Heat transfer of supercritical carbon dioxide in a tube-in-tube heat exchanger-a CFD study

For better design and optimization of the heat exchanger (HX), forced convective heat transfer and flow characteristics of supercritical carbon dioxide (SCO2) in a water-cooled experimental counter-flow tube-in-tube HX were studied numerically with three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport (SST) turbulence model by using computational fluid dynamics method in ANSYS CFX. With a sole tube model of the HX, effects of SCO2 inlet pressure, mass flux, tube diameter and wall heat flux on SCO2 mean heat transfer coefficient (MHTC) were investigated. Influences of turbulence models and discretisation schemes of the advection terms in the SST model, wall temperature of conservative and hybrid values in CFX-Post on MHTC were clarified, and buoyancy effect in the horizontal HX was explored. The SST model can achieve better agreement with the experimental MHTCs of SCO2 than the other models. The buoyancy effect can improve MHTC by the secondary flows in the tube.