PDF Publication Title:
Text from PDF Page: 020
dlfference due to the permeable species, Cs is the solute concentration, E is the applied field, and LiJ are the Onsager transport coefficients (ref. 7). One can see that the magnitude and direction of the total volume flux (solvent and electrolyte) lS a sum of several terms. The approach taken lnvolves determining the relative contributlon of each factor to transport. These factors are (1) Hydrostatlc pressure differences: Because the design of the Redox system is symmetrlc, the hydrostatlc pressure differences were assumed to be small and are not consldered here. (2) Osmotlc pressure differences: The osmotlc pressure in dilute Solutlons is glven by the relation w = RT~CJ (2) where Cj lS the volume concentration of each solute, R is the gas con- stant, and T is temperature. Strictly speaking, this relation is only valid for lnflnltely dllute Solutlons, but it can be used to predlct sign and order of magnltude of osmotlc pressure differences. In the Redox system a number of dlfferent species may be present as a result of complexatlon (e.g., [Cr(H20)SC1]+2, [Cr(H20)6]+3, H30+, and Cl- ln dlscharged chromium Solutlons or FeCl+2, FeC13, FeC14, Fe+3, H30+, and Cl- in charged ferric lon Solutlons). In princlple, if all equilibrium constants for complexation at a glven temperature for a glven system are known, the amounts of each specles and hence the osmotic pressure differences between the two solutions can be calculated. Experiments were run uSlng reactant solutions 1.1 MFeC12' 1 NHC1/O.9 M CrC13, and 1.0 NHCl for a stack of cells that were allowed to charge and discharge repetitlvely. Although Solutlon transfer was minimlzed initially, a net transfer always occurred to the chromium side, ln contrast to the results obtained from statlc dlffusion cell tests. Consequently other factors affectlng volume flux were examined. (3) Relative mobility differences: In the Redox system both ions of the HCl electrolyte are membrane permeable. The degree to which concentra- tions in each Solutlon change during charge and dlscharge is governed by the anlon, cation, and solvent transference numbers, where t+ = f{J+/I)(f is the Faraday constant, I lS the current, and J+ lS the proton flux). The anlonic transference number lS 1 - t+ and tH a is expressed as the number 2 of moles of water transferred per faraday of electriclty. Table 13 depicts how varlOUS factors are affected when the membrane transference numbers are varled for a sample calculation assuming contlnuously charging and dlS- charging cells with 98 percent current efficlency. The Solutlon volumes for iron and chromlum solutions indicate a steadily increaslng chromium solution volume. ThlS effect results from the assumption of less than 100 percent current efficlency. The total lon concentration differences across the mem- brane, WhlCh are proportlonal osmotlc pressure differences, are also given. Positlve values lndlcate that the chromium Solutlon has the hlgher osmotic pressure. ThlS suggests a tendency for water to move to the chromium 17PDF Image | NASA Redox Storage System Development Project 1980
PDF Search Title:
NASA Redox Storage System Development Project 1980Original File Name Searched:
19830006412.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
CONTACT TEL: 608-238-6001 Email: greg@salgenx.com (Standard Web Page)