STEADY AND TRANSIENT MIXED CONVECTION NEAR A VERTICAL UNIFORMLY HEATED SURFACE EXPOSED TO HORIZONTAL FLUID FLOW

Abstract

The numerical solution of flow and heat transfer for steady and transient laminar mixed convection near a vertical uniformly heated surface exposed to a horizontal cross-flow is presented. The transients considered include the simultaneous initiation of flow and heating and the time-varying flow generated by starting or stopping forced convection with the surface heating condition unchanged. The partial differential equations describing the conservation of mass, momentum, and energy were solved in their time-dependent forms by an explicit finite-difference technique. Calculations were performed for fluids with Prandtl numbers of 0.733 and 6.7, nominally air and water. During both steady and transient circumstances, the effects of the horizontal forced flow were dominant near the vertical leading edge, whereas natural convection dictated the flow at large values of the horizontal coordinate. The heat transfer coefficient during mixed convection was significantly higher than that with either forced or free convection atone. During simultaneous starting of flow and heating, the time to reach steady state decreased with increase in cross-flow velocity. For the transients initiated by suddenly imposing a horizontal forced flow on an existing natural convection flow, the local temperature and vertical velocity were found to undershoot before reaching their respective steady-stale values. The overshoot in heat transfer coefficient in such situations was significant for fluids with smaller Prandtl number. The transient initiated by stopping the horizontal flow during mixed convection was associated with overshoot in both vertical component of velocity and local fluid temperature.