Geometry effects on conjugate natural convection heat transfer in vertical eccentric annuli

Purpose - To explore the effect of the annulus geometrical parameters on the induced flow rate and the heat transfer under the conjugate (combined conduction and free convection) thermal boundary conditions with one cylinder heated isothermally while the other cylinder is kept at the inlet fluid temperature. Design/methodology/approach - A finite-difference algorithm has been developed to solve the bipolar boundary-layer equations for the conjugate laminar free convection heat transfer in vertical eccentric annuli. Findings - Numerical results are presented for a fluid of Prandtl number, Pr=0.7 in eccentric annuli. The geometry parameters of NR₂ and E (the fluid-annulus radius ratio and the eccentricity, respectively) have considerable effects on the results. Practical implications - Applications of the obtained results can be of value in the heat-exchanger industry, in cooling of underground electric cables, and in cooling small vertical electric motors and generators. Originality/value - The paper presents results that are not available in the literature for the problem of conjugate laminar free convection in open-ended vertical eccentric annular channels. Geometry effects having been investigated by considering fluid annuli having radii ratios NR₂=0.1 and 0.3, 0.5 and 0.7 and four values of the eccentricity E=0.1, 0.3, 0.5 and 0.7. Moreover, practical ranges of the solid-fluid conductivity ratio (KR) and the wall thicknesses that are commonly available in pipe standards have been investigated. Such results are very much needed for design purposes of heat transfer equipment.