Simulation And Experimental Study Of Miniature Refrigeration System

The development of MEMS makes it possible that the process machinery being miniature and light weight. Miniature refrigeration system, miniature scale mechanical machinery based on the work principle of conventional refrigeration system, is the integration of sensor, controller, power supply and the components of miniature refrigeration system fabricated by MEMS technologies. Miniature refrigeration system is a typical example that micro energy system being applied in engineering. American army has used this technology in Iraq war, and been attentioned all over the world. Miniature refrigeration system can be utilized for the cooling of personnel who is performing labor intensive tasks in a hot environment. What's more, miniature refrigeration system can be widely used in military, air space, industry, agriculture, mine and medical electronic instrument.Vapor compression refrigeration offers several important advantages including low mass flow rate, high COP, low cold plate temperatures and the ability to transport heat away from its source. In this paper, a miniature vapor compression refrigeration system prototype has been developed. The miniature refrigeration system has dimensions of 260mm x 250mm x 120mm, and weighs approximately 2.85 kg. The whole system includes a compact DC motor, a miniature Wankel compressor, a miniature air-cooled parallel type condenser, a spiral-tube type evaporator and capillary tube. The system can run for 2 hours driven by a high performance lithium battery. When the battery is included, the complete system weighs 4 kg.So far few organizations engaged in research of personal refrigeration system and the commercial application of miniature refrigeration system have not been seen. Therefore, the components of the refrigeration system must developed by ourselves. In the beginning of the paper, we introduce the development of the miniature vapor compression refrigeration system, including the development of miniature Wankel compressor, the development of miniature condenser and miniature evaporator. In order to research the matching and operating performance of the miniature refrigeration system we build an environmental chamber which can simulate the formidable conditions. The performance of the miniature refrigeration system is studied experimentally on the platform we built. The motor and its transmission ratio are obtained by the matching experiment between the compressor and motor. The optimal capillary tube length and refrigerant charge quantity is obtained from the experimental results. The operating performance experimental results shows that the compression ratio of the compressor is above 3.0, the refrigerating output of the system is above 300W. The system can run for 2 hours driven by a high performance lithium battery.A steady-state model for air-to-water refrigeration system is set up. By means of lumped parameter method a Wankel compressor model and a capillary tube model are set up. Meanwhile, in a distributed parameter approach a steady-state model of multi-channel parallel type condenser and spiral-tube type evaporator has also been established in the form of concentric counter-flow heat exchangers. In this study the revised X tt formula are used to calculate void fraction correlation in the two-phase region of condenser and evaporator. A refrigerant charge model is established to predict the effect of refrigerant charge inventory on the coefficient of performance (COP) of the refrigeration units.On the basis of above compressor, capillary tube, condenser and evaporator models, the steady-state model of air-to-water refrigeration units is developed with regard to energy and refrigerant inventory conservations among all these components. The results show that the relative error between prediction and experiment values of refrigerant output is less than 5%. The model predicts the performance relationship of the refrigeration system with variations in compressor speed, environmental temperature, entering temperature of chilled water and dimension of capillary tube.This paper described how the entropy generation changed at each component in the vapor compression refrigeration system as the system scale is decreased. And the quantitative evaluation of the entropy generation is made here, it is clear that the micro compressor is the most difficult component to be miniaturized in a miniature heat pump. If a miniature vapor compression refrigeration system is to be successfully operated, a great deal of efforts must be made to develop a workable micro compressor and to minimize the internal heat leak to the evaporator of the refrigeration system.