The effect of flow frequency on heat exchanger used in thermoacoustics

Chin, Jia Yu (2017) The effect of flow frequency on heat exchanger used in thermoacoustics. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Heat exchangers play an important role in the performance of thermoacoustic devices. Due to the complexity of oscillatory flows, the interaction of sound wave energy and heat transfer in oscillatory flows is still not fully understood. The purpose of this study is to determine the effect of flow frequency on heat exchangers used in thermoacoustic system. A simple thermoacoustic model was developed using Computational Fluid Dynamics (CFD). Two flow frequencies were investigated; 13.1 Hz and 26.0 Hz. The model was validated by comparing the simulation results and theoretical results of x-velocity at the middle of the stack. The percentages of error were recorded based on axial velocity for one cycle where fluid flows forward and backward in a cyclic manner. During forward movement (positive value), the maximum error was 7.85%. As flow reversed, the maximum error became 8.85%. Laminar model and SST k-omega model were used for simulation of 0.30% and 0.83% drive ratios, respectively. The total surface heat flux at hot heat exchanger increased with increasing value of frequency. However, as the drive ratios increased the heat transfer performance for 26.0 Hz flow frequency dropped. This may be related to the effect of turbulence and vortex structures. The vortex structures were found distorted as flow frequency increases. Further research is required to study the effect of turbulence and behaviour of vortex structures.

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