Characteristics of rare gas transport phenomenon

    The density of rare gas molecules is small, the mean free path of molecules is large, the collision probability between molecules is small, and the momentum exchange and energy exchange between molecules are different from atmospheric gas, which determines that the phenomenon of rare gas transmission has its own characteristics.

    Diffusion will occur in rare gas, but because there are few collisions between gas molecules, the molecules of the diffusing gas no longer take a tortuous path, but directly shoot into another gas at the speed of the molecule, and the diffusion process will proceed very quickly. , The size of the diffusion coefficient has nothing to do with the mean free path of the molecule, but depends on the speed of movement of the molecule and the size of the container.

    Rare gases can also transfer heat through the movement of molecules, and the mechanism is quite different from that under normal pressure. The gas under normal pressure transfers heat from high temperature to low temperature through multiple collisions of gas molecules. Therefore, there is a continuous temperature gradient in the gas. In rare gas, there are few chances for gas molecules to collide. After the hot walls collide and gain energy, they fly straight to the cold wall and transfer part of the energy to the cold wall through the collision. In this case, there is no continuous temperature gradient in the gas, so the usual concept of thermal conductivity and the Fourier law related to it are not applicable.

    Rare gas is a discontinuous medium. When it moves relative to the solid wall (the flow of gas in the pipe), the gas does not stick to the wall, but slides along the wall at a certain speed, which is called slip phenomenon. The sudden change in velocity between the gas and the wall causes friction, which is called "external friction". The thinner the gas, the smaller the internal friction, and the greater the proportion of external friction in the flow resistance. This external friction force is generated by the collision of gas molecules with the wall surface, and is proportional to the slip speed and the size of the action area.

    There are also some characteristics of the rare gas in a vacuum environment, such as the flow characteristics and heat transfer characteristics of the rare gas.

(Huiputech)