Experimental and numerical investigations of thermal characteristics of heat exchangers in oscillatory flow

Heat exchangers under oscillatory flow conditions constitute a critical component of thermoacoustic engines and coolers for which effective design methodologies are not yet available. In this study, the thermal and pressure drop performance of compact Tube Heat Exchanger (T-HEX) under oscillatory flow conditions is investigated using experimental and numerical methods. A standing wave experimental set-up, driven by the Q-drive linear alternator, and a measurement technique were developed to measure the temperature and acoustic pressure near the T-HEX simultaneously. The symmetric arrangement of three identical heat exchangers, one 'hot' heat exchanger, centrally placed between two 'cold' heat exchangers, is employed for an improved thermal analysis. Furthermore, aerodynamic shape is used on the heat exchangers gas channels to improve flow conditions associated with a sudden change in the cross-section. Experimental results are found to agree well with the predictions from three-dimensional Computational Fluid Dynamics (CFD) models. The Nusselt number and pressure drop due to minor losses show dependency on the drive ratio (measured maximum oscillating pressure to the system mean pressure), the edge shape and hot heat exchanger temperature. At a high amplitude, the edge shape significantly minimises the minor loss pressure difference, with negligible effect on the thermal performance. The results reported in this study will benefit the development of compact heat exchangers for the thermoacoustic engines/refrigerators or Sterling engines/coolers in cryogenic applications.