Development and enhancement in drying performance of a novel portable greenhouse solar dryer

Abstract

The increasing demand for drying technology for agriculture and food products has gained significant attention due to population explosion and inadequate resources available. The present study focuses on the concept of enhancing the drying performance of portable greenhouse solar dryer. The experimental investigations for evaluating the dryer performance were carried out while drying out onion slices. The experimentation was carried out in 4 different modes to demonstrate the effect of various modifications implemented to improve the dryer performance. The active greenhouse solar dryer (AGHSD) is the first working mode which comprises of the conventional drying system with active mode of removing moisture. The second working mode uses recirculating fans along with exhaust fans (AGHSD@circulating fans). In the third working mode an Evacuated Tube-type solar Air Heater was added to along with previous modification (AGHSD@circulating fans + ETAH). The last working mode adds an air flow distribution system to the incoming pre heated air from the Evacuated Tube-type solar Air Heater (AGHSD@circulating fans + ETAH + air flow system). Various performance characteristics like moisture ratio, heat utilization factor, coefficient of energy, heat gain and thermal efficiency of the dryer are used to analyze the changes in the drying performance. AGHSD@circulating fans + ETAH + air flow system reduced the moisture ratio in the onion slices to 5.32% from 95% in one day, compared to 19.99% for AGHSD and 46% for open sun drying. The heat utilization factor and coefficient of energy for AGHSD@circulating fans + ETAH + air flow system and AGHSD@circulating fans + ETAH improve by 10% and 15% respectively as compared to AGHSD. AGHSD@circulating fans + ETAH + air flow system shows improved heat gain of 29.53% and shows the best drying rate for the developed drying system. The thermal efficiency of AGHSD@circulating fans + ETAH + air flow system is around 60% while for AGHSD is around 41% which is higher than the thermal efficiency of 20% for sundried samples.