Influence of Layer Height on Thermal Buoyancy Convection in A System with Two Superposed Fluids Confined in A Parallelepipedic Cavity

Abstract

Convection in a differentially heated two- layer system consisting of air and water was studied ex- perimentally, using laser-interferometry. The cavity used for flow visualization was square in cross-section and rectangular in-plan having dimensions of 447 × 32 × 32 mm 3 . Experiments performed over different layer thick- nesses of water filled in a square cross-section cavity, the rest being air, are reported in the present work. The following temperature differences for each layer height were imposed across the hot and the cold walls of the superposed fluid layers: (i) ΔT=10K and (ii) Δ T= 18 K. The present study was aimed at understanding the fol- lowing issues: (a) the influence of Rayleigh number on the steady thermal field, and (b) flow coupling mecha- nisms between the layers. Experiments show that the thermal field in the fluid layers is primarily determined by the temperature difference and hence the Rayleigh number. In the thicker water layer (1/3 air - 2/3 water) case, with increase in Rayleigh number, the no-coupling mode changes into a thermal coupling mode. For the equal layer heights (1/2 air - 1/2 water) case, the two- layers are thermally coupled at a lower Rayleigh num- ber, while the mechanical and thermal coupling both be- come significant at higher Rayleigh number. Also, for the thicker air layer (2/3 air - 1/3 water) case, a full or joint coupling (mechanical + thermal) was observed for all the Rayleigh numbers obtained in the experiment. keyword: Convection, Superimposed fluid layers, Rayleighnumber, Air-waterinterface, Flowcoupling,In- terferometry.