Flow regime filtration

Mechanical forces can disturb the elaborate structure of the enzyme molecules to such a degree that de-activation can occur. The forces associated with flowing fluids, liquid films and interfaces can all cause de-activation. The rate of denaturation is a function both of intensity and of exposure time to the flow regime. Some enzymes show an ability to recover from such treatment. It should be noted that other enzymes are sensitive to shear stress and not to shear rate. This characteristic mechanical fragility of enzymes may impose limits on the fluid forces which can be tolerated in enzyme reactors. This applies when stirring is used to increase mass transfer rates of substrate, or in membrane filtration systems where increasing flux through a membrane can be accompanied by increased fluid shear at the surface of the membrane and within membrane pores. Another mechanical force, surface... 

Experimental evidence has demonstrated that Dean vortices can be effective for enhancement of membrane performance under laminar conditions [18]. As flow conditions approach the transition and turbulent flow regimes, straight membranes have a better mass transfer and higher wall shear rate than in flows with curved membrane channels. The effects of Dean vortices on the performance of membrane filtration have been studied experimentally and theoretically by Belfort and coworkers [19-22]. Mallubhotla and Belfort [21] assessed the filtration of suspensions of polydispersed polystyrene particles (mean diameter 25 pm) and silica particles (mean diameter 20 pm) with and without the presence of Dean flow using an 180° U-bend channel... 

Pulsate flows were applied to mineral microfiltrations membranes during apple juice filtration [36] illustrating the advantage of this method to enhance permeability compared to steady flow regime. With carefully chosen pulsations permeate flux increased up to 45% at 1 Hz pulsation frequency. Moreover well defined pulsations decreased the hydraulic power dissipated in the retentate per unit volume by up to 30%. In an other work on cross-flow filtration of plasma from blood [37] permeate flux increase was also observed when pressure and flow pulsations at 1 Hz are superimposed on the retentate. 

Figure 3.56 Three operating regimes for cross-flow electro filtration.

The boundary constraints used in pipe flow regimes are inlet velocity profile, zero velocity on solid non-slip walls, and stress free (or for long pipes developed flow) exit conditions. In shell and tube systems with solid and porous walls, used in thickening of suspensions by cross-flow filtration, a different set of boundary conditions must be given. These are the inlet velocity profile, zero velocity on outer shell s solid walls, stress-free conditions at the exit, and the following Darcy flow conditions on porous wall ... 

Many industrial filtrations are performed under variable rather than constant pressure conditions and Chapter 4 describes how sequences of constant pressure experiments can be used to provide scale-up constants that are valid for other pressure/flow regimes. Figure E.3 shows some experimental data for constant rate calcite filtrations where the pressure changes and flow measurements for the filtration have been provided by a software controlled pressure regulator and an electronic balance, respectively. In accordance with theory, a near linear relation is shown between pressure and time. The theoretical predictions also shown on Figure E.3 were produced using... 

PU is a versatile class of thermoplastic polymer that possesses a range of excellent properties, such as excellent elastomeric property, resistance to abrasion, and high durability [42-44]. Sambaer et al. [45] proposed a new approach to create a simple 3D nanofiber membrane model based on the real structure features of PU membranes. The slip/transition/free molecular flow regime, particle-flber interactions, air/particle slip, sieve, and homogenous flow fleld have been considered in this full 3D particle filtration model (Fig. 12.5a). They suggested that in the force... 

Hung CH, Leung WWF (2011) Filtration of nano-aerosol using nanofiber filter under low Peclet number and transitional flow regime. Sep Purif Technol 79(l) 34-42, http //dx.doi.oig/ 10.1016/j.seppur.2011.03.008... 

Fluid filters were realized in the low Reynolds number regime [22,23]. It separates the particles and molecules based on the diffusion coefficient while diluting their concentration. The concept of the diffusion-based filtration is shown in Fig. 5. As the two flow streams of sample and dilutant are introduced... 

Flux enhancement by bubbling is significant in the laminar regime of liquid flow and becomes insignificant as the liquid flow Reynolds number approaches 2500-3000. The enhancement is relatively insensitive to the actual liquid flow over much of the laminar region. This is because the filtration is dominant by the secondary flows induced by the bubbles. 

Let us examine the TFF technique and a typical process regime. Tangential Flow Filtration is the general term used to describe filtration where cross flow parallel to the filter surface is used to enhance filtration rate. This is in contrast to dead ended filtration where the fluid path is solely through the filter. If the membrane used to make the separation is microporous (0.2-0.1+5 urn pore size), the technique is more specifically called mdcroporous tangential flow filtration. Ultrafiltration, a subset of Tangential Flow Filtration, employs a finer, anisotropic membrane able to retain macromolecules, albumin for instance. We will emphasize the use of ultrafiltration membranes in this discussion. 

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