Improvement of the efficiency of a bare solar collector by means of turbulence promoters

A steady-state mathematical model was developed for a bare collector. Results obtained by Sparrow and Tao (Sparrow, E. M. & Tao, W. Q. Enhanced heat transfer in a flat rectangular duct with streamwise-periodic disturbances at one principal wall. J. Heat Transfer, 105 (1983) 851.) for heat transfer and friction in rectangular ducts with periodic disturbances were employed for evaluating the incidence of such disturbances on bare collector efficiency and on its pressure drop. An effective efficiency, which takes into account extra heat obtained, and additional mechanical (electric) energy consumption for moving air when heat-transfer augmentation devices are employed, was defined. Simulation results are given for a bare collector, with and without perturbations, showing efficiency and effective efficiency dependence on collector dimensions, solar radiation intensity, disturbance diameter and pitch, for collector performance optimization.