Q11-3 Observations on Mixed Turbulent Convection in Vertical Tubes

L. Huang and K. J. Farrell

2007

The interaction of forced and natural convection can be very complex because of its dependence on flow regime and flow direction. Aiding flow occurs when both driving forces act in the same direction (heating upflow fluid and cooling downflow fluid); opposing flow occurs when they act in different directions (cooling upflow fluid and heating downflow fluid). This article discusses the buoyancy effect on mixed turbulent convection for single-phase applications in vertical tubes. Using experimental data, we demonstrate that natural convection

• can greatly increase or decrease the convective heat transfer coefficient
• should not be neglected if the mixed turbulent parameter is higher than 0.05, even with Reynolds numbers higher than 10000

High resolution CFD simulations of several experimental conditions confirm the importance of the buoyancy effect on the production of turbulence kinetic energy.