LAMINAR FULLY-DEVELOPED MIXED CONVECTION IN INCLINED TUBES UNIFORMLY HEATED ON THEIR OUTER SURFACE

The problem of conjugate heat transfer involving mired convection lami nar ascending flow of water in inclined circular tubes uniformly heate d on their outer surface has been studied numerically using a unified formulation for the solid and fluid domains. The highly coupled govern ing equations were discretized using the control volume approach, and solved according to the SIMPLER algorithm. Results have clearly demons trated that the conduction within the tube wall has an important influ ence on both the hydrodynamic and thermal fields. High wall thermal co nductivity or large thickness reduces the temperature stratification w ithin the fluid and intensifies the secondary motion, consisting of tw o symmetrical vortices. The effects of wall conduction are particularl y significant for horizontal tubes for which the average Nusselt numbe r is bounded by two limits corresponding to the cases of infinite wall thermal conductivity and zero wad thermal conductivity. For Gr = 2 x 10(5) these limits are 10.42 and 9.03, respectively. These effects are negligible for tubes inclined at 30 degrees and for Grashof number be low 3 x 10(4).