Experimental study of buoyancy and inclination effects on transient mixed convection heat transfer in a channel with two symmetric open cubic cavities with prescribed heat flux

An experimental study in a recirculating water channel with a square cross section is carried out to study the transient laminar opposing mixed convection heat transfer from two symmetric open cubic cavities. The walls of the cavities facing the openings are subject to a constant wall heat flux boundary condition, the other bounding walls of the cavities and the channel are insulated and adiabatic. The experiments are done under different values of buoyancy strength or modified Richardson number, Ri ^* = Gr ^* /Re ² from 32.17 to 300.77, channel inclination of 0 ^∘ ≤ γ ≤90 ^∘ , Reynolds number of 500 ≤Re≤ 1500, and a fixed Prandtl number of Pr = 7. Mean surface temperature distributions and averaged Nusselt numbers have been obtained. Results indicate that depending on the channel orientation and buoyancy strength, the flow and temperature distributions experience an oscillatory behavior and are not symmetric with respect to the channel centerline. In addition, at high Ri ^* numbers, spanwise and axial variation of the heat transfer rates has been reported elucidating the strong three-dimensional (3D) nature of the flow. Empirical correlations for the overall Nusselt number of each cavity are also developed for relations using the Reynolds and modified Grashof numbers over the range of physical parameters considered in this study.