Experimental and CFD investigation of a hybrid solar air heater

Solar air heaters may be used in a variety of applications such as space heating, pre-heating for industrial applications, drying of various materials and pre-heating for solar water desalinators. This research is aimed at evaluating a unique solar air heater design in terms of its thermal efficiency and temperature distributions within the solar air heater. The solar heater is unique as it combines parallel- and counter flows inside the heater in order to reduce mass and improve overall heat transfer. Current modelling techniques are not suitable to this type of SAH, as they apply to SAHs with simpler geometries, like counterflow heaters or parallel flow heaters. The solar air heater is evaluated using computational fluid dynamics and experiment. The computational models are validated experimentally. The computational models account for the solar load, surface to surface radiation, conduction, convection and turbulence. A screening of turbulence models is performed. The average conversion efficiency ranges between 23% and 83% and the average collector efficiency between 11% and 44%. The thermal efficiency values predicted by the computational models show good agreement with the experimentally derived values. The computational models over-predict the thermal efficiency by between 6.75% and 9.01% of the measured quantity, depending on the solar radiative power input used. The model predictions of temperatures show good qualitative agreement with the measured temperatures but do not compare well quantitatively for all points of comparison. The average error between predicted temperature and experimental results for the various points of comparison is 9.165 K.