Packings effective free area

The only available test data [44] indicate that the plain flat plate (26-45% free area) has a decided detrimental effect on the allowable flooding conditions of the tower whereas the wire screen, weir-type, and fused Raschig ring designs have very little effect when using Intalox saddles for packing. 

As the fluid velocity is increased the drag on the particles increases and a point is reached where the pressure drop balances the effective weight of bed per unit cross-sectional area. At this point the fluid drag just supports the solid particles. A small increase in the flow rate causes a slight expansion of the bed from its static, packed state. Further increase in the flow rate allows the bed to expand more and the particles become free to move around and the bed is said to be fluidized. The state when the bed just becomes fluidized is known as incipient, or minimum, fluidization. The fluid velocity required to cause incipient fluidization is called the minimum fluidization velocity and is denoted by umf. 

The behaviour of the column is largely dependent on the stationary phase but the support material can also play a very important role, particularly when a low concentration of liquid phase is used. A good support material should have a very large surface area and a uniform particle size, free from fines and sufficiently robust so that it does not break up into powder with normal handling. It should be chemically inert, without adsorptive effects, and, when coated with stationary phase, should pack easily and uniformly into the column. 

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