Abstract
Thermoacoustic technologies rely on a direct power conversion between acoustic and thermal energies using well known thermoacoustic effects. The presence of the acoustic field leads to oscillatory heat transfer and fluid flow processes within the components of thermoacoustic devices, notably heat exchangers. This paper outlines a two-dimensional ANSYS FLUENT CFD (computational fluid dynamics) model of flow across a pair of hot and cold heat exchangers that aims to explain the physics of phenomena observed in earlier experimental work. Firstly, the governing equations, boundary conditions and preliminary model validation are explained in detail. The numerical results show that the velocity profiles within heat exchanger plates become distorted in the presence of temperature gradients, which indicates interesting changes in the flow structure. The fluid temperature profiles from the computational model have a similar trend with the experimental results, but with differences in magnitude particularly noticeable in the hot region. Possible reasons for the differences are discussed. Accordingly, the space averaged wall heat flux is discussed for different phases and locations across both the cold and hot heat exchangers. In addition, the effects of gravity and device orientation on the flow and heat transfer are also presented. Viscous dissipation was found to be the highest when the device was set at a horizontal position; its magnitude increases with the increase of temperature differentials. These indicate that possible losses of energy may depend on the device orientation and applied temperature field.
Highlights
Introduction and Literature ReviewThermoacoustic systems are usually divided into engines and refrigerators depending on the direction of energy conversion between the acoustic and thermal energy
The velocity amplitudes at the centre of the heat exchanger channel have a maximum discrepancy of 1.8% compared to the experimental data
The differences (b) noted in the temperature profiles and the resulting heat fluxes are likely to be the result of the combination of factors related
Summary
Thermoacoustic systems are usually divided into engines and refrigerators depending on the direction of energy conversion between the acoustic and thermal energy. It is important to highlight that most numerical modelling work presented in this review applies it is speculated that the presence of additional structures such as the stack and heat exchanger may alter a simplified model whereby a thin plate or a pair of adjacent plates with an implementation of the influence of the natural convection effect on the flow even when the velocity is relatively small [11]. The novelty of this study stems from the fact that the model used attempts to take into account a far wider range of physical effects which are commonly neglected in numerical works related to thermoacoustics (i.e., natural convection or the use of a full array of plates to handle asymmetrical flow features) This is undertaken to explain the phenomena reported in [11,17]. The study of device orientation provides a new perspective of the importance of considering such seemingly minor details in modelling heat transfer phenomena in thermoacoustics
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