Permeate velocity when

The dimensionless permeate velocity will be proportional to T when... 

The encapsulation of drug molecules also leads to delivery systems, especially in the case of hydrophilic compounds where a permeation barrier with depot effect is provided. The permeation velocity is controlled by the properties of the membranes, as well as by the lipophilicity and size of the incorporated drug. Even large molecules are released slowly in the body, but unfortunately this also occurs under storage conditions. As liposomes do not have a solid surface, an equilibrium is built up between incorporated or adhered drug and free drug molecules, and this can lead to bursf effects when liposome dispersions are diluted. 

Because of the transverse velocity component, the velocity profile is a modification of the usual Poiseuille distribution. This problem has been solved by Berman (1953), including the effect of a constant permeation velocity in altering the velocity profile in the x direction and in causing a streamwise variation in the bulk average velocity. However, when the Reynolds number based on the permeation velocity is small, as it generally is, the streamwise component has the same form as for an impermeable wall and the transverse component is proportional to the constant permeation velocity v -, that is,... 

In contrast to the cases of gas extraction, gas addition shows an opposite effect on the sohds holdup distribution through the bed, resulting in relatively uniformly increased sohds holdup throughout the bed center but decreased solids holdup close to the membrane walls. When increasing the membrane area, and thereby decreasing the permeation velocity, the effect of gas addition was not reduced (i.e., from cases indicated with (A) to cases indicated with (B)). 

The static cell used for reverse osmosis and ultrafiliration experiments can be used to test the separation of gas mixtures Air in the feed chamber of the test cell and the feed gas line is removed by flushing them with the feed gas stream. The feed gas is then supplied to the feed gas chamber under pressure. The gas permeation velocity is measured by a bubble flow meter connected to the permeate side of the test cell. The permeate sample is also subjected to analysis by gas chromatography. This simple device is useful when an asymmetric membrane is tested and when the permeation rate is high. 

The trials, which were carried out in 1997 and 1998, have provided the data and understanding of the relationships between permeate flow and inlet brine velocity for different operating pressures. The graph in Fig. 11.4 shows that the brine permeability, when kept at constant inlet velocity through a standard membrane, is quite predictable for a known concentration of sulphate in the brine. The upper and lower... 

Since the permeance and permeability are always different from zero, no permeation is equivalent to zero permeation driving force, which occurs when the species partial pressures on both membrane sides are equal to each other. It must be noted that the equilibrium conversion of an MR is independent of the permeation law that expresses the penetrant velocity through the membrane materials. 

When a saturable transporter is involved in the permeation process, the permeability is no longer a constant value but is dependent on the concentration of the substrate. In that case it is necessary to characterize the parameters of the carrier-mediated process, Km, the Michaelis-Menten constant related with the affinity by the substrate and Vmax, the maximal velocity of transport. If a passive diffusion process occurs simultaneously to the active transport pathway then it is necessary to evaluate the contribution of each transport mechanism. An example of how to characterize the parameters in two experimental systems and how to correlate them are described in the next section. 

In the set of relations (3.182)-(3.188), P represents the coefficient for the velocity increase due to the species transport through the wall, Bi is the heat transfer Biot number (Bi = (arj)/ ), Bip is the mass transfer Biot number for the gaseous phase (Bi[) = (kri)/DA) and Bip is the Biot number for the porous wall (Bip = (k5xx,)/DAw)- Two new parameters and D w, respectively, represent the wall thickness and the wall effective diffusion coefficient of species. The model described by the set of relations (3.182)-(3.188) can easily be modified to respond to the situation of a membrane reactor when a chemical reaction occurs inside the cylindrical space and when one of the reaction products can permeate through the wall. The example particularized here concerns the heat and mass transfer of a... 

So far we have said nothing about the range of velocities actually found in a gas sample. In a real gas there are large numbers of collisions between particles. For example, when an odorous gas such as ammonia is released in a room, it takes some time for the odor to permeate the air, as we will see in Section 5.7. This delay results from collisions between the NH3 molecules and 02 and N2 molecules in the air, which greatly slow the mixing process. 

Parametric studies of the effects of TMP, temperature and crossflow velocity on the permeate flux and protein retention rate have been conducted using 0.8 pm alumina membranes at a pH of 4.4. The maximum steady state flux is observed at a TMP of 3 bars. As expected, a higher crossflow velocity increases the steady state permeate flux, as illustrated in Figure 6.3 under the condition of 50 C, TMP of 5 bars and pH of 4.40 [Attia et al., 1991b]. The protein retention rate also improves with the inciease in the crossflow velocity. The permeate flux reaches 175 L/hr-m, accompanied by a protein retention rate of 97.5% when the crossflow velocity is at 3.8 m/s. This improvement in the flux corresponds to a reduction in the thickness of the external fouling layer. 

Recent research efforts brought about new and exciting developments in membrane technology, some with direct implications for the membrane filtration of beer. For example, Stopka et al. [21] reported flux enhancement in the microfiltration of a beer yeast suspension when using a ceramic membrane with a helically stamped surface. A relatively simple modification of the ceramic membrane surface resulted in modified hydrodynamic conditions and disturbance of the fouling layer. As compared with a regular, smooth ceramic membrane of the same nominal pore size, the stamped membrane leads to higher flux and lower power consumption per unit volume of permeate at the same velocity of the feed. 

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