Lean-phase and dense-phase conveying

In fluid-particle flow systems, the following basic characteristics define a dilute phase: (1) a high porosity, which is generally always above 90%； (2) The particles exhibit a net movement toward the container wall. In this system, the velocity of the fluid is greater than the carrying velocity of the particles, and the flow direction is upward as well. In fluidization operations, especially gas-solid fluidization operations, the dilute phase always exists simultaneously with the dense phase. Strictly speaking, there is an intermediate phase between the two phases as well – a phase that possesses characteristics of both the dense phase and the dilute phase. Its limiting height is what is known as the entrainment separation height TDH. 　 Generally speaking, people are *used to referring to phases other than the dense phase as the dilute phase in a general sense.

Gas-solid transport can generally be divided into two forms: dense-phase transport and dilute-phase transport, with the latter also being known as pneumatic transport. There is no clear boundary between dense-phase transport and dilute-phase transport; generally, transport is considered to be in dense-phase when the gas-solid mixture density in the system is greater than 100 kilograms per cubic meter, or when the porosity is less than 90%. Conversely, the gas-solid mixture density of the conveying system