Osmosis, electrical Osmotic pressure

Electro-osmosis - the movement of liquid relative to a stationary charged surface (e.g. a capillary or porous plug) by an applied electric field (i.e. the complement of electrophoresis). The pressure necessary to counterbalance electro-osmotic flow is termed the electro-osmotic pressure. 

Water transport in electrodialysis from the diluate to the concentrate process stream can affect the process efficiency significantly. If a convective flux as a result of pressure differences between flow streams can be excluded there are still two sources for the transport of water from the diluate to the concentrate solution. The first one is the result of osmotic-pressure differences between the two solutions, and the second is due to electro-osmosis that results from the coupling of water to the ions being transported through the membrane due to the driving force of an electrical potential. 

Heat Thermal conduction, Jq = -keVT Chemical osmosis, JCQ = -CjCrKVTllh, where K is the hydraulic coefficient, nh the osmotic pressure head (Ilf = U/pg), (j the coefficient of osmotic efficiency Peltier effect, Jq=Lqlb T), where E is the electric field Thermal filtration... 

Pressure retarded osmosis (PRO) is a process derived from reverse osmosis. This process enables to generate energy from a concentration difference (14], The principle is shown in figure VI - 11. If a semipeimeable membrane separates a concentrated salt solution from water or a dilute solution then osmosis occurs and water flows from the dilute solution (or pure water) to the concentrated solution. Only when a pressure is applied higher than the osmotic pressure water flows from the concentrated solution to the diluted solution. The osmotic water flow can be used to generate electricity by means of a turbine. 

Pressure-retarded osmosis (PRO) is a variation of FO that has been evaluated since the early 1960 s it was first patented by Sidney Loeb in 1973. A comparison of PRO to RO and FO is shown in Figure 16.15. The primary difference between PRO and RO is that the applied pressure for RO is greater than the osmotic pressure, while for PRO the applied pressure is less than the osmotic pressure, thus water still diffuses to the more saline draw solution, thereby increasing the volume of the draw solution flow. This flow is then coupled to a turbine to generate electrical power (see Figure 16.16). Power that is generated using PRO is known as osmotic... 

When the porous medium saturated with the electrolyte is embodied in an external electric field E, there appears a nonzero volumetric body force within the Debye layer, which sets the ions in that region into motion. Far from the particle surfaces, this volumetric force is zero, since the solute there is neutral. However, the electrolyte is brought into motion also in the latter region as a result of the solute s viscosity. These processes lead to the appearance of an interstitial flow velocity field u(R). This velocity field, when integrated over a representative volume of the porous medium, yields a nonzero seepage velocity U in the absence of any macroscopic pressure gradient applied to the porous medium. This process is called electro-osmosis, and the velocity U is called the electro-osmotic velocity. 

Electro-osmosis is another electrokinetic phenomenon-in which an electric field is applied across a charged porous membrane or a slit of two charged nonporous membranes (see figure IV - 31). Due to the applied potential difference an electric current will flow and water molecules will flow with the ions (electro-osmotic flow) generating a pressure difference. As can be derived from nonequilibrium thermodynamics (sec chapter V) the following equation can be obtained indicating that both phenomena, electro-osmose and streaming potential, are similar... 

Li et al. presented a similar design of a circular chamber for lens curvature, adjusted by the combined effects of pressure and electro-osmosis [17]. Figure 7.14 shows the concept. Two cladding streams (fluid 1 and fluid 3) were electrically conducting with high electro-osmotic mobility the core stream (core fluid 2) was non-conducting with low electro-osmotic mobility. 

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