Drying characteristics of lemons and dates under indirect type forced convection solar drying and natural open sun drying

An indirect type forced convection solar dryer unit was designed and built at the College of Engineering, Sultan Qaboos University (SQU) in Muscat (Oman). The unit consists of a solar air heater (i.e., solar collector with corrugations) and a cabinet acting as a drying chamber (i.e., basically a batch dryer). It was manufactured with locally available materials and can be used for drying various agricultural products like fruits and vegetables. In this study, the solar dryer was tested under controlled conditions for drying lemons and dates as the test samples. The dryer unit was investigated experimentally and its performance was evaluated under the climatic conditions of Oman (21° 00 N, 57° 00 E). For comparison purposes, natural traditional sun drying experiments (i.e., solar dryer under open sun with natural convection) was also conducted at the same time. For this effect, the results of drying under the open sun and indirect type forced convection solar drying was drawn under identical weather conditions during summer conditions in June, 2009. The performance of the solar dryers was computed and expressed in terms of the moisture evaporation (crop mass during drying). It was found that the quality of lemons and dates after drying was better and drying time was less in the indirect type forced convection solar dryer in comparison to open sun drying. It is hoped that this study may be useful for further development work.