Effect of inlet temperature on CO2 heat transfer at supercritical pressure in vertical upward flow

Abstract

In this paper, the heat transfer characteristics of CO₂ at supercritical pressure in a vertical tube with an inner diameter of d=10 mm are investigated numerically under uniform heating condition. The SST κ-ω turbulence model are used. Firstly, the reliability and accuracy of the numerical model are verified, and the numerical results can capture the wall temperature curve well. Secondly, thermophysical properties of CO₂ under different pressures are analyzed. Finally, the influence of inlet temperature on CO2 heat transfer at supercritical are studied. The results indicated that when the inlet temperature is less than the pseudo-critical temperature, a temperature overshoot appears, belonging to heat transfer deterioration. As the inlet temperature decreases, the peak point of wall temperature moves towards the low enthalpy region. When the inlet temperature is greater than the pseudo-critical temperature, with increase of bulk fluid enthalpies, wall temperatures are either gently increased, belonging to normal heat transfer. Our results showed that the inlet temperature has a great influence on the CO2 heat transfer at supercritical pressure. The pseudo-boiling heat transfer mechanism perfectly explains the above phenomena.