Theoretical investigation on mixed convection inside horizontal tubes with nominally uniform heat flu

Scope and method of study. The combination of natural convection with forced convection is termed mixed convection. In this investigation, laminar mixed convection in horizontal tubes, with variable properties, uniform heat flux boundary condition, and simultaneously developing velocity and temperature profiles, has been studied theoretically. A three dimensional numerical method has been developed based on the principles of parabolic flow. Computations covered a wide range of operating conditions corresponding to recent experimental work.;Findings and conclusions. Numerical results agreed very well with experimental data. This investigation provided a useful device to explore the complex interaction of fluid flow and heat transfer in the entrance region of horizontal tubes with mixed convection. The buoyancy-induced secondary flow exerts a significant effect on the primary flow and heat transfer. By analysis of experimental data, a heat transfer correlation for engineering design was developed. A new parameter based on experimental data is used to define the boundary between the forced convection and the mixed convection regimes.