Trans-membrane flow

Fluid Flow and Trans-membrane Exchange in a Hemodiaiyzer Module 457... 

Just as there are cation channels, there are also trans-membrane channels involved in the transport of biologically important anions such as Cl-. The crystal structure of the CIC chloride channel from Salmonella typhimurium was reported in 2002.3 Along with the determination of the Streptomyces lividans potassium channel structure, this work won a share of the 2003 Nobel prize in chemistry for Roderick MacKinnon (Howard Hughes Medical Institute, New York, USA). Chloride channels catalyse the flow of chloride across cell membranes and play a significant role in functions such as... 

Therefore, we have to analyse the variation of the rate of permeation according to the temperature (zj), the trans-membrane pressure difference (Z2) and the gas molecular weight (Z3). Then, we have 3 factors each of which has two levels. Thus the number of experiments needed for the process investigation is N = 2 = 8. Table 5.13 gives the concrete plan of the experiments. The last column contains the output y values of the process (flow rates of permeation). Figure 5.8 shows a geometric interpretation for a 2 experimental plan where each cube corner defines an experiment with the specified dimensionless values of the factors. So as to process these statistical data with the procedures that use matrix calculations, we have to introduce here a fictive variable Xq, which has a permanent +1 value (see also Section 5.4.4). 

G. Catapano, G. lorio, E. Drioli, and M. Filosa, Experimental analysis of a cross-flow membrane bioreactor with entrapped whole cells Influence of trans-membrane pressure and substrate feed concentration on reactor performance, J. Membrane Sci 55 325 (1988). 

From the non-zero slope of the permeability as a function of the trans-membrane pressure it follows that defects are present giving rise to non-Knudsen (viscous flow) contributions to the gas permeability (see Chapter 9). These... 

The very serious problem of fouling by proteins is corroborated by many publications [41,70,71]. Various parameters influencing the fouling behaviour have been studied. Clark et al. [70] discuss the influence of protein concentration, trans-membrane pressure, cross flow velocity and pH. For pore sizes of 0.1 pm (Membralox membranes), filtering bovine serum albumin, the flux has a minimum at the pH of the protein isoelectric point. Dumon and Barnier [71] show that the amount of protein adsorption depends on previous adsorption. Contacting with citrate or phosphate lowers a subsequent protein adsorption contacting with nitrate increases the protein adsorption. 

Figures 13 and 14 respectively show the relationship of average trans membrane pressure and circulation rate on flux for both whole cells and lysate suspensions. The lysate was produced via the lysozyme procedure. Qualitatively, the behaviors are quite similar to those seen in Figures 9 and 10 where the cells are lysed by sonication. Beyond minimum circulation flows, little extra flux is attained as the circulation rate increases. The average TMP is the dominant factor in producing flux, however, if Pin - Pout less than about 20 psi, debris can accumulate at the membrane surface and inhibit flow. It should be emphasized that these results pertain to 0.45 micron pore size microporous membrane only.

In terms of optimizing system performance, the flux for both cells and lysate suspensions seem to be most strongly influenced by the average trans membrane pressure, although maintaining a minimum circulation flow is critical also. Flux rates on microporous membranes for lysates are typically less than for whole cell suspensions as would be expected because of the dispersed cell debris present. Filtrates from lysate processing are typically clear, but do depend on the membrane used and the method of lysing the cells. The ultra-... 

Dialysis is a diffusion-based separation process that uses a semipermeable membrane to separate species by vittue of their different mobilities in the membrane. A feed solution, containing the solutes to he separated, flows ou one side of the membrane while a solvent stream, die dialysate, flows on die other side (Fig. 21. -1). Solute transport across the membrane occurs by diffusion driven by the difference in solme chemical potential between the two membrane-solution interfaces. In practical dialysis devices, no obligatory transmembrane hydraulic pressure may add an additional component of convective transport. Convective transport also may occur if one stream, usually the feed, is highly concentrated, thus giving rise to a transmembrane osmotic gradient down which solvent will flow. In such circumstances, the description of solute transport becomes more complex since it must incorporate some function of die trans-membrane fluid velocity. 

Figure 2.65 Flow schematic of trans membrane distillation (TMD) with heat exchanger (HX) for recovery of heat of evaporation.

Measurement of Trans-membrane Potential. For a constant bias potential, negligible current flows through the insulator on the semiconductor chip, so that there is no steady state potential across Rm- The potential across the chip is y - Vm. If in the absence of the membrane an photocurrent inflection point potential was measured at S = pip/ then in the presence of the membrane it will shift positive by the value of the trans-membrane potential as indicated by Equation 3. Measuring Vm is clearly analogous to using the sensor to make pH or redox measurements. 

The above emulsification methods (perhaps except the Couette flow technique) have as a common feature that the final DSD is primarily determined by the interaction of turbulent eddies with interfaces. Note, however, that turbulence is hard to control and to maintain consistently throughout the whole reactor volume. From a practical point of view, it is almost impossible to predict the DSD after a scale-up based on laboratory-scale experiments. Emulsification techniques based on other principles are necessary to overcome these drawbacks. An alternative technique is the so-called membrane emulsification method where the liquid forming the disperse phase is pressed through a porous membrane. The other side of the membrane where the droplets are formed is in contact with the continuous phase. This concept is simple and it is assumed to be superior to the above techniques (35). The basic relationship of membrane emulsification (equation (8.10)) correlates the trans-membrane pressure required to start the drop-wise flow through the pores (ft) with the average pore diameter of the membrane (Dm) with being the contact angle of the mixture with the wall of the pore ... 

Although the redox loop mechanism is no longer believed to explain how electron flow through an electron transport chain causes the generation of a trans-membrane H gradient, there is considerable evidence that the Q.c. operates in mitochondria, bacteria and possibly chloroplasts under low light conditions. 

High-Pe devices are dominated by transmembrane water transport, and detailed discussion must be left to the above cited references. However, it is important to recognize their primary function is to remove water and undesired solutes while retaining one solute which is desired. Rejection of the desired product increases toward an asymptote as water flux increases, and one should operate near this asymptote if at all possible. The relation between water flux and rejection is perhaps best determined experimentally. However, as water flux increases the rejected solute concentration at the interface between the feed stream and the membrane also increases. This process, usually known as concentration polarization, typically produces a significant increase in osmotic pressure which acts to reduce the flow. Polarization is a complex process, but to a good approximation the trans-membrane water velocity is given by... 

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