Experimental Performance of Solar Air Heaters for Drying Applications

This paper presents the results of an experimental investigation on an indirect active type of solar dryer, using two distinct solar air collector and their impacts on drying agricultural products. The thermal performance of the proposed collectors has been evaluated using the first and second laws of thermodynamics. Experimental observations were done in climatic conditions Gödöllő, Hungary on the 2nd and 9th of October 2017. The experiments were also carried out to dry 2 kg of sliced apples spread over the drying trays. The mas flow rate of air was maintained as 0.038 kg/s and the dryer was operated from 10:00 a.m. to 3:00 p.m. When a double-pass solar air collector's results are compared to a single-pass solar air collector's, it's evident that the double-pass solar air collector produces much more energy and efficiency. The experimental results showed that single-pass and double-pass collectors have daily efficiencies of 42.77% and 56.10%, respectively, with average exergy efficiency values ranging from 31% to 49% for single-pass and 51% to 67% for double-pass. The most significant aspect determining the collectors' thermal efficiency was the temperature rise between the collector outlet and inlet. The average drying efficiencies of the solar dryer for the single and double-pass collectors were evaluated as 12.16% and 16.45%, respectively. The maximum temperature rise for double-pass was determined to be 20 °C, whereas single-pass was found to be 6.5 °C. Furthermore, the highest drying rate was achieved when sliced apples were dried with a double-pass collector mode. It reduced 52% of the water content in the apple in the same amount of time as single-pass drying, compared to 35% in the case of single-pass drying.

Performance Evaluation of Solar Air Collector by Chimney Effect for Drying Applications

Solar air collector is one of the main components of a solar dryer unit, which supplies the conditioned air for processing the perishable edible items. Various techniques have been employed to improve the thermal efficiency of the collector system, such as extended surfaces, packed beds, artificial roughness, etc., however, the cost of construction is higher. Therefore, this study was focussed on the collector efficiency enhancement using a chimney without applying the aforementioned. A single-pass solar air collector coupled with drying chamber and chimney was utilized for the experiments. The experiments were conducted in September. The average values of the solar radiation intensity, ambient temperature, temperatures inside the dryer, collector efficiency were graphically presented. The experimental data reported the maximum values of the outlet temperatures for the solar air collector with and without a chimney to be 52.8 °C and 57 °C, respectively. The collector thermal efficiency with and without the chimney was found to vary from 29.6% to 64.8% and from 26.9% to 44.8%, respectively. Furthermore, it was noticed that, with the chimney, the temperature inside the dryer showed uniform tendency.

Experimental Investigation on Effect of Inclination Angle of a Flat Plate Solar Air Collector

This study investigates the effect of inclination angle of a flat plate solar air collector in Kampar, Malaysia. Flat plate solar air collectors have been investigated since the early 1950s for air heating and crop drying. Their performances under natural convection air cooling are very similar to a photovoltaic (PV) panels for power production. A PV panel becomes hot when operating under hot weather which will affect the efficiency and lifespan. The panel could be cooled down by providing an air duct underneath which allowing natural convection air circulating inside the duct. The degree of cooling would depend upon the angle of inclination of the panel. This paper presents some experimental results on the effect of inclination angle on the performance of a flat plate solar air collector under natural convection air cooling.