NATURAL CONVECTION HEAT TRANSFER OF CONCENTRIC/ECCENTRIC ANNULUS SUBJECTED TO INNER TUBE OF CONSTANT HEAT FLUX

This paper describes the experimental results of natural convection heat transfer from vertical, electrically heated cylinder in a concentric/eccentric annulus and develops correlations for the dependence of the average annulus Nusselt number upon the Rayleigh number Wall surface temperature have been recorded for diameter ratio of d/D=0.4, with the apparatus immersed in stagnant air with uniform temperature. Measurements have been carried out for eccentric ratios of E=0, 0.19, 0.34, 0.62 and 0.89 in the range of heat flux of 45 to 430 W/m2. The surface temperature of the heater was found to increase upwards and reach a maximum at some position, beyond which it decreases again. It is observed, that this maximum temperature occurs near h/l=0.8 for 0 <= E < 0.62 at almost all power levels, but shifts downwards for E=0.89. Moreover, empirical correlations between the average Nusselt number and the Rayleigh number are derived for concentric and eccentric annuli.