Experimental Study Of Heat-transfer Process On The Auto-cascade Heat Pump

Along with the energy and environment crisis increasingly exacerbated, as the new heating equipment, heat pump has got more and more attention with the advantages of energy-saving, environment protection and safety. Compared with the traditional single stage heat pump water heater and cascade heat pump water heater, the auto-cascade heat pump water heater has advantages of simple structure and low pressure ratio. It is a practical heat energy manufacture system, which has a broad application future in the callback of industry excess heat and heating supply in the north area of China. Some problems of the auto-cascade heat pump system were summarized and some measurements to improve its performances were proposed, while also experimental research was given and analyzed on this paper. The main content is displayed as follows:1. Firstly the steady equilibrium experiment and thermodynamic analysis on the auto-cascade heat pump were done. Results show that under the condition of steady the system satisfies the quality and energy conservation, compressor is obviously away from adiabatic heat compress, while condenser-evaporator exists lager heat exchange temperature difference, both of these parts which have excessive exergy loss are the main reason of low coefficient of the system, thus further optimization of system should be focused on the two parts.2. Then the throttle control experiments under steady condition were done, also the main and tributary throttling of opening degree changes influence on heat exchange process of the condenser-evaporator and the performance of the system were analyzed. Experimental results show that the heat transfer process of condenser-evaporator clip is at end. By given the main or tributary throttle opening degree, the exergy loss of condenser-evaporator firstly reduces, then increases with another throttle opening degree. Also the main throttle has a more significant effect on exergy loss of the condenser-evaporator than another. Under the stable condition, there is a group of opening degree of main throttle and tributary throttle that exergy loss of condenser-evaporator is minimum, however, COP is not the maximum under this group, COP reduces with increasing opening degree of them. The average COP of system is 1.75 in the throttle control experiments, the maximum COP could reach 2.0, and reducing the throttle degree can improve the performance of the system.3. Through a lot of experiments in the auto-cascade heat pump system, there are some special phenomena, such as liquid temperature is low, the heat transfer coefficient of evaporator is too low, unsteady membrane modal boiling and the refrigeration capacity of evaporator is very low but the system cycle could still operate, these phenomena couldn't be explained by theoretical basis. So detailed description was carried out and analyzed under experimental data, also some opinions were given for these phenomena.