Turbulent mixed convection from a large, high temperature, vertical flat surface

Turbulent mixed convection heat transfer at high temperatures and large length scales is an important and seldom studied phenomenon that can represent a significant part of the overall heat transfer in applications ranging from solar central receivers to objects in fires. This work is part of a study to validate turbulence models for predicting heat transfer to or from surfaces at large temperature differences and large length scales. Here, turbulent, three-dimensional, mixed convection heat transfer in air from a large (3 m square) vertical flat surface at high temperatures is studied using two RANS turbulence models: a standard k–ε model and the v 2 ¯ – f model. Predictions for three cases spanning the range of the experiment (Siebers, D.L., Schwind, R.G., Moffat, R.F., 1982. Experimental mixed convection from a large, vertical plate in a horizontal flow. Paper MC13, vol. 3, Proc. 7th Int. Heat Transfer Conf., Munich; Siebers, D.L., 1983. Experimental mixed convection heat transfer from a large, vertical surface in a horizontal flow. PhD thesis, Stanford University) from forced ( Gr H / Re L 2 = 0.18 ) to mixed ( Gr H / Re L 2 = 3.06 ) to natural ( Gr H / Re L 2 = ∞ ) convection are compared with data. The results show a decrease in the heat transfer coefficient as Gr H / Re L 2 is increased from 0.18 to 3.06, for a free-stream velocity of 4.4 m/s. In the natural convection case, the experimental heat transfer coefficient is approximately constant in the fully turbulent region, whereas the calculated heat transfer coefficients show a slight increase with height. For the three cases studied, the calculated and experimental heat transfer coefficients agree to within 5–35% over most of the surface with the v 2 ¯ – f model results showing better agreement with the data. Calculated temperature and velocity profiles show good agreement with the data.