Standard for moisture content at outlet of cold dry dryers

The export moisture content standards of cold-dry dryers (freeze dryers) vary depending on the application fields. The following are the specific standards and related explanations:

1. The field of compressed air drying

1. Pressure dew point standard：
   • Ministry of Machinery Standards: According to JB/JQ209010 -88 “Technical Conditions for Compressed Air Freeze Dryers”, the “pressure dew point” of the cold dryer should be controlled atbelow 10 deg C。
   • National recommended standard: GB/T12919-91 “Marine Controlled Air Source Purification Device” requires the atmospheric pressure dew point of the cold dryer as follows-17℃ to-25℃, equivalent to extremely low water content under a pressure of 0.7MPa.
   • Actual operating standards: Under good working conditions, the cold drying machine can achievePressure dew point around 5℃, the pressure dew point range marked on some equipment is2℃ to 10℃。
2. Water content conversion：
   • At a pressure of 0.7MPa:
     • 2℃ pressure dew point: Moisture content is approximately0.82g/m³, equivalent to about water vapor content1024ppmv。
     • 10℃ pressure dew point: Moisture content is approximately1.48g/m³, equivalent to about water vapor content7537ppmv。

2. Food freeze-drying field

1. moisture content standard：
   • fruit and vegetable products: Moisture content should be ≤4g/100g。
   • Instant rice noodles, instant soup, etc.: Moisture content should be ≤6g/100g。
   • general requirements: After the main drying of the lyophilizer is completed, the water content of the product is5% or so, extending the drying time can reduce3% or less。

3. Relationship between water content and pressure dew point

• conversion formula：
  • atmospheric dew pointCalculation formula:Td​=b−ln(RH/100)a⋅ln(RH/100)​
  • Conversion of pressure dew point and atmospheric dew point：Td1​=Td2​+k(P1​−P2​)​
  • Conversion of ppm to mg/m³：1ppmH2​O≈0.75mg/m3H2​O(Conditions: 20℃, standard atmospheric pressure).

4. Key factors affecting moisture content

1. equipment performance：
   • Refrigeration system efficiency: The working status of the compressor and refrigerant leakage directly affect the cooling effect.
   • thermal conditions is: Ensure the distance between the fan surface of the cold dryer and the wall surfacemore than 1 meter, clean the radiator dust regularly.
   • gas-water separator efficiency: Insufficient separation efficiency may cause a small amount of condensed water to be reduced to water vapor.
2. operating parameters：
   • drying temperature: Rising temperature may increase the moisture content of the air, so the intake air temperature needs to be controlled.
   • drying time: Prolonged drying time can reduce moisture content, but need to balance efficiency and cost.
   • working pressure: Pressure changes will affect saturated water content, and parameters need to be adjusted according to pressure.
3. environmental conditions：
   • Temperature and humidity of inlet compressed air: The higher the humidity, the greater the load on the cold dryer, requiring pre-filtration and dehumidification.

5. Equipment selection and maintenance suggestions

1. selection：
   • Select a matching model of cold drying machine according to the air compressor gas production to avoid insufficient processing capacity.
   • Priority is given to equipment with high energy efficiency and well-known brand compressors.
2. maintenance：
   • Regular drainage: Check the function of the electronic drain to prevent condensation from accumulating.
   • Monitor refrigerant: Regularly check refrigerant leaks to ensure efficient operation of the refrigeration system.
   • cleaning device: Regularly clean the radiator dust to ensure the heat dissipation effect.

summary

The outlet moisture content standard for cold dry dryers varies depending on the application field:

• compressed air drying: Focus on pressure dew point (2℃ to 10℃), with extremely low moisture content.
• Food freeze-drying: Directly control the moisture content (≤3% to 6%) and extend the drying time.

Through reasonable type selection, optimization of operating parameters and regular maintenance, it is possible to ensure that the moisture content meets the standard requirements.