Effect of width and temperature of a vertical parallel plate channel on the transition of the developing thermal boundary layer

Abstract

Numerical simulations are performed to study the transition of the development of the thermal boundary layer of air along an isothermal heated plate in a large channel which is bounded by an adiabatic plate. In particular, the aim is to investigate the effects of the channel width (b) on the transition of the flow under various plate temperatures. Three different RANS based turbulent k–ε models namely standard, RNG and Realizable with an enhanced wall function are employed in the simulations. The channel width was varied from 0.04m to 0.45m and the numerical results of the maximum values of the flow velocity, turbulent kinetic energy were recorded along the vertical axis to examine the critical distance of the developing flow. The results show that the transition delays when the width is increased from 0.04m to 0.08m and particularly, the critical distance at b=0.08m reaches its maximum with the Grashof number of 2.8×1010. However, the critical distance drops when b is increased further from 0.08m to 0.45m, indicating an early transition of the flow. The transition remains unaffected by the adiabatic plate when b is greater than 0.45m. Comparisons of selected numerical results are made with available experimental data of turbulent flow and a satisfied agreement is received.