Humidity Control Tips for Cold and Hot Shock Test Chambers
The thermal shock test chamber can simulate instantaneous changes between high and low temperatures. This allows for the assessment of the product's reliability and stability parameters, ensuring they meet the required standards. It provides you with the basis for predicting and improving product quality and reliability.
The cold and hot shock test chamber is used to assess the resistance of products such as electronics, automotive, rubber, plastics, aerospace technology, military technology, and communication equipment under repeated temperature fluctuations.
To achieve the testing conditions, it is inevitable to perform humidification and dehumidification operations on the testing chamber. This article aims to analyze the various methods currently widely used in humid testing chambers, highlighting their respective advantages and disadvantages as well as recommended conditions for use.
There are various methods to express humidity, and for testing equipment, relative humidity is typically used to describe it. The definition of relative humidity refers to the ratio of the vapor pressure of water vapor in the air to the saturation vapor pressure of water at that temperature, expressed as a percentage. Knowing the properties of water vapor saturation pressure, it is merely a function of temperature and unrelated to the air pressure the vapor can occupy. Through a vast number of experiments and compilation, people have sought to represent the relationship between water vapor saturation pressure and temperature, with the Goff-Gratch equation being widely adopted in engineering and metrology. It is currently used by meteorological departments to compile humidity lookup tables.
The humidification process in a cold and hot shock test chamber essentially involves increasing the vapor pressure. Initially, the humidification method was to spray water onto the chamber walls, controlling the water temperature to maintain a controlled saturated pressure on the water surface. The water on the chamber wall forms a large surface area, where water vapor pressure is added to the interior of the chamber through diffusion, thereby increasing the relative humidity inside the test chamber. This method emerged in the 1950s.
Due to the initial reliance on simple on/off adjustments using mercury contactor-type conductive gauges for humidity control, the system's adaptability to controlling the temperature of large-volume water heaters was poor. Consequently, the transition process for control was lengthy, failing to meet the increased demand for humidity during alternating hot and humid conditions. Moreover, during the spray rinsing of the chamber walls, it was inevitable that water droplets would fall onto the test samples, causing varying degrees of contamination. Additionally, there were some requirements for the drainage within the chamber. Therefore, from the outset, we adopted steam humidification and shallow water tray humidification. Although the transition process was lengthy, once the system stabilized, humidity fluctuations were minimal, making it more suitable for constant hot and humid testing.
Additionally, during the humidification process, the moisture is not overheated, thus not adding any extra heat to the system. Moreover, when controlling the spray water temperature to be below the critical temperature required by the test, the spray water has a dehumidifying effect.
The definition of relative humidity refers to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure of water at that temperature, expressed as a percentage.
