Conjugate conduction and convection underneath a downward facing non-isothermal extended surface: A numerical study

•Study of conjugate conduction and mixed convection from extended surface.•Isothermal extended surface overpredicts heat transfer as high as 134%.•Fin-tip clearance reduces the heat transfer for all the considered cases.•Effect of Grashof number is prominent for higher fin spacing.

The analysis of the conjugate conduction and mixed convection heat transfer in a downward facing channel constituted by two non-isothermal extended surfaces, a base and an adiabatic shroud is numerically performed. The effect of fin conductivity, Grashof number, dimensionless clearance (C*) and dimensionless inter fin spacing (S*) is carried out through the evolution of the temperature, heat transfer and fluid flow fields. Computed results reveal that buoyancy induced cross-stream flow enhances flow by-pass through the clearance, especially for higher fin spacing. Moreover, it reveals that isothermal surface (infinite conductivity) leads to a significant overprediction of heat transfer as high as 134%, especially at lower fin spacing (S* = 0.1). In addition, enhancing dimensionless fin conductance parameter by 200%, an increase of heat transfer as good as 62% is noted for S* = 0.1. At higher fin spacing (S* = 0.3 and 0.5), effect of Grashof number on heat transfer found to be more profound at higher Grashof number (>105). Zero clearance turns out to be the superior configuration.