Fully developed laminar flow for a horizontal heated curved tube is studied numerically. The tube is heated so as to maintain a constant axial temperature gradient. A physical model is introduced that accounts for the combined effects of both buoyancy and centrifugal force. Results, for a Prandtl number of one, are presented for a moderate range of Dean numbers and the product of the Reynolds and Rayleigh numbers. Detailed predictions of the flow resistance, the average heat-transfer rate and the secondary-flow streamlines are given. Also presented are results on the position of the local maxima of shear stress and heat-transfer rate. The numerical results reveal that the mass-flow rate is drastically reduced owing to the secondary flow for a given axial pressure gradient. Consequently, the total heat- transfer rate decreases for a more-curved tube as well as for a larger axial temperature gradient. A flow-regime map is provided to indicate the three basic regimes where (i) centrifugal force dominates, (ii) both buoyancy and centrifugal forces are important, and (iii) buoyancy force dominates.
Experimental study of heat transfer in oscillatory gas flow inside a parallel-plate channel with imposed axial temperature gradient
