Laboratory spray dryerThe droplet evaporation of liquid (usually water) that spray drying, heat and mass transfer process is happening at the same time, the droplet and the drying medium (air) when exposed to heat by convection by air is passed to the droplet, evaporation, air heat into heat by evaporation. Water transport into the air through the boundary layer around each droplet.

The heat and mass transfer rate is a function of temperature, humidity, air transfer characteristics around each droplet, droplet diameter, and relative velocity between droplets and air. The droplet drying process can be divided into two stages, namely the stage of constant rate of drying, and the drying phase, the actual evaporation time required for droplet and contact temperature of the air, depending on the droplet shape, chemical composition, physical structure and solid concentration. The actual evaporation time is the sum of the constant speed drying time and the drying time at which the required moisture content is reduced.