Prediction of the Oscillatory Heat Transfer Coefficient in Thermoacoustic Refrigerators

Thermoacoustic refrigerators are emerging devices that make use of meaningful high-pressure sound waves to induce cooling. Despite the accelerated progress in the field of thermoacoustics, knowledge of the heat transfer process in the heat exchange of the devices is still developing. This work applies different soft computing techniques, namely, an artificial neural network trained by particle swarm optimisation (ANN-PSO), adaptive neuro-fuzzy inference system (ANFIS), and artificial neural networks (ANNs) to predict the oscillatory heat transfer coefficient in the heat exchangers of a thermoacoustic device. This study provides the details of the parametric analysis of an artificial neural network model trained by particle swarm optimisation. The solution model considers the number of neurons, the swarm population, and the acceleration factors to develop and analyse the architecture of several models. The regression model (R2) and mean squared error (MSE) were used to evaluate the accuracy of the models. The result showed that the proposed soft computing techniques can potentially be used for the modelling and the analysis of the oscillatory heat transfer coefficient with a higher level of accuracy. The result reported in this study implies that the prediction of the OHTC can be considered for the enhancement of thermoacoustic refrigerators performances.

COMPARISON OF ENERGY BALANCES THERMOACOUSTIC REFRIGERATORS

this article analyzes the energy balances of thermoacoustic refrigerators on a running and standing wave, since there are problems with the design of reliable and economical thermoacoustic cooling systems, this analysis will show which type of refrigerator is the most effective.

Thermoacoustic Refrigerators and Heat Pumps: New Insights for A High Performance

Thermoacoustic refrigerators and heat pumps are considered one of the important emerging green technologies. They are based on the use of acoustic pressure waves to supply cooling or heating effects. The oscillating gas interaction with a solid wall called the stack generates thermoacoustic effects. This study presents the effects of the operating conditions and geometric parameters on the temperature difference across the stack and the coefficient of performance of a thermoacoustic heat pump at different cooling loads. The design steps of these systems were also demonstrated. Theoretical study of the operation conditions and geometric parameters was presented using “DeltaEC”. The results showed that higher harmonics are less desirable for thermoacoustic phenomena as they lower the temperature difference across the stack. Further insights into the effects of amplitude pressure, mean pressure and stack geometries were also demonstrated. This study helps to establish the concepts and design steps for thermoacoustic refrigerators and heat pumps.

Numerical Modeling and Performance Evaluation of Standing Wave Thermoacoustic Refrigerators with a Multi-Layered Stack

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.

Design Optimization and Analysis of Thermoacoustic Refrigerators

Thermoacoustic refrigeration, a novel technology, uses eco-friendly gases like helium, air or the mixture of noble gases as working substances in the absence of moving parts. The design, optimization and analysis of thermoacoustic refrigerators using helium and air as oscillating gases are discussed. Pure helium is chosen since it is proven as the best and economical working gas compared to the alternate pure or the mixture of noble gases. Air is chosen since it is abundant in nature and the least cost of the pressurized dry air cylinders. The design optimization strategies discussed in this paper serve as a guide for aspiring researchers in the design and development of thermoacoustic coolers. Cooling power as a function of stack diameter is discussed. Theoretical results of the optimized coolers are compared with DeltaEC simulation results for validation and are in agreement with each other.

Effect of Stack Spacing on the Performance of Thermoacoustic Refrigerators Using Helium and Air as Working Substances

This paper deals with the design of thermoacoustic refrigerators using linear thermoacoustic theory. The refrigerator components are designed at 3% drive ratio by considering the practical limitations of providing sufficient spacing for attaching the loudspeaker to the resonator tube and accommodating instrumentation. The effects of spiral stack spacing in terms of thermal penetration depth on the theoretical performance of refrigerator using helium and air as working substances are discussed. The quarter-wavelength resonator designs with taper and divergent section terminated with hemispherical end are optimized with helium and air for better performance. Theoretical results are validated with DeltaEC software results and are in agreement with each other. Helium shows better performance compared to air but lacks power density. The DeltaEC predicts COP 0.514 at the cold heat exchanger temperature of [Formula: see text]C with helium compared to air (COP 0.616 at [Formula: see text]C) for the 50[Formula: see text]W cooling power 100[Formula: see text]mm diameter quarter-wavelength resonator designs.

Design and Analysis of Thermoacoustic Refrigerators Using Air as Working Substance

In this paper, the design of 50 W thermoacoustic refrigerators operating with air as working substance at 10 bar pressure and 3% drive ratio for a temperature difference of 28 K is described. The design strategies discussed in this paper help in design and development of low cost thermoacoustic coolers compared to helium as the working substance. The design and optimization of spiral stack and heat exchangers, and the promising 0.2[Formula: see text] and 0.15[Formula: see text] resonator design with taper and divergent section with hemispherical end are discussed. The surface area, volume, length and power density of the hemispherical end design with air as working substance is found better compared to the published 10 and 50 W coolers using helium as the working substance. The theoretical design results are validated using DeltaEC software simulation results. The DeltaEC predicts 51.4% improvement in COP (1.273) at the cold heat exchanger temperature of [Formula: see text]C with air as working substance for the 50[Formula: see text]W 0.15[Formula: see text]TDH resonator design compared to the published 50[Formula: see text]W 0.25[Formula: see text]TDH resonator design with helium as working substance.