Description of temperature and humidity control of constant temperature and humidity test chamber

1. When the temperature is too high or too low, the humidity is not easy to adjust. For example, if the temperature is below 0 degrees, the water becomes ice, and there is basically no way to control the corresponding humidity with any device. It is relatively difficult to control the low temperature and humidity of the constant temperature and humidity test chamber. At this time, the low humidity must be dehumidified by dehumidifying the air in the chamber to make the air dry.

2. The principle of cooling and dehumidification is to add a set of refrigeration pipes in the air preconditioning room of the cabinet. When the humid air passes through the refrigeration pipes, the relative humidity will reach 100%RH, and the refrigeration pipes will condense, making the air drier. . This dehumidification method can theoretically reach a dew point temperature below zero, but when the surface temperature reaches 0°C, the water droplets on the surface of the refrigeration tube will freeze, which will affect the heat exchange and reduce the dehumidification capacity. The box body cannot be completely sealed, and the humid air in the atmosphere will penetrate into the chamber body, causing the dew point temperature to rise.

3. On the other hand, the flowing moist air only reaches the saturation state at the moment of contact with the cold pipe, thereby generating water vapor. This kind of dehumidification method is difficult to make the dew point temperature in the chamber below 0 °C, the lowest dew point actually reached The temperature is 5~7°C, the dew point temperature of 5°C is equivalent to the absolute moisture content of 0.0055gkg, and the temperature corresponding to the relative humidity of 20% RH is 30°C.

4. If the required temperature is 20°C, the relative humidity reaches 20%RH, and the dew point temperature at this time is -3°C. Dehumidification is very difficult, because the relative humidity of the constant temperature and humidity chamber is directly related to the temperature. The absolute humidity content, the higher the temperature, the lower the relative humidity. For example, the absolute humidity content is 6gkg, when the temperature is 30°C, the relative humidity is 20%RH, and when the temperature is 7°C, the relative humidity is 90 %RH, when the temperature drops below 5°C and the relative humidity exceeds 100%, condensation will appear in the cabinet.