Papers by Keyword: Gas Diffusion

Abstract: Zeolitic-imidazolate frameworks (ZIFs) have shown promise in gas separation through membranes. Nevertheless, the potential of mixed-layer ZIFs to be tailored for targeted gas separation remains largely unexplored. This study aims to fill this research gap through a Molecular Dynamics (MD) study by proposing two molecular models for mixed-layer ZIFs and evaluating their effectiveness in H₂ and CO₂ separation. MD simulations are conducted to validate and assess the diffusion properties of H₂ and CO₂ within the mixed-layered ZIF models. The results demonstrate that H₂ has higher diffusivity than CO₂ within the proposed ZIF models. Mixed-layer ZIF-8/ZIF-7 exhibits higher diffusion coefficients for both H₂ (4.79 × 10^-9 m²/s) and CO₂ (8.13 × 10^-11 m²/s) compared to pure ZIF-8, attributed to increased pore flexibility from the ZIF-7 layer. However, this enhancement in diffusion comes at the cost of reduced selectivity due to broader pore size distribution. In contrast, mixed-layer ZIF-8(Zn)/ZIF-8(Co) demonstrates a substantial increase in H₂ diffusion (5.17 × 10^-9 m²/s) and an exceptional selectivity of 310.00 for H₂ over CO₂, owing to the altered framework flexibility from incorporating different metal ions. The study further explores the effect of different adsorbate molecular models, revealing that the H₂_COMPASS and CO₂_TRAPPE combination yields the highest H₂/CO₂ selectivity. Additionally, increased molecular loading enhances diffusion. These findings underscore the critical role of structural modifications and molecular model selection in optimizing ZIF-based materials for gas separation applications. The proposed models and simulation results offer a foundation for future studies and the development of efficient and sustainable gas capture technologies.

Abstract: Flow through nano-channels is important in several fields, ranging from natural porous media to microfluidics. It is therefore important to study the flow under controlled conditions. While quite a lot of work has been done on the flow of liquids through nano-channels, comparatively little systematic work has been done on gas flow. Here we present a study of the flow of argon through nano-channels. We study samples with 2000 parallel nano-channels, with quadratic cross section. Each side is 100nm. The total length is 20 m. The nano-channels are made by patterning a Si<110> wafer usingelectron beam lithography (EBL) followed by reactive ion etching and with subsequent anodic bonding between silicon and a borosilicate glass as a top plate. The samples were investigated using a home-built apparatus which allows us to measure flow at high Knudsen numbers (from around 10 to 550). We compare our results with a range of theoretical flow models. As innovation this work provides measurements of gas transport from the home-built apparatus. The system records the pressure profile of each sample and the mass flow rate is calculated numerically from the pressure data.

Abstract: A three-dimensional numerical model was developed based on CFD software FLUENT to simulate leakage process of liquid ammonia tank. The results show the scope of ammonia gas expands with the increasing of wind speed, And the ammonia gas gathers in the upper space of the leaking tank when the wind speed is low.

Abstract: Due to the rising tendency of chemical accidents, it is urgent to develop a real-time gas diffusion simulation system on computer during the emergent chemical accidents, and high computation efficiency of gas diffusion model is indispensable in the simulation system. This paper develops an efficient diffusion model based on Gaussian Puff Model and proposes a special numerical simulation method for the model. With the proposed model and the proposed method, the spatial density distribution of the gas spread can be computed rapidly and displayed visually in GIS. To validate the correctness, efficiency, reliability and flexibility of the model, two groups of simulations in different aspects (space and time) are performed respectively. The result of simulation is as well as expected, and the system based on the model will provide a reliable guarantee for rescue during emergent chemical accidents.

Abstract: Though composites, particularly those consisting of organic materials, have replaced the role of traditional metallic materials in various engineering applications due to their relatively high mechanical strength, low density, flexibility and low cost, their disadvantages caused by relatively high porosity ratio and low crystallinity inherently make this kind of materials the less favorable choices when low permeation property is a major criterion. Here pure aluminum (Al) thin film, which has excellent anti-corrosion property, is introduced into the structure of fabricated composites to improve the composite’s anti-permeation behavior in corrosive environment while the advantageous points of organic composites are exploited at the same time by applying the optimized thermo-mechanical processing techniques in fabrication. Thus greater potentials for organic polymeric composites may be achieved in the future.

Abstract: After a chemical vessel suffering a rupture, BLEVE, fireball, jet fire, and dispersion of toxic substance may be the most common failure ways. Which give rise to a great threat to people’s life, process plants and surrounding environment. This paper presents an overview of the mechanism and the consequences for these failures; finally, ALOHA software simulation resorted to evaluating the consequences for all kinds of hazard, a vertical tank with the size of diameter=10, tank length=20m, containing the propane liquid/gas mixture with a volume of 1571 cubic meters, the mass of the chemical is calculated by the software automatically with a value of 554 tons. All the possible failures have been simulated by the ALOHA software, including：1) leaking tank, chemical is not burning as in escapes into the atmosphere; 2) leaking tank, chemical is burning as a jet fire; and 3) BLEVE, tank explodes and chemical burns in a fireball. Furthermore, there are three types hazard available to analyze the situation that chemical is not burning as it escapes into the atmosphere, they are: a) toxic area of vapor cloud; b) flammable area of vapor cloud; and c) blast area of vapor cloud explosion. The result reveals that the farthest threat zone reaches 2.2km in the case of a fireball triggered by a BLEVE, and the result has been viewed and discussed in details.

Abstract: Gas bubbles entrapped in polymer intermediate layer often lead to voids which are severe defects of adhesive bonding qualities. Although the empirical method had been used for a long time to eliminate the bubbles, theoretic analysis considering the bubble behavior during bonding process is more preferable because of the better universality. The interrelationships between processing parameters and bubble deformation were investigated. A theoretic model describing those interrelationships was developed reasonably using gas diffusion theory to predict the bubble behavior. The mathematic equations of this model were deduced and the solution was obtained with some proper simplifications. Experiments under different conditions were carried out and the experimental results were contrasted with the theoretical predictions. It was obvious that when choosing temperatures and pressures carefully, the model could predict the bubble behavior accurately.

Abstract: A better understanding of the transport properties of gases in oxides is certainly very important in many applications. In the case of metals, a general protection measure against corrosion implies formation of a dense metal oxide scale. The scale should act as a barrier against gas transport and consequently it needs to be gas-tight. This is often assumed but rarely, if ever, confirmed. Hence there is a need for characterization of micro- and/or meso- pores formed especially during the early oxidation stage of metallic materials. This paper presents a novel and relatively straightforward method for characterization of gas release from an oxide previously equilibrated in a controlled atmosphere. The geometry of the sample is approximated to be a plate. The plate can be self-supporting or constitute a scale on a substrate. A mathematical model for calculation of diffusivity and gas content is given for this geometry. A desorption experiment, involving a mass spectrometer placed in ultra high vacuum, can be used to determine diffusivity and amount of gas released with aid of the mathematical model. The method is validated in measurements of diffusivity and solubility of He in quartz and applied in characterization of two Zroxides and one Fe oxide. From the outgassed amounts of water and nitrogen the H2O/N2 molar ratio can be used to estimate an effective pore size in oxides.