NATURAL CONVECTION FLOW RATE IN A HEATED VERTICAL TUBE

Abstract

To obtain the relation between mean natural convection and experimental conditions in a heated vertical open tube consisting of heated and calming sections, experimental and theoretical studies were performed. Correlations between Grashof number (Gr) and Reynolds number (Re) were derived by setting up a mechanical energy balance in the tube. The following equation was obtained semi-empirically in the present experimental conditions.
Gr₀=6.3•Re₀²+32•(L_H+L₀)/D•Re₀
Experimental results were replotted and were in qualitative agreement with the relations between dimensionless tube length and dimensionless flow rate which were solved by Davis et al. by the finite difference method. It was found that the equation obtained semi-empirically was suitable for relations between mean natural convection and operating conditions. It was confirmed that the effects of calming section length on the hydraulic relations between Gr and Re are similar to those on the heat transfer relations between Rayleigh number and Nusselt number reported by Dyer.