The frosting of the cold and hot shock test chamber during operation is mainly related to factors such as low temperature environment, humidity control, sealing performance, and equipment design. The following are specific reasons and analysis:

1、 Low temperature environment causes condensation of water vapor

1. The temperature in the low-temperature zone is too low
   The temperature in the low-temperature zone of the test chamber (such as -40 ℃ to -70 ℃) is much lower than the ambient temperature. When humid and hot air enters the low-temperature zone, water vapor will quickly condense into frost. For example, if the environmental humidity is 60% and the temperature is 25 ℃, and the temperature in the low-temperature zone is -50 ℃, water vapor in the air will frost due to a sudden drop in temperature.

2. Temperature fluctuations cause frosting
   The cold and hot shock test chamber simulates the environment by quickly switching between high temperature (such as 150 ℃) and low temperature (such as -55 ℃). During sudden temperature changes, water vapor in the air inside the box may condense due to local temperature unevenness, especially forming a frost layer on the surface of the low-temperature zone.

2、 Improper humidity control

1. Initial humidity too high
   If the humidity of the test sample or the air inside the box itself is high (such as water containing samples, undried air), in a low-temperature environment, the moisture will directly condense into frost. For example, when testing electronic components, if there is residual moisture on the surface of the component, it will quickly frost after entering the low-temperature zone.

2. Dehumidification system failure
   Some test chambers are equipped with dehumidification devices (such as molecular sieves and condensers). If the dehumidification system fails or has insufficient efficiency, the humidity inside the chamber cannot be effectively reduced, leading to frosting. For example, when the condenser is blocked or the refrigerant is insufficient, the dehumidification capacity decreases and the frost layer thickens.

3、 Sealing performance issues

1. The door is not tightly sealed
   The aging, deformation, or improper installation of the test box door seal can cause external humid and hot air to seep into the box. For example, when the door seal cracks or the compression is insufficient, air leakage will accelerate frosting.

2. Observation window or interface leakage
   If the sealing between the observation window glass and the frame, cable threading holes, and other parts is poor, external moisture can also be introduced. For example, when observing the aging and peeling of window sealant, humid and hot air entering the low-temperature zone will cause frost.

4、 Equipment design defects

1. Unreasonable air duct design
   If the internal air duct design of the test chamber is poor, it will result in poor air circulation in the low-temperature area, and the local temperature will be too low, which will exacerbate frosting. For example, when the air duct is blocked or the fan speed is insufficient, the air flow in the low-temperature area is slow, and water vapor is prone to condensation.

2. Improper matching of refrigeration system

• Excessive cooling capacityIf the power of the refrigeration system is too high and the temperature in the low-temperature zone is too low, exceeding the design range, it will cause frosting. For example, the cooling capacity is designed to be -70 ℃, but the actual demand is -55 ℃. If the temperature in the low-temperature zone is too low, it will accelerate frosting.

• The surface temperature of the evaporator is too lowIf the surface temperature of the evaporator is lower than the dew point temperature of the air, water vapor will directly condense into frost. For example, when the evaporator frost is too thick, it will further reduce the surface temperature, forming a vicious cycle.

5、 Improper operation and maintenance

1. Frequent opening and closing of doors
   Frequent opening and closing of doors during the experiment can cause external humid and hot air to enter the box, accelerating frosting. For example, every time the door is opened for 10 seconds, the humidity inside the box may increase by 5% -10%, and the risk of frost formation in low-temperature areas significantly increases.

2. Long term uncleaned

• Dust accumulation in evaporatorIf dust or dirt accumulates on the surface of the evaporator, it will reduce the heat exchange efficiency, resulting in low surface temperature and frosting. For example, when the evaporator accumulates 1mm of dust, the amount of frost may increase by 30%.

• Blockage of drainage pipeIf the drainage pipe is blocked, the condensed water cannot be discharged and will freeze into frost in the low temperature zone. For example, when the drainage pipe is bent or blocked, condensed water will flow back to the low-temperature area, forming frost.

6、 Solutions and preventive measures

1. Optimize humidity control

• Use a dry air source or pre dry the test sample to reduce the initial humidity.

• Regularly inspect the dehumidification system to ensure that components such as the condenser and molecular sieve are functioning properly.

2. Strengthen sealing performance

• Regularly inspect door seals, observation window sealants, etc., and replace aging components in a timely manner.

• Ensure that cable routing holes, ventilation openings, and other areas are well sealed.

3. Improve equipment design

• Optimize air duct design to ensure uniform air circulation in low-temperature areas.

• Adjust the parameters of the refrigeration system to avoid the evaporator surface temperature being too low.

4. Standardized operation and maintenance

• Reduce frequent door opening and closing, and plan the operation process before the experiment.

• Regularly clean the evaporator, drainage pipes, and other components to prevent dust accumulation or blockage.

• Use anti frost devices (such as electric heating defrosting, hot air bypass defrosting) to assist in defrosting.

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