Influence of resonator length and temperature configuration on the performance of a supercritical CO2 thermoacoustic engine

Abstract

The peculiar properties of CO2 at supercritical pressures and transcritical temperature conditions are favorable for thermoacoustic devices. The printed circuit heat exchanger has been employed to fabricate a standing-wave thermoacoustic engine that works under these conditions. Experiments performed in this paper are devoted to exploring the influences of resonator length and temperature configuration on its performance. Results demonstrate that the oscillation frequency drops when the resonator is elongated, while the pressure amplitude is strengthened. To generalize the experimental data, the power-law relation for pressure amplitude and the bilinear law of frequency are extended to include resonator length as an independent variable, serving as the basis for tuning performance through resonator length. The best temperature configuration is to put the pseudo-critical temperature at the midpoint of heating and cooling temperatures to induce the pressure oscillation at maximum amplitude. Guided by the above results, experiments are performed to explore the extremum of low onset temperature difference. The current record is finally identified as 8.6 °C, close to the literature record of 7.0 °C. This paper elucidates the effects of resonator length and temperature configuration. Conclusions drawn in this paper can guide the design and operation of thermoacoustic devices working with supercritical CO2.