Doctor of Philosophy
Department of Mechanical Engineering
Sharifi-Bidgoli, Hassan, Vapour jet refrigeration systems (VJRS), Doctor of Philosophy thesis, Department of Mechanical Engineering, University of Wollongong, 1995. http://ro.uow.edu.au/theses/1602
A Vapour Jet Refrigeration System (VJRS) is an alternative to the conventional mechanically driven vapour-compression refrigeration system. The VJRS utilises a supersonic ejector as a thermal compressor and has the potential significantly to reduce energy consumption in air conditioning systems. Experimental investigations and analysis of large supersonic jet ejectors such as those used for steam jet refrigeration, has been carried out in past literature. In the present study the performance characteristics of small VJRS ejectors using R12 as the working fluid (ie ejectors with throat diameters of several millimetres only) have been investigated using experimental, analytical and C F D (computational fluid dynamics) techniques.
In practice ejector performance may be affected by the choking phenomena in the secondary stream, superheating of vapour leaving the evaporator and generator, nozzle and diffuser efficiency. The present author developed a model for a small, single-fluid VJRS ejector using the theory of secondary vapour choking which was introduced by Munday and Bagster (1977). This theory was employed by the present researcher to design and test a small R12 ejector. Results of a computer simulation that models secondary choking in the converging part of the ejector and the effects of superheat conditions on the ejector performance are presented.
In the present work further developed has been carried out to examine the optimum nozzle position when the ejectors operated at fully developed choked conditions. It has been confirmed that for the small ejectors the choking phenomenon plays an important role in ejector performance. It was also recognised that the nozzle position is a very important factor of the ejector geometry for small VJRS ejectors.
In the secondary choking theory, ejector performance may be taken to be a function of the "effective area" available to the secondary fluid within the mixing chamber of the ejector. The present study involved experimental investigation of how this effective area is influenced by operating conditions such as evaporator temperature and nozzle position. In the present investigation the geometry of the converging part of the ejector has also been studied and the shock pressure recovery process examined in the constant area mixing tube.
The present author has developed a CFD simulation of the ejector using the PHOENICS-BFC code based on the finite volumetric technique. Comparisons have been made between the predictions of the entrainment ratio using the one-dimensional, constant area analysis, CFD results and experimental results.
In the present study analysis of two-fluid VJRS ejectors carried out based on the one-dimensional analysis, constant area method. It was found that using an appropriate fluid-pair, the entrainment ratio is likely to be substantially better than for the single fluid VJRS.