Experimental and Numerical Investigations of Thermal-Fluid Processes in Oscillatory Flows

Heat exchangers are critical components of energy systems such as thermoacoustic engines and coolers. In this work, experimental and numerical studies were conducted on the heat transfer and acoustic pressure drop performance of heat exchangers in oscillatory flow. Experimental set-up and measurement techniques were developed to simultaneously measure parameters for the estimation of heat transfer and acoustic pressure drop. Three configurations of heat exchangers – tube-heat-exchanger, finned-heat-exchanger and plate-heat-exchanger were studied. Each configuration consists of three identical sets, arranged in series, to facilitate accurate heat transfer and acoustic pressure drop estimation. The influence of operating and geometric parameters on heat exchanger performance was investigated. The main considerations are to maximise heat transfer and minimise acoustic pressure losses from the heat exchanger, for the improvement of a system’s efficiency.

The experimental results show that heat transfer performance, presented as the Nusselt number, strongly depends on drive ratio and mean pressure, especially at the low drive ratios where the gas displacement amplitudes are below, or comparable to, the heat exchanger length. The heat transfer results compared well with results from other studies. A three-dimensional model was developed in ANSYS Fluent, based on the actual experimental set-up. Experimental data was utilised for thermal, acoustic and turbulence boundary conditions and model validation. Good agreement was achieved between the predicted and experimental results. Heat transfer and pressure drop results show dependence on the drive ratio. Ogive edged T-HEX was found to minimise acoustic pressure drop by about 51% at the highest drive ratio in this study. A two-dimensional model was also developed. An appropriate edge shape is found to minimise the acoustic pressure drop and the associated minor losses without significantly affecting the heat transfer performance of the heat exchangers.