Humidification method of high and low temperature damp heat alternating test box

In order to achieve the test conditions, the high and low temperature damp heat test box inevitably needs to humidify and dehumidify the test box. This article intends to analyze a large number of various methods currently used in the damp heat test box and point out their respective advantages and disadvantages. And recommended conditions.

There are many ways to express humidity. As far as testing equipment is concerned, the concept of relative humidity is usually used to describe humidity. The definition of relative humidity refers to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure of water at that temperature and expressed as a percentage. It can be seen from the nature of water vapor saturation pressure that 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 placed. People have sought to show the relationship between water vapor saturation pressure and temperature through a large number of experiments and Gove Greche's formula should be used for the measurement. It is currently used by the Meteorological Department to compile humidity look-up tables. (Guide: Some knowledge about cast iron plates)

The process of humidification is actually to increase the partial pressure of water vapor. The initial humidification method is to spray water on the test chamber wall to control the saturation pressure of the water surface by controlling the water temperature. The water on the surface of the box wall forms a larger surface on which the water vapor pressure is added to the box by diffusion to increase the relative humidity in the test box. This method appeared in the 1950s. Because the humidity control at that time was mainly the simple on-off adjustment of the mercury-electric contact type conductivity meter, the control adaptability to the water temperature of the hot water tank with large lag was poor, so the control transition process was long and could not meet the alternating damp heat. There is a need for more humidification, and more importantly, when spraying the tank wall, it is inevitable that water drops on the test product will form different degrees of pollution. At the same time, there are also 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 longer, the humidity fluctuation is small after the system is stabilized, which is more suitable for constant damp heat test. In addition, overheating of water vapor 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 key point temperature required by the test, the spray water has a dehumidifying effect.

As the damp heat test develops from constant damp heat to alternating damp heat, a faster humidification response is required, and when spray humidification can no longer meet the requirements, steam humidification and shallow water pan humidification methods have begun to be adopted and developed.

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