离心压缩式热泵装置的传递分析

EXERGY TRANSFER ANALYSIS FOR CENTRIFUGAL COMPRESSED HIGH POWER HEAT PUMP DEVICE

依据(火用)传递原理,建立在线运行大功率离心压缩式热泵机组及装置的(火用)传递模型。提出并定义装置和设备(火用)转换率、(火用)功率下降率、(火用)流密度下降率和(火用)阻系数等评价分析准则及其计算式。在此基础上,对热泵在能量转换及传递过程中之能质行为做了(火用)传递分析,得出节流阀、压缩机的(火用)功率下降率最高。原因是节流过程流速、流态在瞬间发生剧烈变化,导致过程(火用)损很大,压缩机的机械性能与冷媒的热物理性能均存在某些不足;蒸发器的(火用)阻系数最高,说明其结构设计有明显缺陷;节流阀的(火用)功率下降率和(火用)流密度下降率相同,表明设备的结构因素与时间条件对节流阀的影响相同。分析结果揭示出机组主要设备的结构设计、热工性能及冷媒热物性对装置用能过程的影响度,得出压缩机在结构设计上仍有改进余地,节流降压因其严重影响装置的合理用能而不宜取,蒸发器的主要问题是在冷媒侧而非结构设计缺陷的结论。对装置同时做的能量分析和(火用)分析计算表明,前者仅给出能的数量利用分析,后者也只是对能量行为的静态分析,而(火用)传递分析由于是对过程能量行为的动态分析,可直接提供机组和设备的结构参数及随机运行工况对用能过程影响的新信息,从而为改进机组设计及指导装置运行提供具体意见。

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 thermophysieal 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 prorides 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.