Humidification method of high and low temperature humid heat alternation test chamber

In order to realize the test conditions, it is inevitable to humidify and dehumidify the high-temperature and low-temperature humid heat test chamber This paper intends to analyze a large number of methods used in the humid heat test chamber at present, and point out their respective advantages and disadvantages and recommended conditions There are many ways to express humidity In terms of test equipment, 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 expressed as a percentage It can be seen from the properties of water vapor saturation pressure that the water vapor saturation pressure is only a function of temperature and has nothing to do with the air pressure at which the water vapor can be located People have found the relationship between water vapor saturation pressure and temperature through a large number of experiments and finishing, among which the formula of gofgritchie has been widely used in engineering and measurement It is used by the meteorological department to compile the humidity check table In fact, the process of humidification is to increase the partial pressure of water vapor The initial humidification method of Zui is to spray water to the wall of the test chamber The water on the surface of the box wall forms a large surface, on which the relative humidity in the test box is increased by adding water vapor pressure to the box through diffusion This method appeared in the 1950s At that time, the humidity was mainly controlled by simple on-off adjustment of mercury electric contact type conductivity meter, which had poor adaptability to the control of water temperature in the hot water tank with large lag Therefore, the transition process of control was long, which could not meet the needs of more requirements for humidification by alternating humidity and heat More importantly, when spraying the tank wall, it was inevitable that water droplets would fall on the test object Products form different degrees of pollution At the same time, there are certain requirements for drainage in the box Therefore, we used steam humidification and shallow water plate humidification in the early stage Although its control transition process is long, the humidity fluctuation is small after the system is stable, so it is more suitable for constant damp heat test In addition, in the process of humidification, if the water vapor is not overheated, it will not increase the extra heat in the system In addition, when the spray water temperature is controlled to be lower than the key temperature required by the test, the spray water has the dehumidification effect With the development of damp heat test from constant damp heat to alternating damp heat, it is required to have fast humidification reaction capacity When spray humidification can not meet the requirements, steam humidification and shallow water pan humidification methods are widely used and developed.