Analysis of drying kinetics, energy and microstructural properties of turnips using a solar drying system

Abstract

This study proposes an indirect solar drying system containing a solar photovoltaic/thermal air collector, a monocrystalline silicon photovoltaic system, a drying oven and two batteries. The drying kinetics and drying quality of turnip slices obtained using the proposed solar drying equipment and via natural drying were compared and analyzed along with the energy provided and required for turnip drying using a solar dryer. The results reveal that the turnip drying time is shorter when using the solar dryer than when using natural drying. The moisture content on dry basis of the turnips decreased to 0.197 from 20.370 using the solar dryer. However, when subjected to natural drying, the moisture content on dry basis took more time to dry from a moistire content of 21.320 to 0.250. The Midilli and Kucuk model was deemed appropriate for depicting the turnip slices’ drying using solar drying equipment and via natural sunlight. Furthermore, the dried turnips obtained via natural drying and using the solar drying system exhibited the highest and lowest values of total colour difference, respectively. Following open sun drying, scanning electron microscopy revealed some obvious molds on the surface of the turnip cells, and the turnip cells were subsequently destroyed. The drying quality of turnips attained via open sun drying was severely reduced. The drying method using the solar drying equipment was thus better than natural drying, particularly in cloudy weather.