GEOMETRY EFFECTS ON CRITICAL CONDUCTIVITY RATIO AND WALL THICKNESS FOR CONJUGATE NATURAL CONVECTION IN ECCENTRIC ANNULI

Conjugate laminar free convection heat transfer in vertical eccentric annuli is numerically investigated using finite difference technique. Numerical results are presented for a fluid of Prandtl number 0.7. The effects of eccentricity on the critical values of conductivity ratio above which and wall thickness below which the conjugate effect can be neglected are presented for the thermal boundary condition of heating one wall isothermally while keeping the other wall at inlet fluid temperature. The analysis is conducted with the eccentricity values 0.1, 0.3, 0.5, and 0.7. Six values of solid-fluid thermal conductivity ratio (KR=1, 5, 10, 50, 100, 1000) and 5 values of the inner and outer cylinder wall thicknesses (Iwall and Owall=0.001 and 0.002, 0.01 and 0.02, 0.05 and 0.1, 0.1 and 0.2, 0.2 and 0.4) are used. The values of solid-fluid thermal conductivity ratio cover the practical range for cases with commonly encountered inner and outer wall thicknesses. The analysis showed that conjugate effect can be increased or decreased by the controlling the geometry parameter, namely eccentricity.