High low temperature test chamber in order to realize the test conditions, inevitably to the operation of the test chamber for humidification and dehumidification, this article is intended to is at present a large number of mainly use in the damp heat test box of various methods were analyzed, and points out their respective advantages and disadvantages, and it is recommended to use conditions.
There are many ways to represent humidity. In terms of test equipment, relative humidity is usually used to describe humidity.
Relative humidity is defined as the ratio of water vapor pressure in the air to the saturated vapor pressure in the water at that temperature and expressed as a percentage.
By the nature of the water vapor saturation pressure, the water vapor saturation pressure is a function of temperature, and water vapor in the air pressure has nothing to do, people through a lot of experiments and arrange for the said the relationship between the water vapor saturation pressure and temperature, which has been used by the engineering and measurement should be gove Craig its formula.
It is used by the current meteorological department to compile humidity check tables.
The humidification process is actually to increase the water vapor pressure. The initial humidification method is to spray water on the wall of the test chamber, and the water surface saturation pressure is controlled by controlling the water temperature.
Water on the surface of the tank wall form a larger surface, in the face to to join in the vapor pressure by means of diffusion in the higher relative humidity in the test chamber, this method appeared in the 1950 s.
Because of the humidity control is mainly connect point with mercury electricity conductivity meter for simple switch quantity adjustment, for large lag the control of the hot water tank water temperature adaptability is bad, so the control of a long transition process, can not meet the requirement of the alternating hot and humid for humidification quantity more need, more important is in the box wall spray, inevitably there are water spray on the sample (s) in the sample (s) to form the different levels of pollution.
At the same time, there are certain requirements for the drainage in the box.
Therefore, we adopted steam humidification and shallow water plate humidification in the early stage. Although it has a long control transition process, the humidity fluctuation after the system is stable is small, which is more suitable for constant humidity and heat test.
In addition, the water vapor does not overheat during the humidification process without adding extra heat to the system.
Moreover, spray water has the function of dehumidifying when the water temperature is controlled to lower than the key temperature required by the test.
With the development of hot and humid test by constant humid to alternating hot and humid, require faster humidifying reaction ability, spray humidification can not meet the requirements, the steam humidification and shallow dish humidifying method began a large number of used and developed.