Constant temperature and humidity test chamber In order to achieve the test conditions, it is inevitable to humidify and dehumidify the test chamber. Now we will introduce various methods commonly used in constant temperature and humidity test chambers to analyze their shortcomings and advantages and reasonable Conditions of use.
Humidity is expressed in many ways. In the case of test equipment, the concept of relative humidity is often used to describe humidity. The definition of relative humidity refers to the ratio of the partial pressure of water in the air to the saturation pressure of water at that temperature and is expressed in hundredths. It is known from the nature of water vapor saturation pressure that the saturation pressure of water vapor is only a function of temperature and is compatible with water vapor. The air pressure has nothing to do. Scientists have obtained a large number of experiments and collation to get the relationship between the water vapor saturation pressure and the temperature. The Goffeglie formula, which has been commonly used in engineering and metrology, is currently compiled by the meteorological department. Adopted.
The process of humidification is actually to increase the partial pressure of water and gas. The initial method of humidification is to spray water to the wall of the test chamber. By controlling the temperature of the water, the saturation pressure of the water surface is controlled, and the water on the surface of the tank wall forms a larger surface. The surface diffusion adds water pressure to the tank to increase the relative humidity in the chamber. This method was originally used in the 1950s. Because the control of relative humidity at that time is mainly a simple switchover adjustment of the mercury-electric contact type conductivity meter, the control adaptability of the water temperature of the hot water tank with large hysteresis is relatively poor. Therefore, the transition process of the control is long and cannot satisfy the alternation. Damp heat requires more demand for humidification. More importantly, when spraying on the tank wall, water droplets will inevitably drip on the test product and cause different degrees of pollution to the test product. Certain requirements. This method was quickly replaced by steam humidification and shallow water pan humidification. However, this method also has its advantages. Although its control process is long, the humidity fluctuation is small after the system is stable, which is suitable for constant damp heat test. In addition, during the humidification process, the moisture is not hot enough to increase the extra heat in the system. In addition, when the temperature of the spray water is controlled to be lower than the point temperature required by the test, the spray water has a dehumidification effect.
As the damp heat test develops from constant damp heat to alternating damp heat, a relatively fast humidification reaction capability is required. When spray humidification is no longer satisfactory, steam humidification and shallow pan humidification methods are widely adopted and developed.
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Label: How to humidify and dehumidify the constant temperature and humidity test chamber
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