Membrane water content, effect

Effect of Hydrophilic Bentonites. All membrane models imply a direct relation between flux and membrane water content. The gross water content of the membranes can be increased by incorporating pre-gelled hydrophilic bentonites into the membranes. The useful bentonite concentration is limited by the fact that pre-gelation introduces water into the casting solution (J ). 

During cell/stack operation, water content in the membrane is affected by the local intensive variables, such as local temperature, water vapor concentration in the gas phase, gas temperature and velocity in the channel, and the properties of the electrode and gas diffusion media. The power fluctuation can result in temperature variation inside the cell/stack, which will subsequently change the local membrane water content. As the water content in the membrane tends to be non-uniform and unsteady, this results in operation stresses. When the membrane uptakes water from a dry state, it tends to expand as there is no space for it to extend in plane and it can wrinkle up as schematically shown in Fig. 4 when the membrane dries out, the wrinkled part may not flatten out, and this ratcheting effect can cause the pile up of wrinkles at regions where membrane can find space to fold. The operation stress is typically cyclic in nature due to startup-shutdown cycles, freeze-thaw cycles, and power output cycles. 

Effects of Key Parameters 2.4.1. Initial Membrane Water Content... 

Figure 4. Effect of current density on voltage evolution during cold start from —30° C with initial membrane water content of /.j = 6.2. (reproduced with permission from Tajiri et al.18)...

Besides the effect of the position and identity of the substituent in the pyridinium groups on the transport number between anions, the water contents of the membranes differ according to the nature of pyridine derivatives reacted with the membranes. Figure 5.38 shows the relationship between the transport numbers of various anions relative to chloride ions and water contents of the membranes reacted with ethyl pyridines.103 The permeation of nitrate and bromide ions decreases and that of fluoride ions increases with increasing membrane water content when ethyl pyridines are reacted with the membranes. However, /cis°4 is independent of water content. This might be due to the low mobility of sulfate... 

When used for automotive applications, fuel cells must respond to changes in the load. Changing the load alters the water production, changing the balance between water produced and water removed, resulting in a change of the membrane water content. The effect of the load resistance on the water activity can be seen in the polarization curves for the STR PEM fuel cell shown in Figure 3.9A [23]. The STR PEM fuel cell was operated in the autohumidification mode. The STR PEM fuel cell was equilibrated at 80C for 12 h with a fixed load resistance (either 0.2 or 20 fi). After equilibration, the polarization curve was obtained by sweeping the load resistance between 0.2 and 20 ft in 100 s. The relative humidity in the anode and cathode streams... 

Water is produced at the cathode/membrane interface, and it must be transported to the anode and cathode flow channels to be removed. At present, we do not have a direct measurement of the water activity in the membrane (the partial pressure of water in the membrane, p> embrane do know the water content in the effluent streams. The experimental data may be integrated from the known initial water content (after the water injection) to the steady state current and partial pressures of water. Integration of Eq. (3.4) gives the steady state membrane water content for known water partial pressure at the anode and cathode. Effective mass transfer coefficients for water from the cathode/membrane interface to the cathode gas flow channel and from the cathode/membrane interface to the... 

Huang and Kim studied the effect of lEC value of SPPO on the membrane water content and the reverse osmosis performance. As shown in... 

Equation 7 shows that as AP — oo, P — 1. The principal advantage of the solution—diffusion (SD) model is that only two parameters are needed to characterize the membrane system. As a result, this model has been widely appHed to both inorganic salt and organic solute systems. However, it has been indicated (26) that the SD model is limited to membranes having low water content. Also, for many RO membranes and solutes, particularly organics, the SD model does not adequately describe water or solute flux (27). Possible causes for these deviations include imperfections in the membrane barrier layer, pore flow (convection effects), and solute—solvent—membrane interactions. 

The lack of understanding of the effect of the allelopathic agents on whole plant photosynthetic processes, namely, changes in stanatal opening, membrane permeability, water content and marry other processes that affect the overall photosynthetic processes. 

The oxidation of chloride at the anode results in an anode boundary layer that contains less chloride than the bulk anolyte (Fig. 6.2). The membrane is pressed against the anode by differential pressure, and thus is integrated into the anode boundary layer. Good internal mixing is necessary to minimise the layer effect and to maintain a steady supply of chloride to the anode for reaction. The ionic concentration and the thickness of this layer will have an effect on the water content, the... 

---