PDF Publication Title:
Text from PDF Page: 013
Membranes 2020, 10, 221 13 of 72 It is also possible to calculate the limiting current density value by substituting CMemb by 0 in i Equation (13): dIlim =−NbtMemb−NbtClimδ ii (16) FDi CSol i It appeared that the limiting current density value is directly proportional to the concentration of charged species in solution. If we want to calculate the limiting current value dIlim , the previous equation is of little interest, because in practice, it is very difficult to measure experimentally the thickness δ of the DBL [49]. Therefore, a similar approach to the one employed in ultrafiltration can be used to measure this limiting current value. The term Dδ is considered as a mass transfer coefficient, Km, which can be related to other physical basic units by Sherwood’s correlations: N =K de =AN aN 0,33 (17) Sh mDi Re Sc With NSh the Sherwood number (dimensionless), Km the mass transfer coefficient (in m/s), de the spacer thickness (in m), Di the diffusivity coefficient (in m2/s), A a constant, NRe the Reynolds number (NRe = ρvde ), a another constant, NSc the Schmid number (NSc = η ), ρ the fluid density (in kg/m3), η ρ.D v the fluid velocity in the spacer (in m/s), and η the fluid viscosity (in Pa.s or decapoise). Constants A and a can be determined experimentally and can subsequently be used for the design of similar equipment. From the previous equation, it appears that the mass transfer coefficient Km is a function of the apparatus design (de), the flow type (NRe) and the physical properties of the solution (D, ρ and η). The Km value will also vary according to the fluid velocity in the spacer: Km ≈ va (18) For thin spacers, the exponent a varies, in most cases, from 0.5 (for a laminar flow) to 0.90 (for a turbulent flow). In practice, spacers used in ED are very thin (0.2–2 mm), which will contribute to the establishment of a laminar flow, and minimize the electrical resistance of the solution. The current density applied for conventional electrodialysis in its main industrial applications is generally in the range of 100 to 400 A/m2, however in water treatment the current density is <80 A/m2. For EDBM at an industrial scale, the current density applied is more between 500 and 1000 A/m2. 3.4. Overpassing the Limiting Current Density and Occurence of Vortex The operation of electrodialytic equipments in overlimiting current densities was demonstrated to be responsible for an additional supply of counter-ions at the membrane surface, which occurs because of the exaltation effect and current-induced convection, accompanied by water splitting at the membrane/solution interface [50–52]. These phenomena, observed in overlimiting conditions, have major impacts on electrodialytic process performances. 3.4.1. Exaltation Effect One mechanism of ion transfer when CP is developed is current exaltation. This effect was firstly described, in membrane systems, by Kharkats [53]. Due to CP phenomenon, the increase in current density causes the increase in ion depletion at the interface of the membrane in the DBL of thickness d (Figures 5 and 9), as well as in the space-charge region (SCR) [54] (Figure 9). Indeed, the DBL, at the interface of the membrane, is generally divided into two regions: an electroneutral region (0 ≤ x ≤ δ1) and the space-charge region (SCR) (δ1 ≤ x ≤ δ). When in ohmic and limiting conditions, the SCR occupies a negligible space (<10 nm) (Figure 9). However, when overlimiting conditions are reached, the SCR thickness increases due to the appearance of a non-equilibrium zone and then extends up to several hundred nanometers, which is wider than the electric double layer (EDL) thickness (several nanometers) [51]. In this extended SCR, the concentration in counter-ions, although low, is significantlyPDF Image | Electrodialytic Processes
PDF Search Title:
Electrodialytic ProcessesOriginal File Name Searched:
membranes-10-00221.pdfDIY PDF Search: Google It | Yahoo | Bing
NFT (Non Fungible Token): Buy our tech, design, development or system NFT and become part of our tech NFT network... More Info
IT XR Project Redstone NFT Available for Sale: NFT for high tech turbine design with one part 3D printed counter-rotating energy turbine. Be part of the future with this NFT. Can be bought and sold but only one design NFT exists. Royalties go to the developer (Infinity) to keep enhancing design and applications... More Info
Infinity Turbine IT XR Project Redstone Design: NFT for sale... NFT for high tech turbine design with one part 3D printed counter-rotating energy turbine. Includes all rights to this turbine design, including license for Fluid Handling Block I and II for the turbine assembly and housing. The NFT includes the blueprints (cad/cam), revenue streams, and all future development of the IT XR Project Redstone... More Info
Infinity Turbine ROT Radial Outflow Turbine 24 Design and Worldwide Rights: NFT for sale... NFT for the ROT 24 energy turbine. Be part of the future with this NFT. This design can be bought and sold but only one design NFT exists. You may manufacture the unit, or get the revenues from its sale from Infinity Turbine. Royalties go to the developer (Infinity) to keep enhancing design and applications... More Info
Infinity Supercritical CO2 10 Liter Extractor Design and Worldwide Rights: The Infinity Supercritical 10L CO2 extractor is for botanical oil extraction, which is rich in terpenes and can produce shelf ready full spectrum oil. With over 5 years of development, this industry leader mature extractor machine has been sold since 2015 and is part of many profitable businesses. The process can also be used for electrowinning, e-waste recycling, and lithium battery recycling, gold mining electronic wastes, precious metals. CO2 can also be used in a reverse fuel cell with nafion to make a gas-to-liquids fuel, such as methanol, ethanol and butanol or ethylene. Supercritical CO2 has also been used for treating nafion to make it more effective catalyst. This NFT is for the purchase of worldwide rights which includes the design. More Info
NFT (Non Fungible Token): Buy our tech, design, development or system NFT and become part of our tech NFT network... More Info
Infinity Turbine Products: Special for this month, any plans are $10,000 for complete Cad/Cam blueprints. License is for one build. Try before you buy a production license. May pay by Bitcoin or other Crypto. Products Page... More Info
| CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com | RSS | AMP |