Increase In Ambient Pressure Research Articles

Estimation of turbulence characteristics from PIV in a high-pressure fan-stirred constant volume combustion chamber

In this paper, a systematic experimental study was conducted to clarify characteristics of turbulence field generated by two opposite fans in a cubic constant volume combustion bomb (CVCB). The effect of the fan speed (1000–2900rpm) and ambient pressure (0.1–3.0MPa) on root-mean-square fluctuations, probability density functions, integral length scales and energy spectra was investigated. To overcome the limitation of the 2D-PIV, three sheet velocity fields were measured to reconstruct the three-dimensional boundary of the homogeneous region. Experimental results showed that a nearly homogeneous turbulence field in a flat region around the center of the CVCB was generated while a slight departure from isotropy was unavoidable in the current configuration. The turbulence intensity was independent of the ambient pressure, but positively proportional to the fan speed. Absence of both fan speed and ambient pressure’s effect was observed for the integral length scales. Analysis of the turbulent energy spectra implied that the increase of fan speed and ambient pressure resulted in a smaller critical eddy scale where the viscosity dissipation effect started emerging.

Influence of pulse width on the laser ablation of zinc in nitrogen ambient

Time-resolved spectroscopic measurements of expanding plasma plumes generated by irradiating a solid zinc target with laser pulses of 7 ns and 100 fs durations are carried out in the ambient pressure range of 0.05–200 Torr of nitrogen. At the relatively high input fluence of ~16 J/cm2, fast and slow atomic species are found to appear at different times in the optical time-of-flight (OTOF) spectra, the dynamics of which is primarily determined by the pulse duration of the excitation laser. In fs LPP, the average speed of fast species is unaffected by an increase in ambient pressure, while in ns LPP, the speed is found to reduce with pressure. The slow species shows a sharp peak in the OTOF spectra with a narrow velocity distribution for fs LPP, indicating a large number density and low electron temperature, which is consistent with optical emission spectroscopic (OES) studies. On the other hand, for ns LPP, the OTOF of slow species shows a more broadened profile which can be attributed to strong plume–laser interaction. The dynamics of slow species is heavily influenced by the presence of shock waves, which leads to the occurrence of much slower species at larger pressures.

Hydro-power plant equipped with Pelton turbines: Basic experiments relating to the influence of backpressure on the design

Free-jet turbines working under backpressure conditions represent an economical alternative to conventional hydro-electric plant configurations. However, the air introduced into the tailwater generates an air/water mixture. Its reaction to a rising ambient pressure is at present being studied at the above Institute. This report deals with the effect an increase in ambient pressure has on the volume and consistency of the two-phase mixture and the rise velocity of air bubble swarms. In addition, a test set-up is described which was used to study the physical reaction of the water/air mixture to a change in ambient pressure conditions. The results and their effects on the configuration of free-jet turbines working under backpressure are discussed.

ARC DISCHARGE SYNTHESIS OF CNTS IN HYDROGEN ENVIRONMENT IN PRESENCE OF MAGNETIC FIELD

In this study the effect of hydrogen ambient environment on the growth of carbon nanotubes by arc discharge plasma in presence of external magnetic field is investigated. The samples collected from cathode deposit are analyzed by field emission scanning electron microscopy and Raman spectroscopy. Results show an increase in carbon nanotube growth with increase in hydrogen ambient pressure. The magnetic field considerably enhances the growth of carbon nanotube as observed in FESEM micrographs. In Raman spectrum, high intensity of G peak as compared to D peak indicates the presence of high quality nanotubes. Magnetic effect remarkably decreases ID/IG ratio from 1.55 to 0.31 for ambient pressure 10 mbar.

Ambient pressure effect on non-premixed turbulent combustion of CH4–H2 mixture

The present work is devoted to the study of the effect of ambient pressure on non-premixed turbulent combustion of a mixture of 20% of hydrogen and 80% of methane. The simulations were conducted using the PDF approach and modified k-ε turbulence model. The flamelet model was used with the GRI 2.11 detailed kinetic mechanism. The flame consists of two coaxial jets of air and a jet of CH4–H2 mixture with pilot flame. After validating the model used we have varied the ambient pressure from 1 to 10 atm. We observed that the increase of ambient pressure leads to a slight increase of the flame temperature and the mass fraction of NO and a decrease in the radial and axial expansions.

Experimental study of temporal evolution of initial stage diesel spray under varied conditions

Understanding of the initial stage of spray development is important in modelling of the injection process for optimisation of diesel engine design. The near-field spray characteristics of a single-hole diesel injector were studied using an ultra-high speed CCD digital video camera with the speed of up to 1M fps. The effects of injection and ambient pressure on the spray behaviours have been examined in terms of initial spray penetration and tip velocity. Acceleration was observed during the initial stage of the spray process and the time corresponding to the spray tip peak velocity (tp) was extracted and compared to the breakup time (tb) in Hiroyasu correlation. It was found that tp is a natural and effective way to discriminate between the two stages during the spray process. The ambient pressure increase reduces the transition length considerably before the value reaches 1.5MPa and after that, the effect becomes much smaller. Finally, empirical correlations for the prediction of spray penetration development were proposed.

Pressure buffering by the tympanic membrane. In vivo measurements of middle ear pressure fluctuations during elevator motion

ObjectivesThe tympanic membrane (TM) represents a pressure buffer, which contributes to the overall pressure regulation of the middle ear (ME). This buffer capacity is based on its viscoelastic properties combined with those of the attached ossicular chain, muscles and ligaments. The current work presents a set of in vivo recordings of the ME pressure variations normally occurring in common life: elevator motion. This is defined as a situation of smooth ambient pressure increase or decrease on a limited range and at a low rate of pressure change. Based on these recordings, the purpose was a quantitative analysis of the TM buffer capacity including the TM compliance. MethodsThe pressure changes in seven normal adult ME's with intact TM's were continuously recorded directly inside the ME cavity during four different elevator trips using a high precision instrument. The TM buffer capacity was determined by the ratio between the changes in ME and the ambient pressure. Further, the ME volumes were calculated by Boyle's Law from pressure recordings during inflation-deflation tests; subsequently the TM compliance could also be calculated. Finally, the correlation between the ME volume and buffer function was determined. ResultsTwenty-one elevator trips could be used for the analysis. The overall mean TM pressure buffering capacity was 23.3% (SEM = 3.4), whereas the mean overall compliance was 28.9 × 10−3 μL/Pa (SEM = 4.8). A strong negative linear correlation was found between the TM buffer capacity and the ME volumes (R2 = 0.92). ConclusionsThese results were in fair agreement with the literature obtained in clinical as well as temporal bone experiments, and they provide an in vivo reference for the normal ME function as well as for ME modeling. The TM buffer capacity was found more efficient in smaller mastoids. Possible clinical implications are discussed.

Secondary Electron Emission of ZnO Films

We investigated secondary electron emission characteristics of ZnO thin films prepared by pulsed laser deposition method with respect to the ambient oxygen pressure and the substrate temperature during the deposition. X-ray diffraction, UV-Vis spectrometry, atomic force microscopy, and γ-FIB were used to examine the structural, optical transmission, surface morphology, and secondary electron emission properties of the films, respectively. The secondary electron emission coefficient of the ZnO films increases as the O/Zn ratio of the films increases which was thought to result from either the ambient oxygen pressure increase or the substrate temperature decrease and as the grain size of the films decreases. It was confirmed that ZnO has better secondary electron emission characteristics than those of MgO, which is currently widely used as a material for PDP protecting layers.

Design Space of Foil Bearings for Closed-Loop Supercritical CO2 Power Cycles Based on Three-Dimensional Thermohydrodynamic Analyses

The closed-loop Brayton cycle with supercritical CO2 (S-CO2) as an operating fluid is an attractive alternative to conventional power cycles due to very high power density. Foil gas bearings using CO2 are the most promising for small S-CO2 turbomachinery but there are many problems to address: large power loss due to high flow turbulence, lack of design/analysis tool due to nonideal gas behavior, and lack of load capacity when they are used for large systems. This paper presents high-level design/analysis tool involving three-dimensional (3D) thermohydrodynamic (THD) analyses of radial foil bearings considering real gas effect and flow turbulence inside the film. Simulations are performed for radial foil bearing with 34.9 mm in diameter and lubricated with CO2 and N2 under various ambient conditions up to above 40 bar gauge pressure. The simulation results using the turbulence model still underpredict the measured data in open literature. However, the error between the prediction and measurements decreases as either speed or ambient pressure increases. In addition, general behavior of substantial increase in power loss with ambient pressure agrees with the measured data. The simulation results indicate the importance of detailed THD analysis of the foil bearings for prediction of power loss under severe turbulent condition. A conceptual layout of rotor system for 10 MWe S-CO2 loop is also presented along with realistic rotor weight and bearing load. A hybrid foil bearing with diameter of 102 mm is suggested for gas generator rotor, and its power losses and minimum film thicknesses at various operating conditions are presented.

Visualization studies of the spray from swirl injectors under elevated ambient pressure

This paper presents the results of a visualization study on spray formed by swirl injectors with different geometries under elevated ambient pressure. A spray test facility with an ambient pressure chamber was constructed, and sprays were recorded using a high-speed camera. The parameters of the spray characteristics, e.g. the spray cone angle and breakup length of liquid sheet, were measured, and the effects of the ambient pressure and injector geometrical parameters on the spray were obtained. Experimental results indicated that when other parameters in the swirl injector remained constant, the increase of ambient pressure caused a decrease in the spray cone angle and the breakup length of liquid sheets. However, the mass flow rates remained nearly constant. An increase in nozzle diameter increased the spray cone angle, and the variation of breakup length according to nozzle diameter was somewhat irregular. The increase in the diameter of the tangential inlet reduced the spray cone angle; the breakup length scarcely varied.

The pressurization effect of jet fracturing using supercritical carbon dioxide

Hydro-jet fracturing is a unique hydraulic fracturing method, and has been recognized worldwide as an effective well-stimulation method for oil and gas production. However, because of controversy about the method's impact on water consumption and environmentally quality, hydraulic fracturing faces increasing restrictions. The demand for decreased water usage has promoted research on the use of non-aqueous fracturing fluids. In particular, the idea of using supercritical carbon dioxide (SC-CO2) fluid has attracted a lot of interest. Using SC-CO2 as a fracturing fluid is more effective and has significant advantages compared with water-based fluids. The unique properties of the SC-CO2 fluid facilitate fracture propagation, formation of complex fracture networks, and elimination of flow blockage in the rock matrix and pores. Therefore, the SC-CO2 jet fracturing technique may effectively enhance oil and gas recovery. Similar to hydro-jet fracturing, the pressurization effect in the perforation tunnel is a key precondition for successful jet fracturing with SC-CO2. This study investigated these effects using numerical simulations and experimental studies. Our results show that the pressurization effect during SC-CO2 jet fracturing improves with an increase in pressure difference, ambient pressure, nozzle diameter, and fluid temperature. However, pressurization becomes weaker with increasing casing hole diameter and annulus spacing. Comparing SC-CO2 and water jet fracturing pressurization effects suggests that using SC-CO2 jetting has advantages over water jet fracturing under in situ reservoir conditions. As the working depth increases, SC-CO2 jet fracturing achieves better pressurization than the water jet. The novel approach in our preliminary study begins to prove the feasibility of applying SC-CO2 jet fracturing to leverage unconventional resources.

The Influence of Water Characteristics on Plasma-Containing Bubble Dynamics

Pulsed discharge in conductive water can produce a plasma-containing bubble and radiate intensive acoustic pulses. The bubble dynamics, which determines the characteristics of the acoustic wave, is sensitive to the water temperature and ambient pressure. This paper presents the high-speed records of plasma-containing bubble behavior under different water temperatures in the range 18 °C–80 °C and ambient pressure in the range 0.1–1 MPa. The results show that a higher water temperature generates a larger bubble, larger oscillation period, and higher efficiency of the conversion of electric energy into bubble energy. The bubble energy and energy efficiency increase fast with water temperature since the rise in the initial water temperature decreases the energy consumption during the predischarge period. The ambient pressure also has an obvious effect on the maximum bubble radius and oscillation period. Both of them decrease fast when the ambient pressure increases. But, the bubble energy and energy efficiency are not so sensitive to ambient pressure, which indicates that the ambient pressure has little influence on the parameters of pulsed discharge.

Effects of ambient hydrostatic pressure on the material properties of the encapsulation of an ultrasound contrast microbubble.

Ultrasound contrast microbubbles experience widely varying ambient blood pressure in different organs, which can also change due to diseases. Pressure change can alter the material properties of the encapsulation of these microbubbles. Here the characteristic rheological parameters of contrast agent Definity are determined by varying the ambient pressure (in a physiologically relevant range 0-200 mm Hg). Four different interfacial rheological models are used to characterize the microbubbles. Effects of gas diffusion under excess ambient pressure are investigated in detail accounting for size decrease of contrast microbubbles. Definity contrast agent show a change in their interfacial dilatational viscosity (3.6 × 10(-8) Ns/m at 0 mm Hg to 4.45 × 10(-8) Ns/m at 200 mm Hg) and interfacial dilatational elasticity (0.86 N/m at 0 mm Hg to 1.06 N/m at 200 mm Hg) with ambient pressure increase. The increase results from material consolidation, similar to such enhancement in bulk properties under pressure. The model that accounts for enhancement in material properties with increasing ambient pressure matches with experimentally measured subharmonic response as a function of ambient pressure, while assuming constant material parameters does not.

Characterization of Near-Field Spray of Nongelled- and Gelled-Impinging Doublets at High Pressure

Atomization mechanism of gelled propellants in an impinging jet flowfield is significantly different from that of nongelled liquid propellants and is not clearly understood. This study explores the effect of liquid fluid properties such as viscosity and surface tension on the liquid sheet breakup with a special emphasis on the effect of ambient pressure. A rheologically matched non-Newtonian fluid that is nonreactive and nontoxic is used as a simulant for the gelled hypergolic propellants. Near-field spray characteristics such as the sheet formation and breakup length of the liquid sheet are experimentally determined using shadowgraph. Various sheet breakup regimes have been identified for both nongelled and gelled simulants over a range of flow conditions. For all fluids, the breakup length is found to decrease as the ambient pressure increases. Near-field imaging and its analysis show that the ambient pressure affects jet surface dynamics before impingement by increasing the jet surface disturbance length scale and sheet dynamics after impingement by shortening the surface wavelength, resulting in shorter breakup length with the increase of ambient pressure.

Effects of Temperature and Ambient Pressure on Spray Characteristics of Biodiesel Combustion

s: Diesel fuel injection is the most dominant in ignition process of the diesel engines combustion. Diesel engines have been widely used in heavy-duty and light-duty vehicles due to their higher fuel economy, efficient and powerful than spark ignition (SI) engines. The principal objective of this research is to seek the effect of temperature and pressure on the spray characteristics, as well as fuel-air mixing characteristics. Experiments were performed in a constant volume chamber at specified ambient gas temperature and pressure. This research was continued with injecting diesel fuel into the chamber using a Bosch common rail system. Direct photography technique with a digital camera was used to clarify the real images of mixture formation such as spray penetration, fuel evaporation and spray interference. The liquid phase of the spray reaches a maximum penetration distance soon after the start of injection, while the vapour phase of the spray continues to penetrate downstream. The condition to which the fuel is affected was estimated by combining information on the wall chamber temperature, ambient temperature and photographs of the spray. The increases in ambient pressure inside the chamber resulting in gain of spray area and wider spray angle. Thus predominantly promotes for a better fuel-air premixing.

A Review Paper on Simulation and Modeling of Combustion Characteristics under High Ambient and High Injection of Biodiesel Combustion

This paper describes simulation of combustion characteristics under high ambient and high injection of biodiesel combustion by using CFD simulation. Diesel engine performance and emissions is strongly couple with fuel atomization and spray processes, which in turn are strongly influenced by injector flow dynamics. The principal objective of this research is to seek the effect of temperature and pressure on the spray characteristics, as well as fuel-air mixing characteristics. Experiments were performed in a constant volume chamber at specified ambient gas temperature and pressure. This research was continued with injecting diesel fuel into the chamber using a Bosch common rail system. Direct photography technique with a digital camera was used to clarify the real images of spray pattern, liquid length and vapor penetration. The method of the simulation of real phenomenon of diesel combustion with optical access rapid compression machine is also reviewed and experimental results are presented. The liquid phase of the spray reaches a maximum penetration distance soon after the start of injection, while the vapor phase of the spray continues to penetrate downstream. The condition to which the fuel is affected was estimated by combining information on the block temperature, ambient temperature and photographs of the spray. The increases in ambient pressure inside the chamber resulting in gain of spray area and wider spray angle. Thus predominantly promotes for a better fuel-air mixing. All of the experiments will be conducted and run by using CFD. The simulation will show in the form of images.

SHS in the Ni–Al system: Influence of mechanical activation, vacuum heat treatment, and ambient pressure

Explored was the influence of mechanical activation (MA), vacuum heat treatment (VHT), and ambient pressure on combustion of Ni–Al mixtures. Burning velocity was found to grow with increasing MA time. An increase in ambient pressure hampered the elongation of burned samples. No elongation was found for non-activated and heat-treated samples. VHT strongly accelerated combustion and prevented the formation of cracks on the surface of burned samples. The results were rationalized in terms of convection–conduction combustion theory.

Pressure-sensitive fasteners for active disassembly

This paper presents a number of novel active fasteners developed to significantly lower disassembly costs during reconditioning, remanufacturing, and recycling of products. In the initial stage of the fastener development process, the applicability of distinct trigger signals for active disassembly (AD) is evaluated. Based on this evaluation, the high robustness of using a pressure increase or decrease as a nondestructive trigger for AD is demonstrated. Since previously proposed pressure-sensitive fasteners face considerable drawbacks upon implementation in electronic products due to the ongoing trend of miniaturization, a second generation of pressure-based active fasteners is developed. Evaluation of these fasteners by means of axiomatic design techniques and prototyping demonstrates that the presented snap-fits, which make use of a closed-cell elastomer foam, are most robust. Subsequently, the contraction forces that closed-celled foams can exert as a function of an increase in ambient air pressure are experimentally determined. Furthermore, the implementation of pressure-sensitive foam-based snap-fits in both a modem and a payment terminal is described. Results of these experiments demonstrate that the contraction force of a cross-linked metallocene polyethylene closed-cell foams can reach up to 6 N/cm2 at an overpressure of 2 bar and that the foam-based snap-fits can be released at a pressure increase of 2 bar.

Real-Time Contrast Ultrasound Muscle Perfusion Imaging with Intermediate-Power Imaging Coupled with Acoustically Durable Microbubbles

There is growing interest in limb contrast-enhanced ultrasound (CEU) perfusion imaging for the evaluation of peripheral artery disease. Because of low resting microvascular blood flow in skeletal muscle, signal enhancement during limb CEU is prohibitively low for real-time imaging. The aim of this study was to test the hypothesis that this obstacle can be overcome by intermediate- rather than low-power CEU when performed with an acoustically resilient microbubble agent. Viscoelastic properties of Definity and Sonazoid were assessed by measuring bulk modulus during incremental increases in ambient pressure to 200mm Hg. Comparison of invivo microbubble destruction and signal enhancement at a mechanical index (MI) of 0.1 to 0.4 was performed by sequential reduction in pulsing interval from 10 to 0.05 sec during limb CEU at 7MHz in mice and 1.8MHz in dogs. Destruction was also assessed by broadband signal generation during passive cavitation detection. Real-time CEU perfusion imaging with destruction-replenishment was then performed at 1.8MHz in dogs using an MI of 0.1, 0.2, or 0.3. Sonazoid had a higher bulk modulus than Definity (66±12 vs 29±2kPa, P=.02) and exhibited less inertial cavitation (destruction) at MIs≥0.2. On invivo CEU, maximal signal intensity increased incrementally with MI for both agents and was equivalent between agents except at an MI of 0.1 (60% and 85% lower for Sonazoid at 7 and 1.8MHz, respectively, P<.05). However, on progressive shortening of the pulsing interval, Definity was nearly completely destroyed at MIs≥0.2 at 1.8 and 7MHz, whereas Sonazoid was destroyed only at 1.8MHz at MIs≥0.3. As a result, real-time CEU perfusion imaging demonstrated approximately fourfold greater enhancement for Sonazoid at an MI of 0.3 to 0.4. Robust signal enhancement during real-time CEU perfusion imaging of the limb is possible when using intermediate-power imaging coupled with a durable microbubble contrast agent.

Experimental Validation of the Temperature-Resistant and Salt-Tolerant Xanthan Enhanced Foam for Enhancing Oil Recovery

Xanthan enhanced foam (XGF) is a newly developed chemical agent for enhanced oil recovery in high-temperature and high-salinity reservoirs. In this paper, laboratory experiments were performed to characterize the morphology and foam properties of XGF, to study its performance under different temperature and different salinity conditions, respectively. Based on simulate reservoir formation conditions of Xidaliya field, a series of research on XGF were conducted. The experimental results showed that the scanning electron microscopy of XGF reflected a more viscoelastic and stable nature of the foam system. High temperature had a great adverse impact upon the stability of XGF, and the increase of salinity in the solution helped to improve the stability of foam. The foam stability increased remarkably when XG4 is added, and an increase in ambient pressure made enhancement of foam stability became more noticeable. In the presence of crude oil, Xanthan could enhance the stability of emulsions and was more favorable to stabilize foam. XG4 enhanced foam had dramatic properties for mobility controlling and oil displacement in the porous media.