Modeling and experimental study of a triangular channel solar air heater

In this study, a pilot plant of a triangular channel solar air heater with a U-turn airflow pattern was constructed and its performance was investigated using a developed model and experimental data under different operating conditions. A new equivalent radiation-convection circuit was developed as the most sophisticated part of the model. Based on the circuit, a mathematical model with minimal simplifying assumptions was developed to predict the performance of the heater. Compared with the results of an integral model of overall energy balance equations, the developed model showed a 50% reduction of error in prediction of thermal efficiency and outlet air temperature. The maximum thermal efficiency of the system could be obtained at an air mass flow rate of 0.045 kg/s (i.e. mass flux of 8.18 kg/m(2).s). Considering the air pressure drop (as the most important penalty) and outlet air temperature, the highest thermohydraulic performance was obtained at a channel internal peak angle of 60 degrees. Besides, the results indicated that to achieve a certain thermal efficiency, the presented solar air heater requires less surface area than that of a flat plate solar air heater for the same input solar radiation.