two-phase injector, isobutane, heat transfer, mass transfer
Renewable energy sources may be applied to drive refrigeration and air-conditioning systems, e.g. solar radiation, geothermal resources, heat derived from biomass or waste heat rejected form various thermal processes. In this case absorption refrigeration systems and ejection systems may be used for cooling applications. In both these systems the crucial problemÂ is the development of a suitable liquid pump. Â Energy consumption to drive these systems is not a major problem here as in most cases amount of energy required to drive a mechanical pump is a contribution of at most a few percent of the overall energy balance of the system and in most cases is of the order of magnitude 1%. Therefore the most important problem is a special difficulty to select of a commercially available liquid pump for the thermal driven cycle (absorption or ejection one). Such pumps should be low cost, small size and should produce sufficiently high compression rate for the discussed applications. They should also be adapted to work in particularly hard operating conditions resulting from the application in the discussed systems low boiling fluids: these are high penetrating substances, most of them are chemically aggressive and high susceptible to erosion caused by cavitation destruction. Under present conditions most of the pumps that could be applied have inadequate overall dimensions as well as are very expensive so the contribution of the cost of the relevant pump is dominant in the total cost of the system. As an effect refrigeration systems driven by renewable thermal sources are commercially unprofitable and unattractive. Â Mechanical liquid pump liquid is the only element of the refrigeration system that consume electric power.Â Therefore it is also desirable that the whole system would be fully thermal driven one, without consumption of electric power to drive. The above is another important condition to search for the alternative solution for that would be competitive to mechanical classic liquid pumps. Two-phase vapour-liquid ejectors may be thought as required alternative. The general motivations of application of the two-phase injector instead of a mechanical pump in the discussed systems are: â€¢Â Â Â two-phase injector is driven by part of vapor that is generated already in the system; in this case the refrigerationÂ system is fully thermal driven; â€¢Â Â Â two-phase injector operates also as pre-heater of liquid phase supplied to the vapour generator that additionallyÂ improve the system efficiency; â€¢Â Â Â this type of injector is more simple and reliable than mechanical liquid pump since it has no moving parts.Â Â Â Paper deals with experimental investigation of two-phase vapour-liquid injector as a liquid pump in refrigeration systems. The selected experiment results for the injector are presented for the case of isobutane as working fluid. Investigations covers the operation characteristics of the injector as well as heat transfer coefficient.