Optimization of thermoacoustic engine driven thermoacoustic refrigerator using response surface methodology (original) (raw)

Thermoacoustic engines (TAEs) are devices which convert heat energy into useful acoustic work whereas thermoacoustic refrigerators (TARs) convert acoustic work into temperature gradient. These devices work without any moving component. Study presented here comprises of a combination system i.e. thermoacoustic engine driven thermoacoustic refrigerator (TADTAR). This system has no moving component and hence it is easy to fabricate but at the same time it is very challenging to design and construct optimized system with comparable performance. The work presented here aims to apply optimization technique to TADTAR in the form of response surface methodology (RSM). Significance of stack position and stack length for engine stack, stack position and stack length for refrigerator stack are investigated in current work. Results from RSM are compared with results from simulations using Design Environment for Low-amplitude Thermoacoustic Energy conversion (DeltaEC) for compliance. 1. Introduction As the name thermoacoustics suggests, it involves conversion of heat energy and acoustic energy in one another. Thermoacoustics has become area of interest for many researchers due to the advantages of thermoacoustic technology like absence of moving components making devices more reliable and less maintenance prone, constructional simplicity, usability of noble gases and low grade energy sources, structural stability. Though the theory of thermoacoustics is well established there is no simple approach available for design of thermoacoustic devices. A quantitative engineering approach to design of thermoacoustic refrigerator (TAR) is given by Tijani et al. [1]. More detailed explanation on working of thermoacoustics is given by Swift [2]. Thermoacoustic devices mainly consists four components. A hot heat exchanger, a stack-often called the heart of thermoacoustic device, a cold heat exchanger and a resonator tube. Thermoacoustic engines develop acoustic power by using heat energy. Acoustic oscillations are generated due to the thermal interaction between the oscillating gas and the surface of the stack. The heat exchangers exchange heat with surroundings and maintain much required temperature gradient along the length of the stack for generation of acoustic work whereas thermoacoustic refrigerator uses acoustic energy to produce cooling effect. In figure 1 a simple illustration of thermoacoustic engine and in figure 2, a simple illustration of thermoacoustic refrigerator is shown. It is peculiar for thermoacoustic systems that performance of these systems is very sensitive to physical dimensions and operating conditions. Minor change in combination of geometric parameter and operating parameter affects the performance steeply. Due to this it is very much required to trace the effect of different parameter for required output and to categorize significant parameter for particular performance output.

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