2. Sizing a countercurrent permanent contact column (axial mixing)

2.1 Definition

Piston flow is an ideal flow that assumes material movement solely by convection, like the movement of a piston. To a first approximation, this is the very fast flow in a cylindrical tube that is very long in relation to its diameter. At low or moderate flow rates, the phases are subject to a greater or lesser degree of mixing. This results in a loss of efficiency. The same applies to dispersed phases in the form of drops or bubbles. The displacement of these drops or bubbles depends on their size. This results in an inhomogeneity that the piston model is unable to take into account. When mixing in the direction of flow is taken into account, we speak of axial mixing. This is studied experimentally by measuring the residence time distribution (RSD) using tracers. A tracer...