Firstly, we need to understand why helium is used as the gas for leak detection?
1. Helium has a small molecular weight, strong diffusivity, and high permeability, which means it can pass through extremely small pores.
2. The volume content of helium in air is about 5ppm, indicating that the helium content in normal air environment is very small, that is, the helium background is very good.
3. Helium is a non-toxic, colorless, and odorless inert gas, which means that under normal circumstances, it can exist as a medium in all objects without reacting.
4. It is easy to distinguish from other substances in the mass spectrometer spectrum.
Based on the above characteristics, helium gas is the best choice as a tracer gas for leak detection.
Helium is a colorless and odorless inert gas. The relative molecular mass is 4.003, the molecular diameter is 2.18 × 10-10m, the molecular mass is 3.65 × 10-27kg, the density at standard state is 0.1769kg/m3, the critical temperature is 5.25K, the critical pressure is 2.26 × 105Pa, the boiling point at 1atm pressure is 4.214K, the melting point is 0.9K, the triple point temperature is 2.186K, the triple point pressure is 51.1×10-2Pa, the thermal conductivity at standard state is 510.79J/(m · h · K), the specific heat at constant pressure at standard state is 5233J/(kg · K), the dynamic viscosity coefficient at standard state is 1.86×10-5Pa · s, 1L liquid helium gas The volume of helium gas converted to standard state is 700L.
According to national standards, bottled helium gas is classified into three types based on purity: industrial helium, pure helium, and high-purity helium.
1. Industrial helium: helium content ≥ 99%, dew point ≤ 43 ° C
2. Pure helium is divided into three levels: high-quality products with helium content ≥ 99.995%; First grade helium content ≥ 99.993%; Qualified products have a helium content of ≥ 99.99%.
3. High purity helium is divided into three levels: high-quality products with helium content ≥ 99.9996%; First grade helium content ≥ 999993%; Qualified products have a helium content of ≥ 99.999%.
Helium is used as a tracer gas in leak detection, with low purity requirements, and industrial helium is generally selected.
The above is the relevant knowledge about the characteristics and purity classification of helium gas introduced by the editor. The helium mass spectrometer leak detector not only has high sensitivity, but also is easy to operate, with automatic helium peak scanning, automatic calibration, and automatic range switching.
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