Numerical Simulation of Turbulent Mixed Convection Heat Transfer Variation along a Vertical Flat Channel for Aiding Flows

摘要

Numerical modelling results on variation of turbulent mixed convection heat transfer along a vertical flat channel, when forced and natural convection directions coincide (aiding flows), are presented in this paper. Investigations with two-side symmetrical heating (q{sub}(w{sub}1) = q{sub}(w{sub}2) = const) were performed in a wide range of buoyancy parameters Bo = Gr{sub}q/(Re{sup}3.425Pr{sup}0.8) - from forced convection to natural convection. The computer code PHOENICS, which allows solving the system of mean flow equations of momentum, energy, and continuity, has been used for numerical simulation. Low Reynolds number Chen-Kim (CK) and Lam-Bremhorst (LB) k-ε turbulence models were used for closing the system of equations. The results obtained for numerical heat transfer simulation (for a two-dimensional case) were compared to the data from the experiments carried out at the Lithuanian Energy Institute (LEI). It was shown, that under a small effect of buoyancy [when buoyancy parameters are less than a critical value (Bo ≤ Bo{sub}(cr))], the Chen-Kim turbulence model simulates the heat transfer results in vertical short (x/d{sub}e ≤ 20) channels better than the Lam-Bremhorst model. It was also demonstrated that the Lam-Bremhorst turbulence model could be used for heat transfer simulation with uncertainties less than 15% in the quasi-stabilized region (x/d{sub}e ≥ 30) for a wide range of variation of buoyancy parameters.