Water membrane tested

Specifications for gas turbine fuels prescribe test limits that must be met by the refiner who manufactures fuel however, it is customary for fuel users to define quality control limits for fuel at the point of delivery or of custody transfer. These limits must be met by third parties who distribute and handle fuels on or near the airport. Tests on receipt at airport depots include appearance, distfllation, flash point (or vapor pressure), density, freezing point, smoke point, corrosion, existing gum, water reaction, and water separation. Tests on delivery to the aircraft include appearance, particulates, membrane color, free water, and electrical conductivity. 

The committee notes that the analysis of the cell membrane failure that occurred in the 500-hour DMMP (discussed in the next section) suggests that the cell membrane tests did not represent worst-case conditions for membrane life under actual operating conditions and that limited credence can be given to the conclusions from this test (AEA, 2001k). It also notes that in the absence of organics, parasitic oxidation of water may offset the Ag2+ attacks that were anticipated in this test. 

Based on a simple economic analysis, it appears that, when seawater is used as the salt solution, a membrane with a water flux in PRO of about 1 x 10 2cm3/cm2-sec ( <200 gal/ft2-day) is required to make the process economically viable in today s economy, even if the installed membrane cost is as low as 100/m2. The highest flux we projected under these PRO conditions among the RO membranes tested was only somewhat greater than 1 x 10 cm3/cm -sec ( 2 gal/ft -day), for a power output of 1.6 watt/m2. 

Membrane test to screen water for bacterial contamination developed in Germany -1944... 

Seawater membranes are used to treat high-salinity (35,000 to 50,000 ppm total dissolved solids (TDS)) feed waters. These membranes can operate at pressures up to 1,500 psi. Typical membrane test conditions are as follows ... 

Brackish water membranes are designed to treat lower-salinity feed waters, up to about 4,000 to 5,000 ppm (TDS). Maximum operating pressure for brackish water membranes is typically 600 psi. These membranes are typically tested at the following conditions ... 

As with seawater membranes, there is no one uniform test condition for all brackish water membranes of the same type. Thus, a direct comparison between manufacturers requires a close look at the test conditions. 

Brackish water membranes can be shipped from the manufacturer wet or dry. Wet membranes have been performance tested at the factory. However, testing is usually conducted for shorter (hours) versus longer (days) periods. As noted in Figure 14.2 (Chapter 14.3.2), there is a period of time after start up during which membrane performance is not stable due to compaction. Flux and rejection both decrease during this period. Unless a membrane is wet tested until stable performance is achieved, the performance specifications for that membranes based on the wet test are not accurate.7... 

In 1996, a paper was published which was dedicated to selecting suitable membranes for separations in organic solvents [466]. Membranes tested in an asymmetrical channel included polysulfone MWCO 20,000 g/mol, regenerated cellulose MWCO 20,000 g/mol, PTFE pore size 0.02 mm, polyaramide MWCO 50,000 g/mol, poly(vinylidene fluoride) MWCO 50,000 g/mol, poly(phenylene oxide) MWCO 20,000 g/mol and a DDS fluoro polymer MWCO 30,000 g/mol. The first membrane was tested with water, the others with THF or a THF/ace-tonitrile mixture. Numerous problems occurred with the different membranes. The best membrane for THF was found to be the DDS fluoro polymer membrane. 

Water Flux The permeability of a UF membrane is determined by pore size, pore density, and the thickness of the membrane active layer. Water flux is measured in the absence of solute, generally on a newly made or freshly cleaned sample. The test is simple, and involves passing water through the membrane generally in dead-end flow under carefully controlled conditions. In a water flux test, the membrane behaves as a porous medium with the flow described by Darcy s law. Adjustments for viscosity and pressure are made to correct tne results to standard conditions, typically the viscosity of water at 25°C and the pressure to 50 psi (343 kPa). The water flux will be many multiples ofthe process flux when the membrane is being used for a separation. Virgin membrane has a standard water flux of over 1 mm/sec. By the time the membrane is incorporated into a device and used in an application, that flux drops to perhaps 100 pm/s. Process fluxes are much lower. 

Brackish Water Membrane—The flux and rejection of the membrane is determined when the membrane is tested on a feedwater of an aqueous sodium chloride solution with a concentration of... 

The principle of the water intrusion test derives from the mercury intrusion test, which (applicable to both hydrophilic and hydrophobic membranes) is restricted to laboratory conditions. The membrane is placed in contact with the fluid (water in the case of the water penetration test, mercury in the case of the mercury intrusion test), and the pressure is increased, with the purpose of forcing the fluid into the pores. The volume of fluid forced into the pores is a measure of pore size and void space volume and thus of filter integrity. 

Over the whole range of variation of the Cl- HC03— ratio in the cathode compartment, the transport number of chloride was somewhat higher than the molar ratio of chloride in the solution. In other words, in all the three membranes tested chloride ion transport is favored over bicarbonate ion transport. This fact is not unrelated to the data on water transport. The electro-osmotic water transport with chloride ions is smaller than with bicarbonate ions. It is known that, other factors being equal, low water transport and high mobility of ions in a membrane-as measured, for instance, by electrical conductivity-are correlated (13,16). 

Gusses A.M., Speth T.F., Allgeier S.C., Summers R.S. (1997), Evaluation of surface water pretreatment processes using rapid bench-scale membrane test, Proc. AWWA Membrane Technology Conference, New Orleans, Feb. 97, 765-782. 

Figure 15. Permeate flow rate per unit membrane area (gallons/day/ft ) and NaCl rejection of brackish water membranes offered by GE (<>), FilmTec/Dow (x), Koch (o), Toray (a), Trisep (+), andNitto Denko/Hydranautics (Is). All values taken from the manufacturers web sites. Test conditions for all membranes were 2000 ppm NaCl feed concentration, 225 psi feed pressure, 77 F feed temperature, and 15% permeate recovery. Feed pH for test conditions varied slightly in the tests from 6.5-8. Note that a 1500 ppm NaCl feed was used to obtain the Nitto Denko/Hydranautics values normalization to 2000 ppm NaCl reduces permeability by S%.

A specific device is used for performing the test, known as the rubber balloon apparatus. It consists of a volumetric cylinder, one end of which is made of a thin elastic membrane. The volumetric cylinder is filled with a known mass of water before testing. The device is placed over the hole, and with the aid of low air pressure, the water occupies the available space (Figure 1.16). 

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