Expander design, Simulation, Efficiency Improvement, Expansion Control
A traditional vapour compression refrigeration system consists of a compressor, a condenser, a throttling device and an evaporator. The typical throttling devices are capillary tube and expansion valves. Unfortunately, such devices waste expansion energy. To overcome this issue, expanders have been proposed in recent years. An expander can be observed as a compressor operating in a reversed cycle. It expands fluid and produces power which could be used to supply energy to the compressor or other components. The expansion process is more gradual, unlike that in typical throttling devices. Naturally, an expander is most attractive and has been studied most frequently in systems employing a large pressure difference, such as a trans-critical carbon dioxide refrigeration system. Meanwhile, most refrigeration systems in the world are still operating on the conventional Evans-Perkins vapour compression systems. It is, therefore, necessary to study the implementation of expander concept in conventional refrigeration systems. In this study, a rotary vane expander is developed to improve the energy efficiency of an existing R-22 heat pump system. One of the main advantages of rotary vane expanders is it requires no valve to control the fluid flow. The expander is developed by converting a commercially available automotive air conditioning 4-vane rotary compressor. To collect the required design parameters, simulations and experiments are carried out with the heat pump system. The design procedure will be presented and discussed in this paper. Relevant practical issues, such as expansion control will be discussed and addressed.