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It is worth noting that the corresponding temperature range should be indicated after the humidity indicator, or the low dew point temperature of zui should be given. Because the relative humidity is directly related to the temperature, for the same absolute moisture content, the higher the temperature, the smaller the relative humidity, such as the absolute moisture content of 5g / Kg (refers to 5 grams of water vapor in 1 kg of dry air) ), when the temperature is 29 ° C, the relative humidity is 20% RH, the temperature is 6 ° C, the relative humidity is 90% RH, when the temperature drops below 4 ° C, the relative humidity exceeds 100%, condensation will appear in the box phenomenon. To achieve high temperature and high humidity, it is only necessary to spray water vapor or atomized water droplets into the air of the cabinet to humidify.
Low temperature and low humidity are relatively difficult to control because the absolute moisture content at this time is very low, and sometimes it is much lower than the absolute moisture content in the atmosphere. It is necessary to dehumidify the air flowing in the tank to make the air dry. At present, most of the temperature and humidity chambers at home and abroad use the principle of refrigeration and dehumidification. A set of cooling tubes is added to the air pre-conditioning room of the cabinet. When the humid air passes through the cold pipe, its relative humidity will reach 100% RH, and the air will become drier due to air saturation on the light pipe.
This dehumidification method can theoretically reach a dew point temperature below zero, but when the surface temperature of the cold spot reaches 0 ° C, the water droplets on the surface of the light pipe will freeze, thereby affecting the heat exchange on the surface of the light pipe, and the dehumidification ability is lowered. And because the box can not be absolutely sealed, the humid air in the atmosphere will penetrate into the box, so that the dew point temperature will rise. On the other hand, the humid air flowing between the light pipes is saturated with water at the moment of contact with the light pipe (cold spot), so that the dehumidification method is difficult to make the dew point temperature in the case below 0 °C.
The actual zui low dew point temperature is 5 to 7 °C. The dew point temperature of 5 ° C corresponds to an absolute moisture content of 0.0055 g/Kg, and the temperature corresponding to a relative humidity of 20% RH is 30 °C. If the required temperature is 20 ° C and the relative humidity reaches 20% RH, the dew point temperature is -3 ° C at this time. It is very difficult to dehumidify by means of cooling, and it must be achieved by using an air drying system.
Selection of humidity range for temperature and humidity test chamber
The humidity indicators given by the environmental test chambers at home and abroad are mostly 20-98% RH or 30-98% RH. If the damp heat test chamber does not have a dehumidification system, the humidity range is 60-98%. This type of test chamber can only be high. Wet test, but its price is much lower.