Study on a heat-driven thermoacoustic refrigerator for low-grade heat recovery
Recovering low-grade heat from renewable energy sources and waste heat is crucial for improving energy utilizing efficiency as well as reducing CO2 emissions. Conventional thermoacoustically-driven refrigerators have a high onset temperature and low cooling efficiency, which significant limit their capacity for low-grade heat utilization. This paper investigates a novel thermoacoustically-driven refrigerator with gas-liquid resonators which enable a lower onset temperature and better cooling performance for harvesting low-grade heat. Theoretical analyses were performed on multi-stage systems to explore the onset characteristics and steady performance. Onset characteristics analysis was conducted by using a transfer matrix method. The effects of mean pressure, liquid volume ratio and the expected liquid mechanical damping coefficient on the onset temperature difference and working frequency were studied for systems with different numbers of stages. A comparison of system onset performance was made with conventional systems containing a gas-only resonator. The research illustrated that for a mean pressure of 1 MPa, the proposed system can significantly reduce the onset temperature difference from 144.1 K to below 35.5 K. In addition, an analysis was then conducted to study the parametric sensitivity of the thermodynamic performance. Calculation results show that the proposed system can achieve a baseline cooling power of 2.7 kW and a thermal-to-cooling efficiency of 0.67 at a heating temperature of 420 K and a cooling temperature of 270 K. This represents significant increases by a factor of 5.6 in cooling power and 1.5 in efficiency from a gas-only to a gas-liquid resonator.