Numerical Analysis Of Supercritical CO₂ Flow And Heat Transfer

Supercritical fluids have been the research hotspot in recent years due to their good flow and heat transfer properties.The supercritical CO2 is relatively easy to reach its supercritical state,and it has richer application prospects.It is expected to be used in the fourth generation nuclear power system and the latest solar thermal power generation system in the future.At present,there are many studies on the flow and heat transfer of supercritical CO2 in straight tubes,and the heat transfer coefficient of supercritical CO2 in spiral tubes is larger than that in straight tubes due to its special rotating structure.At present,there are few studies on the flow and heat transfer performance of supercritical CO2 in helical tubes.Based on this,this paper uses Fluent to study the flow and heat transfer characteristics of supercritical CO2 in spiral tubes.First,the physical model of the spiral tube is established,and the accuracy of the SST k-ω model in Fluent to simulate the heat transfer characteristics of supercritical CO2 in the helical tube is verified.The influence of inlet mass flow velocity and wall surface heat flow density on the heat transfer process was then studied.The main conclusion is that as the inlet mass flow velocity increases,the peak value of the heat transfer coefficient will increase accordingly.When the temperature of the CO2 fluid is in the pseudocritical temperature region,as the heat flux density increases,the heat transfer coefficient decreases.When the temperature of the CO2 fluid is far from the quasi-critical temperature zone,the greater the wall heat flux density is,the heat transfer coefficient is corresponding larger.After that,the influence of the structural parameters of the helical tube on the heat transfer characteristics of supercritical CO2 in the spiral tube was studied.The effects of inlet diameter,pitch,and spiral curvature diameter on the heat transfer process are mainly studied,and a structure with a variable spiral diameter helical tube is also proposed.Then,the paper discuss the differences of heat transfer characteristics between helical coils with equal spiral diameter and helical coils with variable spiral diameter.The main conclusions are that when the temperature of CO2 is in the quasi-critical temperature region,the larger the inlet diameter is,the heat transfer coefficient is larger;the pitch has a rather smaller effect on the heat transfer coefficient of the helical tube;For the variable diameter helical tube,the smaller the diameter change angle β is,the value of the heat transfer coefficient is larger;the heat transfer coefficient of the equal spiral diameter helical tube with a smaller spiral curvature diameter is larger than that of the variable spiral diameter helical tube.However,due to the fluctuation of the heat transfer coefficient of the variable spiral diameter helical tube,the heat transfer coefficient of the variable spiral diameter helical tube will be greater than that of the constant spiral diameter helical tube when CO2 is at a certain temperature.