دانلود رایگان مقاله لاتین هیسترزیس از سایت الزویر
عنوان فارسی مقاله:
تاثیر هیسترزیس جذب در ضرایب انتشار نمایش با پتانسیل های مختلف رطوبت
عنوان انگلیسی مقاله:
The influence of sorption hysteresis on diffusion coefficients represented with different moisture potentials
سال انتشار : 2016
برای دانلود رایگان مقاله هیسترزیس اینجا کلیک نمایید.
مقدمه انگلیسی مقاله:
1. Introduction
A common approach in the study of transport of water vapor in cement-based materials is to combine a sorption isotherm with a transport coefficient. This is not trivial as cement-based materials are known to show sorption hysteresis and scanning behavior and a significant effort has been put into describing this complex path (history) dependent property [1–5]. In addition, transport coefficients (diffusion coefficient and permeability) are functions of the moisture state, for example of relative humidity (RH) or moisture content (MC) [6–9] rather than constant values. In a recent paper [10] we also showed that at least for cement mortars made with ordinary Portland cement (OPC) there is a significant difference between the moisture diffusion coefficients when a mortar is on the absorption or on the desorption limbs of the sorption isotherm, even if the two values are determined in the same RH interval. We then expressed the diffusion coefficient with vapor content as potential as this is the most natural choice for the steady-state cup measurements that we did. A problem with moisture transport coefficients is that they can be expressed using many different potentials. This is in contrast with for example heat transport which is always treated using temperature as potential; or diffusion of chloride ions in concrete where concentration (mass of ions per volume material) is the preferred potential. For moisture transport we can use vapor content (v, mass vapor per volume air), volumetric moisture content (c, mass of moisture per volume material) or a dozen other potentials. This opens for the question of which of these possibilities that is best in the sense that it gives the smallest dependence of the transport coefficient on the potential or whether the system is in absorption or desorption. Our previous results [10] gave 3–4 times higher diffusion coefficients in desorption than in absorption in the RH-range 75–95%; in a similar study on self-levelling flooring compounds Anderberg and Wadsö [11] found a 30% higher transport in desorption than in absorption in a similar RH-interval. We know of no other studies of this subject. It is well known that sorption hysteresis above 50% RH is caused by that the filling (absorption) and emptying (desorption) of a pore does not take place at the same RH [1,5,12]; the RH for emptying of a pore is lower than the RH at which the same pore is filled. This could also affect the transport, as the rate of transport is significantly higher in a water filled pore than in a pore in which vapor diffuses [10]. As there are many different pore sizes, pore shapes, pore connections etc. in cement based materials, the sorption situation is complex, and it is not possible to theoretically determine the values of transport coefficients with different potentials and on different limbs of the sorption isotherm. It is the aim of this work to determine how the transport coefficients should be represented to introduce a minimum of sorption hysteresis in the transport coefficient. This includes both the potential used for the coefficient and what potential it should be a function of. Originally we evaluated Dv(φ), where φ is the relative humidity, i.e., v/vsat, which at isothermal conditions essentially equals Dv(v) (we here assume that the ideal gas law holds). Some examples of other alternatives are Dv(c), Dc(v) and Dc(c). In this study we recalculate Dv to other potentials and present these transport coefficients as functions of different potentials.
برای دانلود رایگان مقاله هیسترزیس اینجا کلیک نمایید.
کلمات کلیدی:
Implementation of sorption hysteresis in multi-Fickian ... - De Gruyter www.degruyter.com/view/j/hfsg.2007.61.issue-6/hf.2007.113/hf.2007.113.xml Nov 1, 2007 - Source Normalized Impact per Paper (SNIP) 2015: 0.954 .... At higher relative humidities, slow sorption and faster bound-water diffusion cause effects, which ... Implementation of sorption hysteresis in multi-Fickian moisture ... Diffusion in and Through Solids - Page 191 - Google Books Result https://books.google.com/books?id=7SQ9AAAAIAAJ Richard Maling Barrer - 1941 - History 40) it is not possible to trace out the same isobaric curve on sorption and desorption. There is a hysteresis effect illustrated by Fig. 40. It is interesting to find in the ... Diffusion NMR of Confined Systems: Fluid Transport in Porous Solids ... https://books.google.com/books?isbn=1782621903 Rustem Valiullin - 2016 - Science However, as with gas sorption, the interpretation of cryoporometry data is also complicated by hysteresis and pore–pore co-operative effects. NMR diffusometry ... Hysteresis Effects for Sorption in Glassy Polymers - Macromolecules ... pubs.acs.org/doi/abs/10.1021/ma950969l by JS Vrentas - 1996 - Cited by 49 - Related articles Jun 3, 1996 - Hysteresis Effects for Sorption in Glassy Polymers .... Application of irreversible thermodynamics to the solvent diffusion in an amorphous glassy ... Sorption Hysteresis as a Probe of Pore Structure - American Chemical ... pubs.acs.org/doi/pdf/10.1021/la00034a016 by H Liu - 1993 - Cited by 66 - Related articles is discussed. The extent of sorption hysteresis reflects the connectivity of the pore network. An analysis ... The effective diffusion coefficient of a porous solid can be calculated ... medium theory calculations showing the effect of varying. 2 on the ... Advances in Applied Bioremediation - Page 64 - Google Books Result https://books.google.com/books?isbn=354089621X Ajay Singh, Ramesh Chander Kuhad, Owen P. Ward - 2009 - Science The operation of processes leading to true sorption hysteresis may result in ... Promotion of contaminant diffusion through the influence of biofilms in the ...
