Low Atmospheric Pressure Research Articles

Evolution and stability of bubbles in cement-based materials under low air pressure: A Theoretical and experimental Study

In recent years, more and more infrastructures are being built in high-altitude regions where the atmospheric pressure is lowered. However, low atmospheric pressure affects bubble stability, which deteriorates the frost resistance of concrete and the sustainability of civil infrastructures in high-altitude regions. Currently, the evolution of bubbles in cement-based materials under low air pressure is unclear. Therefore, we developed the bubble dynamic differential equation which considering the viscosity of cement paste to describe bubble evolution and stability in cement-based materials; investigated the effect of nano-bubble water (NBW) on bubble stability in cement-based materials; and revealed the stabilization mechanism of bubbles reinforced by NBW. An experimental apparatus that integrates pressure regulating, bubbling, observation, and data recording is designed. The high-precision microscope and air-void analyzer are employed to study the dynamic evolution of bubble distribution over time and the hardened air-void parameters. The bubble dynamic differential equation indicates that the decrease of initial bubble size can improve bubble stability. The experimental results show that the average bubble diameter at low air pressure (0.5P) is larger than that at standard air pressure (P), and bubbles evolve more rapidly at 0.5P; when NBW is used, the average bubble diameter at P and 0.5P is reduced by 24.5% and 48.8%, respectively, and bubbles evolve more slowly. The stabilization principle of bubbles reinforced by NBW is discussed. It is proved that low atmospheric pressure affects the generation and evolution of bubbles, while NBW can reduce initial bubble size and improve bubble stability in cement-based materials. This research not only establishes bubble dynamic differential equation in cementitious materials, but also proposes an effective approach to improve bubble stability of cement-based materials at low atmospheric pressure, which promotes the sustainable development of infrastructures in high-altitude regions.

A Review of Plasma-Synthesized and Plasma Surface-Modified Piezoelectric Polymer Films for Nanogenerators and Sensors.

In this review, we introduce recently developed plasma-based approaches for depositing and treating piezoelectric nanoparticles (NPs) and piezoelectric polymer films for nanogenerator (NG) and sensor applications. We also present the properties and an overview of recently synthesized or modified piezoelectric materials on piezoelectric polymers to highlight the existing challenges and future directions of plasma methods under vacuum, low pressure, and ambient air conditions. The various plasma processes involved in piezoelectric NGs and sensors, including plasma-based vapor deposition, dielectric barrier discharge, and surface modification, are introduced and summarized for controlling various surface properties (etching, roughening, crosslinking, functionalization, and crystallinity).

3D-printed magnetic-based air pressure sensor for continuous respiration monitoring and breathing rehabilitation

The rapid development of point-of-care testing has made prompt diagnosis, monitoring and treatment possible for many patients suffering from chronic respiratory diseases. Currently, the biggest challenge is further optimizing testing devices to facilitate more functionalities with higher efficiency and performance, along with specificity toward patient needs. By understanding that patients with chronic respiratory diseases may have difficulty breathing within a normal range, a respiration sensor is developed focusing on sensitivities in the lower air pressure range. In contrast to the simpler airflow data, the sensor can provide respiratory air pressure as an output using a magnetic-based pressure sensor. This unconventional but highly reliable approach, combined with the rest of the simple 3D-printed design of the sensor, offers a wide range of tunability and functionalities. Due to the detachable components of the respiration sensor, the device can be easily transformed into other respiratory uses such as an inspiratory muscle training device or modified to cater for higher-ranged deep breathing. Therefore, not only does it reach very low air pressure measurement (0.1 cmH2O) for normal, tidal breathing, but the sensor can also be manipulated to detect high levels of air pressure (up to 35 cmH2O for exhalation and 45 cmH2O for inhalation). With its excellent sensitivities (0.0456 mV/cmH2O for inhalation, -0.0940 mV/cmH2O for exhalation), impressive distinction between inhalation and exhalation, and fully reproducible and convenient design, we believe that this respiration sensor will pave the way for developing multimodal and multifunctional respiration sensors within the biomedical field.

An Experimental Study on the Flash Boiling Characteristics of Liquid Ammonia Spray in a Constant Volume Chamber under High Injection Pressure

The spray characteristics of liquid ammonia under various ambient pressures and temperatures were analyzed in a constant volume chamber to cover a wide range of superheat degrees. The injection pressure was set as 70 and 80 MPa with ambient pressure ranging from 0.2 to 4 MPa. The ambient temperature was 500 K. The results showed that the higher the injection pressure, the greater the kinetic energy obtained. The droplet fragmentation was enhanced, and the phenomenon of gradual separation of the gas–liquid region occurred with increasing injection pressure. Under flash boiling spray conditions, the spray developed faster than non-flash boiling and transition flash boiling spray under the same injection pressure. In addition, the flash boiling spray tip penetration of the gas and liquid increased more than that of cold spray, and the fluctuation of the late stage of the injection was relatively large. Therefore, the injection pressure has a greater effect on the spray tip penetration of flash boiling spray. Moreover, ambient pressure greatly influences the flare flash boiling spray. The spray resistance phenomenon was found during the spray development in the flare flash boiling condition. With the increase in ambient pressure, the spray tip penetration of flash boiling spray decreases due to the reduction in the pressure difference inside and outside the spray hole and the restriction of ambient gas. Meanwhile, owing to the low ambient pressure and ambient density, the liquid penetration in the initial phase of the flare flash boiling spray will be abnormally shorter than that of the non-flash boiling spray.

Dielectric barrier discharge plasma-assisted catalytic ammonia synthesis: synergistic effect of Ni-MOF-74 catalyst and nanosecond pulsed plasma

Ammonia is one of the most important chemical raw materials in both manufacture and life of human. Traditionally Haber-Bosch method for ammonia synthesis involves high temperature and high pressure conditions, leading to significant energy consumption and environmental pollution. Non-thermal plasma (NTP) is a promising alternative approach to ammonia synthesis at low temperature and atmospheric pressure. In this study, the synergistic effect of nanosecond pulsed dielectric barrier discharge (np-DBD) and Ni-MOF-74 catalyst was investigated in ammonia synthesis by utilizing nitrogen and hydrogen as feedstock. The results demonstrated that the plasma catalytic-synthesis process parameters play a crucial role in the synthesis process of ammonia. The highest ammonia synthesis rate of 5145.16 μmol·g−1·h−1 with an energy efficiency of 1.27 g·kWh−1 was observed in the presence of the Ni-MOF-74 catalyst, which was 3.7 times higher than that without Ni-MOF-74 catalyst. The synergistic effect of Ni-MOF-74 catalyst and nanosecond pulsed plasma was explored by in-situ plasma discharge diagnostics.

Characteristics of motor temperature distribution in plateau

The motor temperature distribution characteristics help to understand the working condition of the unit, thus improving efficiency. Currently, the motors are gradually being used at high altitudes. However, the plateau region has low air pressure, thin air and large differences in humidity. There is a lack of research on the effect of its complex and special working environment on motor temperature. Therefore, in this study, the numerical analysis of the motor temperature field is carried out from the novel perspective of plateau characteristics. In this paper, the finite volume method is used to analyse the flow-heat-solid coupling of a 20 MW motor. By comparing and verifying the experimental data with the simulation data, it is found that the error between the two is within 5 %. In order to have a more comprehensive picture of the motor's operation in the plateau environment, the temperature effects of different air pressure, air intake and relative humidity on the motor were investigated. The results of the study show that air pressure changes have a large effect on the temperature of the stator structure. The temperature decreases when the air pressure increases and the temperature difference decreases gradually with the increase of air pressure. The largest temperature difference in the stator structure occurs when the air pressure increases from 10 kPa to 40 kPa. The change in air intake has a positive effect on the stator structure temperature, which decreases when the air intake increases. After simulation calculations, it was found that the best heat dissipation effect was achieved in the range of air intake between 3.5 m/s and 4.5 m/s. Relative humidity has a minimal effect on the stator structure temperature. The conclusions of this paper can provide certain theoretical reference for the temperature change law of the motor under plateau operation, which is of great significance to improve the comprehensive hydraulic performance.

Flow characteristics and resistance coefficients of local components of building heat-moisture-oxygen transport pipelines in the Tibetan Plateau

The Tibetan Plateau is characterized by low-pressure, cold, hypoxic, and dry ambient conditions. Thus, in addition to heating, buildings in the region need humidification and oxygenation. It is noted here that the existing specifications of the resistance coefficients of the gas flow in the HVAC pipeline do not consider the effect of the variation in air components on the local resistance of the pipeline due to the low air pressure conditions as well as the humidification and oxygenation. In this paper, the effects of various parameters on the local resistance loss are investigated and reported, including the atmospheric pressure, inlet velocity, humidity, oxygen concentration, pipe diameter, wall roughness, velocity ratio, and area ratio between the branch and the main pipes. The results showed that the decrease in atmospheric pressure leads to a shorter longitudinal distance of effective dissipation of the secondary flow, primarily concentrated in 25D-27D. Additionally, the resistance losses generated in the elbow, the tee straight branch pipe, and the side branch pipe are reduced, with a maximum reduction of 42 %, 33 %, and 46 %, respectively, under low pressure conditions. Also, with the increase in the inlet velocity and the decrease in the pipe diameter, the local resistance of the elbow pipe is increased by a maximum of 14 times and 22 %. Moreover, when the velocity ratio increases and the area ratio between the branch pipe and the main pipe decreases, the local resistance loss of the straight branch pipe and the side branch pipe increases. Based on this study, the recommended value of the local resistance coefficient of the elbow and tee under low pressure is identified. This can provide a reference for the proper design of heat-moisture-oxygen transport pipelines in the plateau area.

Improving the air bubble stability of air-entrained mortar in low air pressure environments via adopted rheology and surface tension methods

Air bubble stability in cementitious materials in low air pressure (AP) environments is influenced by the Ostwald ripening process, which causes coarsening behavior of air bubbles. This research reports the enhancement of air bubble stability in low AP via the adoption of rheology and surface tension methods. Besides, the evolution of air bubbles during the cement early hydration process is proposed. It was found that incorporating viscosity-modifying agents (VMAs) and shrinkage-reducing admixtures (SRAs) resulted in improving air bubble stability by 37.7 % and 23.4 %, upon undergoing AP change from 100 to 60 kPa. Calculation of air bubbles via ripening equations under low AP revealed that VMA induced a notable decrease in the effective diffusion flux within fresh cement mortar, leading to a reduction of 9.8 % in air bubble ripening within 120 min. Conversely, SRAs were primarily aimed at reducing the initial dimensions of air bubbles.

Synthesis of Sodalite Zeolite from Alkaline Fusion of Kaolin and Crystallization at Low Temperature and Ambient Pressure

Synthesis of Sodalite Zeolite from Alkaline Fusion of Kaolin and Crystallization at Low Temperature and Ambient Pressure

Numerical Study of Plasma Characteristics Under Magnetohydrodynamic Flow Control in Mars Entry

Magnetohydrodynamic flow control is an active thermal protection method for atmospheric entry vehicles. This study examined the plasma characteristics under magnetohydrodynamic flow control and its thermal protection ability at multiple altitudes (20–60 km) on a typical direct Mars entry path using numerical simulation considering the Hall effect. The simulation considered a spherical-conical capsule with an entry velocity of 8 km/s at an altitude of 60 km, equipped with a dipole magnet generating a magnetic field of approximately 0.3 T at the stagnation point of the capsule. The results showed that magnetohydrodynamic flow control can mitigate convective aerodynamic heating at high altitudes (45 km or more), where the high electrical conductivity of the plasma creates strong magnetohydrodynamic interaction. In contrast, at low altitudes (35 km or less), magnetohydrodynamic flow control is ineffective owing to low electrical conductivity. The high electrical conductivity at high altitudes is attributed not only to large flight velocities under low atmospheric pressures but also to the enlargement of the shock layer owing to the strong magnetohydrodynamic interaction, which expands the ionization progression area. Furthermore, the results indicated that considering the Hall effect in the numerical modeling of magnetohydrodynamic flow control in Mars direct entry is essential.

Prediction of liquid circulation flow rate in RH degasser: improvement of decarburization at low atmospheric pressure

Prediction of liquid circulation flow rate in RH degasser: improvement of decarburization at low atmospheric pressure

Activating the synergistic effect in Ni-Co bimetallic MOF for enhanced plasma-assisted ammonia synthesis

Plasma-assisted ammonia synthesis (PAAS) can produce ammonia using highly energetic, electronically excited nitrogen and Hydrogen radicals at low temperatures and atmospheric pressure, which has been regarded as a prospective alternative to the Haber − Bosch process. PAAS can exclusively use renewable power (solar, wind, etc.) to achieve green, decentralized and efficient ammonia synthesis. However, current catalysts for PAAS are suffering from low efficiency, poor stability and cyclability. Herein, we demonstrate a one-step hydrothermal synthesis of Ni-Co bimetallic metal–organic frameworks (MOFs) for PAAS. Attributed to the amplified gas transport capability and bimetallic coupling, the Ni-Co-MOF exhibits significantly improved PAAS performance: 88.21 μmol g−1·min−1, above 30 % increase over 5 wt% Ni/Al2O3. The high stability of Ni-Co-MOF under the harsh electric field enables its durable performance (36 h) and excellent cyclability (24 cycles). Finally, to determine the viability of PAAS for industrial applications, we construct a hypothetical zero-carbon ammonia plant using only renewable energy sources, and the outcomes indicate that PAAS has significant competitiveness for future ammonia production.

Thermal Buckling of FG Nanobeams via an Indeterminate Integral Variable with Trigonometric Displacement Models in Conjunction with the Gradient Elasticity Theory

This contribution presents a new methodology and a new indeterminate integral variable of displacement field using trigonometric deformation in conjunction with gradient elasticity theory. The aim, for the first time, is to explore the thermal buckling behavior of functionally graded (FG) nanobeam thus elastic gradient theory takes into account the size effect on the critical thermal buckling load of FG nanobeams. Secondly, the impact of various factors, such as nonlocal coefficient, porosity parameter, material index, thermal loading type, and aspect ratio on the critical thermal buckling load of FG nanobeams. The material characteristics are considered to vary in thickness as the power law varies and the pore network is assumed to be empty or filled with low-pressure air.

Transparent Nanofibrous Membranes with Optimized Optical Channel Structure for Window Screens

AbstractNanofibrous membranes, characterized by their flexibility, high porosity, and tunable structure, are emerging as a promising contender for advanced transparent materials with sufficient breathability and pliability. However, the considerable surface light reflection and internal light scattering of nanofibrous membranes pose a challenging task in achieving transparency. In this study, transparent nanofibrous membranes are fabricated by constructing a topological structure with optimized optical transmission channels, which provide the minimum equivalent thickness to minimize light loss in nanofibrous membranes. The resultant fabricated membrane exhibits a high light transmittance of up to 81%, along with a sufficient porosity of 84% and flexibility. Additionally, the membrane demonstrated effective PM0.3–10 removal efficiency (>91%), low air pressure drops (<110 Pa), high air permeability (≈104 mm s−1), and good waterproof performance. Therefore, the prepared transparent nanofibrous membrane may serve as a transparent air filtration window screen to enhance indoor comfort for people.

One-dimensional biomass-based carbon nanotubes loaded with MoS2 as catalysts for the electrocatalytic nitrogen reduction reaction

In recent years, electrochemical conversion of nitrogen to ammonia at low temperature and atmospheric pressure has become a hot research topic because of its advantages of low carbon emission, low energy consumption and high energy transfer rate. The development of catalysts with high catalytic activity and flexibility are an important topic in the current nitrogen reduction reaction. In this paper, CNT@MoS2 composite catalysts were prepared by catalytic pyrolysis of biomass to prepare one-dimensional carbon nanotubes and then combined with MoS2 by a hydro thermal method. It was found that 120 CNT@MoS2 had better NRR activity and selectivity, NH3 yield rate of 21.2 μg h−1 mg−1 was achieved at −0.44 V vs. The Faraday efficiency can reach 5.4%. The catalytic performance is more than 3 times higher than CNT. The mechanism of MoS2-catalyzed NRR was further investigated by DFT theoretical calculations. The results of the theoretical calculations are in good agreement with the experimental results, providing a reasonable explanation for the high reduction performance of the catalyst. This study offered a promising avenue for exploring and rationalizing the design of electrocatalytic materials for NRR.

Impact of air entrapment on capillary absorption in porous building materials

When the water content of a porous material is high, air entrapped in the pore space is expected to affect water transfer through the pores. To understand the effects of air entrapment on water transfer in porous building materials in the high-water-saturation region, we examined the water transfer characteristics corresponding to significantly small air entrapment effects. First, we conducted two sets of water uptake experiments. In the first experiment, using three building materials, the time evolution of the amount of water absorption was measured at a low air pressure near vacuum (several kPa). In the second experiment, the water content profile during water uptake was measured using the gamma-ray attenuation method. The experimental results showed that low air pressure accelerated the water uptake by the brick and aerated concrete specimens, whereas water uptake by the calcium silicate board specimens was not significantly affected. These differences among materials were analyzed from a pore structure viewpoint. Moreover, gamma-ray attenuation measurements confirmed that the obtained water content profile was qualitatively similar at atmospheric and low air pressures, although the low air pressure increased both the water content of the material after capillary absorption and the wetting front propagation rate. Finally, simultaneous water and air transfer calculations based on the air and liquid water balance in a material reproduced the measured water absorption rates well, confirming that air entrapment and pressure development in the pores can significantly reduce the rate of water uptake and water content after capillary absorption. The calculation results also indicated that the air pressure in a material did not significantly increase at early water uptake stages where local water content was not high, which supported the general assumption that treating the liquid-water transfer in porous building materials as a one-component flow is valid in most cases.

A novel approach for modifying air-voids in concrete by short-term low-air pressure intervention

If it is desired to experimentally verify the regularity in the effects of air-voids on the properties of concrete, methods of altering voids must be relied on. Consequently, this research explored a method that reduced the curing air pressure after mixing concrete so as to modify air-void characteristics. In addition, in order to avoid introducing variables besides air-voids, a limit was placed on the duration of low-pressure maintenance, which was restoring the air pressure to atmospheric pressure after the formation of the concrete's air pressure transient resistant strength. The results showed that if the reduction in air pressure was insufficient, the differential pressure between the inside and outside of the original bubbles was not enough to cause them to break through energy barriers resulting in expansion. Only bubble regeneration due to the decrease in gas solubility was observed. When the differential pressure exceeded the energy barriers, bubble expansion could be achieved. In addition, it was possible to achieve the air pressure transient resistant strength in short time, which was achieved in only 7 h for the concrete used in this paper. Water loss calculation, X-ray diffraction, thermogravimetry-derivate thermogravimetry, scanning electron microscope, and mercury intrusion porosimetry were used to evaluate the hydration of the concrete confirming that the low-air pressure curing of 7 h had almost no effect on hydration. The method proposed can provide an effective means of specimen preparation for scientific research involving the effects of air-voids on the properties of concrete.

Improving our understanding of future tropical cyclone intensities in the Caribbean using a high-resolution regional climate model

The Caribbean region is prone to the strong winds and low air pressures of tropical cyclones and their corresponding storm surge that driving coastal flooding. To protect coastal communities from the impacts of tropical cyclones, it is important to understand how this impact of tropical cyclones might change towards the future. This study applies the storyline approach to show what tropical cyclones Maria (2017) and Dorian (2019) could look like in a 2 °C and 3.4 °C warmer future climate. These two possible future climates are simulated with a high-resolution regional climate model using the pseudo global warming approach. Using the climate response from these simulations we apply a Delta-quantile mapping technique to derive future changes in wind speed and mean sea level pressure. We apply this Delta technique to tropical cyclones Maria and Dorian’s observed wind and pressure fields to force a hydrodynamic model for simulating storm surge levels under historical and future climate conditions. Results show that the maximum storm surge heights of Maria and Dorian could increase by up to 0.31 m and 0.56 m, respectively. These results clearly show that future changes in storm surge heights are not negligible compared to end-of-the-century sea level rise projections, something that is sometimes overlooked in large-scale assessments of future coastal flood risk.

Arcing Stabilization Effect and Ablation Characteristics for C–Cu Electrodes at Low Air Pressure

Arc ablation is a widespread problem in electrical contact systems. The fault of the system caused by arc ablation significantly restricts its lifespan. Facing the development goal of electrified aircraft and low vacuum high-speed railways, the problem of arc ablation at low air pressure cannot be ignored. In this paper, an experimental platform for arcing and ablation at low air pressure is built. The influence of low air pressure on the characteristics of arc ablation is explored. The results show that the stability of the arc column at low air pressure varies significantly. Under the condition of different air pressures, the traces and morphology in the ablation region of the electrode differ significantly. These are caused by Rayleigh-Taylor instability between the arc and air, and by the motion of the arc root which is driven by the arc column. Importantly, the low-pressure stabilization effect for the arc is found. The corresponding relationship between electrode ablation traces, surface morphology, and air pressure is revealed. The action mechanism of air pressure on the arcing process and ablation characteristics of the electrode are clarified. This research provides theoretical support for restraining arc ablation and prolonging the lifespan of the electrical contact system.

Advancing CO2 to CO conversion: Detailed impact analysis of atmospheric molecules in an ultrashort pulse laser filament plasma reactor

AbstractCapturing carbon dioxide (CO2) and transforming it into valuable fuels offers a dual benefit: the potential to reduce atmospheric CO2 levels and decrease our dependency on fossil fuels. Plasma‐assisted CO2 to carbon monoxide (CO) conversion stands out within the various CO2 recycling methods, with research primarily emphasizing its energy efficiency and conversion efficacy. However, investigations of CO2 conversion under real air conditions are relatively scarce, and the effects of the other atmospheric molecules on the CO2 conversion process require further exploration. We have induced plasma chemical reactions by generating ultrashort pulse laser filaments inside a sealed‐off cavity with variable air pressures. Simultaneously, we applied mid‐infrared laser absorption spectroscopy to monitor the time evolution of the reaction products. The peak CO2‐to‐CO conversion ratio was achieved at an air pressure of 8000 Pa, which resulted in a CO concentration of 82 ppm. The experimental results suggested that nitrogen (N2) plays a promoting role in CO2‐to‐CO conversion, while the presence of oxygen (O2) seems to hinder the process. The hydroxyl radical (OH) arising from water molecules (H2O) limits the accumulation of CO at lower air pressures. However, at higher air pressures, the reduced OH radical concentration shows negligible impact on the CO2‐to‐CO conversion ratios. In addition, the study revealed that atmospheric plasmas produce a high concentration of hydrogen cyanide (HCN), which is directly proportional to the levels of ambient humidity. This research contributes to the development of strategies to mitigate the production of harmful gases like HCN in CO2 conversion, thereby promoting the ecofriendly conversion of atmospheric CO2.