Pure water permeability constant

All symbols are defined at the end of the paper. Equation 10 defines the pure water permeability constant A for the membrane which is a measure of its overall porosity eq 12 defines the solute transport parameter D /K6 for the membrane, which is also a measure of the average pore size on the membrane surface on a relative scale. The Important feature of the above set of equations is that neither any one equation in the set of equations 10 to 13, nor any part of this set of equations is adequate representation of reverse osmosis transport the latter is governed simultaneously by the entire set of eq 10 to 13. Further, under steady state operating conditions, a single set of experimental data on (PWP), (PR), and f enables one to calculate the quantities A, Xy 2> point... 

Membrane Specifications. At a specified operating temperature and pressure, a cellulose acetate membrane is completely specified in terms of its pure water permeability constant A and solute transport parameter D /k6 for a convenient reference solute such as sodium chloride. A single set of experimental data on (PWP), (PR), and f at known operating conditions is enough to obtain data on the specifying parameters A and (DAM/X6)jjg(. 2 at any given temperature and pressure. 

Figure 16. Decrease of separation (or increase of solute permeabilities) of seawater reverse osmosis desalination at several concentration levels of NaOCl. Initial membrane constants pure water permeability constant = 97.0 nmol m Pa s and the solute permeability constant for NaCl = 0.9 X 10 cm s . Operational conditions k = 7.(97 X 10 cm s Ap = 6.0 MPa, and T = 25°C.

Reverse-Osmosis Experiments. All reverse-osmosis experiments were performed with continuous-flow cells. Each membrane was subjected to an initial pure water pressure of 2068 kPag (300 psig) for 2 h pure water was used as feed to minimize the compaction effect. The specifications of all the membranes in terms of the solute transport parameter [(Dam/ 6)Naci]> the pure water permeability constant (A), the separation, and the product rate (PR) are given in Table I. These were determined by Kimura-Sourirajan analysis (7) of experimental reverse-osmosis data with sodium chloride solution at a feed concentration of 0.06 m unless otherwise stated. All other reverse-osmosis experiments were carried out at laboratory temperature (23-25 °C), an operating pressure of 1724 kPag (250 psig), a feed concentration of 100 ppm, and a feed flow rate >400 cmVmin. The fraction solute separation (/) is defined as follows ... 

Plotting the reciprocals of membrane constant(pure water permeability) against time elasped as shown in Fig. 3, a much more straight line can be obtained for each operating pressure 2000, 1500,1000 and 600 psi. But during the initial period of the operation of less than seven to three hours, the reciprocal values increase steeply untill they reach the straight lines. 

A is often referred to as the water permeability constant. Note that if the soluble spedes rejection is not complete, the osmotic pressure difference across the membrane must be related to the osmotic pressure difference between the feed and the permeate streams, instead of that between the feed and pure water. Another factor commonly reported for membrane performance is the salt or solute rejection efficiency (ratio), R, defined as... 

Ilias and Govind [1993] also used the CFD approach to solve coupled transport equations of momentum and species describing the dynamics of a tubular ultraflltration or reverse osmosis unit. An implicit finite-difference method was used as the solution scheme. Local variations of solute concentration, u ansmembranc flux and axial pressure drop can be obtained from the simulation which, when compared to published experimental data, shows that the common practice of using a constant membrane permeability (usually obtained from the data of pure water flux) can grossly overestimate... 

After formation, we utilized pure water to measure the tydraulic permeability, Lp (cm/atm-mln) of the dynamic layer. For a constant crossflow velocity, Lp is seen to decrease with an increase in the pressure of formation, as seen from Trials 1-4 in Table 1. This could be interpreted either as due to an increase in the thickness of the dynamic layer or a "tightening" of... 

The most common method to measure alcohol permeability through membranes is the diffusion cell method under non-stationary conditions. In this method the membrane separates two reservoirs the receptor reservoir containing pure water, and the donor reservoir containing the alcohol solution of known concentration. Usually the alcohol solution in the donor reservoir is refreshed during the experiment to maintain its concentration, Cj, constant along the time. The non-stationary alcohol concentration in the receptor reservoir, c, is followed as a function of time by in situ or ex situ sensors. By integrating Eq. 6.4 the time dependence of is given by... 

An ultrafiltration membrane shows a pure water flux of 100 l/m. h at 2 bars. This membrane is used to concentrate a polj mer solution. After a certain period a constant flux is obtained of 10 l/m-.h at 5 bars. The permeability of the formed gellayer containing particles with a size of 5 nm and a porosity of 50% can be described by Kozeny-Carmaiui. 

Similarly a number of researches (I4,i5,ie,i7,i8,i9,20) at low humidity showed that the permeation velocity was proportional to the vapour-pressure difference. The more hygroscopic the substance, however, the lower is the humidity above which this relationship breaks down. Pure rubbers and waxes sorb little water, and the permeability constants calculated from Pick s law are little affected by variations of humidity at the surfaces of the membrane. Many rubbers, however, contain hydrophilic impurity and sorption occurs freely. Figs. 150(6) and 151(9) show that the permeation rate and the sorption isotherms follow similar courses. 

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