Heat transfer characteristics of SCO₂ under different thermal boundary conditons

The flow and heat transfer characteristics of SCO₂ in a vertical tube under three different thermal boundary conditions are numerically studied. It is found that the temperature raise of bulk fluid in a tube is much quicker under the first type thermal boundary condition (constant wall temperature boundary) than under the second type and third kind thermal boundary conditions (constant wall heat flux boundary and two-fluid coupled heat transfer boundary). Although there are differences in the wall heat flux distribution, the temperature raise process and heat transfer coefficient of SCO₂ along the flow direction have some similarities under the second type and third kind thermal boundary conditions. When using SCO₂ as working fluid, the assumption of constant wall heat flux is more accurate than constant wall temperature in the numerical study of heat exchanger in engineering applications.