Low Pressure Conditions Research Articles

The effect of ball pressure and maximal isometric neck strength on head acceleration during purposeful heading in adult football players during heading drills

ObjectiveThis randomised repeated measures study explored the effect of ball pressure and maximal isometric neck strength on head acceleration during purposeful heading in adult football players during heading drills within a laboratory environment. MethodsRecreational football players (n ​= ​17) attended one familiarisation session to determine baseline maximal isometric neck strength, followed by two experimental sessions where they randomly trialled two conditions (>72-h apart). The first condition included 20 rotational headers with a match-ball at low-pressure (58.6 ​kPa; 8.5 psi) and the second included 20 rotational headers with a match-ball at high-pressure (103.4 ​kPa; 15.0 psi) whilst instrumented with an inertial measurement unit. ResultsA statistically significant difference between conditions for both peak linear head acceleration (F ​= ​15.2; p= ​ < ​ 0.001) and peak angular head velocity (F ​= ​5.71; p ​= ​0.018) during purposeful heading. The low-pressure ball condition demonstrated a 12 ​% reduction in peak linear acceleration and 6 ​% reduction in peak angular velocity when compared with high-pressure ball condition. Additionally, neck strength significantly predicted head acceleration during purposeful heading (p ​ = ​ <0.05). ConclusionThese findings suggest that lower ball pressure and higher neck strength can lower head acceleration during heading in adult football players during heading drills within a laboratory environment.

Wax appearance temperature in crude oils measured by surface plasmon resonance

To predict and quantify the wax appearance temperature in crude oils, we proposed and implemented a well-explored sensing method known as surface plasmon resonance. This phenomenon occurs when an incident light beam couples into a metallic surface. As sensing method, this phenomenon has been widely used in biosensing applications. In this research, we showed the effectiveness of the surface plasmon resonance sensing technique in hydrocarbon sensing in general and in crude oil wax appearance prediction in particular. To the authors knowledge, this is the first exploration of monitoring wax deposition events from crude oil using surface plasmon resonance measurements. A compact optical sensor was developed from an ultra-thin layer of gold deposited on a sapphire prism and supported by a new data analyzing metric to analyze the acquired reflected beam intensity profile and detect the precipitation of crude oil wax or other hydrocarbon particles under varying-temperature and low-pressure conditions. The obtained wax appearance temperatures using the introduced on-site method were found to be comparable with the literature measurements using the common in-lab Cross-Polarization Microscopy method.

Sand fixation and human activities on the Qinghai-Tibet Plateau for ecological conservation and sustainable development

The sand fixation ecosystem services and human activities on the Qinghai–Tibet Plateau (QTP) play a crucial role in local sustainable development and ecosystem health, with significant implications for surrounding regions and the global ecological environment. We employed an improved integrated wind erosion modeling system (IWEMS) model for the QTP to simulate sand fixation quantities under the unique low temperature and low pressure conditions prevalent on the plateau. Using the human footprint index (HFI), the intensity of human activities on the plateau was quantified. Additionally, an econometric model was constructed to analyze the impacts of the natural factors, the HFI, and policy factors on the sand fixation capacity. The results revealed that the average sand fixation quantity was 1368.0 t/km2/a, with a standard deviation of 1725.4 t/km2/a, and the highest value during the study period occurred in 2003. The average value of the HFI for 2020 was 6.69 with a standard deviation of 6.61, and the HFI exhibited a continuous growth trend from 2000 to 2020. Despite this growth, the average human activity intensity remained at a low level, with over 50 % of the area having an index value of <4.84. Overall, a strong negative correlation was observed between the sand fixation ecological capacity and the HFI on the QTP. However, extensive regions exhibited high values or low values for both indicators. The sand fixation capacity on the QTP is influenced by both natural and human factors. In light of these findings, suggestions are made for optimizing protected area design, rational control of human activity scales, and targeted human activity aggregation within certain regions as part of ecological conservation strategies. This study has implications for assessing sand fixation ecological functions in high-altitude regions and enhancing sand fixation capacity within the region, providing valuable practical guidance.

Low temperature reaction kinetics inside an extended Laval nozzle: REMPI characterization and detection by broadband rotational spectroscopy.

Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20K of 6.66 ± 0.47 × 10-11cm3 molec-1s-1.

Polymer-ceramic pressure-sensitive paint with high pressure sensitivity and pressure-sensitivity constancy in low-pressure environments

The accurate measurement of tiny pressure variations in low-pressure environments requires pressure-sensitive paint (PSP) with high pressure sensitivity and pressure-sensitivity constancy for aerodynamics testing. In this study, polymer-ceramic pressure-sensitive paints (PC-PSPs) were developed using platinum(II) meso-tetra(pentafluorophenyl) porphyrin (PtTFPP) and palladium(II) meso-tetra(pentafluorophenyl) porphyrin (PdTFPP) as luminophores; titanium dioxide (TiO2) and mesoporous silica (mSiO2) as particles; and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), poly(isobutyl-methacrylate) (PIBM), ethylene-vinyl acetate copolymer (EVA), and polyacrylate (B1000) as polymers. The static characteristics were calibrated and evaluated under low-pressure conditions. The results showed that PC-PSPs using PtTFPP with a short-lifetime and high oxygen-permeable polymer led to high pressure sensitivity. By contrast, if PdTFPP with a long-lifetime was used, the pressure sensitivity was dominated by the luminescence lifetime rather than the oxygen permeability of the polymer. PdTFPP/mSiO2-PTMSP exhibited a remarkable pressure sensitivity of 78.46%/kPa. PC-PSPs employing PIBM, EVA, and B1000, respectively, exhibited excellent pressure sensitivity constancy above 96% after near-vacuum storage for one hour. However, PTMSP-based PC-PSPs exhibited poor pressure-sensitivity constancy owing to the aging of the polymer in vacuum, which can be improved by employing the long-lifetime PdTFPP luminophore and mSiO2 particles. Furthermore, PC-PSPs using mSiO2 particles exhibited lower signal levels, higher pressure sensitivities, lower temperature dependencies and photodegradation than those using TiO2 particles. PdTFPP/mSiO2-PIBM and PdTFPP/mSiO2-B1000 exhibited application potential under low-pressure conditions owing to their favorable static characteristics.

Separation characteristics of low-temperature coal tar containing solid particles by vacuum distillation: Effects of distillation pressure and solid particle content

The separation of low-temperature coal tar (LTCT) containing solid particles by vacuum distillation is essential in various applications, such as in-situ pyrolysis. However, the separation characteristics of solid-containing LTCT using vacuum distillation have yet to be fully understood. Therefore, explorations were conducted with variations in pressure and solid particle concentration by analyzing pitch with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The FTIR demonstrated that the organic constituents exhibit greater regularity at higher temperatures, leading to a 2 % reduction in the tightly bound cyclic OH tetramers, an intricate hydrogen bonding. The structural parameters indicate a 2 % decrease in farH, alongside a decline in AR from 0.332 to 0.293. This suggests that the low-pressure distillation conditions contribute to an increased retention of aromatic hydrocarbons in pitch, potentially complicating its subsequent utilization. The reduction in F from 2.273 to 2.029 signifies a shorter aliphatic chain, indicative of an intensified degradation effect. The elevated content of solid particles results in a more rigid texture of pitch in micromorphology. This study examined LTCT pitch to clarify the separation mechanism of solid-containing LTCT, offering insights into appropriate vacuum distillation conditions for LTCT separation and aiding in the effective utilization of pitch products.

Deep epithermal Au mineralization at Tuanjiegou, northeast China

To better understand the physicochemical features of deeply mineralized intervals of low-sulfidation (LS) Au deposits, the Early Cretaceous Tuanjiegou Au deposit in northeastern China was characterized as it comprises alteration and mineralization styles that reflect deeper portions of the mineralizing system. From shallow to deeper portions of the Tuanjiegou deposit, the mineralization is zoned from sulfide-poor quartz bands through hydrothermal breccia to deep pyrite–marcasite-rich veinlets that occur along hydrofractures within a granodiorite porphyry stock. The zoned alteration halo is centred on the ore zones, and comprises an inner phyllic alteration zone (illite + quartz + muscovite) and an outer intermediate argillic alteration zone (illite ± smectite), with propylitic alteration being limited. Given that apatite fission track ages are extremely sensitive to the ambient temperatures of 60–120 °C, the overlap in the closure dates of magmatic apatite (108.1 ± 3.8 Ma) and zircon (108.2 ± 1.2 Ma) from the granodiorite porphyry is indicative of shallow emplacement of the granodiorite porphyry, likely at depths slightly >0.7 km. A similar paleodepth (900 ± 188 m) was estimated from homogenization temperatures (291 ± 14 °C) of boiling fluids. Preservation of the deep portions of the Tuanjiegou ore system may imply that the productive ore intervals of poorly explored LS epithermal deposits globally are underestimated. Given the evidence for a magmatic origin of the ore-forming fluids at Tuanjiegou, we highlighted that ore-forming fluids are released initially from a water-saturated, oxidizing felsic melt under low-pressure (∼4 km) conditions.

Unveiling the non-equilibrium process in multilayer mixture adsorption

The Brunauer–Emmett–Teller (BET) theory [S. Brunauer et al., “Adsorption of gases in multimolecular layers,” J. Am. Chem. Soc. 60, 309–319 (1938)] constitutes a cornerstone in gas-adsorption physics. Recently, the kinetic BET equation of single-kind adsorbate has been proposed [H. Yu and X. Zhang, “Molecular-kinetic study of multilayers gas-adsorption in a rarefied gas environment,” Phys. Fluids 34, 123106 (2022)], while its counterpart of mixed adsorbates is currently unknown. Gas mixtures are commonly found in both natural and artificial systems. To address this limitation, we have proposed a kinetic BET theory for adsorbate mixtures in this paper. Moreover, we gave an analytical solution addressing low gas pressure conditions. In this condition, we predicted the “over-adsorption” of one species in the mixture with a higher desorption rate over time, and the “inertia effect” during the crowed-out process of the fast-desorbing species. Further, we also simulated the reciprocal influence of multilayer gas adsorption on the non-equilibrium fluids. Our findings provide valuable insights into gas-adsorption experiments and can facilitate technological advancements.

Effect of different hypoxic and hypobaric interventions on blood gas and erythrocyte-related indicators in rats.

To explore the effects of hypoxic and hypobaric conditions on blood gas and erythrocyte-related indicators in rats. SD male rats were exposed to low-pressure hypoxic conditions simulating an altitude of 6500 m in a small or a large experimental cabin. Abdominal aortic blood samples were collected and blood gas indicators, red blood cells (RBCs) count, and hemoglobin (Hb) content were measured. The effects of exposure to different hypoxia times, different hypoxia modes, normal oxygen recovery after hypoxia, and re-hypoxia after hypoxia preconditioning on blood gas indicators, RBCs count and Hb content were investigated. The effect of blood gas indicators was correlated with the length of exposure time of hypoxia and the reoxygenation after leaving the cabin. Hypoxia caused acid-base imbalance and its severity was associated with the duration of hypoxia; hypoxia also led to an increase in RBCs count and Hb content, and the increase was also related to the time exposed to hypoxia. The effects of reoxygenation on acid-base imbalance in rats caged in a small animal cabin were more severe that those in a large experimental cabin. Acetazolamide alleviated the effects of reoxygenation after leaving the cabin. Different hypoxia modes and administration of acetazolamide had little effect on RBCs count and Hb content. Normal oxygen recovery can alleviate the reoxygenation and acid-base imbalance of hypoxic rats after leaving the cabin and improve the increase in red blood cell and hemoglobin content caused by hypoxia. The improvement of hypoxia preconditioning on post hypoxia reoxygenation is not significant, but it can alleviate the acid-base imbalance caused by hypoxia in rats and to some extent improve the increase in red blood cell and hemoglobin content caused by hypoxia. Due to excessive ventilation and elevated RBCs count and Hb content after hypoxia reoxygenation, oxygen partial pressure and other oxygenation indicators in hypoxic rats are prone to become abnormal, while blood gas acid-base balance indicators are relatively stable, which are more suitable for evaluating the degree of hypoxia injury and related pharmacological effects in rats.

Effect of Interaction between Carbon Dioxide and Fluid Phase/Rock Interface on Carbon Dioxide Storage

The interaction between CO2, formation water, and rock surfaces after CO2 flooding and the mechanism by which it affects CO2 storage were studied in this paper. The results show that variations in the solubility of CO2 in crude oil under pressure are similar to those observed in formation water. The solubility of CO2 increases as pressure increases under a low-pressure conditions. The solubility of CO2 in crude oil increases significantly when crude oil is in a low-viscosity state, and this makes it easier to diffuse CO2 into the oil phase at high temperatures. More resistance is encountered when CO2 diffuses into the liquid-containing space of an irregular core, making the coefficient of diffusion into the oil–water two-phase flow in the porous medium smaller. After the core is corroded by a CO2-saturated aqueous solution, the quartz content in the mineral component increases and the plagioclase and potassium feldspar content significantly decrease. The dissolution of the feldspar leads to the formation of a large amount of secondary kaolinite, thus increasing the kaolinite content. In the early stage of CO2 erosion during dynamic displacement, the combined effect of particle migration and inorganic precipitation leads to a slow growth in core permeability and porosity. As the erosion progresses, the influence of particle migration and inorganic precipitation on permeability gradually decreases, while the porosity of the core gradually increases. The secondary pores play a role, and the erosion of the CO2–water system makes the permeability and porosity of the core gradually increase. During dynamic displacement, CO2 is mainly stored in the reservoir in free and irreducible states. Under the pressure of the reservoir, some of the CO2 participates in erosion reactions and is stored in the rock or the solution in the form of minerals or ions. In addition, a small portion of the CO2 is dissolved in the residual water and residual oil that remain after the dynamic displacement. The results of this paper can provide some theoretical support for the design of a CO2 storage site.

Effect of Hydrogen Pressure and Punch Velocity on the Hydrogen Embrittlement Susceptibility of Pipeline Steels Using Small Punch Tests under Gaseous Hydrogen Environments at Room Temperature

The in situ small punch (SP) test method is a simple screening technology developed to assess the hydrogen embrittlement (HE) characteristics of structural steels. This method can easily adjust the influencing parameters such as test temperature, gas pressure, and punch velocity depending on the hydrogen service environment. With increased hydrogen consumption, using pipelines for mass hydrogen transportation is being considered. This study evaluated the HE susceptibility of API-X52 and API-X70 steels, considering the hydrogen usage environment. The study investigated the effects of hydrogen pressure and punch velocity on the HE behaviors of each pipe steel at room temperature using the SP energy and relative reduction in thickness (RRT) to determine their effect on HE susceptibility quantitatively. The study found that hydrogen pressure produced a different HE effect; the lower the hydrogen pressure, the more HE was relieved. Particularly, when the punch velocity was high, such as 1 mm/min, the HE effect was significantly relaxed. However, when the punch velocity was below 0.01 mm/min, HE occurred even at low hydrogen pressure conditions, meaning hydrogen diffusion within the specimen during the SP testing reached a critical hydrogen concentration to create a brittle fracture. Both pipeline steels showed similar HE behaviors under a wide range of H2 pressures and punch velocities, showing an inverse S-curve for quantitative factors of SP energy and RRT against the H2 pressure at 1.0 mm/min punch velocity. The study classified the observed HE behaviors into four types based on quantitative and qualitative aspects. These findings confirm that the in situ SP test is a useful screening technique, and the factor RRT can be effectively applied to the HE screening of pipeline steels in low and high-pressure hydrogen environments.

Analysis of Deformation and Properties of Composite Melon Petals via Vibration Pretreatment-Microwave Compound Curing.

The transition of large-scale cryogenic propellant tanks from metal to composite materials is the main trend in the global aerospace industry. Aiming to address the challenges of achieving the manufacturing of integrated and cost-effective manufacturing of aerospace cryogenic composite tanks that cannot be realized through the conventional autoclave process, and those of existing out-of-autoclave processes that are unable to effectively suppress defects under low-pressure conditions, a vibration pretreatment was innovatively introduced into the microwave curing process of composite materials in this study. Based on a systematic analysis of the inhibitory mechanisms of vibration pretreatment on void formation and the uniform heating mechanisms of microwaves in composite materials, the experimental results showed that the compound curing process enabled the production of components with complex structural features under low-pressure conditions while achieving equivalent surface precision and comprehensive properties, including porosity, interlaminar shear strength, and cryogenic permeation resistance, as those obtained through the standard 0.6 MPa autoclave process. This holds great promise for the application of out-of-autoclave processes in the manufacturing of large-scale aerospace cryogenic composite tanks.

A model of the axial plume temperature profile of rectangular pool fires dominated by convection under different atmospheric pressures and aspect ratios

This paper experimentally studied the axial plume temperature profile of heptane pool fires dominated by convection under different atmospheric pressures and aspect ratios. Results indicate that McCaffrey's axial temperature model in the plume region is not applicable at low-pressure conditions. The Gaussian plume model proposed by Tang et al. was verified based on the experiments of 36 cm2 pool fires, which are dominated by conduction, for different atmospheric pressures and aspect ratios. By mathematical derivation of the plume mass flow rate of pool fires, the relationship between the air entrainment coefficient and atmospheric pressure was obtained, and the experimental results of the air entrainment coefficient with different pressures can be well correlated with the analytical model. Finally, by introducing the air entrainment coefficient and temperature decay factor, a new axial plume temperature model for pool fires dominated by convection was developed, considering different atmospheric pressures and pool aspect ratios, which shows a good agreement with experimental results. This work can provide some good references for the fire safety of pool fires related to liquid fuel leakage.

Reconstructing the timing and conditions of fragmentation from water speciation in ash during a deep submarine eruption: 2012 eruption of Havre, Kermadec Arc

The lack of visual observations and difficulty recreating ambient conditions in the laboratory mean deep subaqueous volcanic eruptions (>500 m water depth) remain enigmatic. However, the pressure and temperature dependency of water speciation and solubility in volcanic melts and glasses, and water's high diffusion rate, offers a potential window into the processes and conditions during deep subaqueous volcanism.The 2012 submarine eruption of Havre Volcano is the ideal laboratory in which to use water species distributions to understand submarine eruption processes. Post-eruption AUV mapping, and ROV observation and sampling generated an unprecedented amount of contextual information for a deep submarine eruption including on the magma ascent conditions, eruption sequence, and magma fragmentation. Here we present high spatial resolution synchrotron-FTIR measurements of water speciation in glassy ash (125–500 μm) from several subunits (1, 2 and 3) of a widespread ash with lapilli deposit produced in the 2012 eruption.Measurements record OH depletion profiles around vesicles, along with H2Omol enrichment profiles. In several thick vesicle walls far-field regions unaffected by processes at the bubble margins have also been identified. By focusing on OH concentrations, which is effectively non-diffusing below the glass transition, we can remove the effects of secondary rehydration and calculate the pressure and water depth at which ash grain quenched.Far-field regions record quench depths within the 650–900 m water depth range for pre- and post- eruption vent depth, suggesting ash grains equilibrated at vent depth. OH depletion profiles produce quench pressures on vesicle margins typically corresponding to 200–400 m water depth shallower, suggesting a 2–4 MPa decompression before ash quench. Diffusion modelling suggests that at eruption temperature the observed OH depletion profiles formed through exsolution in <2 s. The difference in quench pressure within the ash is not reflective of a difference in the depth of quenching. Rather it is reflective of the rapidity of the quench process relative to the diffusion rate.The results imply transient low-pressure conditions formed during ash generation in the 2012 Havre eruption. We discuss several physical processes in the context of submarine volcanism that may explain the formation of transient low-pressure regions. The results have implications for how we understand submarine eruption processes and highlight the potential of high resolution FTIR for studying submarine volcanism.

Effective thermo-electric-mechanical modeling of capacitively coupled plasma in low-pressure conditions: Modeling and application in dry etching

In semiconductor dry etching process, capacitively coupled plasma (CCP) is widely used in low-pressure environments. However, the kinetics of species particles in low-pressure conditions are different from the general environments. Traditional continuum models are popular in industry due to their simplicity, but they struggle to account for the kinetics of particles in low-pressure conditions. Although particle-in-cell (PIC) modeling is suitable for simulating the behavior of a single particle, it is difficult to perform such industrial simulations due to the high computational cost. To account for both kinetics and engineering applicability, this study presents an effective thermo-electric-mechanical modeling structure of CCP at low-pressure conditions. This modeling structure includes balance laws of continua derived from the global energy equilibrium containing thermal, electric and mechanical energies. The ion momentum, which is ignored in traditional plasma continuum models, is considered in the balance laws, and electron energy distributions are obtained by solving the Boltzmann equation to obtain the properties of electron transport. In addition, the model variables are calculated based on mixed kinetic theory accounting for the fraction of each species. The results of the proposed modeling are compared to those of a PIC model to validate its ability to describe the distribution of electrons with respect to pressure conditions. Based on the proposed numerical formulations, this study built a MATLAB-based program to guide the design of a screen baffle in dry etching equipment. This program captures the critical aspects of the practical application of screen baffle design in the context of the dry etching process. The results of this paper showed that the proposed model can be applied to engineering applications under low-pressure conditions.

New correlations for bubble departure and liftoff diameters in vertical subcooled boiling flow under low-pressure conditions

The bubble departure and liftoff diameters are crucial parameters affecting wall boiling heat transfer in subcooled boiling flow. This study aimed to develop new correlations for these diameters of a growing bubble on the heated wall in vertical subcooled boiling flow. By analyzing a force balance model, the major non-dimensional parameters were derived to express the bubble diameters. Especially, it revealed that, in addition to the Reynolds number, the Capillary number should be considered to better account for the effect of mass flux on the bubble departure diameter. Finally, the correlations of the two bubble diameters were developed by utilizing the available experimental data. The mean absolute percentage errors of the new correlations were 18.57% and 22.16%, respectively for the bubble departure and liftoff diameters when compared with experimental data. The applicable ranges of correlation of bubble departure diameter cover the superheated Jacob number of 0.0056−0.035, subcooled Jacob number of 0.0081−0.086, liquid Prandtl number of 1.006−1.76, product of Capillary and Reynolds numbers of 181.6−575.23, and density ratio of 0.0006−0.05. For the bubble liftoff diameter, the applicable ranges are 0.0014 – –0.045 for the superheated Jacob number, 0.0024–0.111 for the subcooled Jacob number, 1.29–1.75 for the liquid Prandtl number, 2883.4–99,716.21 for the Reynolds number, and 0.000615–0.00175 for the density ratio.

Characterizing burning behaviour of convection-controlled pool fires at sub-atmospheric pressure by stagnation theory

Pool fires play a critical role in examining the burning behaviour of diffusion flames and are sensitive to changes in scale and environmental conditions. Understanding the evolution of pool fires under low-pressure conditions, common in plateau or flight scenarios, is essential for both fire safety and energy utilization. This study investigates the effects of pressure on pool fires through a series of small-scale experiments carried out in a pressure chamber that provides stable conditions ranging from 95 kPa to 40 kPa. Pool scales between 7 cm and 16 cm were examined, a range dominated by convective heat transfer. Methanol and heptane were chosen to discern fuel-specific variations in burning behaviour under decreased pressure. The findings demonstrate an increase in the axial flame temperature with reducing pressure, while radiative output exhibits an inverse relationship with pressure. Additionally, convective heat transfer toward surroundings appears to rise with decreasing pressure. A modified stagnation theory solution is proposed to model the mass burning rate of convection-controlled pool fires under low pressure, which shows satisfactory agreement with the experimental data. This research could potentially contribute to the comprehension of pool fires and the safety of energy in sub-atmospheric pressure conditions in the future.

Evolution and Action Mechanism of Relative Negative Pressure Zone in Spiral Groove Gas Face Seal for Aero-Engine

Abstract As an advanced sealing technology, the application of gas face seal in aero-engine is few; if possible, lower specific fuel consumption, higher thrust-weight ratio, and effective secondary flow control at minimal cost would be brought. A relative negative pressure zone (RNPZ) was found in the spiral groove gas face seal, and the evolution and action mechanism of RNPZ was investigated in detail, which may promote the above application. Three film thicknesses of spiral groove gas face seals at different rotational speeds and inlet pressures were numerically compared to obtain the pressure field in the groove area and the formation of RNPZ. Then, the radial and circumferential velocities in the groove were calculated to quantify the impact of the obstruction effect, viscous pumping, and shear effect, which revealed the evolution mechanism of the RNPZ stage by stage. At last, the action mechanism of RNPZ was clarified through the hydrodynamic performance analysis. It is found that the pressure field evolution in the gas face seal is in stage Ⅲ under the high rotational speed and low inlet pressure conditions in an aero-engine. Under the same film thickness, RNPZ can suppress leakage to a certain extent in stage Ⅱ, while in stage Ⅲ, it increases the opening force and stiffness-leakage ratio. This work can provide theory and data to help with the subsequent optimization design of gas face seals for aero-engine.

Experimental study on the transporting and crushing effect of gas on coal powder during the develop stage of coal and gas outburst in roadway.

In recent years, coal and gas outburst disasters are still occurring and difficult to prevent, seriously endangering the safety of coal mine production. It is well known that the transporting and crushing of outburst coal is the main pathway of energy dissipation during the coal and gas outburst process. However, a consensus regarding how much gas involves in outburst and affects energy dissipation is still lacking. Quantitative study on the gas effect on migration and fragmentation characteristics of outburst coal in restricted roadway space can improve the energy model and guide the prevention and control of gas outburst. In this paper, an improved visual coal and gas outburst dynamic effect simulation experiment system was used to conduct outburst simulation experiments at different gas pressure conditions. The results showed that the movement of outburst coal in the roadway has experienced various flow patterns. In the initial stage of the outburst, under low gas pressure condition, the motion of the outburst coal was dominated by stratified flow. However, as the gas pressure increases, the initial acceleration increases, and the outburst coal mainly move forward rapidly in the form of plug flow. The average velocity at 0.3, 0.5, and 0.8MPa gas pressure condition were 6.75, 22.22 and 35.81m/s, respectively. Gas also has a crushing effect on outburst coal. With increasing gas pressure, the number of coal powder particles of the same mass increased significantly, and the range of the particle size distribution of the particles decreaed, and the median particle size decreased. As the gas pressure increases, the outburst intensity gradually increases, and the total energy involved in the outburst work also increases. However, the energy dissipation pathways are different. At 0.3MPa, the energy dissipation is dominated by crushing energy, which is about six times the ejection energy. As the gas pressure increased to 0.8MPa, the proportion of the ejection energy gradually increases to about twice that of the crushing energy. Under the experimental conditions, 2.71-13.43% of the adsorbed gas involves in the outburst (AGIO) through rapid desorption, and the proportion increases with increasing gas pressure. This paper improves the energy model of coal and gas outburst, which is applicable to risk assessment and prevention of outburst disasters.

Efficiency of gas preparation technology using a block drying plant

The object of research is the technology of gas drying using a mobile block installation. The task to ensure compliance of the composition of natural gas with the values of a number of basic characteristics before its supply to main pipelines has been solved. The results of a complex analysis of the gas preparation technology of the deposit, which is located in an agricultural area and is at a late stage of exploitation, are reported. It was established that in order to ensure the supply of conditioned gas to the system of main gas pipelines under the conditions of low gas pressures, the construction of gas treatment plants is required, first of all, for its drying. The method of ensuring gas quality considered in the current paper involves the use of a block-type gas drying installation as part of a low-temperature separation installation and a source of artificial cold. As the latter, it is envisaged to use a freon-refrigerating unit. The study shows that the proposed block gas drying units can be unified for different gas productivity and are characterized by relatively low capital and operating costs. The main advantages of the introduction of gas preparation block installations and the scheme of connecting the installation to the existing line are presented. Based on the results of the economic efficiency indicators, it was established that the use of a block gas drying unit is a profitable project with the value of the accumulated reduced free cash flow of almost 843 thousand conditional units; the investment payback period is 3 years. The results could be effectively used in the gas distribution sector, provided that the gas is extracted from a field close to exhaustion, which is characterized by low reservoir pressures