Effect Of Pressure Research Articles

Cavitating flow through a Venturi using CFD: effects of inlet and outlet pressures

Hydrodynamic cavitation is a complex physical phenomenon that appeared in hydraulic systems (pumps, turbines, valves, Venturi tubes …etc.) when the fluid pressure decreases below the saturated vapor pressure. The works carried out in this study aimed to get a better understanding of the cavitating flow phenomenon. For this, we have numerically studied a cavitating bubbly flow through a venturi nozzle. The cavitation model is selected and solved using commercial code computational fluid dynamics (CFD). The numerical results are compared to the previous experimental and numerical data.The obtained results showed that the effect of the inlet pressure (10, 7, 5 and 2 bars) and outlet pressures (6.5, 6, 5, 4, 3.5, 1.5, and 1 bars) of the Venturi on pressure, velocity of the fluid flow and the vapor fraction formation. We found that the inlet and outlet pressures of the venturi are strongly affected on the evolution of the pressure, velocity and vapor fraction formation in the cavitating flow. The results presented in this study provide insight and useful guidance to the designer of hydrodynamic cavitation devices, identifying key geometrical and physical parameters of cavitation onset and intensification that can be manipulated to achieve the desired level of cavitation flow.

Enhanced antioxidant activities, polyphenols, flavonoids, and free amino acid contents of Nelumbo nucifera bee pollen via high hydrostatic pressure treatment

ABSTRACT The aim of the present study was to address the effect of high hydrostatic pressure (HHP) on bioactive compounds and antioxidant activity of Nelumbo nucifera (Lotus) bee pollen (LBP). The total phenolic contents (TPC) and free amino acids were determined and flavonoid composition was identified by UPLC-Triple-TOF-MS. Five analytical methods including DPPH, ABTS, reducing power, FRAP, and silver nanoparticles antioxidant capacity were used for the antioxidant activity analysis. The results revealed a significant increase in the TPC and free amino acid compositions after HHP treatment. The DPPH, ABTS, reducing power, FRAP, and AgNPAC of the extracted fractions were augmented by over 13.94, 2.9, 2.68, 85, and 2.6 times, respectively. PCA analysis showed a strong correlation between TPC, some distinct flavonoids, and antioxidant activities. These results indicated that HHP enhances the antioxidant activity of LBP via increase in amino acids, TPC, and some flavonoids such as Licoagrone, Kuwanon K, Cyanidin 3-rutinoside, etc.

Predicting Leidenfrost Temperature and Effects of Impact Conditions on Droplet Size Distribution in Film-Boiling Regime

Abstract The interaction of a droplet with a solid wall is relevant in various engineering applications. The properties of the resulting secondary droplets are determined by the wall temperature, ambient pressure, impact momentum, and impact angle. This paper presents a comprehensive characterization of drop-wall interactions and the subsequent atomization as a function of the combined effects of such parameters. A drop-wall interaction model is derived for F-24 droplets using smoothed particle hydrodynamics (SPH). The model can predict different impact outcome regimes (deposition, rebound, contact-splash, and film-splash) for different ambient pressures, wall temperatures, and impact parameters. The model also addresses the effect of ambient pressure on the Leidenfrost behavior. Size distributions of secondary droplets are compared for vertical and nonvertical impacts of F-24 droplets on superheated surfaces in the film-boiling regime. The non-dimensional Sauter mean diameter (SMD) of the secondary droplets varies based on the position in the impact plane for all the nonvertical impacts but remains almost unchanged for vertical impacts. The leading arc for nonvertical impact consists of larger secondary droplets, and the size decreases toward the trailing arc. An empirical relation is proposed to represent this trend. This research sheds light on successive droplet impacts by studying the effects of impact frequency on SMD evolution. The results are compared to single droplet impact cases for different fuels and Weber numbers. The size of secondary droplets for successive impacts is observed to be nearly indistinguishable from that of single-droplet vertical impacts.

Effect of central plasma pressure on high-order harmonics of 1/1 quasi-interchange instability in a central weak magnetic shear tokamak configuration

Abstract Numerical investigations of linear and nonlinear stages of quasi-interchange instability in a cylindrical tokamak geometry with a flat q-profile in the core region are conducted using eigenvalue and initial value codes, respectively. It is found that there exists a dependent relationship between the central plasma pressure p 0 (of the initial pressure profile) and the dominant harmonic of the quasi-interchange instability. As p 0 increases, m = n > 1 mode would be dominant in the linear stage and even in the nonlinear stage, where m and n are the poloidal and toroidal mode number, respectively. In addition, with p 0 increasing, the fast growth of other harmonics is inevitable and will deeply affect the evolution of m = n dominant quasi-interchange instability.

Elevated Blood Pressure and Culprit Aneurysm Rebleeding During the Unsecured Period of Aneurysmal Subarachnoid Hemorrhage: A Systematic Review.

In aneurysmal subarachnoid hemorrhage, rebleeding prior to securing the culprit aneurysm leads to significant morbidity and mortality. Elevated blood pressure has been identified as a possible risk factor. In this systematic review, we evaluated the association between elevated blood pressure and aneurysm rebleeding during the unsecured period. We searched MEDLINE, Embase + Embase Classic, and CENTRAL, from inception to March 8th, 2024. We included studies of adults with aneurysmal subarachnoid hemorrhage reporting at least one blood pressure measurement during the unsecured period and a measure of association with rebleeding. Results were stratified by blood pressure thresholds, effect measure, and adjustment for confounding. Separate meta-analyses were performed for each of these groups. Our search identified 5,209 citations. After screening, 15 studies were included in our review. All studies were observational in design and at moderate or high risk of bias. Meta-analysis of the unadjusted results produced mixed findings across the systolic blood pressure (SBP) thresholds: SBP > 140mmHg, unadjusted odds ratio (uOR) 1.03 (95% confidence interval [CI] 0.55-1.93; I2 = 66%); SBP > 160mmHg, uOR 3.35 (95% CI 1.44-7.81; I2 = 83%); SBP > 180mmHg, uOR 1.52 (95% CI 0.40-5.81; I2 = 89%); and SBP > 200mm Hg, uOR 7.99 (95% CI 3.60-17.72; I2 = 0%). Meta-analysis of adjusted results was only possible at an SBP > 160mmHg; adjusted hazard ratio 1.13 (95% CI 0.98-1.31; I2 = 0%). The overall quality of evidence as assessed by the Grading of Recommendations, Assessment, Development, and Evaluations tool was rated as very low. Based on very low quality evidence, our systematic review failed to determine whether there is an association between elevated blood pressure during the unsecured period and increased risk of culprit aneurysm rebleeding.

Effect of pressure, temperature, and particle size on cold sintered ZnO for transparent thick films on polymer substrates

AbstractThe role of pressure, temperature, and particle size on cold sintering of ZnO has been investigated with a view to developing transparent thick films for device applications. Coarse ZnO (∼90–250 nm, cZnO) particles exhibited equiaxed grain growth under all conditions eventually achieving grain sizes of ∼ 0.5–1.0 µm at 300°C/375 MPa. In contrast, nano‐ZnO (40–80 nm, nZnO), exhibited grain growth along the c‐axis with a broader grain size distribution (0.5–4 µm) at higher temperatures and pressure (300°C/375 MPa) than cZnO. The broader grain size distribution is attributed to greater dissolution for nZnO compared with cZnO coupled with redistribution of Zn acetate/acetic acid into pores. ZnO continues to dissolve and reprecipitate within the pores throughout the densification process resulting in localized, larger grain sizes. In plane grain growth normal to the pressing direction was observed at and near the sample surface particularly in nZnO, which is attributed to constrained‐sintering. Some abnormal grain growth (10–20 µm) was also sporadically observed near or at the surface of nZnO (300°C/375 MPa) due to greater rates of reprecipitation as the transient solvent volatilizes adjacent to the die wall/plunger. Tape casting was used to fabricate single and multiple layers (≈30 µm) of ZnO on Kapton® to demonstrate the potential for device fabrication. Transparency was achieved by choosing cold sintering conditions (200°C/250 MPa) for nZnO that gave ∼95% relative density while restricting a majority of grain growth to <200 nm so that internal light scattering from grain boundaries was avoided.

Time pressure effects on decision-making in intertemporal loss scenarios: an eye-tracking study.

This study utilized eye-tracking techniques to investigate decision-making behavior in intertemporal loss scenarios under both time pressure and no time pressure conditions. Results revealed shorter decision-making times and decreased large later (LL) option selection frequency under time pressure. Participants under time pressure exhibited reduced Mean Fixation Duration (MFD) and Search Measure (SM) values, indicating altered information processing. Mediation analyses confirmed that task choice outcomes were influenced by SM and MFD, suggesting a shift towards heuristic decision-making under time pressure.

Generalisation of the yield stress measurement in three point bending collapse tests: application to 3D printed flax fibre reinforced hydrogels

This paper describes the extrusion pressure's effect on composite hydrogel inks' filaments subjected to three point bending collapse tests. The composite considered in this work consists of an alginate-poloxamer hydrogel reinforced with flax fibres. Increased extrusion pressure resulted in more asymmetrical filaments between the support pillars. Furthermore, the material and printing conditions used in the present study led to the production of curved specimens. These two characteristics implicitly limit the validity of the yield stress equations commonly used in open literature. Therefore, a new system of equations was derived for the case of asymmetrical and curved filaments. A post-processing method was also created to obtain the properties required to evaluate this yield stress. This new equation was then implemented to identify the strength of failed hydrogels without flax fibre reinforcement. A statistical analysis showed this new equation's significance, which yielded statistically higher (i.e. 1.15 times larger) strength values compared to the numbers obtained with the open literature equations. At larger extrusion pressures, longer periods were needed for the material to converge towards its final shape. Larger extrusion pressure values led to lower yield stresses within the composite hydrogel filament: a 5 kPa increase in extrusion pressure lowered the yield stress by 19%. In comparison, a 15 kPa increase led to a 29% decrease in the yield stress. Overall this study provides guidelines to standardize three point bending collapse tests and analysis comparison between different materials.

Numerical simulation of condensation of supercritical water gasification products in a supersonic nozzle

The clean and efficient separation of supercritical water gasification products (SCWGP) has emerged as a significant challenge in supercritical water gasification technology. This paper proposes the use of a supersonic nozzle for the condensation and separation of H2 and CO2 from SCWGP, leveraging the high-pressure characteristics of these products. By establishing a flow model and a condensation model for the supersonic nozzle, the effects of inlet pressure and inlet temperature on the condensation process are analyzed. The analysis reveals that the latent heat released during condensation causes an abnormal distribution of pressure and temperature within the nozzle. When the inlet pressure of the nozzle is increased from 7.0 to 9.0 MPa, the liquid phase mass fraction at the outlet rises from 5.3 × 10−3 to 0.056. Similarly, when the inlet temperature is lowered from 300.0 to 290.0 K, the liquid phase mass fraction at the outlet also rises from 5.3 × 10−3 to 0.058. The increase in inlet pressure leads to the condensation location shifting toward the throat by ∼8.5 × 10−3 m⋅MPa−1, while the impact of inlet temperature is approximately −2.3 × 10−3 m⋅K−1. The nucleation rate in the nozzle is always concentrated in a small region.

Understanding the effects of pore pressure–induced crack deformation on the acoustic anisotropy of rocks with aligned cracks

AbstractCracks are extensively existing in rocks and play a significant role in the acoustic anisotropy of cracked rocks. Rocks in nature are affected by pore pressure, whereas the crack deformation with pore pressure and the impacts of the crack deformation on the anisotropic acoustic properties remain little known. Combining the theoretical model with the laboratory measurements of the anisotropic velocities of artificial sandstone samples with and without aligned penny‐shaped cracks, we invert for the crack parameters that characterize the crack deformation as a function of pore pressure and theoretically simulate the impacts of pore pressure–induced variation in the crack parameters on the anisotropic velocities. The results show that with increasing pore pressure, the inverted crack porosity increases exponentially, whereas the inverted crack aspect ratio decreases exponentially and the two crack parameters are linearly correlated. Moreover, model calculation demonstrates that the anisotropic velocities exhibit distinct reductions with the variation in the crack parameters caused by increasing pore pressure. In particular, the reduction in the velocity of the shear wave travelling parallel to the crack plane with polarization perpendicular to the crack plane is the most pronounced. We also demonstrate that the effects of the pore pressure–induced increasing crack porosity on the anisotropic velocities are more pronounced than the impacts of the decreasing crack aspect ratio. The findings not only reveal the variation of the crack geometry with pore pressure and the effects of the crack deformation on the anisotropic velocities of the cracked rocks but also can provide theoretical support for improving the characterization of the cracks through seismic survey.

Effects of Pressure on Nitrogen Content and Solidification Structure during Pressurized Electroslag Remelting Process with Composite Electrode

The nitrogen content and solidification structure of the 1Mn18Cr18N ingots produced by the customized laboratory‐scale vacuum induction melting furnace and the pressure electroslag remelting furnace (PESR) with novel composite electrode under different pressure and the same power consumption are compared and studied. The results show that there are perfectly uniform radial chromium and nitrogen profiles during the PESR process. The nitrogen uptake reaction in the PESR process with composite electrode takes place on the liquid metal film on the electrode. Nitrogen uptake could be improved by increasing the nitrogen partial pressure. In addition, the basin depth at a pressure of 0.1 and 1.22 MPa is about 41 and 38 mm, the angle of the grains with respect to the vertical axis is 35° and 31°, respectively. The flat metal basin profile resulted from the thermal resistance at the slag–mold interface decreasing with increasing pressure. Primary and secondary dendritic arm spacing (PDAS and SDAS) variations exhibit an increasing and subsequently decreasing the trend as they move further away from the center in a horizontal direction. Both PDAS and SDAS decrease with increasing pressure from 0.1 to 1.22 MPa.

First-principles calculations to investigate thermodynamic, mechanical and electronic properties of Penta-C72 carbon under pressure effect

The current work explores the mechanical characteristics, band structure modifications, elastic constant changes, and anisotropy of the carbon allotrope Penta-C72 at high pressure. First-principles simulations were used to analyse the structural features, stability, electronic, mechanical, and thermodynamic properties of Penta-C72, a metastable sp3 -bonded structure made up of carbon pentagons joined by bridge-like connections. The structural and dynamical stability of Penta-C72 under high pressure is confirmed using formation energy, phonon band maps, and thermodynamic properties. Besides, Born's mechanical stability criterion is fulfilled based on the elastic constants of Penta-C72, indicating its mechanical stability. Also, the anisotropic mechanical behaviour is shown by the material. Using the Reuss, Voigt, and Hill approximations, the elastic moduli under high pressure were computed, including bulk modulus (K), shear modulus (G), and Young's modulus (E). Besides, Penta-C72 exhibits a rise in anisotropy and moduli with increasing pressure. This investigation explores the changes in the band gap upon variation in the pressure. It is observed that there is a transition from semiconducting to metallic property above 10 GPa. Beyond 10 GPa, the material exhibits metallic behaviour. The study emphasizes that Penta-C72’s exceptional mechanical stability, directional anisotropy, and customisable electronic characteristics make it a strong contender for various engineering applications.

Effect of Excess Pore Pressure on Earthquake‐Induced Displacement of Partially Saturated Sandy Soil Slopes: Flexible Sliding Block Analysis

Effect of Excess Pore Pressure on Earthquake‐Induced Displacement of Partially Saturated Sandy Soil Slopes: Flexible Sliding Block Analysis

Effect of ambient pressure on the fire characteristics of lithium-ion battery energy storage container

As lithium-ion battery energy storage gains popularity and application at high altitudes, the evolution of fire risk in storage containers remains uncertain. In this study, numerical simulation is employed to investigate the fire characteristics of lithium-ion battery storage container under varying ambient pressures. The findings reveal that the peak heat release rate of fires at normal pressure is significantly higher than at lower pressure. Specifically, the heat release rate at 100 kPa is 9215 kW, exceeding the value at 40 kPa by 42%, which is only 3900 kW. This peak heat release rate also demonstrates a power function relationship with ambient pressure. In addition, fires tend to last longer in lower pressure, where high-temperature areas expand and spread rates increase. Moreover, higher pressures produce elevated peak concentrations of CO and CO2, while smoke spreads faster in lower pressure, despite lower peak smoke concentrations. The study findings can serve as a foundation for assessing the fire hazards and designing fire protection measures for lithium-ion battery storage containers exposed to varying ambient pressures.

Influence of Reaction Conditions on the Yield of Supercritical Multicomponent Thermal Fluids

Supercritical multicomponent thermal fluid (scMCTF) is a novel medium with great potential for heavy oil thermal recovery. The production rate of scMCTF will affect the injection efficiency of thermal fluid, and then affect the development effect of thermal recovery. However, at present, there are few reports on the production rate of each component of scMCTF, and their understanding is not clear. According to the existing production rate data of supercritical water (scH2O) gasification products, based on the generation mechanism of scMCTF, the production rate of thermal fluid generation products under different generation conditions was calculated, and its influencing factors were identified. The results show the following: (1) The factors affecting the production rate of scMCTF generation products can be divided into three categories: reaction raw material factors, reaction condition factors, and catalytic factors. (2) The hydrocarbon number of raw material, reaction temperature, reaction time, and catalyst concentration were positively correlated with the production rate of the product. (3) The concentration of the reaction raw material is negatively correlated with the production rate of the product. The higher the concentration of the raw material is, the lower the concentration of H2O is, and the steam reforming reaction is inhibited, which leads to the decrease in the production rate. (4) The effect of reaction pressure and catalyst load on the product is not significant. (5) The reaction product production rate increased first and then decreased with the ratio of H2O to oil in the raw material emulsion and the ratio of preheated H2O to raw material discharge. (6) The effect of metal salt catalysts is relatively stable, and the catalytic effect of simple metal catalysts is significantly different under the action of different types of accelerators, so it is necessary to study the degree of synergization of different accelerators on the catalytic effect. The results can lay a foundation for the subsequent experimental and theoretical research design.

Intelligent control of pressure based on ureteral access sheaths: renal pelvic pressure during flexible ureteroscope perfusion at different sites.

This study aimed to evaluate the accuracy and effectiveness of renal pelvic pressure (RPP) control during flexible ureteroscopic perfusion at various sites. Flexible ureteroscopy for the intelligent control of RPP was based on a ureteral access sheath (UAS) that integrated pressure measurement and suction functions (with automatic adjustment). Eleven consecutive patients with indurating nephrostomy tubes were enrolled. The nephrostomy tube was connected to a disposable invasive blood pressure sensor. The RPP was zeroed after the pressure stabilized. The flow rate and control value were set at 100ml/min and - 5 mmHg, respectively. An 8.5 Fr flexible ureteroscope was irrigated at the renal pelvis, as well as the upper, middle, and lower calyces of the kidney for 1min. All 11 patients with upper urinary tract calculi underwent successful UAS placement. Pressures measured by the sheath and fistula during perfusion were - 5.07 ± 1.41 and - 4.89 ± 1.07 mmHg at the renal pelvis, -5.16 ± 1.36 and - 5.12 ± 1.32 mmHg at the upper calyces, -4.98 ± 0.87 and - 5.39 ± 1.01 mmHg at the middle calyces, as well as -4.95 ± 1.56 and - 5.64 ± 1.24 mmHg at the lower calyces, respectively. There were no significant differences in pressure between the sheath and fistula groups or in sheath and fistula pressures among parts. The RPP fluctuated; however, all values were within the safe limit of 20 mmHg. The UAS-based pressure monitoring technology can accurately and reliably monitor and control RPP within a set range.

Analysis of Flow Field Characteristics in a Mechanical Defoaming Device.

To improve the froth breakdown performance of flotation foam, a mechanical defoaming device based on vacuum and rotation was developed. The device is mainly composed of a rotating disk and a baffle and generates negative pressure when rotating at high speed. Through the synergistic effects of negative pressure, collision, extrusion, and shearing, the flotation foam effectively separates the liquid and gas phases. The flow field characteristics of the defoaming device are meticulously analyzed through numerical simulation, leading to a comprehensive evaluation of its defoaming performance. The effects of different rotational speeds on fluid velocity, pressure, turbulence, and traces are studied. It can be obtained that when the rotational speed is 900-1800 rpm, the device generates a pressure zone of -2.5 to -12.5 kPa, which can meet the requirements of the defoaming design.

Numerical simulation analysis of effect of borehole gas extraction under fluid‐structure interaction

AbstractTo study the effect of coal pressure on gas extraction under fluid‐solid coupling, the effect of gas extraction radius under different pore sizes and treatment methods was simulated by using COMSOL Multiphysics software, the time evolution law of gas pressure on coal surface was obtained, and the numerical simulation results were verified by the observation of flow rate and concentration in experimental mine combined with fluid‐solid interaction. The results show that the distance of extraction radius increases with the increase of borehole diameter, and the relation between extraction time and extraction radius is a power function, but the increase gets smaller and smaller until it becomes zero. For Φ98 mm borehole and Φ120 mm borehole, hydraulic treatment can increase the efficiency of gas extraction by 31.3% and 22.7%, respectively. For hydraulic treatment and conventional treatment, the ratio of gas drainage effect by enlarging hole size is 6.3% and 13.8% respectively. Compared with the areas without gas extraction under the four conditions, the descending speed of gas pressure from fast to slow is Φ120 mm hydraulic flushing treatment, Φ98 mm hydraulic flushing treatment, Φ120 mm conventional treatment, Φ98 mm conventional treatment. Compared with four different conditions, after 180 days of extraction the coal gas pressure decreased by 75.3% within reasonable hole spacing. At the same time, in multi‐hole pumping, the influence area of adjacent borehole is larger than that of single‐hole pumping, and the spacing of borehole should be less than twice the radius of pumping.

Underestimation of global soil CO2 flux measurements caused by near-surface winds

Soil respiration (Rs) is the largest source of atmospheric CO2, and an accurate understanding of the relationship between near-surface winds, CO2 release from the soil surface, and measurement methods is critical for predicting future atmospheric CO2 concentrations. In this study, the relationship between wind speed and soil CO2 fluxes is elucidated on a global scale through meta-analysis, and the flux measurement methodology is further explored in conjunction with the results of a controlled trial to clarify the uncertainty of the measurement results. The results indicate that near-surface wind speed is positively correlated with soil CO2 release and that near-surface winds result in increased soil CO2 gas release. Wind disturbance affects both the concentration gradient and gas chamber measurements, and the lower calculated soil CO2 release conflicts with the notion that the wind pump effect and Bernoulli effect of negative pressure cause a greater surface gas exchange. The results of the log-response ratios indicate that near-surface winds lead to an underestimation of 12.19–19.75% in widely-used gas chamber method measurements. The results of this study imply that some of the current Rs measurements are biased and that the influence of near-surface winds on Rs measurements needs to be urgently addressed to assess the terrestrial carbon cycle more accurately and develop climate change response strategies.

Air infiltration characteristics in oxygen-enhanced and heated chambers on the Qinghai-Xizang Plateau

The Qinghai-Xizang Plateau is characterized by a low-pressure and oxygen-deficient environment due to its high altitude, causing discomfort and major safety problems for the inhabitants. To address this, oxygen-enriched chambers can be used to alleviate the plateau reaction. However, little consideration has been given to air infiltration in these chambers, with a lack of information on the corresponding infiltration heat loss phenomenon. This paper addresses this by investigating the phenomenon of air flow in an oxygen-enriched chamber using experiments and simulations. The results highlight that when there is a difference in oxygen concentration between the interior and exterior of the chamber, mass transfer occurs due to both the molecular diffusion in addition to a flow due to the air density difference caused by the variation in concentration. Also, the simultaneous stack effect is roughly equivalent to 10 times the oxygen pressure, and the two pressure effects act in opposite directions. It is also noted that both the oxygen pressure and the stack effect decrease as the atmospheric pressure decreases. Overall, the oxygen-enriched chambers exhibit less infiltration in plateau areas with a low atmospheric pressure compared to plains areas with a relatively high atmospheric pressure. Finally, this study establishes formulas that can be used to calculate air infiltration rates in oxygen-enriched chambers. This study fills a gap in the existing literature regarding the air infiltration mechanism in oxygen-enriched chambers at high altitudes and low pressures, providing a theoretical foundation for improving indoor environments in the Qinghai-Xizang Plateau and other high-altitude regions.