The drying conditions are the flow velocity, humidity and temperature of the drying medium (usually hot air).

When the hot air from the stable surface through the wet material, because the air temperature is high, the material temperature is low, so there is a heat transfer between air and material force, air heat transfer to the material in a convection mode, the material received the heat to the water evaporation, water is continuously flow away. The moisture content of the material decreases, when the moisture content of the material down to the balance of water, the end of the drying process.