Temperature Separation in a Vortex Tube and convection driven by vorticity

Why the temperature gradient in the vortex tube deviates significantly from the adiabatic gradient is a very important but unresolved issue in vortex tube research. In compressible fluids, the vorticity of a fluid parcel that is different from its environment can affect its own pressure or density, just like temperature. Gases near the wall have very high vorticity, and when they detach from the wall, their higher vorticity compared to the environment makes their density lower than the environment. Driven by vorticity, some fluid parcels undergo multiple collisions near the axis, achieving temperature separation.