Elements of fluid mechanics - Application to porous media

Among the many process engineering problems encountered by engineers and pharmacists working in the chemical, petroleum, pharmaceutical, cosmetics and food industries, the flow of one or more fluids through a fixed or mobile porous medium is of paramount importance. We need only mention the main unit processes in process engineering (drying, fluidization, sedimentation, crystallization, distillation, ion exchange, liquid-liquid extraction, etc.) to see the plethora of pipes, columns, tanks and reactors within which the process(es) is (are) carried out.

Similarly, in the healthcare industry, formulation involves the design, development, production and distribution of porous (or non-porous) materials whose composition, preparation and arrangement function to deliver an action or provide a service (e.g. galenics).

After a brief review of the fundamental principles of fluid mechanics as applied to the flow of perfect or viscous Newtonian fluids in pipes, this text provides the essential basics on the hydrodynamics of flows in porous media encountered in sedimentation and granulation processes, reactions requiring packing, fluidization and filtration.

Our goal is to propose the relationship(s) that exist:

• between the fluid flow rate and the characteristic properties of the mobile porous medium and of the fluids to maintain this porous medium in optimum operating conditions for carrying out the process and producing the desired product (sedimentation, fluidization);

or

• between the head losses required to ensure a known, optimum fluid flow rate, taking into account the characteristic properties of the fixed porous medium (reactors, filtration).

It goes without saying that this text is by no means exhaustive, and the reader is advised to refer to the highly specialized works listed in the bibliography for more in-depth knowledge of a particular process.