I. Principles of Vacuum Freeze-Drying
Vacuum freeze-drying consists of three steps: pre-freezing → sublimation drying → desorption drying. Together, the three stages make the freeze-drying cycle for one batch approximately 12-24 hours.
II. Three Major Core Systems
Refrigeration System
The refrigeration system supplies cooling to both the shelves (for pre-freezing) and the water vapor trap (cold trap). The water vapor trap temperature must reach -40°C to -50°C, creating a water vapor pressure differential. The compressor uses a Hanbell RC2 series screw compressor or a Bitzer reciprocating compressor, with R404A refrigerant.
Vacuum System
The vacuum level is maintained at 10-100Pa. It uses a rotary vane pump + Roots pump combination. First, the rotary vane pump is started to evacuate to below 1kPa, then it automatically switches to the Roots pump for boosting. The vacuum pump uses the Leybold brand.
Heating Plate Temperature Control System
The shelf temperature range is -55°C to +120°C. The circulating fluid is an antifreeze solution made of water + ethanol + ethylene glycol. The shelves are a hollow aluminum profile structure, and each layer is equipped with two PT100 temperature probes.
III. Application Cases and Process Parameters
Strawberry Freeze-Drying
Pre-freezing at -30°C, sublimation at -10°C to 0°C, vacuum at 30-50Pa, time 14-16 hours. A 175m² unit processes 2000kg of fresh strawberries per batch, with a yield ratio of 8-10:1.
Mango Freeze-Drying
Eutectic point -24°C, pre-freezing -35°C, sublimation gradient curve from -8°C to +5°C, vacuum 20-40Pa, 16-18 hours. The difficulty lies in the high sugar content; it is prone to collapse in the late drying stage.
Shiitake Mushroom Freeze-Drying
Eutectic point -18°C, pre-freezing -28°C, sublimation -5°C to 10°C with slow temperature rise, vacuum 25-60Pa, about 12 hours. Yield ratio 6-8:1.
Pet Food Freeze-Drying
The pre-freezing rate must be fast (>2°C/min), the ice crystals are fine, and the texture after rehydration is closer to fresh meat. Sublimation at -5°C to 5°C, vacuum at 30-50Pa, 10-12 hours.
Functional Food Freeze-Drying
Probiotics must not exceed 30°C throughout the entire process. The protective agent formulation (sucrose, trehalose, mannitol) is as important as the freeze-drying curve.
IV. CVD Series Product Parameters
| Model | Drying Area | Loading Capacity | Power | Overall Dimensions |
|---|---|---|---|---|
| CVD-100 | 1m² | 10kg | 6kW | 2000×700×1700mm |
| CVD-1000 | 10m² | 100kg | 28kW | 3600×1700×2100mm |
| CVD-5000 | 50m² | 500kg | 184kW | 6000×2600×2900mm |
FAQs
Q1: The freeze dryer cannot reach the target vacuum level during vacuum pumping? First check the vacuum pump oil level and oil quality, then check the chamber door gasket.
Q2: The freeze-dried strawberries come out shriveled? The pre-freezing temperature is not low enough, or the pre-freezing time is insufficient.
Q3: What capacity can the cold trap handle? The water capture capacity of CVD-1000 is approximately 90-100kg/batch.
Q4: Does freeze-drying equipment need an air compressor? Yes. Pneumatic butterfly valves and pneumatic stoppering devices both require compressed air.
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