Osmosis cell

The boundary condition on the low pressure side of a reverse osmosis cell requires that the salt and water fluxes through the membrane determine the bulk salt concentration on the low pressure side. Thus, the following relationship results ... 

The general experimental procedure was similar to that reported in the literature (25). The six flow type reverse osmosis cells were connected in series and were constructed in a design similar to that reported by Sourirajan (25). The cells were placed in a constant temperature box and the system was controlled to 25 1°C. The feed flow rate was maintained constant at 400... 

FIGURE 13.10 An osmosis cell In an osmosis cell, water flows through a semiper-meable membrane from a less concentrated solution into a more concentrated solution. As a result, fluid rises in one side of the tube until the weight of the excess fluid creates enough pressure to stop the flow. This pressure is the osmotic pressure of the solution. 

Consider the molecular views of osmosis cells. For each cell, determine the direction of water flow. 

Osmosis is a naturally occurring process in which water flows from an area of low solute concentration to high solute concentration. It is most easily demonstrated in an osmosis cell, where two solutions are separated by a semipermeable membrane (Figure 12-21). A semipermeable membrane selectively allows water to pass through it but blocks other substances. If a salt water solution is placed on one side of an osmosis cell and fresh water on the other, osmosis will occur. The side of the membrane containing the salt water will rise as fresh water flows through the membrane and into the salt water solution. 

FIGURE 12-21 In an osmosis cell, water flows from the side containing pure water through a semipermeable membrane to the side containing a solution. 

FIGURE 12-22 In reverse osmosis, pressure is applied to the solution side of the osmosis cell, forcing water to flow from the solution side to the pure water side. Because the membrane is semipermeable, water molecules are allowed to pass while the solute molecules are not. 

Figure 3.9. Reverse osmosis cell and test system. (Reproduced from [5] with permission.)...

The treatment so far has heen based on a particular feed concentration, Q , in the reverse osmosis cell (Figure 6.3.28 (a)). As time progresses, water from the feed solution will be removed as permeate therefore the feed concentration of species i, e.g. NaCl, will increase. If we require the process to yield a particular concentration of salt in the permeated water, then the salt rejection required of the membrane, / i,reqd> will have to increase. Further, since the osmotic pressure of the feed solution increases with time, either the solvent flux will go down with time or the driving pressure difference, AP, has to go up. To these factors, one has to add the complication of concentration polarization. To illustrate the effect of increasing feed salt concentration with time, we will ignore first the effect of any concentration polarization and then focus on the consequence of different values of fractional water recovery, re. For the reverse osmosis cell shown in Figure 6.3.28(a), it is defined as... 

Figure 12.16 t illustrates an osmosis cell. The left side of the cell contains a concentrated saltwater solution and the right side of the cell contains pure water. A semipermeable membrane—a membrane that selectively allows some substances to pass through but not... 

The power required to run a reverse osmosis device is given by Po = QAP, where Po is the power, Q is the volumetric flow rate of fluid pumped to the pressure of the reverse osmosis cell, and iP is the pressure increase from ambient to the inlet of that cell. 

Figure E.IO Electro-osmosis cell A, A, calomel electrodes B, plug of material C, C, leads to platinum gauze electrodes D, air bubble and scale...

Electrical properties were measured for various membranes after they were used in reverse osmosis desalination to study the possible correlation between electrical properties and membrane performance. Membranes were air-dried upon removal from the reverse osmosis cells and placed in the system used for measuring the electrical properties described above. The results of this study are given in Table IX. The tabulated values for the conductances(G) have been corrected for the 0.599M solution resistances of 16.6, 22.8, and 11.4 ohm cm for NaCl, choline chloride, and MgCl2, respectively. 

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