Abstract
A vapour-compression refrigeration circuit employing a microprocessor-controlled expansion valve has been developed primarily to investigate the performance of hydrocarbon refrigerants but has also proved an ideal demonstration and teaching system. Unlike more conventional systems in which the capillary or thermostatic expansion valve must be matched to the refrigerant, the use of a stepper-motor-driven valve allows refrigerants, or refrigerant mixtures, of unknown composition to be investigated. Further, the valve may be controlled to maintain the refrigerant flow rate and evaporator exit superheat at any desired value. The flexibility of the system allows students to investigate the behaviour of the vapour compression system over a range of operating conditions whilst the pre-programming of set points (e.g. minimum superheat, maximum pressure) ensures that the system cannot be driven beyond its safe working limits.
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