Gas Penetration Research Articles

Fluid transport properties of normal concrete substrate and a new green fiber reinforced concrete overlay composite

AbstractThe fluid transport properties of normal concrete (NC) substrate as old concrete and ultra‐high performance fiber reinforced concrete called Green Universiti Sains Malaysia Reinforced Concrete (GUSMRC) as a repair material were investigated. GUSMRC is a new green concrete in which 50% of its volume contains ultra‐fine palm oil fuel ash. The NC substrate surfaces were first subjected to different surface treatments (grinding and sand‐blasting) prior to casting the GUSMRC repair material to form the NC/GUSMRC composite. The GUSMRC was bonded to the old concrete using the overlay and half–half layering conditions. The fluid transport properties of the monolithic GUSMRC (repair material) were also assessed. Results showed that GUSMRC has a high resistance against fluid and gas penetration and can be employed as a repair material to enhance the old concrete impermeability. The overlay layering condition improved the NC/GUSMRC composite impermeability by 2–2.8 times more than the half–half layering, and the surface treatment method had a negligible impact on the composite impermeability.

Improved sensing performances of NO2 sensors based on YSZ and porous sensing electrode prepared by MnCr2O4 admixed with phenol-formaldehyderesin microspheres

The phenol-formaldehyde (PF) resin microspheres were firstly used as the template in the sensing electrode (SE) preparation process of sensors based on Y2O3 stabilized ZrO2 (YSZ). The PF resin microspheres were synthesized by a facile hydrothermal method. The high char yield and the few morphological changes of PF resin microspheres before and after sintering at 900 °C indicated the perfect thermal stability at high temperature. The sensors using MnCr2O4 admixed with various contents PF microspheres (0 wt%, 5 wt%, 10 wt%, and 20 wt%) were fabricated and their sensing performances on NO2 gas were also investigated. The sensor with sensing electrode prepared by MnCr2O4 with 10 wt% PF showed the best NO2 sensing performance with a response of 110.8 mV to 100 ppm NO2 as well as the higher sensitivity (87.4 mV/decade) with the NO2 concentration ranging from 10 to 500 ppm at 550 °C. According to the mixed-potential mechanism, the porous electrode is good for gas penetration, so the gas can easily reach the MnCr2O4/YSZ/gas triple phase boundary (TPB) to participate in the electrochemical reactions. Additionally, the sensor exhibited excellent selectivity and repeatability, which indicated its potential application in the NO2 detection.

Modeling Gas–Liquid Flow Between Rotating and Nonrotating Annular Disks

When a liquid is forced to flow radially outward in the gap between two coaxial, parallel annular disks—one rotating and one stationary—the liquid occupies the entire gap until the speed of the rotating disk reaches a critical value. Beyond that critical speed, gas from the outer radius starts to enter into the gap, a process referred to as aeration. The higher the rotational speed, the greater is the extent of penetration by the gas into the gap. The extent of gas penetration strongly affects the torque exerted between the two disks because of the large difference in the gas and liquid viscosities. In this study, a reduced-order model is developed to predict the onset of aeration, extent of gas penetration into the gap, and drag torque as a function of the disk's rotational speed, gap between disks, properties of the liquid, and mass flow rate of the liquid forced through the gap. The model developed was validated by comparing predictions with experimental data.

Revisiting the role of natural gas as a transition fuel

The objective of this paper is to assess the potential of natural gas as a transition fuel towards a low- and zero-carbon economy. We use the previously established global energy market model (GEM) to first provide a close match of the historical energy mix and the associated carbon levels. The model is then used to make simulations of how the energy mix and carbon quantities would evolve in the long distant future—the year 2150—if past dynamics were an indication of the future. A similar GEM modeling exercise was carried out in a previous work, using historical data up to the year 2005, showing that natural gas would help slow global carbon growth in the next 50–100 years, thus paving the way towards a low carbon future dominated by non-fossil energy use. The present study uses the most recent statistics, from 2005 to 2017, to verify the accuracy of the original GEM projections. Our findings show continued penetration of natural gas in the energy mix until the mid-twenty-first century and an eventual reduction of carbon levels starting around that time.

A highly sensitive breathable fuel cell gas sensor with nanocomposite solid electrolyte

AbstractThe present work deals with a poly(vinyl alcohol)‐based membrane mixed with poly(4‐styrenesulfonic acid) to be used as a proton‐conducting solid‐state electrolyte in an electrochemical gas sensor for the detection of alcohol. A cross‐linking bonding semi‐interpenetrating network is formed between the polymer backbones, providing the membrane with superior mechanical property and excellent water retention. Meanwhile, the graphene oxide nanosheets are incorporated into the polymer fibrous backbones, creating impermeable block layers to limit ethanol gas penetration. Importantly, the modification of graphene oxide facilitates the protons transportation in both in‐plane and through‐plane channels of the membrane, boosting excellent conductivities of 0.13 S cm−1 (in‐plane) and 22.6 mS cm−1 (through‐plane) at 75°C, respectively. An alcohol fuel cell sensor assembled with this semi‐interpenetrating network solid electrolyte membrane is fabricated based on direct ethanol fuel cell principle, exhibiting excellent sensitivity, linearity, as well as low ethanol detection limits of 25 ppm.

A rheological approach to study the early-age hydration of oil well cement: Effect of temperature, pressure and nanoclay

Abstract The pumpability of cement slurries during cementing and their ability to resist penetration of formation gas once placed are critical for the success of oil and shale gas well cementing. Pumpability and ability to resist gas migration, which can be quantified through rheological parameters, develop over time due to hydration, which is highly dependent on the well conditions, namely temperature and pressure levels, as well as mix composition, including the use of rheological modifiers. In this study, we utilized a rotational rheometer with a high-pressure cell to investigate the effect of temperature, pressure and nanoclay on the viscosity and static yield stress of oil well cement slurries. The results emphasize the importance of considering shear rate in evaluating viscosity evolution and time to reach the limit of pumpability. The growth of yield stress was described by a non-linear structural build-up model, which connects the static yield stress with hydration, and its ability to predict the effect of temperature, pressure and nanoclay on yield stress evolution was assessed.

FRACTAL ANALYSIS OF THE PENETRATION FLOW THROUGH MICRO-NANO POROUS GASKETS WITH EFFECTS OF SLIPPAGE AND STRESS-SENSITIVITY

The airtightness of non-metallic sealing structures undergoing harsh conditions is very crucial to the reliability of equipment in many industrial fields. In this study, the gas penetration through a non-metallic sealing material (NSM) with micro-nano porous structure under stress was investigated in detail based on the transport theory of fractal porous media. A complete theoretical model for predicting the stress sensitivity of the gasket permeability was developed, in which the slippage effect was of concern due to very fine pore size. The permeability of a flexible graphite gasket under different stresses was numerically predicted via scanning electron microscopy (SEM) and image processing. The influencing factors on the permeability of the NSM were analyzed quantitatively and good agreements with existing experimental results demonstrate the validity of the proposed model. Since the effects of the pore-size distribution and flow pattern regime were taken into account, the parameters of the model had a clear physical meaning and the model was suitable for determining the mechanism of penetration leakage through the NSM. In addition, the model could also be used for the analysis of other tight porous media with complex microstructure under stress deformation.

Use of poly(ε-caprolactone)-based films for equilibrium-modified atmosphere packaging to extend the postharvest shelf life of garland chrysanthemum.

A uniaxial‐stretched poly(ε‐caprolactone)/poly(propylene carbonate; PCL/PPC) composite film was prepared using a twin‐screw extruder, and its utility as an equilibrium‐modified atmosphere packaging (EMAP) film extending the shelf life of garland chrysanthemums stored at 2~4°C was explored. The oxygen, carbon dioxide, and water vapor penetration properties, mechanical properties, and gas permselectivity of PCL/PPC film used to package garland chrysanthemums were determined and compared to those of controlled low‐density polyethylene (LDPE) and PCL films. Physicochemical properties such as package headspace gas composition, weight loss, leaf color, total chlorophyll content, ascorbic acid content, lipid peroxidation extent, and the sensory traits of garland chrysanthemums were investigated over a storage period of 14 days to compare the preservative effects of the various packages. PPC blending decreased the PCL gas and water vapor permeability and slightly increased the CO 2 permselectivity. These effects on gas and water vapor permeability, combined with the effects on gas permselectivity, enhanced preservation of packed garland chrysanthemums. Furthermore, an O2 inner atmosphere level of 2%~5%, and a CO 2 concentration not greater than 8%, was established by the PCL/PPC film in the absence of condensation. The results thus suggest that biodegradable film can be used as an EMAP film to better maintain the quality of freshly harvested garland chrysanthemums and to afford a longer shelf life during cold storage compared to LDPE film. Sensory evaluation indicated that the garland chrysanthemums were market‐acceptable after 14 days of storage; LDPE‐packed chrysanthemums were acceptable only up to 8 days of storage. The film thus improved storage life compared to that afforded by LDPE.

Modelling the process of interaction of porous titanium adsorbent with a multi -component gas environment

A model of mass transfer of two-component gas through an absorbing porous body was developed. The mathematical model is a problem of Stefan problem type. Analytical solutions of the model in the quasi-stationary regime were obtained. For the transfer of nitrogen-oxygen mixture by titanium porous adsorbent, the dependences of the gas penetration depth and the mass absorbed by the adsorbent on the temperature, the pressure of the gas mixture and the diameter of the porous material particles were calculated. It was found that the size of the nitrogen absorption area was several times smaller than the size of the oxygen absorption area. Also, the mass of the absorbed nitrogen was half the mass of the absorbed oxygen. This is due to the remoteness of the nitrogen absorption area from the outer surface of the titanium adsorbent.

Effect of Ingress on Flow and Heat Transfer Upstream and Downstream of a Rotating Turbine Disc

Ingress is the penetration of a hot mainstream gas in a turbine annulus through the rim seal into the wheel-space between the rotating turbine disc (the rotor) and the adjacent stationary casing (the stator). Purge flow is used to prevent or reduce ingress, and the sealing effectiveness relates the flow rates of the purge and ingress. In this paper, an adiabatic effectiveness is used to relate the temperatures of a thermally-insulated rotor, the purge flow and the ingress. A non-dimensional buffer parameter, Ψ, is used to relate the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, respectively. This paper reports the first experimental study of the effect of ingress and purge flow on the adiabatic temperatures of both upstream and downstream surfaces of the rotor. Measurements of concentration and swirl over a range of purge have been obtained in wheel-spaces upstream and downstream of the rotor in a turbine rig. In transient heating tests, fast-response thermocouples were used to measure the temperature of the air in the wheel-space core; simultaneously, the temperatures of the upstream and downstream rotor surfaces were determined from infra-red sensors. The extrapolated steady-state temperatures (obtained using a maximum-likelihood estimation analysis) were used to determine the adiabatic effectiveness as a function of purge flow rate. The buffer effect of the purge flow for both wheel-spaces was quantified via comparisons between the variation of Ψ with purge flow rate. It was shown that the sealing effectiveness for the downstream wheel-space was larger than for the upstream. Consequently, and consistent with the theoretical model, the buffering effect of the purge flow was shown to be smaller downstream.

Impact of heat and mass transfer in porous catalytic monolith: CFD modeling of exothermic reaction

Impact of mass and heat transfer on exothermic reaction performance in porous catalytic monolith with triangular channels is investigated by CFD modeling. Detailed analysis of spatial distributions of process characteristics for methane oxidation shows that in the initial part of catalyst volume there is the active subsurface layer. The domain of sharp gradients of the reaction rate is revealed that includes the parts of external surface and thin subsurface layers near the monolith inlet, which results in sharp rearrangement of 3D-field of temperature and reagent concentrations. It is shown that the formation of such conditions is strongly influenced by complex gaseous flow reconstruction with gas penetration into the catalyst volume, significant heat release, and heat transfer between channel wall and gas flow. Though the region with high reaction rate is rather short this could be of high importance for reactor design and selection of optimal operation conditions.

Multi-Stage Fracgun SDP Perforation Technology for Deep Horizontal Wells

Multi-stage fracgun SDP perforation technology for deep horizontal wells developed in recent years is to form a plurality of radial hole in reservoir through deep penetrating perforation technology and gas fracturing technology, which could enlarge the drainage area and reduce production pressure drop. This paper analyzes the technical principles, and then proves the mechanism with well and layer selection of tests wells through technical applicability. On the basis of these, Deep Composite Directional perforation design plan of the test well was proposed, and the on-site operation situation was illuminated from the aspect of field test preparation and construction techniques. The testing results showed that both wells site construction had met the requirement of the design and made the yield increasing effect at some certain degree, however, there are also a large production change, it is thought that the key to the successful implementation of deep penetration composite directional perforation in horizontal well is the control of perforation depth and orientation, the application results are determined by well situation and reservoir layer, The design should be based on the technical adaptability of reservoir geological conditions and engineering conditions for a detailed demonstration.

Enhancing gas separation efficiency by surface functionalization of nanoporous membranes

Here we report evidence for substantial changes in the separation efficiency of nanoporous anodic alumina membranes with nanochannel diameters ranging from 10–100 nm modified with octadecylphosphonic acid in the transitional flow regime. Softening of surface by alkyl groups with a surface density ∼2 groups/nm2 leads to a general permeance decrease in 3–500 times, depending strongly on the penetrant gas nature and the channels diameter. The divergence of the permeance, for different gases, increases with the decreasing diameter of the pores. For a surface-functionalized membrane, with 10-nm channel diameters, it results in n-C4H10/CH4 ideal and mixed gas separation factors up to 32.3 and 9.0 respectively at a n-C4H10 permeance up to 3.5 m3/(m2·bar·h). The effect is related to the changes of the ratio of molecule travelling time to residence time in the adsorbed state, as well as a strong influence of surface saturation by the absorbed molecules on the tangential momentum accommodation coefficient, which is supported by the derived model. Synergetic contribution of these two factors allows to enhance the separation factor of permanent and condensable gases strongly beyond the Knudsen limit, while maintaining a high permeance of porous membranes.

Macroscopic and mesoscopic simulation of viscoelastic free surface flow in gas‐assisted injection moulding process

AbstractIn this work, an improved simple coupled level‐set and volume of fluid (S‐CLSVOF) method is proposed to trace the moving interfaces in gas assisted injection moulding (GAIM) process based on the viscoelastic FENE‐P model. Firstly, the Kreisselmeier‐Steinhauser (KS) function constructed by means of Boolean operations is adopted as the shape level set (LS) function to precisely represent the complex mould cavities. Then, the benchmark problem of two‐dimensional deformation is used to verify the ability of the S‐CLSVOF method for capturing the moving interfaces. The stress birefringence is calculated and compared with the experiment result. Finally, the proposed method is further applied to the mould filling and gas penetration processes in GAIM. The macroscopic bubble appearance, temperature distribution, and the behaviour of the mesoscopic molecular orientation are shown and analyzed in detail. Due to the complexity of the gas‐liquid interaction, the phenomenon of asymmetrical gas flow is clearly observed in the gas penetration process. The influences of the macroscopic parameters on the macroscopic gas flows and mesoscopic molecular orientation are also discussed, such as insert positions, melt temperatures, and gas delay time. The numerical results illustrate that the coupled method can be applied to the multiscale numerical simulation of viscoelastic flows with complex free surfaces and provide significant guidance for the GAIM process.

A visualization experimental study on gas penetration through interlayer to improve SAGD performance

Abstract Low-permeability interlayer is common in reservoir, which can hinder the steam chamber expansion and the gravity drainage in SAGD. It is crucial to find an economical and practicable method to promote the steam chamber to break through the interlayer. In this work, four condensation heat transfer experiments were conducted to investigate the effect of flue gas on steam condensation heat transfer. On this basis, 2D visualization tests, including a SAGD experiment and two flue gas assisted SAGD experiments, were carried out to see if the steam chamber can break through the interlayer under the effect of flue gas. Results show with the increase of gas proportion in the steam-flue gas mixture, the condensation heat transfer coefficient decreased and the condensation pattern was transformed from drop condensation to film condensation gradually. This indicates that flue gas can inhibit the condensation heat transfer, which has great influence on the heat transfer and steam chamber growth in SAGD. Visualization tests show the interlayer could block the steam chamber development. After the interlayer was heated sufficiently, flue gas could penetrate the interlayer and promote steam chamber to break through the interlayer because of its inhibiting effect on condensation heat transfer. Besides, the horizontal sweep efficiency was improved significantly under the synergistic effects of steam, gas, and interlayer. The gas addition can reduce the adverse impact of interlayer on SAGD performance, which provides a potential method to improve SAGD development in the reservoir with interlayer.

Transparent high-pressure nozzles for visualization of nozzle internal and external flow phenomena.

A new design for transparent high-pressure nozzles is presented in this work. This new design enables using the innovative Selective Laser Etching (SLE) method to manufacture transparent nozzles with outstanding accuracy. Therefore, not only the simultaneous visualization of the flow mechanics inside and outside the nozzle is enabled, but the manufacturing method applied also allows for the realization of individual nozzle geometries. Thus, nozzle internal flow phenomena (e.g., cavitation, swirl, and air inlet) and their influence on primary breakup can be analyzed with realistic nozzle geometries, e.g., for automotive applications. In addition, targeted three dimensional nozzle geometric parameters can be designed and manufactured in order to get specific tailor-made spray characteristics (e.g., droplet size distribution, spray angle, and penetration length). The basis for the transparent nozzle design is a two-parted nozzle, consisting of a re-machined original serial nozzle body and a transparent nozzle tip. The innovative SLE is used to produce the geometry of the transparent nozzle tip in fused silica, and laser polishing is utilized to achieve a maximum optical quality of nozzle surfaces for visualization. Bonding of both nozzle parts is achieved by a specially designed adhesive method. For a first feasibility study, a transparent nozzle with a simplified nozzle geometry is manufactured and used for a first study. In this study, simultaneous investigation of nozzle internal flow phenomena and their impact on spray breakup are visualized. First microscopic images of the nozzle internal flow show the formation of cavitation, its effect on nozzle internal temperature (apparent by differences in the fluid refractive index), and also the corresponding impact on spray breakup during injection. The penetration of ambient gas into the nozzle is verified at the end of injection as well as the influence of this air on the spray formation during the start of injection.

POST-HARVEST QUALITY OF OZONATED MACAUBA FRUITS FOR BIODIESEL PRODUCTION

ABSTRACT The presence of microorganisms, especially during storage, can lead to the rapid deterioration of macauba fruits (Acrocomia aculeata) and reduce the quality of extracted oil for biodiesel production. An alternative to ensure the quality of the oil is the use of ozone gas, a oxidizing agent that has high antimicrobial and sanitizing power. The objective of this study was to evaluate the influence of high concentrations of ozone gas on macaúba fruit and its effect on the quality of the oil throughout storage for the production of biodiesel. Ozonation was performed 20 days after harvest using fruits with and without the epicarp. Ozone was applied at a concentration of 18.0 mg L-1 and a flow of 1.5 L min-1 for 10 h. After ozonation, the fruits were stored for different periods, and the physical-chemical parameters of the oil were evaluated. The ozonation of fruits without the epicarp visually reduced microorganism attack. In general, the ozonation process of macauba fruits maintained the visual characteristics of the fruits and the physical-chemical characteristics of the oil for biodiesel production compared to untreated fruits. The average acidity values of the oil were lower in the treatments with the ozone gas. Removal of the epicarp tends to facilitate the ozonation process, potentially by improving gas penetration into the fruit.

Combustion synthesis of α-Si3N4 assisted by molten salt additives

Combustion synthesis (CS) of silicon nitride (Si3N4), assisted by molten salt additives under high N2 pressure, is reported. The effect of salt additives (NaCl, MgCl2, and MgCl2∙6H2O) on the reaction temperature and the final α-Si3N4 content is studied. The maximum reaction temperature (Tmax) decreased with an increase in the amount of the salt additives. NaCl is found to be the most suitable as it results in 57.8% α-Si3N4 at 30 mass% concentration. MgCl2 is strongly hygroscopic, and MgCl2∙6H2O decomposes at very low temperature. Therefore, they absorb heat at low temperatures, which makes it difficult to reach the ignition temperature, thereby hindering the reaction propagation. Si3N4 is necessary as a diluent for creating pores in the raw materials to allow effective penetration and contact of N2 gas with the Si particles.

Investigation on isothermal wicking performance within metallic weaves for screen channel liquid acquisition devices (LADs)

Wicking performance within the metallic screen is one of the key foundation to preventing gas penetration for screen channel liquid acquisition devices (LADs), which are designed to provide vapor free propellant for space crafts. In this study, based on the theoretical analysis on screen microscopic structure and wicking characteristics, a vertical isothermal wicking experiment was carried out using three selected Dutch Twill Weaves (DTWs) with HFE-7500 as the test fluid. According to the agreement between experimental results and the wicking theory, three macroscopic structural parameters named porosity, equivalent capillary diameter (ECD) and permeability were obtained both in warp and shute directions for 200 × 1400 DTW (woven with 200 warp wires and 1400 shute wires per square inch), 325 × 2300 DTW and 510 × 3600 DTW, respectively. Results show that, a finer mesh screen at the same direction is of a larger porosity, a smaller ECD and a smaller permeability, while the same mesh is of a smaller ECD and a larger permeability at the warp direction over the shute direction. In general, the wicking velocity is higher in a coarser mesh and is higher along the warp direction.

When Catalysts Breathe

In this issue of Joule, Yi Cui and colleagues developed a breath-mimicking structure for electrocatalysis applications where gas no longer has to be dissolved into the electrolyte. Specifically, a highly efficient three-phase contact between gas, electrolyte, and catalyst is formed, facilitating both O2 evolution (OER) and reduction (ORR) reaction processes. A low overpotential of 190 mV at 10 mA/cm2 is reported in the OER process while in the ORR process significantly higher current densities are observed.