Theoretical analysis of two coupling modes of a 300-Hz three-stage thermoacoustically driven cryocooler system at liquid nitrogen temperature range

Abstract

Highly reliable, compact, and efficient cryocoolers with a cooling power of several watts to several hundred watts at liquid nitrogen temperatures around 77K are indispensable for cooling superconducting devices and infrared detectors, especially in aerospace applications. This paper introduces three-stage traveling-wave thermoacoustically driven cryocooler systems operating around 300Hz that meet the demand. In addition to the potential reliability due to the lack of moving components in a thermoacoustically driven cryocooler, this configuration has the potential for both compact size and high efficiency owing to the slim resonance tube and acoustic power recovery. Numerical simulations are performed to investigate two coupling modes: coupling the cooler at the branch of the engine (BR-coupling) or coupling the cooler parallel to the engine (PA-coupling). First, the two topologies are carefully designed to obtain high total exergy efficiency and the optimal dimensions are presented. Then, the axial distributions of the phase difference and the acoustic power are further provided to better illustrate the coupling characteristics. Furthermore, a theoretical analysis is performed on the influence of the two acoustic tubes in the PA-coupling mode and the result shows the importance of the tube dimensions. With a heating temperature of 850K, total exergy efficiencies of 11.4% and 14.8% have been achieved in the BR-coupling and PA-coupling modes, respectively. The PA-coupling mode’s higher efficiency is due to recycling the acoustic power entering the pulse tube cryocooler, whereas BR-coupling fails to recycle any acoustic power. However, the energy feedback in PA-coupling may cause structural complexity. Generally speaking, both coupling mode systems show encouraging prospects for aerospace applications.