Talking about the difference between humidification and dehumidification in constant temperature and humidity test chamber
Constant temperature and humidity test chamber In order to achieve the test conditions, it is inevitable to humidify and dehumidify the test chamber. Here, various methods are used in the constant temperature and humidity test chamber to analyze their advantages and disadvantages. And recommended conditions.
There are many methods for indicating the humidity of a constant temperature and humidity test chamber. For the test equipment, the concept of relative humidity is usually used to describe the humidity. Relative humidity is defined as the ratio of the water vapor pressure in the air to the saturated vapor pressure of water at that temperature and is expressed as a percentage. It is known from the nature of water vapor saturation pressure that the saturation pressure of water vapor is only a function of temperature. It is independent of the air pressure at which water vapor can be used. Through a large number of experiments and collation, people have found a relationship between water vapor saturation pressure and temperature, which has been A large amount of measurement should be adopted by the Goffeglie formula. It is used by the current meteorological department to compile a humidity checklist.
The humidification process of the constant temperature and humidity test chamber actually increases the partial pressure of water vapor. The initial humidification method is to spray water to the test chamber wall, and the water surface saturation pressure is controlled by controlling the water temperature. The water on the surface of the tank wall forms a large surface, and the water vapor pressure is added to the tank through the diffusion method on the surface to increase the relative humidity in the constant temperature and humidity test chamber. This method appeared in the 1950s. . Because the control of humidity at that time is mainly a simple switchover adjustment of the mercury-electric contact type conductivity meter, the control of the water temperature of the hot water tank with large hysteresis is poor, so the transition process of the control is long and cannot meet the alternating heat and humidity. The need for more humidification, and more importantly, when spraying the wall of the tank, it is inevitable that water droplets will drip on the sample to form different degrees of contamination on the sample. At the same time, there are certain requirements for the drainage inside the tank.
This method was quickly replaced by steam humidification and shallow water pan humidification. But this method still has some advantages. Although the control transition process of the constant temperature and humidity test chamber is long, the humidity fluctuation after the system is stable is relatively small, and it is more suitable for the constant damp heat test. In addition, the moisture in the humidification process does not increase the extra heat in the system. Also, when the temperature of the spray water is controlled to be lower than the point temperature required for the test, the spray water has a dehumidification effect.
With the development of the damp heat test from the constant temperature and humidity test chamber to the alternating damp heat, a relatively fast humidification reaction capability is required. When the spray humidification is no longer satisfactory, the steam humidification and shallow water pan humidification methods are widely adopted and developed.
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