Plume separation from an adiabatic horizontal thin fin placed at different heights on the sidewall of a differentially heated cavity

The separation of plumes from an adiabatic horizontal thin fin attached to a sidewall of a differentially heated cavity at quasi-steady stage is experimentally and numerically studied at three Rayleigh numbers (0.92×109, 1.84×109 and 3.68×109) and over a range of fin positions. Regular plume separation is observed over the present range of parameters during the quasi-steady stage. Both experimental and numerical results reveal that the plume separation frequency increases with the Rayleigh number and decreases with the fin height measured from the leading edge. A higher Rayleigh number leads to a more unstable flow above the horizontal thin fin which in turn leads to a higher plume separation frequency. The decrease of the plume separation frequency with the increasing fin height is mainly due to the reduction of the adverse temperature gradient in the unstable layer above the thin fin as a result of the cavity-wide temperature stratification. It is further revealed that the heat transfer through the sidewall is improved by the presence of the thin fin. An optimum fin height for maximum heat transfer enhancement has been identified for the case with a Rayleigh number of 0.92×109. For the other two higher Rayleigh number cases considered in this study, the heat transfer through the sidewall monotonically decreases with the fin height.