Frequency matching is of great importance to a thermoacoustically driven pulse tube refrigeration system. To compute the resonance frequency of thermoacoustic engines, the fluid impedance method is introduced. The calculations of the thermoacoustic engines with different arrangements of buffer have been carried out. The influence of the buffer arrangements and the volume on the resonance frequency as well as the acoustic power of thermoacoustic engines is also discussed.

Based on review and analysis of thermodynamic efficiency e of the Carnot cycle and the cycle with two isothermal and two polytropic processes, another thermodynamic cycle with two isentropic and two polytropic processes, which can achieve the Carnot value of thermodynamic efficiency, is testified theoretically. Thermodynamic efficiency expressions of a number of ideal regenerative refrigeration cycles are derived, including the ideal pulse tube refrigeration cycle. A classified branch chart and a plot of ideal thermodynamic efficiency of regenerative refrigeration cycles are given for the purpose of comparison.

An experimental investigation on two-component multi-phase helium and nitrogen mixtures in a single-stage pulse tube refrigerator was carried out. The experimental results show that both coeÅcient of performance (COP) and cooling power can be improved to some extent at above 70 K when the nitrogen fraction in the mixture is less than 25%. An approximate stable temperature platform at the triple point 63.15 K of nitrogen, which is independent of nitrogen’s fraction, is obtained when the cooling power is below 7 W.

A refrigeration cycle with two isentropic and two isobaric processes, referred to as the modi

The computation with heat transfer, fluid flow and thermodynamics indicates that higher pulse tube refrigeration performance can be achieved with He–H2 mixtures as working fluids than that with pure He in the cooling temperature region of 30 K. In addition, it is found that Er3Ni, a regenerative material, is able to absorb H2 and forms Er3NiHx. The hydrogen absorption capacity of Er3Ni is about 3.5 H/Er3Ni in the H2 pressure region of 0.1-2.0 MPa at 30 ℃. The calculation shows that the regenerative performance of Er3NiH3.5 is better than that of Er3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K cooling temperature region is obviously enhanced with He–H2 mixtures and Er3NiHx regenerative material.