The humidification process in a constant temperature and humidity test chamber essentially involves increasing the water vapor partial pressure. The initial humidification method was to spray water onto the chamber walls and control the water temperature to regulate the saturation pressure of the water surface. The large surface area of water on the chamber walls allowed water vapor to diffuse into the chamber, thereby increasing the relative humidity. This method, once stabilized, resulted in minimal humidity fluctuations and was suitable for constant humidity and heat tests. However, it could no longer meet the requirements for humidification volume and might cause varying degrees of contamination to the test items.

There are several common humidification methods for constant temperature and humidity test chambers:
Shallow Water Pan Humidification
A shallow water pan is installed inside the chamber, equipped with electric heating elements. The water is heated to evaporate, thereby increasing the humidity. The advantages of this method include stable humidification, minimal humidity fluctuations after the system stabilizes, no overheating of water vapor (which prevents excessive heat addition to the chamber), simple structural design, and low maintenance costs. The downside is the relatively slow humidification speed. Additionally, bacteria and microorganisms can easily breed in the water pan if it is not used for a long time, necessitating regular cleaning.
Ultrasonic Humidification
A hole is drilled in the side of the chamber, and an ultrasonic air humidifier is used to atomize water. The mist is then introduced into the chamber through a pipe. This method is cost-effective and provides rapid humidification, quickly increasing the humidity inside the chamber. However, it consumes a large amount of water, and the humidifier needs to frequently activate the dehumidification system, which may affect the continuity and stability of the test.
Steam Pot Humidification
Water is heated to boiling to produce steam, which is then introduced into the chamber to increase humidity. The advantage of this method is the rapid humidification, which can meet the demand for quick humidification during humidity and heat alternation tests, with fast humidity changes. The downside is the complex structure of the steam pot and its associated equipment, which leads to a higher failure rate. Moreover, steam humidification adds heat to the chamber, making temperature control more challenging.
Spray Water Humidification
Water is sprayed onto the inner walls of the test chamber, increasing the water-covered surface area. As the water diffuses into the chamber, the water vapor pressure inside the chamber increases, thereby raising the relative humidity. Once the system stabilizes, the humidity fluctuations are minimal. The humidity can be precisely controlled by adjusting the amount and temperature of the sprayed water. However, if water droplets directly fall on the test items, contamination may occur. Additionally, this method increases the water accumulation inside the chamber, necessitating a well-designed drainage system.
Overcooled Steam Humidification
Water is converted into micrometer-sized mist using methods such as ultrasonic waves, high-pressure water mist, or centrifugal spraying. The mist absorbs heat from the sample and turns into water vapor, thereby increasing humidity. This method offers stable humidification, minimal humidity fluctuations after system stabilization, high humidification efficiency, and rapid response to humidity change demands. However, the equipment is complex, requiring specialized devices to convert water into micrometer-sized mist. Although the humidification speed is faster than that of shallow water pan humidification, it is not as quick as steam humidification.
The humidification system of a constant temperature and humidity test chamber is similar to its heating system. It involves heating water with a heater to produce steam, thereby achieving the humidification purpose of the constant temperature and humidity machine. The dehumidification system of the constant temperature and humidity test chamber relies on the refrigeration system. The evaporator is placed inside the chamber. The high-humidity gas inside the chamber condenses into liquid upon contact with the cold evaporator. This process is repeated until the high-humidity gas inside the chamber is significantly reduced, achieving the dehumidification purpose.