Abstract, International Journal of Research Studies in Science, Engineering and Technology [IJRSSET], 2014 June
This paper presents an overview of moisture removal mechanisms used for the dehumidification of drying chambers in small-scale drying equipment. These mechanisms are based on the existence temperature gradient or pressure gradient between the entry and the exit of the drying chamber. Dryer design based on those physical effects without using pump or fan lead to natural air circulation and depend on weather conditions. They require too long time to get crops dried due to the fact that the buoyancy forces are not strong enough to dehumidify rapidly the drying chamber. Dryers using motorized fans to force air circulation rely on pressure gradient between the entry and the exit of the drying chamber. Their main limitation is that drying air renewal depends on drying air temperature regardless of its moisture content. In all cases, the geometry of most drying chambers is not properly designed in order to ease the removal of humid air. Important losses are recorded during drying because crops stay in a humid environment for too much time. That problem is more critical in humid tropical zones where ambient air and crops are both high moisture content.
Keywords: Moisture, small-scale dryers, pressure gradient, temperature gradient, natural convection, forced convection.