The humidification process in a high and low temperature damp heat test chamber essentially involves increasing the partial pressure of water vapor. In the 1950s, the earliest method was to spray water onto the walls of the test chamber. The saturation vapor pressure over the water surface was controlled by adjusting the water temperature. As water evaporated from the tank wall, it created a large surface area that contributed to the water vapor pressure inside the chamber, thereby raising the relative humidity. However, this approach had a major drawback: when water was sprayed on the chamber walls, droplets inevitably fell onto the test samples, causing contamination. Additionally, proper drainage within the chamber was essential. As a result, this method was soon replaced by shallow pan and shallow trough humidification techniques.
Shallow pan humidification involved placing a water tray near the heater inside the test chamber and raising the water temperature appropriately. As the temperature of the water increased, so did its vapor pressure, which helped raise the humidity level in the air. However, this method had limitations, especially during low humidity tests, where the diffusion from the water tray and fluid exchange made it difficult to achieve and maintain precise humidity levels.
Beijing Yashilin's high and low temperature damp heat test chamber employs the most advanced shallow trough humidification method available in China. This technique uses heating pipes to generate steam, which is then distributed throughout the chamber via a circulating fan, ensuring even humidity distribution. A humidity sensor, combined with a wet bulb gauze, measures the environmental humidity, and the data is displayed on a control meter connected to the sensor. Compared to other methods, shallow trough humidification offers more uniform moisture distribution and is easier to clean and maintain. This innovation has significantly improved the accuracy and reliability of humidity control in modern test chambers.
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