Collision of gas molecules
Collision changes the speed of gas molecules. A large number of molecules collide with each other frequently, which affects the gas transport process (see gas transport phenomenon). In the theory of gas dynamics, the internal structure of molecules and various forms of motion other than translation are not considered, so all collisions are elastic collisions, and the sum of momentum and energy before and after collision remains unchanged. Because there are few opportunities for more than three molecules to collide at the same time, only the main two body collision process is considered when studying the collision of gas molecules.
The primary theory of gas transport process mainly studies each specific transport process from the situation of molecular collision; The impact of collision should also be considered in the mathematical theory of transport. The calculation of the rigid sphere model is simple and can provide some preliminary theories for many practical problems. Its disadvantage is that the properties of the gas molecules differ greatly from those of the actual gas molecules, and the calculation results are not in good agreement with the actual situation; The force center model is close to the properties of the actual molecules, but the calculation is complex, and the actual molecules have internal structures. Only when the gas molecules are far away can they be regarded as particles. Therefore, when the gas density is not too high, the results calculated with this model are in good agreement with the actual situation; When the gas density is very high, the results calculated by this model are quite different from the actual situation.
