Combined convection heat transfer in an inclined (ψ=60o) and vertical (ψ=90o) annulus has been experimentally studied for opposing thermally developing and thermally fully developed laminar air flows with adiabatic inner tube and uniformly heated outer tube (r1/r2=0.41) for Reynolds number range from 450 to 1000 and heat flux is varied from 150 W/m2 to 780 W/m2. The hydrodynamically developed condition has been achieved by using entrance section annular pipe (calming section) having the same

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... ensions as test section (L/Dh≈40). The mixed convection regime has been bounded by the convenient selection of Re and heat flux ranges, so that the obtained Richardson number varied approximately from 0.05 to 0.97. The average heat transfer results have been correlated with an empirical correlation by dimensionless groups as logNum against logRa/Re and compared with available literature showed that the heat transfer process in the hydrodynamically fully developed region of duct is better than that in the developing region of this duct.