Abstract
Thermoacoustic refrigerators have huge potential to replace conventional refrigeration systems as an alternative clean refrigeration technology. These devices utilize conversion of acoustic power and heat energy to generate the desired cooling. The stack plays a pivotal role in the performance of Standing Wave Thermoacoustic Refrigerators (SWTARs), as the heat transfer takes place across it. Performance of stacks can be significantly improved by making an arrangement of different materials inside the stack, resulting in anisotropic thermal properties along the length. In the present numerical study, the effect of multi-layered stack on the refrigeration performance of a SWTAR has been evaluated in terms of temperature drop across the stack, acoustic power consumed and device Coefficient of Performance (COP). Two different aspects of multi-layered stack, namely, different material combinations and different lengths of stacked layers, have been investigated. The combinations of four stack materials and length ratios have been investigated. The numerical results showed that multi-layered stacks produce lower refrigeration temperatures, consume less energy and have higher COP value than their homogeneous counterparts. Among all the material combinations of multi-layered stack investigated, stacks composed of a material layer with low thermal conductivity at the ends, i.e., RVC, produced the best performance with an increase of 26.14% in temperature drop value, reduction in the acoustic power consumption by 4.55% and COP enhancement of 5.12%. The results also showed that, for a constant overall length, an increase in length of side stacked material layer results in an increase in values of both temperature drop and COP.
Highlights
The excessive emission of the conventional Chlorofluorocarbons (CFCs) refrigerants has caused severe damage to the Earth’s stratospheric protective ozone layer
The effects of various multi-layered stack material combinations and effect of variation in length of layered materials has been analyzed in terms of temperature difference achieved by the refrigerator, energy flux consumed by the stack and Coefficient of Performance (COP) attained by the Standing Wave Thermo-Acoustic Refrigerators (SWTARs)
The computational domain used in this work comprise of a thermoacoustic couple consisting of a single plate of stack, similar to the one proposed by Ishikawa and Mee [11] but with an expanded domain
Summary
The excessive emission of the conventional Chlorofluorocarbons (CFCs) refrigerants has caused severe damage to the Earth’s stratospheric protective ozone layer. Numerical studies of SWTAR have utilized simplified computational domains for numerical simulations, i.e., modeling a single stack space with truncated domain and no heat exchangers, denoted as Thermoacoustic Couple (TAC) [13]. A more comprehensive computational domain, comprising of both the heat exchangers and stack plate, is important for accurate performance simulation, evaluation of Coefficient of Performance (COP) and successful operation of the apparatus [24] It has been utilized in few recent studies for the performance prediction of SWTAR. Based on the temperature profiles obtained at the stack ends, the heterogeneous stack combinations showed reduced return diffusive heat transfer, increasing their efficiency In light of this information, there might be a possibility to improve the performance of the standing wave thermoacoustic devices by deliberately varying the thermal properties inside the stack. The effects of various multi-layered stack material combinations and effect of variation in length of layered materials has been analyzed in terms of temperature difference achieved by the refrigerator, energy flux consumed by the stack and COP attained by the SWTAR
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