In the environmental experiments of new energy power batteries, components, board level and unit level modules, it is easy to cause condensation and other physical phenomena on products when the temperature rises rapidly. This condensation phenomenon is related to product material, chamber size, temperature rise and fall rate, relative humidity, air pressure in the chamber, air flow rate and other factors. The worse the heat absorption of materials, the larger the size of the test chamber, the faster the rate of temperature rise and fall, and the greater the relative humidity, the easier the condensation will occur.

During the temperature test of the test chamber, the common causes of condensation are as follows:

1. Thermal inertia problem. When the ambient temperature in the test chamber rises, the temperature of the product surface is lower than the ambient temperature due to thermal inertia. When the humid and hot ambient air meets the product surface that is lower than the dew point, the water vapor will condense on the surface to form condensation.

2. The rate of product temperature rise and fall. If the product is sealed, when the ambient temperature in the test chamber decreases, the temperature of the inner wall of the product housing will drop faster than the air temperature in the chamber, and the hot and humid air in the chamber will also condense into dew drops on the inner wall of the product housing. As most products are not completely sealed, condensation generally occurs in the heating stage.

3. Condensation problem possibly caused by refrigeration system. During the test, it was found that there were water drops blowing out from the air outlet, and there were water drops stuck in the air duct and on the wind wheel. This phenomenon is mainly caused by the uneven heat transfer of the evaporator.

4. The problem of environmental test chamber structure. When the cooling capacity of the environmental test chamber is large and the air volume during the condensation test is too small, the water vapor in the ambient air will condense to form a mist blowing phenomenon due to the low air outlet temperature, and water droplets may form around the air outlet.

First, the harm of condensation:

In general, simple condensation water is not enough to cause product failure, but in the environmental stress screening test chamber, condensation water will combine with other factors to produce physical/chemical effects, which will affect the safety and quality of the product, such as metal oxidation/electrochemical corrosion, chemical or electrochemical destruction of organic and inorganic surface coatings, adhesion or adhesion caused by the change of friction coefficient, material expansion caused by absorption effect, physical strength reduction Typical failure failure caused by electrical short circuit, etc.

Second, anti condensation analysis of temperature chamber:

In the environmental stress screening, the root cause of condensation on the surface of the test object is that the temperature of the surface of the test object is lower than the dew point of the air in the temperature chamber. Therefore, there are several possible ways to prevent condensation on the surface of the test object:

1. Improve the circulation of the gas in the chamber, so that the temperature of the tested object in the temperature chamber is always synchronized with the temperature change of the gas in the chamber, and the difference between the temperature of the tested object and the temperature of the gas in the chamber is very small, which is not enough to cause condensation on the surface of the tested object.

2. Take appropriate measures to make the dew point rise rate of the gas in the chamber lag behind the temperature rise rate of the surface of the tested object, so that the dew point of the gas in the chamber is always lower than the temperature of the surface of the tested object, and prevent condensation on the surface of the tested object.

3. Control the absolute humidity of the gas in the chamber, so that the dew point of the gas in the chamber is always lower than the lower limit temperature of the gas in the chamber, so as to avoid condensation on the surface of the tested object.

Among the above control methods, methods 2 and 3 have certain feasibility. When we try to reduce the absolute humidity of the gas in the chamber, we can effectively reduce the dew point of the gas in the chamber to ensure that the temperature of the tested object is higher than the dew point of the gas in the chamber and prevent condensation on the surface of the tested object.

Third, KOMEG's solution to condensation:

After long-term observation of environmental stress screening test, KOMEG professionals found that the factors affecting the change of gas dew point in the constant temperature and humidity test chamber mainly include the following two points:

1. Ambient humidity: When the ambient operating humidity of the test chamber is relatively high, condensation is likely to occur in the chamber.

2. Tightness of the chamber: the better the tightness of the chamber, the less the influence of environmental humidity on the gas in the chamber.

Environmental humidity is an uncontrollable factor. Due to the needs of work or engineering reasons, it is difficult to achieve absolute sealing of the chamber. Gas exchange is inevitable inside and outside the general constant temperature and humidity test chamber, which is the difficulty of the general constant temperature and humidity test chamber in preventing condensation.

In order to overcome the influence of environmental humidity on the dew point of the gas in the chamber through the gap of the chamber, KOMEG at this stage adopts the method of supplementing dry air in the chamber to make the air pressure inside the chamber greater than that outside the chamber, prevent the water vapor outside the chamber from entering the chamber, and control the humidity inside the chamber, so as to ensure that the dew point of the gas in the chamber is lower than the surface temperature of the tested object, eliminate the basic conditions for condensation, better solve the problem of condensation of the tested object, and avoid condensation for customers, Provides reliability solutions.

Finally, we summarize several conclusions and suggestions:

1. A small amount of condensation during the environmental experiment will not damage the performance of the equipment, nor affect the analysis of the experimental results.

2. In order to prevent the generation of a large amount of condensation and cause wrong guidance to the analysis of the experimental results, the products are generally preheated in advance during the environmental experiment.

3. The environmental experiment has a great impact on the experimental samples, which may change the mechanical, physical and electrical properties of materials. Therefore, in the early stage of product design, considering the actual use conditions, select appropriate components and parts, and adopt derating design, redundancy design, tolerance design, climate and environmental protection design, cushioning and vibration reduction design, thermal design and other means to effectively improve the reliability of products. In the environmental experiment, only by applying appropriate experimental conditions, exposing existing problems and seeking appropriate improvement measures, can the adaptability of the product be further determined to make the product meet the use requirements.