Experimental study of natural convection in an annulus between two eccentric horizontal square ducts

Free convection in an open-ended horizontal eccentric annulus between two eccentric horizontal square ducts with different eccentricities has been experimentally studied with several heat fluxes. Constant heat flux for outer duct and insulated inner square rod boundary conditions were used. The wall temperature of the outer duct was measured along the length for different eccentricities. The eccentricity ratio was changed (E = −1, −0.5, 0, 0.5, 1) in both upper (negative eccentricity) and lower direction (positive eccentricity). Results indicate that with the increase of eccentricity in both directions, the convection heat transfer coefficient decreases. Also, the lower heat transfer rate is found to be at the middle section between both ends led to maximum surface temperature. The generated Rayleigh number due to the heat flux was changed from 4 × 105 to 2.9 × 106. Empirical relations are derived from the average Nusselt number as a function of the Rayleigh number and the eccentricity ratio.