Optimal design of thermoacoustic engines driven by LNG using particle swarm optimization

Abstract

The objective of this study is to optimize the design of thermoacoustic engines driven by LNG in order to exploit its unused energy at low temperature. LNG at 111K provides low temperature heat source while the environment has a role of high temperature heat source. The design variables such as regenerator channel radius, regenerator length, regenerator position, frequency and loop tube length were optimized based on Particle Swarm Optimization method in two cases of maximizing the acoustic power and the efficiency of energy conversion. In the optimization process the calculation of the acoustic field inside the regenerator and the buffer tube was simplified so that the temperature would have a given distribution. The comparison with the calculation assuming adiabatic condition verified that the proposed method was effective to derive optimal solution. It is also suggested that objective function needs to be estimated with the theoretical method to obtain precise value of the power generation. The optimization results indicate the strategies to design the thermoacoustic engine utilizing LNG. There is a clear trade-off relationship between the power generation and the efficiency. Consequently, it was found that the maximal power intensity of 1.9 MW/m² with 4 m loop tube or the maximal efficiency of 52% with 2 m loop tube would be attainable. Based on the power intensity, the scale of the loop tube was estimated to generate 1 or 10 kW of acoustic power.