- Volume Selection
When tested (an application, part or the full machine) put on the weather room for the test, to ensure the product tested. Air may meet environmental conditions specified in the test details. These processes will be followed between the weather area of the weather and the outside of the test product:
a) The voice of the product tested (large X is randomly) will not pass (20 ~ 35)% of the Carapace Service (recommended)
b) The ratio of the air surface of the tested product to the total of the test room and the section should not be more than (35 ~ 50) % (approx.)
c) The distance between the surface of the test product and the wall of the laboratory should be at least 100 ~ 150mm (150mm is recommended).
The above three points are closely related. Taking one cubic meter cubic chamber as an example, the area of 1: (0.35 ~ 0.5) is equal to the ratio of 1: (0.207 ~ 0354). 100 ~ 150 mm from the tank wall corresponds to the maximum volume of 1: (0.343 ~ 0.512). To summarize the above three points, the working room of the weather laboratory should be at least 3-5 times the outside of the tested product.
The reasons are as follows:
1) When the sample is placed in the room, the duct is used, and the interruption of the duct will cause the air flow to increase. Air conditioner and duvet.
Switch between modes. This is not compatible with the reproduction of environmental conditions, since it is specified in the relevant standards that the air flow around the test sample in the laboratory will not exceed 1.7 m / s for the test environment temperature l, to prevent test check. And the surrounding air by creating an irrational fire. When there is no load, the average wind speed in the test room is 0.6 ~ 0.8m / s, no more than 1m / s. when meeting the limits of space and area specified in a) and b), the speed of the air flow can increase (50 ~ 100)%, and the average wind speed is (1 ~ 1, 7) m / s . . Meet the requirements specified in the standard. If the volume or surface area of the sample increases indefinitely during the test, the air volume will increase more than the air volume specified in the test standard during the actual test; -question the validity of the test results. .
2) Indices accuracy of environmental parameters (such as temperature, humidity, salt spray sedimentation rate, etc.) in the office of all-weather buildings without soil load.
Once the sample is placed in the laboratory, the test results will be affected by the uniformity of the environmental parameters in the laboratory. The bigger the chance of a sample, the greater the impact. The measured test results show that the temperature difference between the windward and leeward sides of the flow field can reach
3 ~ 8 ℃ and more than 10 ℃ in severe cases. Therefore, the requirements of a) and b) should be followed as much as possible to ensure the integrity of the environment around the tested product.
3) According to the principle of heat conduction, the temperature of the airflow near the tank wall is usually 2-3 ℃ different from the temperature of the center of the flow field.
In the upper and lower areas, it can reach 5 ℃. The difference between the tank wall temperature and the flow field temperature near the tank wall is 2 ~ 3 ℃ (depending on the tank wall structure and material). The greater the difference between the test temperature and the surrounding air, the greater the surface temperature difference. Therefore, a distance of 100 ~ 150mm from the tank wall is unusable.
- High temperature selection
Currently, the range of test room temperature abroad is generally – 73 ~ + 177 ℃ or – 70 ~ + 180 ℃. Many home builders (1)
In general, it is – 80 ~ + 130 ℃, – 60 ~ + 130 ℃, – 40 ~ + 130 ℃. There is also a high temperature up to 150 ℃. These temperature ranges can meet the temperature testing needs of many military and civilian products. Except for special needs, such as products installed around the engine and other hot items, can’t increase the temperature in the blind. Because of the high temperature, the greater the temperature difference inside and outside the house, the worse the uniformity of the flow field inside the house. A small workplace is available. On the other hand, the higher the temperature, the higher the heat-resistant materials required of insulation (such as glass wool) in the centre of the building wall. The higher the required insulation material of the building, the higher the production cost of the building.
- Humidity selection
The humidity level given by environmental and foreign laboratories is 20 ~ 98% RH or 30 ~ 98% RH. If the temperature test is not available
For dehumidification systems, the relative humidity is 60-98%. This type of laboratory can perform high humidity tests, but the price is low. It should be noted that the corresponding temperature range or the lowest dew point temperature should be indicated after the humidity index. Because relative humidity is directly related to temperature, for the same absolute humidity content, the higher the temperature, the lower the relative humidity. For example, the absolute amount of water is 5 g / kg (referring to 5 g of water vapour and 1 kg of dry air). When the temperature is 29 ℃, the relative humidity is 20% RH; when the temperature is 6℃, the relative humidity is 90% RH. When the temperature drops below 4℃, the humidity is above 100% and condensation occurs in the room.
To achieve maximum temperature and humidity, simply spray steam or atomized water droplets in the air of the room for humidity. Low temperatures and low humidity are often difficult to control because the relative humidity at this time is very low, sometimes less than the absolute humidity content in the air. It is important to clear the air circulating in the room to keep the air dry. At present, most of the temperature and humidity at home and abroad follow the principle of refrigeration and dehumidification, which is to add one refrigeration unit to the indoor air conditioner. When water passes through the cooling pipe, its relative humidity will reach 100% RH. Because the air is full of condensate and heat, the expanded air becomes dry. Apparently, this process of dehumidification can reach the dew point below freezing. However, when the surface temperature of the cold area reaches 0 ℃, the water flowing on the heat pipe will drop, which will affect the temperature change on the heat pipe and reduce the dehumidification power. . Also, since the room cannot be completely sealed, the moisture from the sky enters the room and raises the dew point. On the other hand, the humid air that circulates between the heat pipe reaches the perfect condition at the time it is connected to the heat (cold) and the wet air is separated. Therefore, this exhaust system is difficult to keep the indoor air temperature below 0℃. In fact the minimum cloud temperature is 5 ~ 7 ℃. The dew point of 5 ℃ is the total water content of 0.0055g / kg, and the corresponding temperature and humidity of 20% RH is 30 ℃. If the temperature should be 20 ℃ and the humidity reaches 20% RH, the dew point at this time is -3 ℃. It is difficult to remove it from the refrigeration, and the ventilation system should be chosen.
