Display omitted
•Binary and ternary gas diffusion is investigated in situ with FTIR Spectroscopy.•The binary diffusion of CH4/CO2, CH4/C2H6, CH4/C3H8 and C2H6/C3H8 is studied.•Ternary gas diffusion ...of CH4/CO2/C3H8 is measured at 0.1 MPa and 308.15 K.•The Maxwell – Stefan theory of multicomponent diffusion is effectively applied.•Osmotic, reverse and barrier diffusion are observed and predicted.
The unsteady diffusion of the ternary gas mixture CH4(α) – CO2(β) – C3H8(γ) is measured with FTIR Spectroscopy in the transmission mode at 308.15 K, 0.1 MPa and equilibrium compositions xα,∞=0.333 and xβ,∞=0.363. A parallel is drawn between the experimental approach and the classical Two-Bulb method. The geometry of the setup is calibrated by measuring the equimolar counter-diffusion of C3H8/CO2 at 308.15 K and 0.1 MPa. Then, analogous experiments are conducted for the gas pairs CH4/CO2, CH4/C2H6, CH4/C3H8 and C2H6/C3H8 to measure their mutual diffusivity. Last, the ternary diffusion of CH4(α) – CO2(β) – C3H8(γ) is measured and modelled with the Maxwell – Stefan theory of multicomponent equimolar diffusion for ideal gas mixtures. Osmotic, reverse and barrier diffusion are observed and predicted for methane before reaching equilibrium.
In the paper, we solve two Stefan problems. The first problem recovers an unknown moving boundary by specifying the Cauchy boundary conditions on a fixed left-end. The second problem finds a ...time-dependent heat flux on the left-end, such that a desired moving boundary can be achieved. Then, we solve an inverse Cauchy-Stefan problem, using the over-specified Cauchy boundary conditions on a given moving boundary to recover the solution. Resorting on a homogenization function method, we recast these problems into the ones having homogeneous boundary and initial conditions. Consequently, the approximate solution is obtained by solving a linear system obtained from the collocation method in a reduced domain. For the first Stefan problem the moving boundary can be determined accurately, after solving a nonlinear equation at each discretized time. For the second Stefan problem, we can obtain the required boundary heat flux without needing of iteration. Numerical examples, including non-smooth ones, confirm that the novel methods are simple and robust against large noise. Moreover, the Stefan and inverse Cauchy-Stefan problems are solved without initial conditions.
•One-phase cylindrical Stefan problem with size-dependent thermal conductivity and convection is considered.•Time dependent temperature and Newton type temperature boundary conditions are subjected ...at the outer surface of the body.•Heat Balance Integral Method is applied to obtain the numerical result of the problem.•Convection produced pronounced impact on propagation rate of the melting interface.•It is observed that size-dependent thermal conductivity produced pronounced effect on melting process.
The melting of a phase change material is the most applicable process in thermal energy storage system to capture heat transfer phenomena arising in a class of moving boundary problem. Demand of present technology motivates researchers to develop new theories and techniques for thermal management of a material. Experimental work on melting of a material may be difficult and development of robust theoretical formulation in cylindrical geometry with convection is critical. While there is already available study on cylindrical moving boundary problem, but still insufficient modeling of a size-dependent thermal conductivity and convection effect is not addressed properly, which is being considered in this paper and is expected to improve the previous understanding. In this work, a one-dimensional moving boundary problem with size-dependent heat conductivity and convection effect is analyzed in cylindrical geometry. In the mathematical model, we have considered a time-dependent temperature boundary condition which later assumed in periodic form, and a convective boundary condition at the outer surface of the body. The numerical result of the problem is obtained successfully via heat-balance integral method. Our numerical result is compared with a previous work and found in good acceptance. From mathematical framework, it is found that convection delayed melting process. With a size-no independent thermal conductivity, the rate of moving front decreases more in comparison to the fixed thermal conductivity.
Membrane characterization and modeling of membrane processes are essential steps in the development and implementation of new membrane filtration processes. The generalized Maxwell–Stefan equation is ...frequently used to describe these processes. However, predictive modeling on the basis of characterization experiments using single solutes is still troublesome in a lot of cases. Consequently, a better understanding of the effect of the interaction between different components on the membrane separation characteristics is required. In this work, four well-known commercially available membranes, Desal 5DK, Desal 5DL, Desal G5, NTR-7450, and a newly introduced membrane NF have been characterized. The pore radii of these membranes determined from glucose retention experiments increase in the following sequence: Desal 5DK ≈ NF < Desal 5DL < Desal G5 < NTR-7450. The pore radii and effective membrane thickness determined on the basis of glycerin experiments are within 6% of those determined using glucose. The presence of salt ions, especially of those for which the membranes show low retention, leads to reduction of the retention of neutral components (glucose). The retention reduction, at maximum 10% (absolute) in this study, depends on the membrane selected. For NF and Desal 5DK a high glucose retention drop coincides with a high concentration of the anion salt (Cl
−) ions in the permeate, independent of the cation salt ion used. This phenomenon can be explained by several hypotheses. One of these, supported by generalized Maxwell–Stefan model calculations, is that the presence of a pore size distribution leads to the observed shift in selectivity. In the presence of salt ions in the pores, the flux through small pores is reduced to a larger extent than that in bigger pores. Consequently, the retention for glucose drops and a shift in the apparent pore radius is determined. Regardless of the mechanism that causes the reduction of the glucose retention, it is essential that this effect is incorporated in predictive models for nanofiltration to predict the loss of organic components to the permeate sufficiently accurately, since this loss may affect permeate disposal costs or product yield.
Les fantasmes coloniaux ne se trouvent pas seulement chez les écrivains des grandes puissances coloniales. On les retrouve également chez les écrivains autrichiens, dont Stefan Zweig. La nouvelle Le ...voyage dans le passé révèle l'héritage impérialiste de l'Europe occidentale, qui est indispensable comme cadre de développement de l'histoire : le protagoniste européen se rend dans un pays lointain pour s'enrichir aux dépens de la population locale. Cet état de fait reste implicite, comme c'était le cas chez des prédécesseurs et modèles littéraires de Zweig comme Balzac. Les études littéraires postcoloniales sont en mesure de comprendre ces relations de pouvoir et donc de mieux situer la fiction dans un contexte politico-économique global.
Carbon dioxide (CO2) is the main contributor to global warming; therefore, research efforts aim at its capture. Membranes, in particular, zeolite membranes offer a promising approach for CO2 ...separation and capture. Membranes are typically characterized by their selectivity and permeance that are highly dependent on the operating conditions namely, total feed pressure and composition. Therefore, more reliable characterization parameters are required such as Maxwell- Stefan exchange diffusivities.
In this work, a model based on Maxwell−Stefan equations and Extended Langmuir isotherm was developed to investigate the transport of binary mixtures of CO2 and N2 through thin silicalite-1 membranes. The exchange diffusivities, D12 and D21, of CO2 and N2 were determined at different total feed pressures and feed compositions. All gas separation tests were conducted at stage cut not exceeding 5%. The single component diffusivities of CO2 and N2 required by the model were found experimentally using the results of the respective single gas permeation tests. The results displayed that as CO2 concentration in the feed increased from 15% to 85%, the values of D12 and D21 decreased from 2.8 × 10−10 to 1.1 × 10−10 m2/s and 2.8 × 10−10 to 1.3 × 10−10 m2/s, respectively, while the N2 permeance decreased by about one order of magnitude from 2.7 × 10−7 to 2.4 × 10−8 mol/m2.s.Pa. Consequently, the exchange diffusivities showed considerably smaller dependence on the operating conditions compared to the permselectivity and permeance. Hence, they are more appropriate in describing the intrinsic transport characteristics of silicalite-1 membranes.
•A single component and binary mixtures of CO2 and N2 permeation were investigated.•Permeation tests were conducted using a silicalite-1 membrane.•A model based on Maxwell−Stefan and Extended Langmuir isotherm was developed.•A strong interaction between CO2 and N2 molecules and a difference in their adsorption capacities is reported.
Der Stefan George-Werkkommentar bietet eine systematische Erschließung des gesamten dichterischen und übersetzerischen Werks des Autors. Konzeptionell orientiert am Aufbau der Sämtlichen Werke bietet ...er über siebzig Beiträge, die das Werk Georges Zyklus um Zyklus charakterisieren und jeweils in detaillierten Modellinterpretationen ästhetische Verfahren und dichtungstheoretische Positionen rekonstruieren.
In heat transfer, the melting of a PCM is one of the most applicable processes in energy storage systems. Obtaining a fast conversion rate from solids into liquids with minimum cost is the major ...demand of the modern technology, which can be made possible by reducing operational time. While there are already available works on the melting of a PCM, there is still insufficient modelling of the quadratic form of temperature-dependent thermal conductivity and the generalized form of temperature-dependent convection. This paper attempts to address these gaps. We have successfully developed a wavelet-based approximation function for the temperature profile in HBIM. A comparison of the proposed temperature profile with a previous available temperature profile in HBIM is presented in particularly, and the obtained results show excellent acceptance. The effect of various problem parameters like Stefan number, Péclet number, and coefficient of variation on temperature and melting front is extensively analyzed. In each case of temperature-dependent convection, it is obtained that there is an increment in the temperature field with increasing the values of the Stefan number, Péclet number, and coefficient of variation. As a result, melting process gets accelerated. Moreover, the exponential profile of temperature-dependent convection is the best fit to achieve fast melting of a PCM.
PDF
