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Purpose of Dewar vacuuming and replacing with nitrogen
Date: Jul 31, 2020
The Dewar flask is replaced with nitrogen during the vacuuming process, which is determined by the characteristics of nitrogen. Compared with ordinary air, high-purity nitrogen is oxygen-free, almost moisture-free, and oil-free. It has low thermal expansion coefficient, low thermal conductivity, slow heating, and lower heat accumulation speed, so it can greatly ensure the thermal insulation performance of the Dewar bottle.
1. Heating the inner tank to 250 degrees to vacuum, mainly to allow the air inside to fully heat and expand, so that the air can be extracted as much as possible, and a higher vacuum can be formed after cooling.
2. If it is said that the vacuuming process and the welding process level are very high, it can ensure that the vacuum is not destroyed, and it is also feasible without nitrogen filling, because under the condition of high vacuum, due to the fact that the heat transfer medium is small, the heat transfer is fast. The movement is also very slow, which can basically meet the demand for relative insulation.
3. Nitrogen filling is mainly used for compensation when the above 2 processes are immature. As long as one process fails in 10 bottles, it should be filled with nitrogen. After the nitrogen is filled, the pressure in the bottle is close to normal pressure, so if the welding quality is not good, the air is not easy to leak in, and the nitrogen filled in the bottle can be maintained at the beginning of use due to its low thermal expansion coefficient and low thermal conductivity. Relatively adiabatic.
4. The welding process is the key issue. If the welding quality is not good enough, the Dewar flask will be affected by thermal expansion and contraction during use. Nitrogen will overflow the cylinder when it is heated, and air will leak in when it is cooled. After long-term use, the nitrogen will be replaced by air, thus making the cylinder Loss of thermal insulation performance and easy to cause abnormalities such as bottle explosion.
1. Heating the inner tank to 250 degrees to vacuum, mainly to allow the air inside to fully heat and expand, so that the air can be extracted as much as possible, and a higher vacuum can be formed after cooling.
2. If it is said that the vacuuming process and the welding process level are very high, it can ensure that the vacuum is not destroyed, and it is also feasible without nitrogen filling, because under the condition of high vacuum, due to the fact that the heat transfer medium is small, the heat transfer is fast. The movement is also very slow, which can basically meet the demand for relative insulation.
4. The welding process is the key issue. If the welding quality is not good enough, the Dewar flask will be affected by thermal expansion and contraction during use. Nitrogen will overflow the cylinder when it is heated, and air will leak in when it is cooled. After long-term use, the nitrogen will be replaced by air, thus making the cylinder Loss of thermal insulation performance and easy to cause abnormalities such as bottle explosion.
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