Humidification method of high-low temperature wet heat alternating test box

In order to achieve the test conditions, the high-low temperature damp heat tester inevitably needs to humidify and dehumidify the test box. This article intends to analyze the advantages and disadvantages of the various methods used in a large number of damp heat test cases and to suggest their use. conditions of.

Humidity is expressed in many ways. In terms of test 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. From the nature of water vapor saturation pressure, it can be seen that the saturation pressure of water vapor is only a function of temperature and the air pressure where the water vapor can be irrelevant. Through a lot of experiments and sorting, we have found that the relationship between water vapor saturation pressure and temperature has been widely used in engineering and measurement. It should be Goffage's formula. It is used by the current meteorological department to prepare the humidity checklist.

The process of humidification is actually to increase the partial pressure of water vapor. The initial way of humidification is to spray water to the wall of the test chamber and control the water temperature to control the saturation pressure of the water surface. The surface of the wall of the tank forms a larger surface. This method of adding moisture vapor pressure to the tank by means of diffusion to increase the relative humidity in the test box occurs in the 50s of the last century. Because the control of humidity at the time was mainly a simple switch quantity adjustment using a mercury-electricity contact type conductivity meter, the adaptability to the control of the water temperature of the large-lagging hot water tank was poor. Therefore, a long transition process was not able to satisfy the alternating humid-heat-to- humidification amount. The more demanding requirement is more important when the wall of the tank is sprayed. Inevitably, there is water droplets on the sample to form different levels of pollution on the sample. At the same time there are certain requirements for the drainage inside the box. Therefore, we used steam humidification and shallow water tray humidification at an early stage. Although its control transition process is longer but the system is stable and the humidity fluctuation is smaller, 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 shower water temperature is controlled to be lower than the point temperature required by the test.

With the development of a damp heat test, the development of constant humid heat to alternating humid heat requires a relatively rapid humidification reaction capability. Spray humidification cannot meet the requirements. Steam humidification and shallow water tray humidification methods have been widely adopted and developed.

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