Modeling of Flat Plate Solar Air Heater with Ribbed Surfaces

In this study the design and operation of a solar air heater with repeated ribs was investigated. A thermal model for a flat plate solar air heater developed to predict the thermal performance. In constant solar heat gain, the amount of extractable energy estimated by considering heat balance in the solar air heater. Convective heat transfer coefficients inside and outside the heater channel must be known to determine wasted and useful heat. Outside the heater channel, heat transfer coefficient is nearly constant. On the other hand, heat transfer coefficient inside the channel is a function of surface type and the air velocity. The heat transfer coefficients were extracted from available experimental data. Numerical simulation conducted as well to validate the experimental data. Thermal performances of solar air heater with smooth and ribbed surface were compared. Repeated ribs considered with e/d = ۰.۰۳۶ and p/e = ۱۰. Air velocity range was between ۲ to ۱۰ m/s. In addition, the effect of insulation was studied. In a given solar air heater, operating at the designed conditions, up to ۶۰% of the solar energy could be converted into useful heat. Operation of solar air heater outside the design range decreases the thermal efficiency, in severe cases the heater even can waste more energy to the ambient compared to the absorbed energy. It was found that application of ribs with mentioned specification could improve the thermal performance by more than ۵%.

کلیدواژه ها:

Solar energy ، solar air heater ، repeated ribs.