Theoretical Simulation And Experimental Research On Gas Cooler Of CO₂ Heat Pump Water Heater

In this study, the performance of the gas cooler of CO₂ heat pump water heater is the object to discuss. The com puting si mulation, visualization and experim ental measurement of the gas cooler have been carried out.The perform ances of system s were com pared at dif ferent evaporation temperature, high pressure and outlet tem perature of the gas c ooler by theoretical analysis on COP and exergy efficiency of CO₂ transcritical cycle system. It is founded that the cooling water temperate outlet can be increased by increasing the evaporation temperature or degree of superheat, even by adopting the suitable high pressure.Based on distributed-parameter method, the heat transfer model of gas cooler is established. The heat transfer proces s of the gas cooler is simulated at various m ass flow rate and tube number . The influences of CO₂ mass flow rates, the tube inn er diameter and tube number are analyzed. It is founded that the cooling water temperate outlet can be increased by increas ing mass flux of CO₂ or increasing heat transfer coefficient of cooling water side, even by adopting the suitable inner tube number and proper tube inner diameter but by the pay of increase of pressure drop.The high transparen t q uartz s ight gla ss is installed on the gas cooler . The turbulent flow of CO₂ inside the inner tube at two phase state is observed by using the high speed photography equipm ent. Meanw hile, the state and flow process of lubricant in refrigerant at different temperature and pre ssure is observed through the way of adding fluorescein in lubricant. W ith the rising of inlet tem perature in gas cooler, the lubricating oil on the surface of the tube changes from droplets to the film.The gas cooler with four inner tube s is designed and m anufactured, and compared with the gas cooler with three refrigerant tubes. It is concluded that at the same suction param eter, the perfor mance of new gas cooler including outlet temperature of cooling water , COP , heat capacity and h eat transfer coef ficient increased, and so does the pressure drop.