Abstract
Food is necessity for human being. As the world population is increasing, it is very difficult to fulfil everyone's need of food. One of the alternatives of this problem is the preservation of crops, vegetable and fruits when it is available in abundant amount. Drying is one of the best methods to preserve agricultural products for long time but it requires lot of energy. As availability of electricity per capita in developing and under developed countries is very less, thus the electricity uses for heating purpose cannot be economically and environmentally justified option. So entrapment of thermal energy from solar radiation may be the best option for drying. Solar energy can be utilized for drying in different ways namely open sun drying and closed drying (direct and indirect). Open sun drying have various disadvantages like contamination of dust particles, bacteria in crop, decolouration of the product after drying etc. To overcome these problems greenhouse drying or closed drying has been developed. This review is an attempt to explore different types of drying systems was developed across the world. Further different thermal modelling, mathematical modelling and performance evaluation on the basis of characteristic curve have been discussed. One of the thermal modelling has been discussed in detail to evaluate heat transfer coefficient, heat absorbed and moisture evaporate with experimental validation to give practical exposure to the researchers. (C) 2016 Elsevier Ltd. All rights reserved.