Comparative performance study of different types of solar dryers towards sustainable agriculture

Solar drying is becoming a popular option to replace mechanical dryers due to the high cost of energy, and the increased awareness of consumer orientation to clean energy products. In this study, three different low-cost solar dryers, viz. natural convection dryer (NCD), forced convection dryer (FCD), and heat pump integrated dryer (HPD) were examined, and thin-layer mushroom (agaricus bisporus) drying experiments were carried out on each. In this study, three main topics were determined: (i) to analyse the drying characteristics of mushroom slices in different thicknesses, (ii) to determine the effect of pretreatment on the drying time, (iii) to compare the collector efficiencies. For these purposes, 12 experiments were conducted between 9:00–18:00, the average daily solar irradiance was around 790 W/m2. In 10 drying experiments out of 12, it was observed that the samples were completely dried out within the experiment period, while the drying process of the half-cut mushrooms in NCD and FCD were completed after 18:00. The results show that cutting thin slices reduced the drying time by an average of 40.83 mins. Also, the process of pretreatment caused shorter drying time by an average of 26.66 mins, almost 7% in all cases. The average thermal efficiencies were found 59.74%, 67.66%, and 77.45% for NCD, FCD and HPD, respectively. According to these results, the most affecting factor in overall drying process is found to be drying air which is hot and holds less moisture. In addition, it turned out that the drying rate increases with the increase of the temperature and speed of the drying air