The working principle is shown as follows.The materials in the hopper are uniformly distributed on the mesh-belt by the batch charger. The mesh-belt generally adopts 12-60 meshes stainless steel mesh and it is drawn by a transmission device and move into the dryer . The dryer is composed of several sections. For each section, the hot air is circulated separately. Part of exhausted gas is exhausted by a special moisture elimination blower. In the cocycle unit, air from the recycle blower (5) comes down to the lower cavity through side air passage, air flows upwards through heat interchanger (4) then is heated. After it is distributed by distribution device（3）, it blows to the mesh-belt in the form of spraying jet and goes into the upper cavity. The drying process is the one that is finished for heat and mass transfer by the hot airflow through the material layer. The upper cavity is joined to the air inlet of blower with the wind pipe. Part of gas fluid circulates but part of low temperature and higher humidity content gas fluid is discharged as exhaust gas through humidity-discharging pipe, adjusting valve and humidity-discharging blower. In the lower recycle unit, the wind from the recycle gas blower goes into the upper cavity first. It goes down and is heated by the heat interchanger then through the lower cavity of material layer. The lower cavity is joined to the air inlet of blower with side air passage and return airway. Most of gas fluid circulates but part is discharged. The upper and lower units can be furnished at will according to the needs of users. The unit quantity can also be chosen according to the need。
Generally, three sets of equipment are used in series for evaporate vegetables. Part discharges and forms incipient drying stage, middle stage and final drying stage. At the incipient drying stage, since the material contains high water content and poor ventilation property, the small thickness of material laying, quicker operating speed and higher drying temperature are adopted. The drying temperature comes above 120 degrees centigrade at incipient drying stage. The detention time of material at final drying stage is 3 to 6 times as much as that at incipient drying stage and the height of material laying at final drying stage is 2 to 4 times as much as that at incipient drying stage.The drying gas fluid at the temperature of 80 degrees can be used for the material whose temperature is not required above 60 degrees. The multi-stage combination can make full use of the performance of mesh-belt drier and makes drying uniform。