Effect of Turbulent Prandtl Number on Convective Heat Transfer to Turbulent Upflow of Supercritical Carbon Dioxide

A two-dimensional model is developed to simultaneously solve the momentum and energy equations and thus predict convection heat transfer to an upward flow of supercritical carbon dioxide in a round tube. The effect of the turbulent Prandtl number, Pr_t, on heat transfer coefficients has been extensively studied. A number of constant values of Pr_t, as well as a number of suggested equations accounting for variations of Pr_t with flow conditions, have been examined. The investigation has been carried out for both regimes of enhanced and deteriorated heat transfer. The results of this study show that the increase of Pr_t, even in the viscous sublayer, cause the heat transfer coefficients to decrease. The models of Pr_t leading to best agreement with experiments in either regimes of heat transfer were recognized. From the effect Prt has on heat transfer coefficients, it has been deduced that the buoyancy effects in upward flow of a supercritical fluid causes the Pr_t to decrease and hence the heat transfer coefficients to increase.