Analysis of turbulent flow in channels roughened by two-dimensional ribs and three-dimensional blocks. Part II: Heat transfer

The heat-transfer characteristics of a turbulent flow in channels with two-dimensional ribs and three-dimensional blocks are investigated in the context of surface roughness effects. This Part II of a two-part paper focuses on heat transfer while Part I   was devoted to resistance. Reynolds-averaged Navier–Stokes equations, coupled with the k–ω–t2¯–εt turbulence model with near-wall treatment for velocity and temperature fields, are solved by a finite-volume method. Calculations are carried out for two-dimensional ribs with square, triangular, semicircular and wavy cross-sections over a range of rib spacing (pitch) and Reynolds numbers. It is found that heat transfer and flow resistance behave in a similar manner, with highest heat transfer occurring when the resistance is maximum. For all cases, the space-averaged temperature profile exhibits a logarithmic region, with a “heat-transfer roughness function” that varies with a constant power of the roughness Reynolds number. The constant power in the formula is found to be slightly larger than that in existing experimental correlations. Analysis of flow with three-dimensional blocks reveals similar characteristics. A log region exists in the space-averaged temperature profile for all cases for which the velocity profile has a log region.