Experimental Study And Thermodynamic Analysis Of Low-temperature Heat Pump Evaporator

The evaporation of heat-sensitive materials is a severe problem in operations. To solve the question, an experiment of low-temperature heat pump evaporator was conducted in this paper. Water and R22were used as material fluid and working medium respectively to study the relationships between the system coefficient of performance COP, heating capacity, evaporation capacity, evaporation temperature, cooling capacity, working medium flow rate and actual compressor input power. The results showed that, when the evaporation temperature increase, the heat load, the material evaporation and condensation capacity, the system heating coefficient of performance COP, compressor theoretical power consumption and the theoretical heating medium flow rate all increased. The evaporation temperature was under40℃, and the COPR was from2.8to5.4, the compressor isentropic efficiency was between0.53-0.61, condenser heat transfer resistance decreased by increasing evaporation temperature, the minimum evaporator heat transfer resistance was at the34-35℃. The system can achieve an evaporation of4-8.1kg/h and the steam recovery was71%-91%, which can efficiently deal with heat-sensitive materials at low temperature evaporation. With glucose solution as the material fluid, the experimental results show that with the increase of compressor frequency and input power, system heating and cooling capacities, evaporation and condensation capacities, compressor effective input power and efficiency all have the same trend of increase. And can achieve an evaporation of4.5-9kg/h and condensation of3.4-8kg/h. With fine energy-saving performance, the efficiency of the compressor is70%-90%, COPR was3.2-4.9.In order to further study on the system performance of the low-temperature heat pump evaporator, R134a was used as the working fluid to analysis the system thermodynamic characteristics. System thermodynamic properties was studied in the condition of20-40℃ranged evaporation temperature with3specific temperature differences,5℃,7℃,10℃. It was found that the system COP, heating capacity, evaporation capacity and the working fluid flow rate increases along with the evaporation temperature, but decreases when the temperature difference increases, however, the compressor power consumption increases. With the increase of suction superheat at the same evaporation temperature, the system COPH did not change significantly within the selected range, while the evaporation capacity slowly increases and the working fluid flow rate decreases. For R134a, the increases of superheat benefit the system. And when the evaporation temperature is fixed, higher the degree of subcooling can achieve higher system COPH and higher evaporation capacity while working fluid flow rate remains unchanged.