Diffusion Of Carbon Dioxide Research Articles

Accelerated carbonation of hardened cement pastes: Influence of porosity

Recently, with the development of accelerating mineral carbonation technology, the preparation of building materials by using carbonation curing cement-based materials has attracted wide attention. The diffusion and transfer mechanism of carbon dioxide in porous cementitious materials was the key point that restricts the improvement of materials carbonation rate. In order to obtain comprehensive information that affects accelerating carbonation rate of porous cement-based materials, this paper talks about the influences of paste porosity controlled by water to cement ratio (w/c) on carbonation and the paste micro-structures evolution. Also, mineral compositions before and after carbonation curing were evaluated. Results show that the carbonation rate, carbonation depth and compressive strength are improved after carbonation, while total porosity of complete carbonation zone decreases with the growth of paste porosity. The pores with diameter larger than 200 nm played a leading role in carbon dioxide diffusion, which were reduced by 84.25% of the total volume after carbonation curing. The carbonization reaction mainly occurred in the first six hours in carbonation curing, while the subsequent carbonation curing were unprofitable to the carbonation effect due to the generation of calcium carbonate prevents the diffusion of CO2, making the subsequent carbonation become difficult. XRD results revealed that during carbonation curing the major reactants were C2S, C3S and some hydration products of Ca(OH)2 after 1 d hydration.

Modelling of process of displacement of methane from gas hydrate reservoir at dioxide carbon injection

The paper presents a mathematical model for describing the process of displacing methane with carbon dioxide from a reservoir saturated with methane and its hydrate. For gas substitution kinetics, a scheme has been proposed in which the intensity of the process is defined by the diffusion of carbon dioxide through the hydrate layer formed between the gas mixture flow and methane hydrate. The numerical research of influence of main parameters on dynamics of process is conducted. Influence of coefficient of diffusion mixing of the gas mixture and permeability for the time of complete gas-replacement in reservoir is studied.

Bronchopulmonary Dysplasia: Crosstalk Between PPARγ, WNT/β-Catenin and TGF-β Pathways; The Potential Therapeutic Role of PPARγ Agonists.

Bronchopulmonary dysplasia (BPD) is a serious pulmonary disease which occurs in preterm infants. Mortality remains high due to a lack of effective treatment, despite significant progress in neonatal resuscitation. In BPD, a persistently high level of canonical WNT/β-catenin pathway activity at the canalicular stage disturbs the pulmonary maturation at the saccular and alveolar stages. The excessive thickness of the alveolar wall impairs the normal diffusion of oxygen and carbon dioxide, leading to hypoxia. Transforming growth factor (TGF-β) up-regulates canonical WNT signaling and inhibits the peroxysome proliferator activated receptor gamma (PPARγ). This profile is observed in BPD, especially in animal models. Following a premature birth, hypoxia activates the canonical WNT/TGF-β axis at the expense of PPARγ. This gives rise to the differentiation of fibroblasts into myofibroblasts, which can lead to pulmonary fibrosis that impairs the respiratory function after birth, during childhood and even adulthood. Potential therapeutic treatment could target the inhibition of the canonical WNT/TGF-β pathway and the stimulation of PPARγ activity, in particular by the administration of nebulized PPARγ agonists.

Study on Surface Properties of Aramid Fiber Modified in Supercritical Carbon Dioxide by Glycidyl-POSS.

The outstanding diffusivity and permeability of supercritical carbon dioxide (scCO2) are extremely beneficial for grafting reaction. In this work, aramid fibers (AF) are modified in scCO2 by glycidyl-polyhedral oliomeric silsesquioxane (POSS) with 2-ethyl-4-methylimidazole (2E4MZ) on the basis of cleaning with acetone. The surface morphology and chemical structure of the modified AF were measured and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Thermogravimetric (TG), and Atomic force microscope (AFM). The interfacial shear strength (IFSS) was measured by a micro-bond pull-out test, then the modified AF/EP composites were prepared and the interlaminar shear strength (ILSS) was characterized. Research has shown that some of the glycidyl-POSS molecular chains permeated into the surface of the fiber and grafted onto the surface of the AF after modification, and the other glycidyl-POSS self-assembled on the surface of the fiber. XPS indicated the introduction of C–O and –COO–, which confirmed the existence of chemical reactions between AF and glycidyl-POSS. AFM and SEM images revealed that 2E4MZ, not only promoted the grafting reaction of glycidyl-POSS, but also intensified the self-assembly of glycidyl-POSS, both of which increased the roughness of the fiber. A monofilament tensile test and micro-bond pull-out test showed that there was a negative effect on the tensile strength after scCO2 processing. The tensile strength of modified AF, with glycidyl-POSS, increased the highest strength of 25.7 cN dtex−1, which was 8% higher than that of pristine AF. The improvement of ILS roughness and the polar chemical groups produced in grafting reaction. These results indicated that AF, treated in scCO2, with glycidyl-POSS, which is a suitable way of fiber modification, can significantly improve the surface adhesion of AF reinforced composites.

Carbon dioxide diffusion coefficient in noninvasive high-frequency oscillatory ventilation.

The carbon dioxide (CO2 ) diffusion coefficient (DCO 2 ) reflects CO 2 removal during high-frequency oscillatory ventilation (HFOV). We hypothesized that despite leak flow during noninvasive HFOV (nHFOV) DCO 2 continues to indicate ventilation efficacy. A neonatal airway model including CO2 production and an adjustable oropharyngeal leak was connected to a ventilator via bi-nasal prongs. Pressures and gas flows were measured at prongs, trachea, and leak. Oscillatory tidal volumes below (V T trachea ) and above the leak (V T prong ) were calculated from tracheal and leak flows. DCO 2 was calculated using V T trachea (DCO 2 trachea ) and V T prong (DCO 2 prong ) and compared with CO 2 partial pressure (pCO 2 ). Effects of leak flow (0, 5, or 10L/min) on DCO 2 were assessed at fixed pressure amplitudes or predefined oscillatory volumes under steady-state pCO 2 conditions in the modeled lung. DCO2 trachea correlated strongly with pCO 2 , independent of the leak flow level (P < 0.0001). DCO 2 prong correlated with pCO 2 without and with moderate leak (P < 0.0001) but not with maximum leak (P = 0.1432). V T trachea correlated with the quotient of tracheal pressure amplitude and frequency irrespective of the leak (P < 0.0001). Based on the pressure amplitude at prong level (A prong ) V T trachea continued to follow a linear model of which the slopes decreased with increasing leak flow. V T prong correlated with the quotient of A prong and frequency, irrespective of the leak (P < 0.0001). DCO2 obtained at the airway opening at prong level reflects ventilation efficacy during nHFOV even in the presence of moderate oropharyngeal leak.

Impatiens ‘New Guinea’ (Impatiens hawkeri Bull) Hormonal Effects during the Post-transplant Biomass Accumulation

Pot ornamental plant productivity is related to the environmental growth facilities but negatively affected by the pot root restriction syndrome so during nursery as the post-transplant stage. The physiological mechanism involved included both the synthesis and translocation of auxins and cytokinins. However, clear sink-source and dose-response relationships of exogenous plant regulators such as indole acetic acid (AIA) and benzyl amino purine (BAP) and environment on biomass accumulation in most ornamental foliage plants, including New Guinea Impatiens (Impatiens hawkeri) are lacking. The aim of this work was to analyze the effects of an exogenously shoot-applied auxin and a cytokinin, separately or successively, on the post-transplant biomass accumulation of I. hawkeri through the anatomical, morphological and physiological changes observed. Two experiments were performed. The first experiment included the response to only BAP-sprayed plants (0, 5, 50, or 100 mg L-1). For the second experiment, rooting cuttings of I. hawkeri were sprayed with different concentrations of IAA (0, 5, 50, or 100 mg L-1) followed by different BAP concentrations (0, 5, 50, or 100 mg L-1) one week later to run-off at sunset. Results showed that (a) a single BAP or AIA dose increased increase post-transplant biomass accumulation through a higher leaf area expansion and photo assimilate production, (b) as a result of both AIA and BAP spray, the higher NAR the higher post-transplant biomass accumulation, (c) leaf anatomical changes (leaf thickness, intercellular spaces) let a higher carbon dioxide diffusion and fixation with a correlative increase in photo assimilates, (d) a higher root system would be related to a higher cytokinin synthesis. In summary, similarities between responses to either hormone, together with the lack of any IAA - BAP interaction, provide two independent routes for commercial growers to increase the productivity of I. hawkeri ornamental plants by using early foliar sprays.

Experimental diffusion coefficients of CO2 and H2S in some ionic liquids using semi-infinite volume method

The diffusivity of carbon dioxide and hydrogen sulfide was studied in five ionic liquids containing two different cations and four anions, namely, 1-ethyl-3-methylimidazolium (emim) based ionic liquids with bis-(trifluoromethyl)sulfonylimide (NTf2) anion and 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, (eFPT) as well as 1-(2-hydroxyethyl)-3-methylimidazolium (hemim) based ionic liquids (ILs) with different anions, viz. hexafluorophosphate (PF6), trifluoromethanesulfonate (OTf) and bis-(trifluoromethyl)sulfonylimide (NTf2). Experimental trials were carried out at temperatures of 303.15, 313.15 and 323.15 K and low initial pressures by means of semi-infinite volume method. The results show that the diffusion coefficients of CO2 and H2S in RTILs increase with increasing temperature, but with different orders, and the diffusivity of CO2 and H2S in (emim) based ILs is greater than that in (hemim) based ILs. In addition, the measured diffusion coefficients of CO2 and H2S have been fitted through Wilke-Chang empirical equation.

Regional distribution of chest wall displacements in infants during high-frequency ventilation.

The distribution of ventilation during high-frequency ventilation (HFV) is asynchronous, nonhomogeneous, and frequency dependent. We hypothesized that differences in the regional distribution of ventilation at different oscillatory frequencies may affect gas exchange efficiency. We studied 15 newborn infants with a median gestational age of 28.9 (26.4-30.3) wk and body weight of 1.0 (0.8-1.4) kg. Five ventilation frequencies (5, 8, 10, 12, and 15 Hz) were tested, keeping carbon dioxide diffusion coefficient constant. The displacements of 24 passive markers placed on the infant's chest wall were measured by optoelectronic plethysmography. We evaluated the amplitude and phase shift of displacements of single markers placed along the midline and the regional displacements of the chest wall surface. Blood gases were unaffected by frequency. Chest wall volume changes decreased from 1.6 (0.4) ml/kg at 5 Hz to 0.7 ml/kg at 15 Hz. At all frequencies, the abdomen (AB) oscillated more markedly than the ribcage (RC). The mean (SD) AB/RC ratio was 1. 95 (0.7) at 5 Hz, increased to 2.1 (1.3) at 10 Hz, and then decreased to 1.1 (0.5) at 15 Hz ( P < 0.05 vs. 10 Hz). Volume changes in the AB lagged the RC and this phase shift increased with frequency. The AB oscillated more than the RC at all frequencies. Regional oscillations were highly inhomogeneous up to 10 Hz, and they became progressively more asynchronous with increasing frequency. When the carbon dioxide diffusion coefficient is held constant, such differences in regional chest wall expansion do not affect gas exchange. NEW & NOTEWORTHY We characterized the regional distribution of chest wall displacements in infants receiving high-frequency oscillatory ventilation at different frequencies. When carbon dioxide diffusion coefficient is held constant, there is no combination of frequency and tidal volume that optimizes gas exchange. The relative displacement between different chest wall compartments is not affected by frequency. However, at high frequencies, chest wall displacements are lower, with the potential to reduce total and regional overdistension without affecting gas exchange.

A spatially distributed physical model for dynamic simulation of ventilated agro-material in bulk storage facilities

To maintain a high quality and limit storage losses of agro-materials in bulk storage, the dynamic interaction between climate in the facility and product needs to be better understood. In this paper, we present a (2-D) spatially distributed, dynamic full-scale bulk storage model. Also, model calibration and validation results using data from a full-scale potato storage facility are presented. The model predicts convection and diffusion of heat, mass and carbon dioxide as well as the heat, mass and carbon dioxide transfer between bulk and air, respiration and evaporation of the food product and the natural and forced convection in the storage facility. In the CFD model two actuators, a moving hatch and a fan, were successfully implemented. The validated model was used as a tool to investigate the cooling process within the full-scale storage facility. When applying a combination of under- and overpressure instead of the conventionally applied overpressure, a reduction of the temperature gradient in vertical direction and an increased temperature gradient of the temperature gradient in horizontal direction was obtained. A reduction on this horizontal temperature gradient was accomplished by adding an air channel near the roof.

Evidence of Isotope Selective Diffusion of Ambient CO2 Gas in WO3 Nanostructures

We report the isotope selective diffusion of carbon dioxide (CO2) gas through large aspect ratio (length/diameter = 20:1) and porous one-dimensional nanostructure of tungsten oxide (WO3). This novel effect was demonstrated in an ensemble of binary oxide, WO3 nanostructures with large surface area. When atmospheric CO2, which has two major stable isotopes (12CO2 and 13CO2), flows through such an ensemble of nanotubes, it allows only the 12CO2 isotopes to diffuse through it and hinders diffusion of the 13CO2 isotopes. The selective diffusion leads to different isotopic fractionations of ambient CO2 (12C:13C), in other words, generating different isotope-enriched CO2 gases as established through high-precision cavity-enhanced absorption spectroscopy technique. The phenomena are strongly dependent on the surface morphology of nanostructures of binary oxide, and the surface-induced diffusion process is most likely to be the effects of physical processes enabling the Knudsen diffusion, but is not related to any chemical activities.

Analysis of methane production intensity during its displacement from a gas hydrate formation by carbon dioxide

The theoretical model is considered in the one-dimensional approximations and numerical solutions are obtained for the process of replacing methane with carbon dioxide from a hydrate in a formation saturated with methane and its hydrate when carbon dioxide is injected into the formation. The process is considered under thermobaric conditions corresponding to the stability region of methane gas and carbon dioxide and the region of existence of CO2 in the form of a gaseous phase. The case is considered when the rate of carbon dioxide hydrate formation is limited by diffusion of carbon dioxide through the formed hydrate layer between the gas mixture stream and methane hydrate. It is accepted that the hydration substitution process occurs without the release of water from the hydrate. To describe the mathematical model, the main equations are the mass conservation equations for methane, carbon dioxide and their hydrates, Darcy’s law for filtration, Fick’s law for diffusive mixing of the gas mixture, state equations for the gas phase, Dalton’s law, energy equation, diffusion equation for transport CO2 through the hydration layer at the pore microchannel scale. The dynamics of the mass flow rates of the outgoing carbon dioxide and methane recovered has been investigated. The influence of the diffusion coefficient, the absolute permeability and the length of the formation on the intensity of the methane produced as a result of the gas substitution process is analyzed. Three main stages of the process were identified: displacement of free methane from the reservoir; extraction of free methane obtained as a result of the beginning of hydrate substitution in the formation; complete conversion of methane hydrate to carbon dioxide hydrate and complete extraction of methane from the formation. It is determined how the two main factors relate to each other in terms of the degree of influence on the replacement rate: heat and mass transfer in the reservoir and the kinetics of the replacement process.

The Theory of the Replacement of Methane by Carbon Dioxide in Gas Hydrates

A plane one-dimensional theoretical model has been considered and numerical solutions have been derived for the replacement of methane by carbon dioxide in a reservoir saturated with methane and its hydrate during carbon dioxide injection. The case in which the intensity of carbon dioxide hydrate formation is controlled by the diffusion of carbon dioxide through the hydrate layer formed between the stream of a gaseous mixture and a methane hydrate has been considered. The dynamics of the main process parameters and the flow rates of injected and exiting carbon dioxide and recovered methane has been studied. The effect of a diffusion coefficient and absolute permeability on the specific features of gas replacement has been analyzed.

Modelling headspace dynamics in modified atmosphere packaged meat

The dynamics of bacterial growth and concentrations of oxygen and carbon dioxide in the headspace of modified atmosphere packaged (MAP) meat is studied. The work is based on extensive long-time storage experiments on pork chops lasting up to 42 days at temperatures 0 °C and 5 °C and four different headspace gas mixtures with 10%, 20%, 40% and 70% oxygen and 30% carbon dioxide. The headspace dynamics is modelled. The model includes oxygen consuming biochemical processes in the meat and also the coupling between headspace and meat, specifically, the diffusion of oxygen and carbon dioxide into the meat. The model is parametrized from the experimental data, and captures the experimental results. It is concluded that the oxygen consuming processes inside the meat packed with MAP consume less than 1% of the initial oxygen in the headspace, and are not important for the headspace dynamics. On the other hand, the dissolution of carbon dioxide has a significant effect. This is due to the relatively large solubility of carbon dioxide compared to oxygen. From the model we find and characterize three distinct phases behind the headspace volume reduction observed. As the model is dynamical and mechanistic it can be used to give information about the retail-packed fresh meat under different oxygen containing atmospheres, effects of leaks, and more.

Diffusion of Water and Carbon Dioxide and Mixtures Thereof in Mg-MOF-74

Self-diffusion coefficients for CO2, H2O, and mixtures thereof in Mg-MOF-74 have been determined using molecular simulations. The crystal structure was modeled in a rigid and flexible manner with the intent to identify the impact of the flexibility of the framework on the diffusivity. The results show that especially at low loadings the mobility of the molecules is enhanced in flexible lattices because of a small difference in adsorption energy and the enlarged equilibrium distance to the main adsorption sites. In mixtures the flexibility has the same influence; however, because of the presence of the secondary species, water is predominantly located in the close proximity of the magnesium-ion which effectively leads to a segregation effect from the more freely moving CO2.

Diffusion Patterns in Zeolite MFI: The Cation Effect

Zeolite MFI is one of the most important stable porous materials used in catalysis and separation processes. However, some fundamental properties remain in the dark, such as the effect of different aluminum distributions on diffusion. This work, through calculations on cation probability densities, guest energy profiles, and diffusion coefficients, provides a consistent picture of accessibility and mobility for two representative adsorbates, methane and carbon dioxide, and helps to explain the stark differences in diffusion behavior among varying aluminum distributions. A distribution was identified close to the practical limit of maximum aluminum substitution and sodium cation content that actually leads to a collapse in diffusion. For all aluminum distributions studied, the diffusion properties are closely linked to the number of cations. Compensating aluminum negative charge with divalent calcium instead of monovalent sodium increases methane but decreases carbon dioxide diffusion. With respect to incr...

Molecular dynamics simulation of infinite dilution diffusivity of carbon dioxide in supercritical water

We apply equilibrium molecular dynamic simulations for investigating the infinite dilution diffusivity of carbon dioxide in near- and supercritical water (SCW) over the wide temperature ranging from 647 to 973 K at 115, 217, 426 and 663 kg/m3. The diffusion coefficients of SCW and infinite dilution diffusion coefficients (IDDCs) of carbon dioxide are calculated by using the Einstein mean-square displacement method. It is observed that the IDDCs of carbon dioxide in SCW are approximately 1–2 orders of magnitude higher than that in normal water. The analysis of the temperature dependence of the IDDCs of carbon dioxide reveals that they do not conform to the Arrhenius equation. In the near critical region, the IDDCs of carbon dioxide do not exhibit a monotonic change with a variation in temperature, but increase gradually with an increase in the temperature in a region far from the critical state. The anomaly of the temperature dependence of the diffusion of carbon dioxide in SCW can be explained using the microstructure features of the different states of the water. In addition, we observe that the IDDCs of oxygen are slightly larger than those of carbon dioxide under the same conditions.

Modeling the effects of fatigue damage on concrete carbonation

This paper presents the theoretical modeling of carbonation in fatigue-damaged concrete. First, a residual strain-based effective carbon dioxide diffusion coefficient in fatigue-damaged concrete was proposed. Based on that, the general carbonation equations were established for concrete with uniform compressive, gradient compressive and gradient tensile damage patterns. Then a numerical program was written to solve the established partial differential carbonation equations. Subsequently, the numerical carbonation model was validated by comparing the predicted carbonation depths with experimental results. Finally, parametric studies were conducted on carbonation in commonly used concretes with various fatigue damage patterns, which separated the effects of residual strains and residual curvatures. The parametric studies showed that fatigue damage did not alter the widely accepted proportional relationships between carbonation depths and square roots of exposure durations. Moreover, the effects of exposure conditions on carbonation of concrete were far more influenced by residual strains than by residual curvatures.

Experimental and theoretical investigation of CO2 mass transfer enhancement of silica nanoparticles in water

Nanofluids have novel characteristics that make them potentially useful for different applications. Realizing modest mass transfer enhancement in conventional nanofluids, in this study, mass-transfer of carbon dioxide in pure water and water-based nanofluids dispersed with silica nanoparticles at different initial pressures up to 15 MPa and at temperatures of 35 °C and 45 °C was investigated. Deionized water and two nanofluids at different concentrations with volume of 150 cm3 were used for this purpose. CO2 was brought in contact with each solution in a pressure-volume-temperature (PVT) cell with no mixer. Additionally, carbon dioxide diffusion coefficients at different pressures were estimated based on Fick's law. The obtained results demonstrated that water/silica nanofluid with 0.5 wt% and 0.1 wt% increased the carbon dioxide diffusion coefficient up to 39.2% and 11.9% compared to that in pure distilled water, respectively. Moreover, it was observed that the measured diffusion coefficient of carbon dioxide in water increased with temperature rise from 35 °C to 45 °C at constant pressure. However, it could be seen that, the diffusion coefficient decreased with pressure at constant temperature. It was concluded that among the enhancement mechanisms of nanoparticles, (i.e. grazing effect and Brownian motion), Brownian motion would play the main role in mass transfer enhancement.

Insulation performance of foam during the terrestrial and ascent period

To effectively reduce heat leakage, foam insulation is widely used in refrigeration, energy, chemical, cryogenic system and pipe engineering. The present study is aimed to investigate the thermal performance of foam on cryogenic storage system under variable environmental parameters. The heat transfer model through the foam is introduced in detail. The minimum thicknesses of foam for different cryogens are calculated under the influence of the external free convection during the terrestrial condition. Meanwhile, with carbon dioxide diffusion out of and air invasion in the foam cells, the related unsteady process is studied with coupling the mixture gas heat conduction and the external free convection. While during the liftoff of rocket, foam insulation is subjected to the forced aerodynamic heating. The transient thermal performance of foam is particularly investigated under the influence of aerodynamic heating, with the variable physical properties, flight velocity and acceleration, and environmental parameters considered. Finally, the performance comparison between foam and foam/Multilayer insulation is made. Some valuable conclusions are obtained. The present study is of significance to the insulation design for cryogenic fuel storage.

Carbon dioxide diffusion at different relative humidity through coating of cellulose nanocrystals for food packaging applications

Abstract In this paper, the investigation was focused on the CO2 permeability through CNCs coating at various RH values, comparing with the O2 one, aiming to evaluate the potential usage in all the applications of modified atmosphere packaging for intermediate-low moisture foods where the role of carbon dioxide is essential for shelf life extension. For this purpose, PET films were coated with characterized CNCs, obtained from cotton linters, and the CO2 permeance was measured as a function of increasing RH values (from 0% to 80%). After calculating the diffusion and solubility coefficients, and estimating the CO2/O2 selectivity, the possible evolution of different modified atmospheres has been theoretically calculated. The results obtained, let hypothesize that, in consequence of a very high CO2/O2 permeability selectivity, the CNCs coated films can be useful in some modified atmosphere packaging applications, in a range of RH typical of many medium-high RH food products.