Simulation Research On The Performance Of The Rectangular Cross-flow Gas Cooler Based On CO₂ Refrigeration Working Fluid

As a gas cooler of a transcritical CO₂ refrigeration cycle,it needs to work at extremely high pressures.Usually the pressure of the CO₂refrigerant in the gas cooler is as high as 80 to 100atmospheres,which has a great impact on the pressure capacity of the gas cooler.High demands.Aiming at the problem that the gas cooler of the transcritical CO₂heat pump system needs to withstand high pressure,a rectangular block cross-flow gas cooler structure is proposed,and theoretical analysis and numerical simulation are used to analyze the air cooler in different operating conditions.The heat transfer process,heat transfer characteristics and flow resistance characteristics under structural parameters are studied.First,according to the fluid flow and heat transfer characteristics of the rectangular cross-flow gas cooler,the heat transfer performance under multi-dimensional heat transfer directions is analyzed.Using Chiou and Bier theory,using the method of the product of the heat transfer coefficient and the longitudinal thermal conductivity coefficient under the one-dimensional heat transfer model,the correlation formula of the total heat transfer coefficient of the rectangular cross-flow gas cooler with the new structure is established.The theoretical calculation results are compared with the total heat transfer coefficient calculation results of the numerical simulation,and it is found that the maximum error between the two is 7.53%.Then use Fluent software to numerically simulate the heat transfer performance of the air cooler using CO₂gas and low temperature cooling water as the heat transfer medium,and study the operating conditions of the fluid and the influence of structural parameters on the performance of the air cooler.The simulation results show:（1）When the inlet flow rate of CO₂ gas changes between 2.0 m.s^-1-4.5m.s^-1,the total heat transfer coefficient will increase with the increase of the inlet flow rate of the gas;when the gas inlet temperature is at When changing between 30℃and 120℃,the total heat transfer coefficient will firstly have a large rising transition near the critical temperature of the gas（30-40℃）,reach the extreme value at 40℃,and then gradually decrease until it tends to A stable value.（2）With the increase of the low temperature cooling water inlet flow rate from 0.4m.s^-1to0.8m.s^-1,the total heat transfer coefficient and heat transfer efficiency both show a trend of decreasing increase,but compared to the gas side,the cooling water inlet The effect of flow velocity on the heat transfer coefficient is not obvious.When the flow velocity is increased by100%,the growth rate of the heat transfer coefficient is only 2.73%.（3）The use of solid material aluminum with larger thermal conductivity,large channel diameter,and small space between hot and cold fluid channels can all enhance the overall heat transfer coefficient of the air cooler.For the channel diameter less than 9mm,the total heat transfer coefficient is better than the fixed volume in the case of variable volume,and the opposite is the case when it is greater than 9mm;the total heat transfer coefficient of the variable volume under the same spacing of the cold and hot fluid channels is better than the fixed volume case.（4）The fluid flow resistance increases with the increase of the flow rate,the increase of the gas inlet temperature,and the decrease of the channel diameter.The heat transfer efficiency（WP）index under unit flow resistance is used to measure the heat transfer economy of the air cooler.WP increases with the decrease of the inlet flow rate of the cold and hot fluid;as the gas inlet temperature increases,it appears near the critical temperature Firstly increase sharply and then slightly decrease.When the temperature is far from the critical temperature,it increases with the increase of gas temperature;an approximately linear downward trend appears with the increase of the cooling water inlet temperature;in both cases,the WP in the air cooler increases with The increase in the diameter of the fluid channel is approximately linear.