Experimental Researches On Heat Exchange Characteristics Of Zeotropic Mixtures In High Temperature Heat Pump

The application of high temperature heat pump is benefit to energy conservation and environmental protection, but traditional working fluids can damage the ozone layer and cause greenhouse effect. Based on the modified high temperature water-water heat pump system, experimental researches were carried out on the binary hydrocarbons mixture, which is composed of R290 and R600 (50% R290/50% R600, mass ratio) and has a linear relationship between temperature and enthalpy. Then a visual condenser was designed to research the whole condensation process of the working fluid.Evaporator side experimental results show that, when the water flow rate is too high, redundancy area appears in evaporator at the same temperature of heat media (water) going into evaporator. Pinch point (minimum temperature difference) occurs in the evaporator at certain experimental conditions and its location moves with the water flow rate or the temperature of water going into evaporator changing. At different temperature of water going into evaporator, the performance of the system has the same changing regularity when the water flow rate increases, the heating capacity and COP increases at first with the water flow rate increase, but when the water flow rate continues increasing, they basically remains the same level; thermodynamics perfection decreases with the water flow rate increase. The heat transfer performance of the working fluid in high temperature region is better than in low temperature region.Condenser side experimental results show that, when the water flow rate is too high, redundancy area appears in condenser at the same temperature of heat media (water) going into condenser. Pinch point didn’t occur in condenser; the changing of water flow rate influences the distribution of heat transfer temperature difference, but the changing of the temperature of water going into condenser nearly doesn’t. At different temperature of water going into condenser, the performance of the system has the same changing regularity when the water flow rate increases, the heating capacity and COP increases with the water flow rate increase, but the growth decreases; thermodynamics perfection increases with the water flow rate increase.Visual experimental results show that, in the condensation process of the working fluid, some typical two-phase flow patterns will appear, such as churn flow, slug flow, ripple flow and stratified flow, etc. As the temperature of the water going into the visual condenser reduces or the water flow rate increases, the same changing regularity is found that the subcooling of the working fluid increases, liquid working fluid increases, gas phase working fluid decreases, the flow gradually changes from strenuous to gentle, and these typical two-phase flow pattern appears in turn (in each working condition there will appear one or more flow patterns).