Effect of stack geometry and operating frequency on performance of thermoacoustic refrigeration

Abstract

Abstract Different researches have given a broad canvas about investigation of performance of thermoacoustic refrigeration system (TARS) considering geometrical changes in stack, resonator tube and different operating parameters including gas pressure, working medium, frequency and temperature gradient. Limited work is reported involving the variation in stack geometry with different operating frequency to provide the choice of parameters for improving the performance of TARS. In present work, investigation is executed to ascertain the effect of different stack geometry and operating frequencies on the performance of (TARS) thermoacoustic refrigerator system. The difference in temperature at two ends of stack is the performance indictor of thermoacoustic systems. Three different stack geometries constructed from a Mylar sheet of 0.18 mm were used. The parallel plate stack fabricated was 0.13 mm thick and spaced 3 mm while the tubular stack had circular cross section with 3 mm diameter. Tests are performed to measure the performance of TARS for parallel, tubular, and spiral geometry of stacks with varying operating frequencies at the tune of 200 Hz, and 400 Hz, at 2 bar operating pressure with helium gas. From the investigation it is speculated that, the tubular type stack geometry gives improved results, whilst the increased operating frequency had a considerable impact on the temperature achieved at lower and high temperature heat exchangers. Experiments showed that the tubular stack achieved the lowest minimum temperature among the three geometries considered. Temperature achieved for lower temperature heat exchanger were 20.5 °C and 20 °C with tubular stack at 200 Hz and 400 Hz followed by parallel stack as 29°C and 22.8 °C and spiral stack as 28.7 °C and 25.1 °C respectively at 200 Hz and 400 Hz frequencies. The maximum temperature difference between lower and high temperature heat exchanger observed was of 22 °C for tubular stack geometry followed by parallel and spiral stack geometry.