Numerical analysis of thermoacoustically driven thermoacoustic refrigerator with a stack of parallel plates having corrugated surfaces

Zahra Bouramdane,Nadia Martaj,Abdellah Bah,Mohammed Alaoui

doi:10.1007/s44189-022-00002-8

Zahra Bouramdane, Nadia Martaj + Show 2 more

Open Access

https://doi.org/10.1007/s44189-022-00002-8

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Abstract

Most numerical research on thermoacoustic devices with a stack made of parallel plates has considered a rectangular form for the plate. However, a variety of plate shapes can improve the heat transfer and performance of the stack. In this paper, a 2D numerical model based on computational fluid dynamics (CFD) analysis is used to examine the efficiency of thermoacoustic couples using a diversity of plate surfaces. For this investigation, flat plates and others profiles with corrugated surfaces (rounded and triangular surfaces) were tested to compare their performances and the effect of plate form on thermoacoustic systems. The efficiency of the thermoacoustic engine (TAE) is measured in terms of the generated acoustic pressure and the performance of the thermoacoustic refrigerator (TAR) is considered in terms of the temperature gradient along the refrigeration stack. The results showed that plates profile with irregular surfaces improves the generated acoustic pressure due to the increase of the stack porosity known as the blockage ratio (BR). The triangular shape performed better with a 10% gain than using a flat plate, followed by rounded ripples with a 5.2% increase in pressure amplitude compared to flat surfaces. Unlike in TAR, it was revealed that the stack made of flatform could produce a higher temperature difference (∆T) among the refrigeration stack extremities. By using rounded ripples, ∆T undergoes a reduction up to 52%, and 65% if using triangular ripples compared to flatform. From this investigation, it is observed that the stack with corrugated plates is the most suitable for TAE; however, the flat plates generate a higher temperature difference in TAR.

Highlights

The stack is the heart of thermoacoustic machines: it is a solid, rigid, and porous structure, which supports high temperature gradients
Results of each plate shape obtained for the thermally driven thermoacoustic refrigerator will be compared based on effective temperature gradient along with the refrigeration stack and the average temperature reached at the cold side of the refrigeration stack
The results show that the plates with a high ratio l/lp are more effective in increasing the pressure amplitude compared to the plates with lesser l/lp

Summary

Introduction

The stack is the heart of thermoacoustic machines: it is a solid, rigid, and porous structure, which supports high temperature gradients. The results indicate that this approach offers fast approximations for efficiency and energy conversion in thermoacoustic systems It is limited by the necessity of having a great acoustic displacement comparative to the gap among pins. The results indicate that the stack with transverse-pin improves the performance of thermoacoustic energy conversion compared to devices with other stacks. It is shown that the stack made of Mylar sheets revealed a higher efficiency in comparison to both stacks made of random material and parallel plate stack It attained a temperature difference and maximums COP of 7.7 °C and 0.217, respectively. The results display that picking an appropriate value of the ratio of the plate gap to the thermal penetration depth at the cold extremity of the stack in the parallel and the converging stacks can enhance the acoustic energy and the system performance. It is found that the optimum stack geometry for standing wave TARs is the circular stack with a blockage ratio of 0.71; it generates the highest temperature difference and the lowest cold temperature

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