Contact adsorption vacuum freeze-drying
  Contact on an inert adsorbent adsorption drying principles can be applied reduced pressure . Because the evaporation rate of freeze-dried depends on the material surface and the partial pressure of water vapor condensation surface , and other factors , a lower mass transfer resistance is to reduce the possibility of condensation of water vapor distillation zone and the distance between the layers . This - Points can be used directly with inert absorbent material surface contact is achieved , which not only reduces the water vapor diffusion path length , but also increases the surface area of heat and mass transfer . In this case , A- type zeolite adsorbent is more suitable than others , because they are high in moisture content under reduced pressure , in fact, does not change with temperature .
    Freeze- drying the material surface depends on the strength of water vapor and air mixture of the partial pressure of water vapor in the gas and to remove water vapor intensity. The freezing of the solid adsorbent material surface in direct contact , as is the role of coagulation . Adsorbent layer lyophilized curve. Obviously, the hierarchical structure to improve freeze drying rate up to 4 times .
    In general , the release kinetics of the adsorption heat from the adverse effects of the process , the amount of adsorbent decreases. Even if the zeolite caA, 133.3Pa under pressure , the adsorbent increased from 20 ℃ to 80 ℃ adsorption capacity will result in a decrease of approximately 35% F 40% . However, the heat of adsorption can be used to strengthen contacts suck cold Chen drying process without additional energy consumption. For this purpose , first a method to collect the absorbent design released during the adsorption heat , followed by freeze- drying in the absorbent direct this part of the wet material heat transfer junction . A metal with high thermal conductivity ( copper or aluminum) comb structure , placed in the dry material and the adsorbent layer. With no place to collect and transfer the heat of adsorption element compared to vacuum freeze-drying , this method of freeze-dried granular baker's yeast experiments confirmed : Materials and adsorbent ( zeolite ) Double contact , the zeolite adsorption capacity increased by 9 % and the thermal requirements decline 7.9-8.5kj/kg water , dehydrated rates are almost 50% higher .