Four ring food vacuum freeze-drying machineThe working principle is based on the heat and mass transfer mechanism under low temperature and low pressure. Through three stages of freezing, sublimation, and decomposition, the moisture in food is directly converted from solid to gas, thereby achieving drying. The following is a detailed explanation of its core working principle:
1、 Pre freezing stage: Freeze water and fix the form
Purpose: Freeze free water in food into solid ice to prevent product foaming, shrinkage, or solute movement caused by water evaporation during subsequent drying processes, ensuring that the product shape after drying is consistent with before drying.
Operation:
The food is placed on the shelf of the freeze dryer, and the temperature drops below the eutectic point (the eutectic point of different foods varies and needs to be determined through experiments).
The pre freezing temperature is usually 5-10 ℃ lower than the eutectic point and maintained for about 2 hours to ensure complete freezing of moisture.
Key points:
The pre freezing rate affects the size of ice crystals: rapid freezing produces small ice crystals, which dissolve quickly but sublime slowly after drying; Slow freezing produces coarse ice crystals, which sublime quickly but dissolve slowly.
The appropriate pre freezing rate should be selected based on the characteristics of the food to balance drying efficiency and product quality.
2、 Sublimation drying stage: Ice directly sublimates into water vapor
Purpose: To directly sublime solid ice into water vapor in a vacuum environment, and collect it through condensation in a cold trap to achieve water removal.
Operation:
Start the vacuum pump and reduce the pressure in the freeze-drying chamber to 13-130Pa (adjusted according to the characteristics of the food).
Shelf heating provides the necessary heat for sublimation, causing ice crystals to gradually sublime from the outer surface inward.
Water vapor diffuses through the drying layer to the cold trap and condenses into ice.
Key points:
Temperature control:
The temperature of the frozen part should be lower than the melting point to prevent melting.
The temperature of the dry part should be lower than the disintegration temperature (to avoid product collapse or burning).
Pressure control:
The four ring freeze dryer adopts a precise pressure control method without aeration, with pressure fluctuations controlled within ± 1Pa to avoid material oxidation and pollution.
Traditional equipment usually uses the aeration method, with pressure fluctuations of ± 5-7 Pa, which may affect product quality.
Sublimation rate:
Affected by factors such as shelf temperature, product thickness, and thermal conductivity of the drying layer.
The four ring equipment achieves efficient sublimation by optimizing hardware configuration (such as high transparency aviation acrylic doors, intermediate medium circulation technology) and intelligent control system (PLC+PID algorithm).
3、 Analysis of Drying Stage: Removing Residual Moisture
Purpose: To remove unfrozen water adsorbed on the capillary wall and polar groups after the first stage of drying, in order to prevent microbial growth and chemical reactions.
Operation:
Raise the shelf temperature (usually to 30-50 ℃) to further reduce the system pressure.
Residual moisture is transferred to the surface through diffusion and sublimates, and is captured by the cold trap.
Key points:
Temperature and time must be strictly controlled to avoid overheating or collapse of the product.
Four ring food vacuum freeze-drying machineBy monitoring and recording parameters such as vacuum degree and cold trap temperature in real time, ensure thorough drying analysis.