Porous Flow

Porous Flow Is a multiphase flow involving fluids passing through a permeable bed of particles Process examples: Catalytic converter Drying column Filtration (this will be cover in details later) Objective: to predict pressure drop. Pressure drop prediction is complicated by the variety of solid materials and of their packing arrangement (or patterns)

Properties of Porous Particles Porosity/Voidage/Void fraction () Is the fraction of volume that is not occupied by solid materials Specific surface, S Is the surface area of a particle divided by its volume For a sphere: For other shape particles:

Pressure Drop – Laminar Flow

Kozeny equation Laminar Re<1 2

Example 2.1

Pressure Drop – Turbulent Flow

Use the same superficial velocity that was calculated 2.1 Example 2.2 Use the same superficial velocity that was calculated Using laminar and turbulent equations

General Equation for Pressure Drop Calculation Ergun equation

Example 2.3

2

Pressure drop – Compressible Flow Gas flow through a packed bed under conditions where there is appreciable pressure drop ( Compressible flow) Because the pores between the particles are of different sizes, there may well be choked flow in small pores Pressure drops are larger than expected because of coking Computation of pressure drops should consider the overall energy equation:

Two Phase Flows in Porous Media For gas liquid flow, liquid wets the surface of the particle (wetted fluid) Gas flows through the larger pores that are limited with liquid, and thus does not make direct contact with the solid. Consequently, the gas experiences much less resistance to flow than the liquid (Non-wetting fluid)

Saturation Is the fraction of the voidage occupied by the specific fluid We can calculate the saturation for both the liquid and gas phase Adding up to 1

Example 2.4 2.1

Counter-Current Flow

Gas-Liquid Flow