EXERGY TRANSFER ANALYSIS FOR CENTRIFUGAL COMPRESSED HIGH POWER HEAT PUMP DEVICE

Abstract

According to exergy transfer theory, establishment of the exergy transfer mode of unit and device for an online high power centrifugal compressed heat pump is focused on. Some criterions to analyze and evaluate the devices and equipments such as exergy exchange rate, exergy power degressive rate, exergy fluid density degressive rate, and exergy resistance coefficient are raised and defined. The calculation formulas for each criterion are presented also. Using these model and criterions, through an exergy transfer analysis on the energy quality activities during the process of the energy exchange and transfer in the heat pump, the results show that exergy power degressive rate is the highest in throttle and compressor because the flow speed and flow state have the instant drastic changes in the process of flow throttle, which cause the significant loss of exergy, and some deficiencies exist for the compressor mechanism performance and thermophysical properties of refrigerants performance. The exergy resistance coefficient is the highest in evaporator, which reflects that the structure design has the distinct limitation. Exergy power degressive rate and exergy fluid density degressive rate have the same value in the throttle which indicate that the structure factors of the equipment and the time conditions have the same impacts on the throttle. The results of exergy transfer analysis reveal the influence degree of structure design and thermodynamics property of the main equipment, and thermophysical properties of refrigerants impact the process of energy usage in the devices, and indicate the structure design of compressor can be improved further. The method by flow throttling and intensity of pressure decreasing is not appropriate in terms of the significant impacts on the rational energy usage of the devices; the primary problem of the evaporator is caused by the refrigerant factor but not its structure design. From the calculation of the energy analysis and exergy analysis on the devices, it is indicated that energy analysis only reflects the quantitative energy utilizing, and exergy analysis is only the static analysis of energy activities. However, in terms of the dynamic analysis, exergy transfer analysis provides the new information including not only the design parameters for the heat pump device and principle equipments, but also the impacts on the performance of energy usage under the situation with the random running of the equipment system. Therefore, it can provide the detailed suggestions to improve on the heat pump unit designs and direct the device operation.