Conference Year

2014

Keywords

ejector, CFD, entraining performance, swirl, shock pattern

Abstract

Vapour Jet Refrigeration System (VJRS) is preferred among various heat operated refrigeration systems because it has potential of utilizing low temperature heat source, consumes less electrical energy causing less atmospheric pollution and requires less maintenance cost due to absence of moving parts [1]. Ejector, a thermal compressor, is one of the crucial components of VJRS. Performance of the whole system is based on the satisfactory operation of the ejector. Hence, it has to be designed carefully and effectively to realize good performance. Key criteria for enhancing the performance of the ejector demand better mixing of the primary and secondary streams. This would result in better momentum exchange between the two streams which in turn increases the entraining performance and compression ratio. The present work focuses on enhancing the performance of the ejector using *three dimensional CFD analysis with R134a by introducing _swirl_ in the primary stream of ejector*. In literature, compressible and axisymmetric swirl flow ejector working with steam has been investigated [2]. The novelty of the present work is the three-dimensional analysis of swirl flow ejector working with the refrigerant R134a. The flow in the ejector is considered to be steady, compressible and turbulent in nature. The flow domain contains two inlets viz., primary and secondary, and one outlet. Constant pressure boundary conditions are applied for the two inlets and the outlet. Primary inlet condition is given slightly superheated to avoid the condensation of the refrigerant at the exit of the primary nozzle due to expansion of the primary stream in the nozzle [2]. The turbulence model for this study is chosen as k-? model as used by [1]. Real gas thermodynamic behaviour and transport properties of R134a are obtained using ANSYS Fluent through* 'NIST Real Gas Model' which uses REFPROP subroutines*. Validation has been carried out by comparing the computed results of ejector without swirl with the experimental results from literature. Shock patterns, Mach number, radial velocity and tangential velocity variations along the ejector at various swirl angles are studied for a particular design operating condition. *Optimum swirl angle* which gives maximum entraining performance has been obtained. The computed results of ejector with swirl are compared with the ejector without swirl for the same operating conditions. Results indicate that the entrainment ratio gets improved for the ejector in presence of swirl as compared to the ejector with no swirl. Thus, the presence of swirl is expected to improve the coefficient of performance of VJRS.

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