Turbulent heat transfer in spacer-filled channels: Experimental and computational study and selection of turbulence models

Heat transfer in spacer-filled channels of the kind used in Membrane Distillation was studied in the Reynolds number range 100-2000, encompassing both steady laminar and early-turbulent flow conditions. Experimental data, including distributions of the local heat transfer coefficient h, were obtained by Liquid Crystal Thermography and Digital Image Processing. Alternative turbulence models, both of first order (k-epsilon, RNG k-epsilon, BSL k-omega, SST k-omega) and of second order (LRR RS, SSG RS, omega RS, BSL RS), were tested for their ability to predict measured distributions and mean values of h. The best agreement with the experimental results was provided by first-order omega-based models able to resolve the viscous/conductive sublayer, while all other models, and particularly epsilon-based models using wall functions, yielded disappointing predictions.