Abstract: In order to reveal distribution characters of heat transfer pinch point of gas cooler in CO2 inverse-cycle, and explore the change rule of temperature difference between CO2 and heat-transfer fluid, and how to avoid the occurrence of pinch point inside heat exchangers, corresponding theoretical analysis are carried out. A cooling model of CO2 is built, so the occurrence condition of pinch point is obtained, also the situation equation of CO2 is used to compute some relationship between temperature and enthalpy, gradient of (dH/dt)P and probability of occurring pinch point under different pressures. According to the minimum temperature difference at pinch point in the CO2 gas cooler, heat-transfer fluid parameters at inlet and outlet of the cooler and position of pinch point are obtained under different pressures. During the gas cooling process, the position of pinch point moves gradually to back of the cooler with pressure increasing, at the same time, temperature of heat transfer fluids at outlet of the gas cooler reduces firstly and then increases. Increasing limit of temperature heat-transfer fluid in the gas cooler is presented in order to avoid pinch point occurring in 6 kinds of pressures. These may be helpful to rationally selecting CO2 inverse-cycle operation in air-conditioner or heat pump units.

Key words: CO2, Gas cooler, Heat transfer pinch point, Inverse-cycle, five-stage slurry pump, impeller, numerical simulation, solid-liquid two-phase flow, deep-sea mining