In order to achieve the test conditions, the high and low temperature damp heat test chamber inevitably needs to humidify and dehumidify the test chamber. This article intends to analyze a large number of various methods currently used in the damp heat test chamber, pointing out their respective advantages and disadvantages. And recommended conditions.
There are many ways to express humidity. As far as test equipment is concerned, the concept of relative humidity is usually used to describe humidity. Relative humidity is defined as the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure of water at that temperature and is expressed as a percentage. From the nature of water vapor saturation pressure, the saturation pressure of water vapor is only a function of temperature, and has nothing to do with the air pressure where water vapor can be located. People have sought to express the relationship between water vapor saturation pressure and temperature through a lot of experiments and finishing. A large number of measures should be adopted by Goffger's formula. It is used by the current meteorological department to compile the humidity calculation table.
The process of humidification is actually to increase the partial pressure of water vapor. The initial humidification method is to spray water on the wall of the test chamber, and control the saturation pressure of the water surface by controlling the water temperature. The water on the surface of the tank wall forms a larger surface. On this surface, the water vapor pressure is added to the tank by diffusion to increase the relative humidity in the test chamber. This method appeared in the 1950s. At that time, the control of humidity was mainly the simple on-off adjustment of the mercury-electric contact type conductive meter, and the adaptability to the water temperature of the hot water tank with a large lag was poor, so the control transition process was long and could not meet the alternating damp heat The need for more humidification, more importantly, when spraying the tank wall, inevitably there are water droplets on the sample to form different degrees of pollution to the sample. At the same time, there are certain requirements for the drainage in the box. Therefore, we used steam humidification and shallow water pan humidification in the early stage. Although its control transition process is long, the humidity fluctuation after the system is stable is small, which is more suitable for constant humid heat test. In addition, the excessive moisture during the humidification process will 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 by the test, the spray water has a dehumidifying effect.
With the development of the humid heat test from constant humid heat to alternating humid heat, which requires a faster humidification reaction capacity. When spray humidification can no longer meet the requirements, steam humidification and shallow water pan humidification methods have been widely adopted and developed.
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