1. Principle. Grain drying principle is based on the equilibrium moisture content of grain, place food in low relative humidity of the air (drying), food releases moisture and dry. But the food releases moisture slowly at room temperature. So to enhance the grain and drying temperature and lower relative humidity of drying medium, which increasing the velocity of drying medium, to accelerate the evaporation of moisture in cereals and dry. In thermal-convection drying dryer is the use of heated air (or smoke by gas) as a carrier, supply calories of food warming and evaporation and will evaporate the moisture away. That heats the air, as both heat and moisture fluid medium effects. Heat conduction, radiation or high frequency current in the dryer, that is by conduction, radiation or high frequency electric field to supply calories of food warming and evaporation, and insufflating air (heating or air) to take away the food evaporates water. The drying process is a complex process of heat and moisture transfer. Usually this process is divided into 4 phases, namely, preheating and moisture evaporation, tempering and cooling.

2. Grain dryer operating advantages and economic benefits. Drying machines the main advantages are: a timely harvest, reducing field loss, reduce labor intensity and improve labor conditions and increase the productivity. Second, we can prevent pollution from natural drying of food against food mildew. Third, reducing Sun food venue areas, improve land utilization. Four is to improve food quality, better storability and processing. Grain drying job cost accounting, and an analysis of the economic benefits and costs include depreciation charges, payment for the use of State funds and materials such as oil, electricity consumption, labor, repairs, etc. In order to facilitate the analysis, the cost is divided into operating cost and total cost. At present, the scale mechanical operation of the total cost of the food sells for about l/10. Grain drying process can achieve better economic benefits.