Numerical Study on Mitigation of Heat Transfer Deterioration in Supercritical CO₂ Heat Exchanger Application

With the advantages of the thermophysical property of supercritical carbon dioxide (SCO₂), SCO2 has been proposed for being used as the coolant of the secondary system in a nuclear reactor to promote a higher thermal efficiency. However, heat transfer deterioration (HTD) in supercritical fluid became a potential operational problem for the supercritical heat exchanger. Understanding of HTD is importance to heat exchanger tube design. In this paper, both circular and annular tube with the same sectional area is simulated using the ANSYS FLUENT 15.0 with Shear Stress Transport (SST) turbulence model. In general, the SST model can accurately predict the position of HTD peak as found in the experiment but with a difference between the simulated and experimental value of the peak. Nevertheless, the SST model is still regarded as the turbulence model in modeling supercritical carbon dioxide heat transfer in ANSYS FLUENT. Computational Fluid Dynamics (CFD) simulation was performed for SCO₂ on 8.42 MPa with an inlet temperature of 312.15K under heat flux value of 110 kW/m² to illustrate the effect of heat transfer deterioration in the circular and annular tube. Second, the effect of turbulence augmentation to wall temperature are investigated by placing the semi-circular obstacles at the heated wall of the circular tube. The result showed that the addition of Vortex Generator (VG) could lessen the HTD effect and followed by the smoothing effect of the wall temperature along the downstream of the tube.