600rpm and that the throttle opening ratio is 35%.

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Compared with traveling wave thermoacoustic prime mover, standing wave thermoacoustic prime mover has the merit of stability as there is no closed loop in the system. The heat->work conversion efficiency of standing wave type engine is lower than that of traveling wave type theoretically. A standing wave thermoacoustic prime mover has been built to measure its efficiency accurately. Numerical calculations were carried out and the results coincided with experimental results well. Calculations also show that there exists an optimum heat transfer area of stack to get the best efficiency, and also it is true to heat exchangers to improve the efficiency and increase the output power.

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A standing-wave-type thermal compressor can generate the pressure wave with the thermoacoustic effect. Because thit compressor without mechanical moving parts is driven only by the thermal input, reliability of a compressor system can be greatly enhanced. In this study, a tentative thermal compressor for 1-2W@60-80K pulse tube cryocoolers is designed and investigated with Argon gas of 1MPa. This thermal compressor consists of heat exchangers, a stack of SUS, a resonator tube of Max 7m and an attachable buffer tank. First, characteristics of a resonator are studied by using a mechanical linear compressor at various driving frequencies or displacement volumes. Next, the energy flow in the whole thermal compressor system is estimated and energy-conversion efficiencies are obtained.

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