Drying is an excellent way to preserve food and solar food dryers are an appropriate food preservation technology for a sustainable world. Drying preserves foods by removing enough moisture from food to prevent decay and spoilage. Water content of properly dried food varies from 5 to 25 percent depending on the food. The drying of product depends on external variables like temperature, humidity and velocity of air stream and internal variables which is a function of drying material and depends on parameters like surface characteristics (rough or smooth surface), Chemical composition (sugar, starch, etc.), physical structure (porosity, density, etc.) and size and shape of the product. The rate of moisture movement from the product inside to the air outside differ from one product to another and very much depends weather the material is hygroscopic or non-hygroscopic. Non-hygroscopic materials can be dried to zero moisture level while the hygroscopic materials like most of the food products will always have residual moisture content. The solar dryer considered in this paper is the Distributed Passive Solar Dryer (DPSD) or Hybrid Dryer (HD). The product is located on trays or shelves inside an opaque drying chamber. Solar radiation is thus not incident directly on the products. Preheated air warmed during its flow through a low-pressure thermos phonic solar energy air heater, is ducted to the drying chamber to dry the product. Because the products are not subjected to direct sunshine, localized heat damage, do not occur. A typical Distributed Passive Solar Energy Dryer consist a drying chamber, an air-heating solar energy collector and turbo ventilator.
Solar energy, solar collector, turbo ventilator
