In order to realize the test conditions, the constant temperature and humidity test chamber inevitably needs to perform humidification and dehumidification operations on the test chamber. Ding Bao currently analyzes various methods used in the constant temperature and humidity test chamber and points out that they are each The advantages and disadvantages and the recommended conditions for use.
The process of humidification is actually to increase the partial pressure of water vapor. The initial method of humidification is to spray water to the wall of the test chamber, and the water surface saturation pressure is controlled by controlling the water temperature. The water on the surface of the box wall forms a larger surface, and the relative humidity in the test box is increased by adding vapor pressure to the box inside the box through diffusion. This method appeared in the last century. Years. Since the control of the humidity at the time was performed by a simple switch quantity adjustment using a mercury-electrical contact type conductivity meter, the control of the water temperature of the hot water tank with a large delay was relatively poor, so the transition process of control would be long and could not be satisfied. Humidifying heat requires more humidification, more importantly, when sprayed on the wall, it is unavoidable that water drops on the test sample to form different degrees of pollution. 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. However, this method still has some advantages. Although its control transition process is long, the humidity fluctuation is small after the system is stable, and it is more suitable for a constant damp heat test. In addition, the heat of vaporization during humidification does not increase the extra heat in the system. Also, the spray water has a dehumidifying effect when the temperature of the spray water is controlled to be lower than the point temperature required by the test.
Humidity is represented in many ways. For experimental equipment, the concept of relative humidity is often used to describe humidity. Relative humidity is defined as the ratio of the partial pressure of water vapour in the air to the saturated vapour pressure of water at that temperature and expressed as a percentage. Because of the nature of water vapor saturation pressure, the saturation pressure of water vapor is only a function of temperature, and it has nothing to do with the air pressure where the water vapor can be. People have gone through a lot of experimentation and finishing to find the relationship between water vapor saturation pressure and temperature. Among them, the Goff Gretchi formula has been used in a large number of projects and measurements. It is used by the current meteorological department to prepare the humidity checklist.
With the development of the damp heat test from constant moisture heat to alternating damp heat, a relatively fast humidification reaction capability is required, and when the spray humidification has failed to meet the requirements, steam humidification and shallow water tray humidification methods have begun to be adopted and developed in large quantities.
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