Laminar Friction Factors and Colburn Factors for Ducts with Advanced Boundary Conditions

Ducts of various geometrical cross sections appear extensively in engineering applications like heat exchangers. In the available literature analytical, numerical and experimental data are available for the friction factor and the Colburn factor for a variety of thermal boundary conditions. Results for fully developed cases are commonly available, but also for the thermally and hydrodynamically developing entrance regions. However, results are not available yet for the cases with advanced boundary conditions, i.e., having a mixture of uniform heat flux, wall temperature conditions and thermal insulation on the walls. To complicate the situation further, mass transfer may appear at one or more walls, and buoyancy effects can be significant in some applications. Such effects are presented. This paper presents recent numerical investigations and results from the authors. The origin of these advanced boundary conditions is not in the pure heat exchanger area, but rather from recent developments in the heat and mass transfer analysis in the emerging area of fuel cells. The comparison with conventional cases and the discussion of the significance of the advanced boundary conditions are believed to be of key interest to the heat exchanger community as well. The correlations as function of aspect ratio, base-angle and wall Reynolds number are included in the paper, and can be applied for design purposes.
Keyword: Friction Factor, Colburn Factor, Boundary, Heat Exchangers, Duct