Articoli di riviste: "Cushion gas"

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Zhang, Jun An, Kai Ren, Lina Wang e Bo Liu. "Camping Performance Experiment of Gas Thrust Bearing with Elastic Pressure Equalizing Groove". Advanced Materials Research 301-303 (luglio 2011): 547–52. http://dx.doi.org/10.4028/www.scientific.net/amr.301-303.547.

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Camping is a major parameter of floatation cushion dynamic performance, we could get floatation cushion dynamic performance parameter through research floatation cushion camping performance.This paper uses experiment method to measure floatation cushion film gap and then data processing is by wavelet felixgong principle.Through the comparison of two curves we can observe that the camping of the gas lubricated thrust bearing with elastic pressure equalizing groove is obviously bigger than the gas lubricated thrust bearing with stiffness pressure equalizing groove.So elastic cushion could decay the external drive faster which can improve the cushion’s stability and could be widely used in the future.

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Luboń, Katarzyna, e Radosław Tarkowski. "Hydrogen Storage in Deep Saline Aquifers: Non-Recoverable Cushion Gas after Storage". Energies 17, n. 6 (21 marzo 2024): 1493. http://dx.doi.org/10.3390/en17061493.

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Underground hydrogen storage facilities require cushion gas to operate, which is an expensive one-time investment. Only some of this gas is recoverable after the end of UHS operation. A significant percentage of the hydrogen will remain in underground storage as non-recoverable cushion gas. Efforts must be made to reduce it. This article presents the results of modeling the cushion gas withdrawal after the end of cyclical storage operation. It was found that the amount of non-recoverable cushion gas is fundamentally influenced by the duration of the initial hydrogen filling period, the hydrogen flow rate, and the timing of the upconing occurrence. Upconing is one of the main technical barriers to hydrogen storage in deep saline aquifers. The ratio of non-recoverable cushion gas to cushion gas (NRCG/CG) decreases with an increasing amount of cushion gas. The highest ratio, 0.63, was obtained in the shortest 2-year initial filling period. The lowest ratio, 0.35, was obtained when utilizing the longest initial filling period of 4 years and employing the largest amount of cushion gas. The presented cases of cushion gas recovery can help investors decide which storage option is the most advantageous based on the criteria that are important to them.

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Cao, Cheng, Jianxing Liao, Zhengmeng Hou, Hongcheng Xu, Faisal Mehmood e Xuning Wu. "Utilization of CO2 as Cushion Gas for Depleted Gas Reservoir Transformed Gas Storage Reservoir". Energies 13, n. 3 (25 gennaio 2020): 576. http://dx.doi.org/10.3390/en13030576.

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Underground gas storage reservoirs (UGSRs) are used to keep the natural gas supply smooth. Native natural gas is commonly used as cushion gas to maintain the reservoir pressure and cannot be extracted in the depleted gas reservoir transformed UGSR, which leads to wasting huge amounts of this natural energy resource. CO2 is an alternative gas to avoid this particular issue. However, the mixing of CO2 and CH4 in the UGSR challenges the application of CO2 as cushion gas. In this work, the Donghae gas reservoir is used to investigate the suitability of using CO2 as cushion gas in depleted gas reservoir transformed UGSR. The impact of the geological and engineering parameters, including the CO2 fraction for cushion gas, reservoir temperature, reservoir permeability, residual water and production rate, on the reservoir pressure, gas mixing behavior, and CO2 production are analyzed detailly based on the 15 years cyclic gas injection and production. The results showed that the maximum accepted CO2 concentration for cushion gas is 9% under the condition of production and injection for 120 d and 180 d in a production cycle at a rate of 4.05 kg/s and 2.7 kg/s, respectively. The typical curve of the mixing zone thickness can be divided into four stages, which include the increasing stage, the smooth stage, the suddenly increasing stage, and the periodic change stage. In the periodic change stage, the mixed zone increases with the increasing of CO2 fraction, temperature, production rate, and the decreasing of permeability and water saturation. The CO2 fraction in cushion gas, reservoir permeability, and production rate have a significant effect on the breakthrough of CO2 in the production well, while the effect of water saturation and temperature is limited.

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Heinemann, Niklas, Mark Wilkinson, Kate Adie, Katriona Edlmann, Eike Marie Thaysen, Aliakbar Hassanpouryouzband e Robert Stuart Haszeldine. "Cushion Gas in Hydrogen Storage—A Costly CAPEX or a Valuable Resource for Energy Crises?" Hydrogen 3, n. 4 (12 dicembre 2022): 550–63. http://dx.doi.org/10.3390/hydrogen3040035.

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The geological storage of hydrogen is a seasonal energy storage solution, and the storage capacity of saline aquifers is most appropriately defined by quantifying the amount of hydrogen that can be injected and reproduced over a relevant time period. Cushion gas, stored in the reservoir to support the production of the working gas, is a CAPEX, which should be reduced to decrease implementation cost for gas storage. The cushion gas to working gas ratio provides a sufficiently accurate reflection of the storage efficiency, with higher ratios equating to larger initial investments. This paper investigates how technical measures, such as well configurations and adjustments to the operational size and schedule, can reduce this ratio, and the outcomes can inform optimisation strategies for hydrogen storage operations. Using a simplified open saline aquifer reservoir model, hydrogen storage is simulated with a single injection and production well. The results show that the injection process is more sensitive to technical measures than the production process; a shorter perforation and a smaller well diameter increases the required cushion gas for the injection process but has little impact on the production. If the storage operation capacity is expanded, and the working gas volume increased, the required cushion gas to working gas ratio increases for injection, reducing the efficiency of the injection process. When the reservoir pressure has more time to equilibrate, less cushion gas is required. It is shown that cushion gas plays an important role in storage operations and that the tested optimisation strategies impart only minor effects on the production process, however, there is significant need for careful optimisation of the injection process. It is suggested that the recoverable part of the cushion gas could be seen as a strategic gas reserve, which can be produced during an energy crisis. In this scenario, the recoverable cushion gas could be owned by the state, and the upfront costs for gas storage to the operator would be reduced, making the implementation of more gas storage and the onset of hydrogen storage more attractive to investors.

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Pancotto, Verónica, David Holl, Julio Escobar, María Florencia Castagnani e Lars Kutzbach. "Cushion bog plant community responses to passive warming in southern Patagonia". Biogeosciences 18, n. 16 (26 agosto 2021): 4817–39. http://dx.doi.org/10.5194/bg-18-4817-2021.

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Abstract. Vascular plant-dominated cushion bogs, which are exclusive to the Southern Hemisphere, are highly productive and constitute large sinks for atmospheric carbon dioxide compared to their moss-dominated counterparts around the globe. In this study, we experimentally investigated how a cushion bog plant community responded to elevated surface temperature conditions as they are predicted to occur in a future climate. We conducted the study in a cushion bog dominated by Astelia pumila on Tierra del Fuego, Argentina. We installed a year-round passive warming experiment using semicircular plastic walls that raised average near-surface air temperatures by between 0.4 and 0.7 ∘C (at the 3 of the 10 treatment plots which were equipped with temperature sensors). We focused on characterizing differences in morphological cushion plant traits and in carbon dioxide exchange dynamics using chamber gas flux measurements. We used a mechanistic modeling approach to quantify physiological plant traits and to partition the net carbon dioxide flux into its two components of photosynthesis and total ecosystem respiration. We found that A. pumila reduced its photosynthetic activity under elevated temperatures. At the same time, we observed enhanced respiration which we largely attribute, due to the limited effect of our passive warming on soil temperatures, to an increase in autotrophic respiration. Passively warmed A. pumila cushions sequestered between 55 % and 85 % less carbon dioxide than untreated control cushions over the main growing season. Our results suggest that even moderate future warming under the SSP1-2.6 scenario could decrease the carbon sink function of austral cushion bogs.

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Song, Bo, Hongliang Chen, Long Sun, Kunpeng Xu e Xiaoyong Ren. "Improved Method for the Calculation of the Air Film Thickness of an Air Cushion Belt Conveyor". Materials 17, n. 23 (9 dicembre 2024): 6020. https://doi.org/10.3390/ma17236020.

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The air film thickness is an important parameter of an air cushion belt conveyor, which directly affects the compressed air supply power and operating resistance of the system. Therefore, it is important to calculate the bottom thickness of the gas film accurately in the design stage. A calculation method for the thickness of a conveyor air cushion was derived based on the mathematical model of the air cushion flow field for a multi row uniformly distributed air cushion structure. Meanwhile, the algorithm was validated based on a Fluent 3D flow field numerical simulation and experiments. Through verification, it was found that due to the algorithm’s assumption that the increase in the gas flow rate only existed at the axis of the gas hole, there was a sudden change in the calculation results of the gas flow rate at the axis of the gas hole. The sudden change in the gas flow rate had caused the calculation results of the air cushion thickness to experience abrupt and discontinuous changes. Furthermore, the calculation method for air cushion thickness was revised based on the verification results. Compared with the experimental test results, the average error of the calculation results of the algorithm proposed in this paper was 14.27%.

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Prigmore, Sadie, Omolabake Abiodun Okon-Akan, Imuentinyan P. Egharevba, Chukwuma C. Ogbaga, Patrick U. Okoye, Emmanuel Epelle e Jude A. Okolie. "Cushion Gas Consideration for Underground Hydrogen Storage". Encyclopedia 4, n. 2 (14 maggio 2024): 847–63. http://dx.doi.org/10.3390/encyclopedia4020054.

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Due to the increasing world population and environmental considerations, there has been a tremendous interest in alternative energy sources. Hydrogen plays a major role as an energy carrier due to its environmentally benign nature. The combustion of hydrogen releases water vapor while it also has a vast industrial application in aerospace, pharmaceutical, and metallurgical industries. Although promising, hydrogen faces storage challenges. Underground hydrogen storage (UHS) presents a promising method of safely storing hydrogen. The selection of the appropriate cushion gas for UHS is a critical aspect of ensuring the safety, efficiency, and reliability of the storage system. Cushion gas plays a pivotal role in maintaining the necessary pressure within the storage reservoir, thereby enabling consistent injection and withdrawal rates of hydrogen. One of the key functions of the cushion gas is to act as a buffer, ensuring that the storage pressure remains within the desired range despite fluctuations in hydrogen demand or supply. This is achieved by alternately expanding and compressing the cushion gas during the injection and withdrawal cycles, thereby effectively regulating the overall pressure dynamics within the storage facility. Furthermore, the choice of cushion gas can have significant implications on the performance and long-term stability of the UHS system. Factors such as compatibility with hydrogen, cost-effectiveness, availability, and environmental impact must be carefully considered when selecting the most suitable cushion gas. The present study provides a comprehensive review of different types of cushion gases commonly used in UHS, including nitrogen, methane, and carbon dioxide. By examining the advantages, limitations, and practical considerations associated with each option, the study aims to offer valuable insights into optimizing the performance and reliability of UHS systems. Ultimately, the successful implementation of UHS hinges not only on technological innovation but also on strategic decisions regarding cushion gas selection and management. By addressing these challenges proactively, stakeholders can unlock the full potential of hydrogen as a clean and sustainable energy carrier, thereby contributing to the global transition towards a low-carbon future.

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Zhang, Jun An, Hao Dong, Fang Jie Ma e Bo Liu. "Performance Analysis of the Flotation Cushion with Elastic Pressure Equalizing Groove for Aerostatic Slideway". Applied Mechanics and Materials 152-154 (gennaio 2012): 743–48. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.743.

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In order to improve stiffness of the flotation cushion, a new type of flotation cushion with variable-section pressure equalizing groove of elastic plate for aerostatic slideway was designed. Gas film pressure distribution and load carrying capacity of this flotation cushion was studied through theoretical analysis. The grid was generated by taking advantage of overlapping stitching technique. By using the coupling calculation of the gas lubrication governing equation and elastic deformation of thin plate governing equation, the load carrying capacity and stiffness of the new flotation cushion were obtained. Some experiments were made to verify the result of theoretical calculation. The experimental results show that the stiffness of new flotation cushion is much higher than conventional flotation cushion.This new flotation cushion has a wider application space.

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Fedorov, S. V., e V. M. Vasilyev. "Simulation of an air cushion inverted siphon". Вестник гражданских инженеров 18, n. 2 (2021): 158–65. http://dx.doi.org/10.23968/1999-5571-2021-18-2-158-165.

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The article considers the problem of silting-up of sewage inverted siphons. A review of modern methods of hydraulic flushing is presented. To ensure reliable and energy-efficient operation of the inverted siphon, it is proposed to use the air cushion effect. To ensure the stable operation of the structure, a simulation of the inverted siphon installation was performed, consisting of two sections with nodes for receiving runoff from the drop risers, a node that provides water removal and a node for regulating the pressure in the air cushion. As a result of the simulation, there has been obtained the distribution of the volume fraction of the water phase and the gas phase, the pressure distribution in the horizontal and vertical inverted siphon pipelines and the values of the flow velocity during the formation of the air cushion. The use of separation partition walls at the ends of horizontal siphon pipelines allows creating autonomous air cushions and regulating the work for each section separately. The adaptation of the air cushion inverted siphon technology in relation to the main sewer system is considered to be promising.

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Liu, Bin, Xingyuan Huang, Shaoyi Ren e Cheng Luo. "Effect of Pressure Difference between Inner and Outer Gas Layer on Micro-Tube Deformation during Gas-Assisted Extrusion". Polymers 14, n. 17 (29 agosto 2022): 3559. http://dx.doi.org/10.3390/polym14173559.

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In the process of double-layer gas-assiste extrusion of a plastic micro-tube, the tugging effect caused by the pressure difference of the gas cushion layer inside the die has a great influence on the external dimensions of the micro-tube. Therefore, this study establishes a two-phase extrusion model based on compressible gas and incompressible melt. Ansys Polyflow finite element software was used to numerically simulate the extrusion process of the melt to analyze the effect of the gas cushion layer pressure difference on the micro-tube deformation. The research shows that the shrinkage rate of the micro-tube increases with increasing pressure of the outer cushion layer, and the degree of tube wall migration increases, too. In the process of extrusion, the first normal stress difference at the entrance of the gas cushion layer shows a significant effect on the melt velocity field distribution and the extruded micro-tube cross-sectional deformation.

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Zhao, Xiang, Bo Liu e Jun An Zhang. "Numerical Analysis of Bias Load on Integral Flotation Cushion". Advanced Materials Research 650 (gennaio 2013): 506–12. http://dx.doi.org/10.4028/www.scientific.net/amr.650.506.

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This paper adopts the Reynolds equation as the governing equation of gas lubrication; it mainly focuses on the complex flow field of flotation cushion with multiple supply-holes and analyzes the gas pressure distribution of bias load on the integral flotation cushion by the numerical method. At the same time, according to the mass conservation principle, an efficient revision iteration route about outlet pressure boundary condition of each supply-hole has been set, and the pressure distribution and flow rate of each supply-hole at different declination are calculated. The results show that when the flotation cushion deflection angle varies, due to the edge deflation, the outlet pressure of the orifice is not in strict inverse proportion to the thickness of gas film on the orifice on the integral flotation cushion.

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Ren, T., X. Shen e F. Zhang. "Numerical simulation of fingering in the underground hydrogen storage". IOP Conference Series: Earth and Environmental Science 1335, n. 1 (1 maggio 2024): 012049. http://dx.doi.org/10.1088/1755-1315/1335/1/012049.

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Abstract Underground hydrogen storage has garnered interest in recent years owing to the considerable demand for clean energy. Hydrogen is more diffusive than air and has relatively low density and viscosity. These unique properties induce distinct hydrodynamic phenomena during hydrogen storage. Cushion gas has been proven to be a potential remedy for attenuating the adverse impacts of underground hydrogen storage. To investigate the influence of the cushion gas, a microscopic numerical simulation was performed with Fluent software using the Eulerian multi-fluid model. Carbon dioxide, nitrogen, and methane are usually used as the preferred candidates for cushion gases in underground hydrogen storage systems. In this study, nitrogen was used as the cushion gas and was injected along with hydrogen into heterogeneous porous media with volume fractions ranging from 0% to 70%. A parameterization study was then performed to elucidate the influences of the injection rate and viscosity of the fluid on the fingering pattern. Two representative types of fingering, viscous fingering and capillary fingering, were observed under different gas mixtures and boundary conditions. After the simulation, an image analysis was performed to capture the evolution of the fingering pattern. The specific fingering area, number of branches, and fractal dimensions are proposed as geometric indices to describe the shape of the fingering pattern. The results showed that there was a remarkable enhancement in saturation due to the injection of the cushion gas, depending on the concentration of the gas mixture. This study offers insight on the design of gas mixture injection in underground hydrogen storage and can be further extended to the hydrochemo–mechanical coupled numerical simulation of multiphase gas injection in porous media.

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Trushlyakov, V. I., V. A. Urbansky e U. R. Abdrakhimov. "INVESTIGATION OF THE INFLUENCE OF VORTEX RING INTRODUCTION ON THE DESTRUCTION OF TEMPERATURE STRATIFICATION IN A CLOSED VESSEL". DYNAMICS OF SYSTEMS, MECHANISMS AND MACHINES 12, n. 4 (2024): 42–47. https://doi.org/10.25206/2310-9793-2024-12-4-42-47.

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A system for creating forced convection in a gas cushion of a closed container based on the introduction of vortex rings with significant range and low speed is proposed, which will destroy the established temperature layers of the gas cushion with their subsequent mixing. 2 modes of operation of the proposed system are considered: a) with the supply of additional boost gas into the free volume of the piston cylinder forming a vortex ring, b) and without additional supply, in which the free volume of the cylinder is filled with gas from the gas cushion. The Ansys Fluent software package provides mathematical modeling of the formation of temperature stratification in a closed container when it is pressurized with helium gas followed by the supply of vortex rings. The principal possibility of destruction of the established temperature layers during the operation of the proposed ICS is shown.

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Oldenburg, Curtis M. "Carbon Dioxide as Cushion Gas for Natural Gas Storage". Energy & Fuels 17, n. 1 (gennaio 2003): 240–46. http://dx.doi.org/10.1021/ef020162b.

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Liu, Shiduo, Endong Zhao, Bin Ma, Huan Liu, Jianxuan Yang, Guojie Sui, Xin Yuan, Xinfang Ma e Lei Wang. "Analysis of the Influence of Alternating Stress in the Multi-Cycle Injection Production Process". Processes 13, n. 4 (11 aprile 2025): 1158. https://doi.org/10.3390/pr13041158.

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In order to study the influence of multi-cycle stress sensitivity on the injection–production effect, it is necessary to conduct multi-cycle stress sensitivity experiments on reservoir permeability and fracture conductivity first and then calculate the impact on the injection–production effect after the occurrence of the stress sensitivity effect by using the CMG software. After stress sensitivity occurs and the production rate decreases, the constraints of the well should be adjusted. The results showed that the conductivity of the 30–50 mesh ceramsite decreased by 15.94% after 100 cycles, while the conductivity of the 20–40 mesh quartz sand decreased by 51.17%. Under alternating stress, the reservoir permeability decreased significantly during the first 50 cycles, with an average decrease of 20.8%, but remained relatively stable in the later stages. When stress sensitivity was disregarded, the gas production rate of the ceramic and quartz sand stabilized at approximately 3700 m3/h and 2600 m3/h, respectively. When stress sensitivity was considered, the secondary gas cushion for ceramsite had to reach at least 500,000 m3 to maintain a gas production rate of over 3700 m3/h within 40 cycles after the gas cushion. When stress sensitivity was considered, the secondary gas cushion for quartz sand had to exceed 800,000 cubic meters to maintain the gas production rate of over 2600 m3/h within the first 30 cycles after the gas cushion. To sustain the gas production rate over the long term, it was necessary to increase the injection pressure per cycle. The gas injection pressure for ceramsite should be adjusted to more than 17 MPa, and the gas injection pressure for quartz sand should be adjusted to more than 19.3 MPa.

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Luboń, Katarzyna, Radosław Tarkowski e Barbara Uliasz-Misiak. "Impact of Depth on Underground Hydrogen Storage Operations in Deep Aquifers". Energies 17, n. 6 (7 marzo 2024): 1268. http://dx.doi.org/10.3390/en17061268.

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Underground hydrogen storage in geological structures is considered appropriate for storing large amounts of hydrogen. Using the geological Konary structure in the deep saline aquifers, an analysis of the influence of depth on hydrogen storage was carried out. Hydrogen injection and withdrawal modeling was performed using TOUGH2 software, assuming different structure depths. Changes in the relevant parameters for the operation of an underground hydrogen storage facility, including the amount of H2 injected in the initial filling period, cushion gas, working gas, and average amount of extracted water, are presented. The results showed that increasing the depth to approximately 1500 m positively affects hydrogen storage (flow rate of injected hydrogen, total capacity, and working gas). Below this depth, the trend was reversed. The cushion gas-to-working gas ratio did not significantly change with increasing depth. Its magnitude depends on the length of the initial hydrogen filling period. An increase in the depth of hydrogen storage is associated with a greater amount of extracted water. Increasing the duration of the initial hydrogen filling period will reduce the water production but increase the cushion gas volume.

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Chaoran, Liu, Yue Jinzhao, Li Tianhao, Xia Weiwei, Li Dongxue e Duan Zhiyong. "Vibration attenuation analysis of compressional gas cushion press nanoimprint lithography system". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, n. 9 (28 ottobre 2013): 1634–42. http://dx.doi.org/10.1177/0954406213508755.

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Nanoimprint lithography has a great development in decades. Compressional gas cushion press is a novel method in improving the uniformity in nanoimprint lithography process. Based on compressional gas cushion press nanoimprint lithography system, an attenuation ring is added between the chamber wall and the pedestal. The attenuation ring decreases the influence of system vibration on the fidelity of patterning. The physical parameters of the attenuation material are optimized based on the theoretical models of the vibration attenuation and mechanical calculation. According to the optimization physical parameters, Young's modulus of a perfect material of attenuation ring should be smaller than 8 MPa, and Poisson's ratio should be close to 0.5. Therefore, natural rubber is employed as the material of attenuation ring. The simulation results based on COMSOL indicate that nested rectangular structure has the best attenuation effect among the four simulated internal structures. It provides technological supporting for the establishment of attenuation ring in compressional gas cushion press nanoimprint lithography system.

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Liu, Bin, Xingyuan Huang, Xiaohui Zhang, Shaoyi Ren, Qiang Lan e Cheng Luo. "Numerical and Experimental Studies on the Improvement of Gas Chamber Structure during Gas-Assisted Extrusion". Polymers 14, n. 23 (2 dicembre 2022): 5272. http://dx.doi.org/10.3390/polym14235272.

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In the gas-assisted extrusion process, the melt inside the die is in a low-viscosity molten state, so the flow field of the gas cushion layer has a great effect on the cross-sectional shape of the micro-tube. Therefore, this study establishes the gas distribution chamber model of the gas-assisted die. Ansys Fluent software was used to simulate the gas flow field of the gas distribution chamber. The effect of the gas chamber structure on the size of the micro-tube was analyzed by the extrusion experiment. The research shows that the velocity unevenness coefficient of the gas outlet of the single gas chamber die is 11.8%, which is higher than that of the double gas chamber die. The use of a double gas chamber die can improve the stability of the gas cushion layer and the wall thickness non-uniformity of the micro-tube, which verifies the simulation results.

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Xia, Yong, Pei Wang, Pengxia Du, Yue Liu, Bihua Tang, Xueyu Li, Ling Zhou e Deyou Liu. "Gas Loss Mechanism in the High-Pressure Air Cushion Surge Chamber of Hydropower Station for Transient Process". Water 15, n. 15 (1 agosto 2023): 2784. http://dx.doi.org/10.3390/w15152784.

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Water–air interaction (mixing of gas and water and gas dissolution into water) is one of the main reasons for gas loss in air cushion surge chambers. With the increase of water head in hydraulic power generation systems, the heat and mass transfer process at the water–air interface under high-pressure conditions intensifies, and the water–air interaction is further strengthened. If some gas is mixed/dissolved in water and enters downstream pipelines, it will affect the safety of the unit. At present, there has been no theoretical or systematic research on gas loss and related water gas two-phase flow in air cushion surge chambers under high-pressure conditions. Therefore, this article established an air loss model for an air cushion surge chamber based on the VOF model and gas–liquid mass transfer theory. We analyzed the mechanism of gas loss in the gas chamber through simulation and quantitatively expressed the gas loss. The results indicate that during a typical large fluctuation process, the gas–liquid mass transfer process at the water–air interface, air mass, and vortex is very strong, with a pressure chamber of approximately 923.89 m3. The gas dissolved in water enters the water diversion system, with a length of 28.75 m3. High pressure gas enters the water diversion system in the form of air masses. When considering the water inlet on the right side of the air chamber, the total gas loss in the air chamber is slightly lower (854.18 m3) and no mixed air mass was detected entering the connecting pipe.

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Al Homoud, Rana, Marcos Vitor Barbosa Machado, Hugh Daigle, Kamy Sepehrnoori e Harun Ates. "Enhancing Hydrogen Recovery from Saline Aquifers: Quantifying Wettability and Hysteresis Influence and Minimizing Losses with a Cushion Gas". Hydrogen 5, n. 2 (13 giugno 2024): 327–51. http://dx.doi.org/10.3390/hydrogen5020019.

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This study aims to numerically assess the impact of wettability and relative permeability hysteresis on hydrogen losses during underground hydrogen storage (UHS) and explore strategies to minimize them by using an appropriate cushion gas. The research utilizes the Carlson model to calculate the saturation of trapped gas and the Killough model to account for water hysteresis. By incorporating the Land coefficient based on laboratory-measured data for a hydrogen/brine system, our findings demonstrate a significant influence of gas hysteresis on the hydrogen recovery factor when H2 is used as a cushion gas. The base model, which neglects the hysteresis effect, indicates a recovery factor of 78% by the fourth cycle, which can be improved. In contrast, the modified model, which considers hysteresis and results in a trapped gas saturation of approximately 17%, shows a hydrogen recovery factor of 45% by the fourth cycle. Additionally, gas hysteresis has a notable impact on water production, with an observed 12.5% increase in volume in the model that incorporates gas hysteresis. Furthermore, optimization of the recovery process was conducted by evaluating different cushion gases such as CO2, N2, and CH4, with the latter proving to be the optimal choice. These findings enhance the accuracy of estimating the H2 recovery factor, which is crucial for assessing the feasibility of storage projects.

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Bourrianne, Philippe, e Gareth H. McKinley. "When fizzy water levitates". Physics Today 75, n. 8 (1 agosto 2022): 62–63. http://dx.doi.org/10.1063/pt.3.5070.

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Jing, Fengmei, Li Xu, Zhiqun Guo e Hengxu Liu. "A Theoretical Study on the Hydrodynamics of a Zero-Pressurized Air-Cushion-Assisted Barge Platform". Journal of Marine Science and Engineering 8, n. 9 (27 agosto 2020): 664. http://dx.doi.org/10.3390/jmse8090664.

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Thebarge platform has the advantages of low cost, simple structure, and reliable hydrodynamic performance. In order to further improve the hydrodynamics of the barge platform and to reduce its motion response in waves, a zero-pressurized air cushion is incorporated into the platform in this paper. The pressure of the zero-pressurized air cushion is equal to atmospheric pressure and thus does not provide buoyancy to the platform. As compared to the conventional pressurized air cushion, the zero-pressurized one has advantages of less air leakage risk. However, due to the coupling effect on the interface between water and air cushion, the influence of the gas inside the air cushion on the performance of the floating body has become a difficult problem. Based on the boundary element method, the motion response of the zero-pressurized air-cushion-assisted barge platform under regular and irregular waves is calculated and analyzed in the paper. Compared with the barge platform without air cushion, numerical results from the theoretical method show that in regular waves, the air cushion could significantly reduce the amplitude of heave and pitch (roll) response of the round barge platform in the vicinity of resonance. In irregular waves, the air cushion also observably reduces the pitch (roll) motion, though amplifies the heave motion due to the transfer of heave resonance frequency. Thetheoretical study demonstrates that the zero-pressurized air cushion can reduce the seakeeping motion of barge platforms in high sea states, but might also bring negative effects to heave motion in low sea states. One should carefully design the air cushion for barge platforms according to the operating sea states to achieve satisfactory hydrodynamic performance in engineering application.

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Mohammed, Nuhu, Abubakar Jibrin Abbas, Godpower C. Enyi, Salihu M. Suleiman, Donatus E. Edem e Muhammad Kabir Abba. "Alternating N2 gas injection as a potential technique for enhanced gas recovery and CO2 storage in consolidated rocks: an experimental study". Journal of Petroleum Exploration and Production Technology 10, n. 8 (20 giugno 2020): 3883–903. http://dx.doi.org/10.1007/s13202-020-00935-z.

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Abstract The promotion of enhanced gas recovery (EGR) and CO2 storage is still shrouded in contention and is not well accepted, due to the excessive in situ CO2 mixing with the nascent natural gas. This adulterates the recovered CH4 and thus results in a high sweetening process cost thereby making the technique impractical. This has not only limited the field application of EGR in actual projects to a few trails but renders it uneconomical. This study aims to present, experimentally, alternating N2 injection as a potential technique for EGR and CO2 storage in sandstone rock cores. A laboratory core flooding experiment was carried out to simulate a detailed process of unsteady-state methane (CH4) displacement using Bandera grey core plug. This was carried out at 40 °C, 1500 psig, and 0.4 ml/min injection rate by alternative injection of N2 and CO2 in succession designed to suit the application based on optimum operating conditions. The results show that both CO2 storage capacity and CH4 recovery improved significantly when gas alternating gas (GAG) injection was considered. The best results were observed at lower N2 cushion volumes (1 and 2 PV). Therefore, the GAG injection method with N2 as cushion gas can potentially increase both CO2 storage and CH4 recovery of the gas reservoir. This technique if employed will assert the current position and provide vital information for further researches aimed at promoting environmental sustainability and economic viability of the EGR and CO2 sequestration processes.

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Du, Siyu, Mingxing Bai, Yukai Shi, Yuan Zha e Deng Yan. "A Review of the Utilization of CO2 as a Cushion Gas in Underground Natural Gas Storage". Processes 12, n. 7 (16 luglio 2024): 1489. http://dx.doi.org/10.3390/pr12071489.

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A cushion gas is an indispensable and the most expensive part of underground natural gas storage. Using CO2 injection to provide a cushion gas, not only can the investment in natural gas storage construction be reduced but the greenhouse effect can also be reduced. Currently, the related research about the mechanism and laws of CO2 as a cushion gas in gas storage is not sufficient. Consequently, the difference in the physical properties of CO2 and CH4, and the mixing factors between CO2 and natural gas, including the geological conditions and injection–production parameters, are comprehensively discussed. Additionally, the impact of CO2 as a cushion gas on the reservoir stability and gas storage capacity is also analyzed by comparing the current research findings. The difference in the viscosity, density, and compressibility factor between CO2 and CH4 ensures a low degree of mixing between CO2 and natural gas underground, thereby improving the recovery of CH4 in the operation process of gas storage. In the pressure range of 5 MPa–13 MPa and temperature range of 303.15 K–323.15 K, the density of CO2 increases five to eight times, while the density of natural gas only increases two to three times, and the viscosity of CO2 is more than 10 times that of CH4. The operation temperature and pressure in gas storage should be higher than the temperature and pressure in the supercritical conditions of CO2 because the diffusion ability between the gas molecules is increased in these conditions. However, the temperature and pressure have little effect on the mixing degree of CO2 and CH4 when the pressure is over the limited pressure of supercritical CO2. The CO2, with higher compressibility, can quickly replenish the energy of the gas storage facility and provide sufficient elastic energy during the natural gas production process. In addition, the physical properties of the reservoir also have a significant impact on the mixing and production of gases in gas storage facilities. The higher porosity reduces the migration speed of CO2 and CH4. However, the higher permeability promotes diffusion between gases, resulting in a higher degree of gas mixing. For a large inclination angle or thick reservoir structure, the mixed zone width of CO2 and CH4 is small under the action of gravity. An increase in the injection–production rate intensifies the mixing of CO2 and CH4. The injection of CO2 into reservoirs also induces the CO2–water–rock reactions, which improves the porosity and is beneficial in increasing the storage capacity of natural gas.

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Föhl, Artur. "Gas cushion impact protection device for motor vehicles". Journal of the Acoustical Society of America 86, n. 3 (settembre 1989): 1204. http://dx.doi.org/10.1121/1.398038.

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Luo, Guo Jie, Yong Sheng Hu e Kun Huang. "Research on the Effect of Gas Leaking and Gas-Supplementing Measurements of Air Cushion Surge Chamber". Applied Mechanics and Materials 238 (novembre 2012): 414–18. http://dx.doi.org/10.4028/www.scientific.net/amm.238.414.

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Air cushion surge chamber is a water-engineering measurement different from the ordinary measurements and there is great development in 21th century in China. Aimed at the air leakage and supply measurements, the research of engineering layout, run-control methods and air-supplementing measurement are held in this paper, it can be the reference for the designer.

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Jia, Zhihao, Renyi Cao, Baobiao Pu, Hassan Dehghanpour, Linsong Cheng, Qiuyue Zhang e Abeeb A. Awotunde. "Pore-scale binary diffusion behavior of Hydrogen-Cushion gas in saline aquifers for underground hydrogen Storage: Optimization of cushion gas type". Fuel 381 (febbraio 2025): 133481. http://dx.doi.org/10.1016/j.fuel.2024.133481.

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Kowalski, Jan, Lukasz Klimkowski e Stanislaw Nagy. "Numerical Simulation Study on Underground Gas Storage with Cushion Gas Partially Replaced with Carbon Dioxide". Energies 16, n. 14 (8 luglio 2023): 5248. http://dx.doi.org/10.3390/en16145248.

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Carbon dioxide capture, use, and storage (CCUS) issues are currently gaining more attention due to climate change. One of the CCUS methods may be the use of CO2 as cushion gas in underground gas storage (UGS). Typically, high-permeability structures are preferable for gas storage purposes. High permeability ensures good flow in reservoirs and well bottom-hole pressure maintenance. However, in the case of the use of CO2 as a part of the cushion gas, it mixes with natural gas within the reservoir pore space, and high permeability, with the resulting “ease of flow”, can accelerate the migration of CO2 to the near-well zone. For this reason, the analysis of the effect of permeability on CO2 content in withdrawal gas and the overall performance of UGS seems to be of high importance. In this study, we used a compositional numerical simulator to evaluate the effects of not only permeability but also pore structure on gas storage of this type. The simulations covered depletion of the reservoir and 10 cycles of UGS operation. Our results show that the structure (and thus permeability) has a great influence on the migration of CO2 within a reservoir, the mixing zone, and CO2 content in withdrawal gas.

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Huang, Jin, Lu Xia, You Shou Zhang e Si Nian Li. "An Investigation on Formation Mechanisms of Wrinkles on Steel Casting Surfaces". Key Engineering Materials 531-532 (dicembre 2012): 295–98. http://dx.doi.org/10.4028/www.scientific.net/kem.531-532.295.

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The formation mechanisms of horizontal wrinkles and water wave wrinkles on steel casting surface have been investigated in this study. The horizontal wrinkles, which are the traces of rising steel flow overlapping, are caused by low pouring temperature and slow molten steel flow rising rate. The water wave wrinkles are resulted from the use of an alcohol-based refractory coating with poor permeability and strong penetration behavior. This coating may penetrate deeply into the pores of sand mold and are not easy to be dried by flame combustion. When pouring the alcohol containing in the coating will volatilize and generate a large amount of gas, forming a gas cushion at steel-mold interface. With the gas escapes gradually, the gas cushion disappears, leaving a gap between the steel and the mold, the solidifying casting surface layer will freely fall down and creep in this gap under gravity itself, resulting in casting surface wrinkling.

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Sadeghi, Sina, e Behnam Sedaee. "Mechanistic simulation of cushion gas and working gas mixing during underground natural gas storage". Journal of Energy Storage 46 (febbraio 2022): 103885. http://dx.doi.org/10.1016/j.est.2021.103885.

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31

Fedorov, S. V., e V. M. Vasilyev. "Regulation of the air cushionat a sewer network of the siphon type". Вестник гражданских инженеров 18, n. 4 (2021): 91–99. http://dx.doi.org/10.23968/1999-5571-2021-18-4-91-99.

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In order to improve the energy efficiency and environmental safety of the main sewerage system, it is recommended to use the air cushion effect. This effect will allow flushing the system, removing the air to the air purification unit in an orderly manner, lifting the sewage due to the pressure in the air cushion. For provision of reliable operation of the sewer network, it is necessary to maintain the required level of wastewater in the conditions of constantly changing gas-air flow rate. The paper proposes the design of the air cushion control unit, which operates on the basis of a triangular spillway. This design allows making the system self-regulating, automatically removing excess gas-air environment. The jet stream on the spillway moves under the condition of a changing cross-section of the outlet orifice. This condition fundamentally distinguishes the outflow of the air from the existing research in the field of underwater air and gas jets. Therefore, this is the basis for conducting our own research to assess the capacity of a triangular shaped spillway. The study of the jet stream was performed using the ANSYS CFX program. Model calculations were carried out for the range of air flow rate from 0.0078 to 1 l / s. There was used the π-theorem to evaluate the operation of the spillway in a different flow range and at different values of the inclination angle of the edge α. The results of the study can be used in practice to develop a control unit and implement a sewage system operating in the air cushion mode.

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Zuo, Zhihua, Geng Chen, Xueqian Zhou, Huilong Ren e Ning Liu. "Analysis of Wave Load Characteristics of Hovercraft Based on Model Test". Journal of Marine Science and Engineering 12, n. 9 (3 settembre 2024): 1537. http://dx.doi.org/10.3390/jmse12091537.

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The prediction of the wave load on a hovercraft is essential for the design of the hull structure and safety. However, theoretical methods for the prediction of wave loads are still not mature enough due to the unique and complex nature of the air cushion structure, and numerical modeling and simulation are challenging due to the complexity of the gas-solid-liquid three-phase coupling, so the study of wave loads on hovercrafts still relies on experimentation. In this study, we aim to analyze the wave load response characteristics of a four-chamber hovercraft by conducting a wave load model test under medium/low sea states. The load components and amplitude-frequency response characteristics were thoroughly analyzed based on the acquired data of the cushion pressure, acceleration, and bending moment. The main characteristics of the wave-induced response of the hovercraft were described in detail, and an analytical relationship between the cushion pressure and hull acceleration was derived. The reliability of the experimental results was confirmed through a comparison with the derived results. The relationship between the cushion pressure and cushion volume was investigated in terms of the observed geometric volume of the air chamber, and the relationship between the cushion pressure and flow rate was analyzed to validate the derivation of the theory of wave loads on hovercrafts.

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Guodong, J., W. Haige e C. Rongchao. "A Study of High-baric Gas Cushion Drilling Technology". Petroleum Science and Technology 28, n. 12 (23 giugno 2010): 1179–85. http://dx.doi.org/10.1080/10916460903567566.

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Suarez, F. L., J. Springfield e M. D. Levitt. "Identification of gases responsible for the odour of human flatus and evaluation of a device purported to reduce this odour". Gut 43, n. 1 (1 luglio 1998): 100–104. http://dx.doi.org/10.1136/gut.43.1.100.

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Background/Aims—While the social significance of flatus derives mainly from its odour, previous studies have focused on the non-odoriferous components of rectal gas. The aims of the present study were to determine the role of sulphur-containing gases in flatus odour and test the efficacy of a device purported to reduce this odour.Methods—Flatus was quantitatively collected via rectal tube from 16 healthy subjects who ingested pinto beans and lactulose to enhance flatus output. The concentrations of sulphur-containing gases in each passage were correlated with odour intensity assessed by two judges. Odour intensity was also determined after treatment of flatus samples with zinc acetate, which binds sulphydryl compounds (hydrogen sulphide and methanethiol), or activated charcoal. Utilising gas-tight Mylar pantaloons, the ability of a charcoal lined cushion to adsorb sulphur-containing gases instilled at the anus of eight subjects was assessed.Results—The main sulphur-containing flatus component was hydrogen sulphide (1.06 (0.2) μmol/l), followed by methanethiol (0.21 (0.04) μmol/l) and dimethyl sulphide (0.08 (0.01) μmol/l) (means (SEM)). Malodour significantly correlated with hydrogen sulphide concentration (p⩽0.001). Zinc acetate reduced sulphur gas content but did not totally eliminate odour, while activated charcoal removed virtually all odour. The cushion adsorbed more than 90% of the sulphur gases.Conclusion—Sulphur-containing gases are the major, but not the only, malodorous components of human flatus. The charcoal lined cushion effectively limits the escape of these sulphur-containing gases into the environment.

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Muhammed, Nasiru Salahu, Bashirul Haq, Dhafer Al Shehri e Abduljamiu Amao. "Geochemical influences of hydrogen storage in depleted gas reservoirs with N2 cushion gas". International Journal of Hydrogen Energy 87 (ottobre 2024): 782–92. http://dx.doi.org/10.1016/j.ijhydene.2024.09.061.

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Han, Jeongmin, Joohyung Kim e Wonmo Sung. "An Analysis of Relationship between Cushion Gas and Gas Withdrawal in Depleted Gas Reservoir as a Gas Storage". Journal of the Korean Institute of Gas 17, n. 2 (30 aprile 2013): 9–20. http://dx.doi.org/10.7842/kigas.2013.17.2.9.

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ITO, Takao, Takashi SHIMOMA, Hiroaki ISHIKAWA e Osamu TAKAI. "Development and Application of High-Performance Frictional Gas Cushion Device". Journal of the Japan Society for Technology of Plasticity 60, n. 702 (2019): 189–94. http://dx.doi.org/10.9773/sosei.60.189.

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Karimov, I., e I. Halilov. "Hydrodynamics of Absorption Bubbling Apparatus". Bulletin of Science and Practice 7, n. 11 (15 novembre 2021): 210–19. http://dx.doi.org/10.33619/2414-2948/72/26.

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The article proposes an improved design of the energy-saving, compact absorption bubbling apparatus, which cleans the particles and gas mixtures in the exhaust gases of industrial enterprises, has a high absorption efficiency. As a result of theoretical research, an equation has been proposed that calculates the value of the height of the gas cushion “h”, which provides equal distribution of purified gas to the mixing sections of the apparatus and operation in a stable hydrodynamic mode. As a result, depending on this value, it is possible to calculate the gas velocities and the gas consumption supplied to the apparatus.

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Zamehrian, Mohammad, e Behnam Sedaee. "Underground hydrogen storage in a partially depleted gas condensate reservoir: Influence of cushion gas". Journal of Petroleum Science and Engineering 212 (maggio 2022): 110304. http://dx.doi.org/10.1016/j.petrol.2022.110304.

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Kim, Joohyung, Jinsuk Choi e Kanghee Park. "Comparison of nitrogen and carbon dioxide as cushion gas for underground gas storage reservoir". Geosystem Engineering 18, n. 3 (4 maggio 2015): 163–67. http://dx.doi.org/10.1080/12269328.2015.1031916.

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41

Yang, Jinhui, Binshan Ju, An Yang, Zixian Cui, Meng Wang, Yapeng Tian e Hengchen Qi. "Feasibility of Carbon Dioxide as Cushion Gas in Depleted Gas Reservoirs: An Experiment Study on CO2–CH4 Dispersion during Flow Alternation". Energies 17, n. 18 (20 settembre 2024): 4676. http://dx.doi.org/10.3390/en17184676.

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This study investigates the feasibility of utilizing carbon dioxide (CO2) as a cushion gas in depleted reservoirs for enhanced gas storage efficiency and carbon sequestration against the backdrop of rising natural gas stable supply demand and climate change concerns. Simulations of gas storage reservoir scenarios require accurate dispersion parameters at flow alternation conditions to quantify the size of the miscible displacement front. Several experimental studies using core-flooding equipment aimed at measuring related parameters have been reported over the last decade but did not take flow alternation into consideration. We simulated directionally variable displacements to mimic the cyclic injection and extraction processes in gas storage, focusing on the dispersion characteristics of CO2 and methane (CH4) during flow alternation. Key findings were observed using Nuclear Magnetic Resonance (NMR) imaging, which provided real-time data on the spatial distribution and temporal changes of CH4 signals in rock cores. The results revealed that dispersion, influenced predominantly by dispersion coefficients rather than molecular diffusion, was significantly higher during alternating flow compared to concurrent displacement. Additionally, CO2 exhibited a greater dispersion effect when displacing CH4 than the reverse. This enhanced mixing efficiency during flow alternation supports the potential of CO2 as a cost-effective and efficient cushion gas, offering both improved storage performance and the added benefit of CO2 sequestration. These findings contribute valuable insights for the numerical simulation and operational adaptation of CO2 in gas storage reservoirs, emphasizing the importance of understanding fluid interactions under varying flow conditions to optimize storage efficiency and environmental benefits.

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Алєксєєнко, В. Г., e В. Л. Бучарський. "COMPARATIVE STUDY OF THE MATHEMATICAL MODEL OF THE PROPELLANT TANK PRESSURIZATION SYSTEM". Journal of Rocket-Space Technology 33, n. 4 (13 giugno 2024): 125–32. https://doi.org/10.15421/452434.

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Abstract. The pressurization system of launch vehicle (LV) fuel tanks serves to maintain a specified excess pressure in the tank's gas cushion, based on calculated requirements for fuel component supply and tank design. This necessitates the coordination of all elements within the pressurization system. This paper examines a pressurization system consisting of single high-pressure cylinder, the fuel tank and the connecting line with the metering element. To maintain the required excess pressure in the gas cushion, pressurization gas is supplied with the mass flow rate dependent on the parameters within the high-pressure cylinder. This excess pressure ensures a consistent flow rate of fuel components to the pumps or combustion chamber. System elements such as the gas reducer and gas pipes are treated as a single line with an equivalent flow rate coefficient. The objective of this work was to develop a mathematical model of the system described above. The suggested model includes a system of ordinary differential equations for both the high-pressure tank and the fuel tank, which is derived from the conservation laws of mass and energy, as well as the equation of state for the pressurization gas. The model takes into account the gas reducer by allowing for changes in the area of the gas outflow section over time. The model's operation was simulated, revealing that with a constant cross-sectional area of the gas line, the deviation in the mass flow rate of the fuel component during tank emptying is up to 4% of the nominal value. Implementing a linear law of area change reduced this deviation to 1%. Overall, the results confirm the accuracy of the proposed method for calculating tank parameters, making it suitable for designing rocket pressurization systems.

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Kutasi, Orsolya, K. Vörös, I. Biksi, O. Szenci e P. Sótonyi. "Common atrioventricular canal in a newborn foal — Case report and review of the literature". Acta Veterinaria Hungarica 55, n. 1 (1 marzo 2007): 51–65. http://dx.doi.org/10.1556/avet.55.2007.1.6.

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This paper presents the embryological and pathological features as well as the terminology and classification of common atrioventricular canal, a type of endocardial cushion defect. The authors give a complete description of an extremely rare congenital cardiac malformation in an equine neonate. The diagnosis of a complete, balanced common atrioventricular canal of type C in Rastelli’s classification scheme was based on two-dimensional, contrast and colour Doppler echocardiography and subsequent postmortem gross pathology. To support our diagnosis and study the pathophysiological effect of the alteration, physical examination, blood gas analysis and other laboratory tests, electrocardiography and thoracic radiography were also performed. Our search of the literature suggests that this type of developmental anomaly might account for a higher percentage of equine congenital cardiac defects than was thought earlier. We suppose that some previously described congenital heart abnormalities were misinterpreted: these anomalies could have actually represented some type of atrioventricular canal defect, resulting from the failure of the endocardial cushions to undergo complete and proper fusion.

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He, Youwei, Yixiang Xie, Yu Qiao, Jiazheng Qin e Yong Tang. "Estimation of underground hydrogen storage capacity in depleted gas reservoirs using CO2 as cushion gas". Applied Energy 375 (dicembre 2024): 124093. http://dx.doi.org/10.1016/j.apenergy.2024.124093.

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Shoushtari, Sharif, Hamed Namdar e Arezou Jafari. "Utilization of CO2 and N2 as cushion gas in underground gas storage process: A review". Journal of Energy Storage 67 (settembre 2023): 107596. http://dx.doi.org/10.1016/j.est.2023.107596.

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46

Ali, Azeezat, David R. Cole e Alberto Striolo. "Cushion gas effects on clay-hydrogen-brine wettability at conditions relevant to underground gas storage". International Journal of Hydrogen Energy 58 (marzo 2024): 668–77. http://dx.doi.org/10.1016/j.ijhydene.2024.01.151.

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Blokh, S. A., V. Ya Khariton, L. S. Blokh, N. G. Kuchko, V. B. Zmitrovich e M. V. Rivin. "Continuous conveyers with kilns for firing tiles with a gas cushion". Glass and Ceramics 44, n. 1 (gennaio 1987): 18–21. http://dx.doi.org/10.1007/bf00697470.

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Behnamnia, Mohammad, Negin Mozafari e Abolfazl Dehghan Monfared. "Rigorous hybrid machine learning approaches for interfacial tension modeling in brine-hydrogen/cushion gas systems: Implication for hydrogen geo-storage in the presence of cushion gas". Journal of Energy Storage 73 (dicembre 2023): 108995. http://dx.doi.org/10.1016/j.est.2023.108995.

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Naggar, M. Hesham El, e Abdul Ghafar Chehab. "Vibration barriers for shock-producing equipment". Canadian Geotechnical Journal 42, n. 1 (1 febbraio 2005): 297–306. http://dx.doi.org/10.1139/t04-067.

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Most modern manufacturing facilities have hammers or presses in addition to precision cutting equipment as their production machinery. Foundations supporting hammers and presses experience powerful dynamic effects. These effects may extend to the surroundings and affect labourers, other sensitive machines within the same facility, or neighbouring residential areas. To control vibration problems, wave barriers may be constructed to isolate vibrations propagating to the surroundings. This paper examines the efficiency of both soft and stiff barriers in screening pulse-induced waves for foundations resting on an elastic half-space or a layer of limited thickness underlain by rigid bedrock. The effectiveness of concrete, gas-cushion, and bentonite trenches as wave barriers is examined for different cases of soil layer depth, trench location, and embedment of the foundation. The model was formulated using the finite element method, and the analysis was performed in the time domain. The efficiency of different types of wave barriers in vibration isolation for shock-producing equipment was assessed and some guidelines for their use are outlined.Key words: hammer foundation, impact load, gas-cushion trenches, concrete trenches, soilbentonite trench, finite element modeling.

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Barták, Miloš, e Peter Váczi. "Long-term fluorometric measurements of photosynthetic processes in Antarctic moss Bryum sp. during austral summer season". Czech Polar Reports 4, n. 1 (1 gennaio 2014): 63–72. http://dx.doi.org/10.5817/cpr2014-1-7.

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Photosynthetic activity pattern of Bryum sp. was monitored for 28days using a chlorophyll a fluorescence measuring system installed in the field. For the study, long-term research plot, a moss-dominated vegetaiton oasis at seashore located close to the J.G. Mendel station (James Ross Island, Antarctica) was selected. In this study, two measuring sites were used: (1) control plot with moss cover and (2) moss located inside open top chamber (OTC). At both sites, effective quantum yield of photosynthetic processes in photosyntem II (FPSII) was measured and relative photosynthetic electron transport rate (ETRrel) evaluated each 15 min. Simultaneously, microclimate of the sites was measured including air and moss surface temperature, relative air humidity and photosynthetically active radiation. The length of photosyntetically active period depended mainly on hydration of moss cushion. Water availability, however, was not limiting in the measuring period (Jan 8 - Feb 18, 2009), because the sites were well suplied by melt water from neighbouring snowfield. Thus, daily courses of ETRrel were dependent on incident PAR. On sunny days, ETRrel reached values over 400. Inhibition of primary photosynthetic processes due to below-zero temperature and resulting freezing of moss cushions appeared two times within the measuring periods thanks to rapid decreases in air temperature. The effect of low air temperature on ETRrel was less apparent in OTC site since moss cushion freezing period was shorter and less pronounced than in control site thanks to OTC-induced shift in air temperature. For future photosynthetic studies in Antarctic mosses, simultaneous measurements of gas exchange- and chlorophyll fluorescence-related parameters is recommended so that the effects of particular limiting factors for photosynthesis and photosynthetic productivity can be distinguished and evaluated.

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