In order to realize the test conditions, the constant temperature and humidity test chamber inevitably needs to humidify and dehumidify the test chamber. This paper analyzes the various methods used in the constant temperature and humidity test chamber and points out their respective advantages and disadvantages. And recommended conditions.
Humidity is expressed in many ways. In the case of test equipment, the concept of relative humidity is often used to describe 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 process of humidification is actually to increase the partial pressure of water vapor. The initial humidification method of Zui 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 on which the water vapor pressure is added to the tank by means of diffusion to increase the relative humidity in the test chamber. This method appeared in the 1950s. Since 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 box. This method was quickly replaced by steam humidification and shallow water pan humidification. But this method still has some advantages. Although its control transition process is long, the humidity fluctuation is small after the system is stable, which is more suitable for constant damp heat test. In addition, the moisture does not heat up during the humidification process and 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.
As the damp heat test develops from constant damp heat to alternating damp heat, a relatively fast humidification reaction capability is required. When spray humidification is no longer satisfactory, steam humidification and shallow pan humidification methods are widely adopted and developed.
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