Performance improvement of flat plate solar collectors for fruits drying

The use of indirect solar dryer in preserving fruits and vegetables is one of the upcoming technologies in preserving agriculture products. Low performances of solar collectors and high investment costs have been one of the factors that limit the adaptation of solar dryers in Tanzania. This study investigated possible ways to improve the performance of flat plate solar collectors. Several techniques for modifications of traditional solar collector including the effect of varying glass thicknesses, heat transfer enhancements by using baffles and wire meshes, air flow pattern and different types of absorbing materials were addressed. Four flat plate solar collector models were constructed and tilted to an angle of 10° with the ground to avoid buildup of rain water. Results showed that, appropriate collector orientation, good material selection and suitable length to width ratio may improve collector efficiency to 30% compared to less than 25% reported in many projects. By employing double duct counter flow the efficiency was increased by 9.6% while increase of 8% and 7.2% were observed when parking collector with charcoal and wire mesh respectively. Similarly, collector with 4 mm glass thickness and with 8 baffles gave efficiency rise of 6.1% and 5.2% respectively. The study had made an important contribution to solar drying technology based on the solar collector design by providing different mechanisms of improving heat transfer in the collector as well as performances of various recommended absorbing materials. However, collector modification may result to increase in pressure drop, hence this should be considered during selection of appropriate techniques.