Determination of surface convective heat transfer coefficients by CFD

Heat and vapour convective surface coefficients are required in practically all heat and vapour transport calculations. In building envelope research, such coefficients are often assumed constants for a set of conditions. Heat transfer surface coefficients are often determined using empirical correlations based on measurements of different geometry and flows. Vapour transfer surface coefficients have been measured for some specific conditions, but more often, they are determined with the Chilton-Colburn analogy using known heat transfer coefficients. This analogy breaks down when radiation and sources of heat and moisture are included. Experiments have reported differences up to 300%. In this paper, the heat transfer process in the boundary layer is examined using Computational Fluid Dynamics (CFD) for laminar and turbulent air flows. The feasibility and accuracy of using CFD to calculate convective heat transfer coefficients is examined. A grid sensitivity analysis is performed for the CFD solutions, and Richardson Extrapolation is used to determine the grid independent solutions for the convective heat transfer coefficients. The coefficients are validated using empirical, semi-empirical and/or analytical solutions. CFD is found to be an accurate method of predicting heat transfer for the cases studied in this paper. For the laminar forced convection simulations the convective heat transfer coefficients differed from analytical values by ±0.5%. Results for the turbulent forced convection cases had good agreement with universal law-of-the-wall theory and with correlations from literature. Wall functions used to describe boundary layer heat transfer for the turbulent cases are found to be inaccurate for thermally developing regions.