Design and analysis of new solar-powered sustainable dryers: Alfalfa crop

Abstract

Decreasing carbon emissions is possible with the usage of renewable energy sources. Therefore, the usage of renewable energy has increased in the last decade. Due to the fact that the drying process of agricultural products consumes a significant amount of energy, fossil fuel consumption can be reduced by using the solar dryer. In this study, two novel solar drying systems were designed and tested for alfalfa drying. Experiments were carried out in two different drying systems double-pass solar air collector (DPSAC) and photovoltaic thermal solar air collector (PVT). In order to increase the heat transfer surface area, unlike the literature, a drying chamber consisting of two intertwined cylinders was designed and manufactured. The aims of this study are to bring the drying kinetics of alfalfa and the performance, energy, and exergy analysis of the designed system to the literature. The effective moisture diffusivity values were found to be in the range of 9.13 × 10−14 to 1.06 × 10−9 and the value for the highest drying rate was determined as 2.53 × 10−2gwater/gdrymatter.min. The highest thermal efficiency was obtained from DPSAC experiment as 73.7%, while the highest COP value was obtained from the PVT experiment as 12.5. The DPSAC dryer has shown the best performance in drying the alfalfa. The outcomes of the present study demonstrate that the use of DPSAC dryer is suitable when only heat energy is required for the drying system and the use of PVT when both heat and electrical energy are required. It is recommended that these systems can be used together in off-grid agricultural areas. Practical applications: Alfalfa (Medicago sativa L.), a type of forage crop, is a delicious, high-energy, and protein food source for dairy cattle. By drying the alfalfa with high nutritional value in a quality method, several beneficial minerals and vitamins are preserved. The drying process is used since ancient times for the protection of the food material and for storage without degradation. Alfalfa is dried in two new solar-powered sustainable dryers making an important contribution to reducing carbon emissions as well as providing cleaner and more reliable drying methods compared to the conventional solar drying method. This study presents an alternative for the drying process with high energy efficiency for food drying processes, according to the necessity of using both heat and electrical energy. In addition, sustainable solar dryers in this study can be used for drying agricultural products, textile, industry and dewatering municipal waste.