Increase In Total Pressure Research Articles

Effects of total pressure on mode transition in a dual-mode combustor

The mode transition experiments of the dual-mode combustor were carried out under the conditions that the total pressure was 600 kPa, 700 kPa, 800 kPa and 900 kPa, the total temperature was 810 K, and the Mach number was 2.0. According to the wall pressure of the combustor measured in the experiment, the distribution of other airflow parameters of the combustor were obtained through the one-dimensional performance calculation method. The processes of mode transition of the combustor under different total pressures were studied. The study show that the dimensionless peak pressure of the combustor increased with the increase of the entrance total pressure under the same fuel equivalence ratio; the larger the total pressure, the smaller the fuel equivalence ratio required to reach the same dimensionless peak pressure. The results show that there were pure scramjet mode, dual-mode scramjet mode, dual-mode ramjet mode and the combustion state that the pressure disturbance had spread to the entrance of the isolator with the increase of the fuel equivalence ratio. The dimensionless peak pressures of the combustor when mode transition occurred were 0.25, 0.41, and 0.5, and did not change with the change of the total pressure of the incoming flow.

Characterization of a Supersonic Turbine Downstream of a Rotating Detonation Combustor

Rotating detonation combustors (RDCs) offer theoretically a significant total pressure increase, which may result in enhanced cycle efficiency. The fluctuating exhaust of RDC, however, induces low supersonic flow and large flow angle fluctuations at several kHz, which affects the performance of the downstream turbine. In this paper, a numerical methodology is proposed to characterize a supersonic turbine exposed to fluctuations from RDC without any dilution. The inlet conditions of the turbine were extracted from a three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes simulation of a nozzle attached to a rotating detonation combustor, optimized for minimum flow fluctuations and a mass-flow averaged Mach number of 2 at the nozzle outlet. In a first step, a supersonic turbine able to handle steady Mach 2 inflow was designed based on a method of characteristics solver and total pressure loss was assessed. Afterward, unsteady simulations of eight stator passages exposed to periodic oblique shocks were performed. Total pressure loss was evaluated for several oblique shock frequencies and amplitudes. The unsteady stator outlet profile was extracted and used as inlet condition for the unsteady rotor simulations. Finally, a full stage unsteady simulation was performed to characterize the flow field across the entire turbine stage. Power extraction, airfoil base pressure, and total pressure losses were assessed, which enabled the estimation of the loss mechanisms in supersonic turbine exposed to large unsteady inlet conditions.

Gas Separation Polysulfone Membranes Modified by Cadmium-based Nanoparticles

This paper presents new mixed-matrix membranes (MMMs) synthesized via incorporating hexamethylenetetramine dicyanamide cadmium nanoparticles, a metal organic framework (MOF), into the polysulfone (PSF) matrix. The MMMs are characterized using FTIR and SEM analyses, and their gas permeation properties are evaluated at different MOF loadings and various pressures. The results show that the nanoparticle is compatible with the polymer and distributes homogenously in the matrix. Compared to the pristine PSF membrane, the MMM with 2.5 wt. % of the MOF nanoparticles has lower CO2, CH4, N2 and O2 permeabilities but significantly higher CO2/CH4, CO2/N2 and O2/N2 gas pair selectivities (i.e., 41.66, 20.08 and 5.09, respectively, which are 42.6, 61.6 and 60.02 % higher). As the total pressure increases, the gas permeabilities of the pristine PSF membrane and the MMMs decrease, but their sieving abilities increase. These results suggest that gas selectivities of high free-volume polymers with poor sieving abilities can be improved by incorporating the MOF into the polymer.

Experimental study on combustion characteristics of kerosene-fueled scramjet combustor

ABSTRACTKerosene-fueled ignition combustion test was carried out in a scramjet combustor under the condition of total temperature of 810 K, Mach number of 2.0 and different total pressures of 600, 700, 800 and 900 kPa. The combustor model was a dual-mode combustor with double cavity flameholder. Hydrogen was injected in the first cavity, and kerosene was injected in front of the first cavity. Hydrogen, being pilot flame, was the first to be ignited by the spark plug, and then kerosene was ignited by hydrogen. Kerosene was kept burning solely after hydrogen was stopped injecting. Combustion luminosity images were pictured in tests. The test results showed that all the combustion modes of kerosene and hydrogen were upstream cavity stabilization mode under different fueling conditions. Under the higher entrance pressure or the higher kerosene equivalence ratios, the kerosene combustions were upstream cavity stabilization mode. Under the lower entrance pressure or the lower kerosene equivalence ratios, the combustions were downstream cavity stabilization combustion mode. Under the middle entrance pressure or the kerosene equivalence ratios, oscillations of combustion mode occurred. The flameholding capacity of the kerosene-fueled combustor increases with the increase of the entrance total pressure.

Experimental study on H2S and CO2 generation capacities of the Bohai bay heavy oil

Thermal recovery is a conventional technology for heavy oil development. During thermal oil recovery the reservoir could generate H2S and CO2. They will potentially threat the safety of downhole tubing regarding the sweet or sour corrosion. In some Bohai heavy oil fields CO2 and H2S under thermal recovery conditions lead to some corrosion problems of the tubing and equipment. Therefore, to determine the corrosive gas generation capacity is crucial for anti-corrosion design of downhole tubing and casing. Heavy oil samples from Bohai, China were experimentally studied for their pyrolysis characteristics using high-temperature-high-pressure autoclaves. The gases were collected when autoclaves cooled down to the in situ formation temperature. Effects of temperature, water chemistry and core mineral on corrosive gas generation were investigated. The results show that total pressure increase significantly when temperature reached 250°C-280 °C under the single heavy oil condition. The additional water facilitates the reaction process, after more SO42− added in the mimic formation water, higher H2S content is obtained. Under the condition of multiphase of oil, formation water and cores, both of the H2S and CO2 content increase obviously, and the cores' effect on CO2 is greater than H2S. Anti-corrosion design usually concerns only the highest corrosive gas concentration without further analysis. The highest concentration does not always correspond to the best corrosive gases generation capacities of heavy oil. Comprehensive analysis of both the total pressure of reaction process and the quality of the reaction heavy oil is carried out, then the corrosive gases volume per unit mass of heavy oil is calculated. These can determine the strongest corrosive formation environment and the maximum gases generation capacities of heavy oil.

Starting characteristics and phenomenon of a supersonic wind tunnel coupled with inlet model

Supersonic wind tunnel is regarded the most efficient experimental facility for studying the performance of supersonic inlets. In view of this background, the starting problem of a wind tunnel coupled with the inlet model is a critical experimental issue. However, inlet experiments cannot be performed when wind tunnels do not start. To satisfy this requirement, this study adopts numerical simulations to examine the starting characteristics of a wind tunnel coupled with the inlet model to serve as a basis for observing the flow at the starting procedure. Results of steady simulation show that the wind tunnel coupled with the medium-sized inlet model is still at risk in the starting procedure, although the inlet size of the model is considerably smaller than the physical limitation. Furthermore, imposing high total pressure on the wind tunnel inlet can make the wind tunnel restart. However, results also reveal that gradually increasing total pressure does not necessarily restart the wind tunnel, as wind tunnels can start only when total pressure amplitude is large enough. To improve the understanding of the phenomena, unsteady numerical simulations with different total pressure levels are performed on the wind tunnel inlet. Numerical results demonstrate the importance of generating a moving shock wave with adequate intensity that can overcome the structure of the separation zones near wind tunnel walls after sweeping the inlet model. Under this influence, the separation zones become relatively smaller, thereby weakening the intensity of the deduced shock wave. Several changes to improve the startup of the wind tunnel are also observed, such as the attachment of the detached shock wave mechanism situated in front of the inlet model and the disappearance of the shock wave/boundary-layer interactions near the lower wall. These changes can reduce total pressure loss in the wind tunnel and prompt the wind tunnel to restart. In conclusion, a sudden increase in total pressure can easily start the wind tunnel. The valve of the wind tunnel should therefore be opened rapidly regardless whether the wind tunnel is in the starting or non-starting procedure.

Serial assessment of endothelial function 1, 6, and 12\xa0months after ST-elevation myocardial infarction

Knowledge about the changes in endothelial function after ST-elevation myocardial infarction (STEMI) is of substantial interest, but serial data are scarce. The aim of the present study was to noninvasively evaluate whether endothelial function, as assessed shortly after primary percutaneous coronary intervention (PPCI) for STEMI, may improve until 12-month follow-up. This prospective observational cohort study was performed in patients in the RESPONSE randomized trial who participated in a substudy and underwent noninvasive assessment of endothelial function at 1 (baseline), 6, and 12-month follow-up after treatment of a STEMI by PPCI. The reactive hyperemia peripheral artery tonometry (RH-PAT) method was used to assess endothelial function (higher RH-PAT index signifies better function). Of the 70 study participants, who were 57.4 ± 9.7 years of age, 55 (78.6%) were male and 9 (13%) had diabetes. The endothelial function deteriorated significantly during follow-up: the RH-PAT index at baseline, 6, and 12-month follow-up was 1.90 ± 0.58, 1.81 ± 0.57, and 1.69 ± 0.49, respectively (p = 0.04). Although patients were carefully treated in outpatient clinics and adequate pharmacological therapy was prescribed, we noted an increase in total cholesterol (p = 0.001), LDL cholesterol (p = 0.002), HbA1C (p = 0.054), and diastolic blood pressure (p = 0.047) However, multivariate analysis revealed that this increase in cardiovascular risk factors could not explain the observed deterioration in endothelial function. In patients with STEMI, we observed a significant deterioration in endothelial function during 12 months after PPCI that could not be explained by changes in the traditional cardiovascular risk profile.

Influence of impurities in propane coolant on the process of obtaining artificial cold

The study of the influence of propane quality on the total pressure of vapors of the coolant in condensation and vaporization processes and on operation of refrigeration equipment was carried out. Research was carried out in the refrigeration department of the industrial combined unit of deparaffination of raffinates and oil removal from gatch. In the experiment, technical propane with the content of the main component of 91–96 % by weight was used as the coolant, the rest was made up by hydrocarbon impurities. To determine the composition of the coolant, chromatographic method for separation of hydrocarbons was used. The impact of propane quality on total pressure of coolant vapor in the refrigeration cycle was determined. Impurities were found to contribute to an increase in total pressure and temperature in evaporation and condensation processes. A decrease in propane content in the coolant from 95 % by weight to 89 % by weight leads to an increase in pressure in condensers from 57 to 86 kPa, in condensers – from 1,385 to 1,524 kPa. At the same time, there is an increase in temperature of evaporation and condensation by 4–5 o С. Contribution of each separate impurity to total pressure of saturated vapors of the coolant in evaporators and condensers was determined. The most harmful impurities are ethane and butane. Ethane and methane under conditions of cold production are in gaseous state and increase total pressure in the refrigeration cycle. The content of methane in the raw material mixture does not exceed 0.03 % by weight, which is why its impact on total pressure is negligible. Butanes form a liquid film on the surface of the equipment, worsen heat exchange processes, and contribute to an increase in the total pressure. Propylene behaves in the system as a coolant and its impact on total pressure is insignificant. The impact of hydrocarbon impurities on operation of refrigeration department was established. The impurities differently affect operation of the equipment, however, on the whole, this impact is negative. An increase in amount of impurities in the coolant contributes to an increase in power consumption of the compressor, worsens compression process and increases consumption of electricity. A decrease in propane content in the raw material mixture from 97 % to 95 % leads to an increase in total thermal loading on the condenser and the refrigerator by 1.7 %. This causes additional material and energy consumption in the course of cold production

Effects of Blade Inlet Angle on Flow Field of Centrifugal Fan

The effects of blade inlet angle on flow rate of centrifugal fan were numerically simulated using CFD software CFX. In this research, a total of six numerical models were prepared by combining different values of blade inlet angle. The frozen rotor method combined with realizable k-epsilon turbulence was used to simulate the three-dimensional flow inside the centrifugal fans. The results show that with the increase of blade inlet angle, its efficiency and output power decrease at small flow rate and increases at large flow. The total pressure and shaft power increase with the increase of blade inlet angle. CFD investigation showed that the blade inlet angle had a strong effect on the flow rate; It is found that the blade inlet angle play an important role for fan performance.

A comprehensive evaluation of the non gray gas thermal radiation using the line-by-line model in one- and two-dimensional enclosures

In oxy-fuel combustion with CO2 recycle, the non-gray gas radiative heat transfer characteristics of gaseous participating media are different from those in air-fuel combustion. Water and carbon dioxide are the most important gas products of combustion under O2/CO2 atmosphere. A line-by-line model with HITEMP2010 database was comprehensively investigated in one- and two-dimensional enclosures containing H2O/CO2/N2 in this study. The radiative transfer equation was solved using the discrete ordinates method. The thermal radiation characteristics of water and carbon dioxide were determined numerically per their non gray radiative characteristics. The line-by-line model, statistical narrow band model, and statistical narrow band correlation-k model were used to run the calculations. The effect of four factors on radiation were accounted for in the line-by-line model: Spectral line resolution, spatial discretization scheme, quadrature, and total pressure. The calculation results showed that spectral line resolution, which varied from 0.02 to 0.08cm−1, has a significant impact on computing time. The total pressure was the most influential factor overall, however. Increase in total pressure from 1 to 10atm significantly enhanced thermal radiation in regards to the magnitude of the local radiative source term.

Prediction of Pressure Drop in Vertical Pneumatic Conveyors

This paper presents a steady state one-dimensional two-fluid model for gas-solid two-phase flow in a vertical riser. The model is solved using conservative variable approach for the gas phase, and fourth order Runge-Kutta method is used for the solid phase. The model predictions for pressure drop are compared with available experimental data and with Eulerian-Lagrangian predictions, and a good agreement is obtained. The results indicate that the pressure drop increases as the solid mass flow rate, particle size, and particles density increase. In addition, the model predictions for minimum pressure drop velocity are compared with experimental data from literature and the mean percentage error. MPE for minimum pressure drop velocity is -9.89%. It is found that the minimum pressure drop velocity increases as the solid mass flow, particle size and particle density increase, and decreases as the system total pressure increases.

Use of high order precursors for manufacturing gate all around devices

Epitaxial growth of strained and defect free SiGe layers grown with disilane and digermane was investigated. This precursors set allows to cover a broad range of Ge concentration (15–65%) at low temperatures (400–550°C). It was shown that change of carrier gas (from H2 to N2) does not increase SiGe growth rate but significantly reduces Ge concentration. Increase of total process pressure considerably reduces SiGe growth rate which is attributed to peculiarities of digermane decomposition and influence of hydrogen surface passivation on disilane decomposition. It was shown that both disilane and digermane can be successfully combined with conventional precursors like silane and germane. These experiments suggested that digermane decomposition is the main driver of the growth rate increase during SiGe growth. Based on the presented data we demonstrated growth of different SiGe/Si and SiGe/Ge stacks with high quality necessary for production of gate all around field effect transistors.

Experimental investigation on flow unsteadiness during spike stall suppression process in an axial compressor via air injection

Stall recovery process for performance enhancement of an axial compressor has been experimentally carried out using air injection at its rotor blade row tip region. Twelve air injectors had been mounted evenly spaced around the compressor casing upstream the rotor blade row. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. These unsteady results, separately presented in frequency and time domains, provided to distinguish stall inception process and consequent flow induced fluctuations. Time-dependent responses of the flow field properties within the compressor passage and progressive alleviation of stall cells are demonstrated during the tip injection process. Blade tip air injection worked effectively and enhanced the compressor stall margin about 9%. This attractive result occurred for the case where the total mass flow rate passing through the air injectors was as small as 0.8% of the compressor main flow rate. In addition, this augmentation in the stall margin was accompanied by increase in the compressor delivery total pressure. Air injection at the blade row tip region caused its beneficial effects to extend throughout the blade whole span, especially while working at the near-stall conditions.

Pressure Regulations on the Surface Properties of CeO2 Nanorods and Their Catalytic Activity for CO Oxidation and Nitrile Hydrolysis Reactions.

Surface properties of nanoscale CeO2 catalysts in terms of the surface Ce(3+) fraction and concentration of oxygen vacancy can affect their catalytic performance significantly. Continual adjustment on surface properties of CeO2 with the morphological preservation has not been realized by synthetic methods. The revisited studies show that surface properties of CeO2 nanorods can be effectively regulated by synthetic pressures while the rodlike morphology is well-preserved. Such phenomena are ascribed to the contact possibility between Ce(3+) species and dissolved O2, which is balanced by the rapidly increased and gradually saturated dissolution/recrystallization rate of Ce(OH)3 and linearly increased concentration of dissolved O2 with the increase of total air pressure or partial pressure of O2. Surface-property-dependent catalytic activity of CeO2 nanorods synthesized under various pressures was also demonstrated in two benchmark reactions-catalytic oxidation of CO and hydrolysis of nitrile. Such a finding of the pressure regulation on the reducible metal oxides provides an effective approach to rationally design novel catalysts for specific reactions, where ceria are supports, promoters, or actives.

Influence of total gas partial pressure on the structural formation of SiC thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were prepared at low temperature using the hot wire chemical vapor deposition from SiH4 and CH4 gases. The SiH4 to CH4 flow rate ratio was kept constant at 0.05 and the effects of total gas partial pressure and the deposition pressure on the structural and compositional properties of the SiC thin films were investigated. The deposition rate of the films increased with the increase in total gas partial pressure but decreased with the increase in deposition pressure. Fourier transforms infrared spectra and X-ray diffraction revealed the formation of nanocrystalline SiC at low total gas partial pressure and high deposition pressure. Only Si-rich amorphous SiC was grown at higher total gas partial pressure as verified by Raman scattering spectroscopy.

Solar fuel production at high temperatures using ceria as a dense membrane

In this paper, ceria was proposed as a candidate material of membrane reactor for solar fuel production. A thermodynamic model of the membrane reactor system based on ceria with heat recovery was established and solar-to-fuel efficiency of both inert gas-assisted and pump-assisted CO2 splitting was calculated under a broad range of conditions. For system using inert gas, gas heat recovery is the determining factor for energy conversion efficiency. The energy efficiency is calculated to be >10% at 1800 K when the oxygen pressure at the inlet of reduction zone is lower than 10−6MPa. Increase of total pressure of the oxidation zone could improve the energy efficiency due to decrease of gas heat loss. Significant promotion in efficiency could be expected when a pump is applied to avoid using inert gas. Solar-to-fuel efficiency could be above 40% assuming good heat recovery. For the membrane reactor with a pump applied to maintain a vacuum atmosphere of the reduction zone, a simplified steady state model was put forward to predict the converting process and estimate the productivity. The diffusion rate of oxygen ions in the membrane is fast enough for conversion of considerable amount of CO2 in the reactor with a limited geometry.

Influence factors on stress corrosion cracking of P110 tubing steel under CO2 injection well annulus environment

Stress corrosion cracking (SCC) behavior of P110 tubing steel in simulated CO2 injection well annulus environments was investigated through three-point bent tests, potentiodynamic polarization and EIS measurements. The results demonstrate that SCC of P110 tubing steel could occur in acidulous simulated environment, and the sensitivity of SCC increases with the decrease of pH, as well as increase of sulfide concentration and total environmental pressure. Both anodic dissolution and hydrogen embrittlement make contributions to the SCC. Adequate concentration of corrosion inhibitor can inhibit the occurrence of SCC on account of the inhibition of localized anodic dissolution and cathodic hydrogen evolution.

NUMERICAL PREDICTION OF AIR-PARTICLES FLOW IN VERTICAL PIPES

This paper presents a steady state one-dimensional two-fluid model for gas-solid two-phase flow in a vertical raiser. The model is solved using conservative variable approach for the gas phase and fourth order Runge-Kutta method is used for the solid phase. The model predictions for pressure drop are compared with available experimental data and with Eulerian-Lagrangian predictions and a good agreement is obtained. The results indicate that the pressure drop increases as the solid mass flow rate, particle size and particles density increase. In addition, the model predictions for minimum pressure drop velocity are compared with experimental data from literature and the mean percentage error, MPE for minimum pressure drop velocity is -9.89%. It is found that the minimum pressure drop velocity increases as the solid mass flow, particle size and particle density increase while it decreases as the system total pressure increases.

Flow in a Y-Intake at Supersonic Speeds

Numerical simulation of the flow in a twin intake via solution to unsteady viscous compressible equations using a stabilized finite-element method has been carried out for various sideslip angles and backpressure ratios. Various flow regimes that are possible in the entire parameter space are identified. They are classified on the basis of shock structure and their locations and the unsteadiness in the flow. Buzz instability is observed in the intake at low system mass rates for nonzero sideslip angles. The onset of buzz is identified by zero mass flow rate in the leeward duct. It is associated with asymmetric movement of the bow shocks upstream of the duct entry. The onset of buzz is accompanied with a loss in static and total pressure recovery and increase in flow distortion. The effect of initial condition is studied. The flow in a certain regime is sensitive to the time history of the backpressure. Hysteresis in the flow as well as in the onset of buzz are observed. The effect of bleed is studied. The amount of bleed and the regions on which it is applied are varied to understand their effect on the performance of the intake. The onset of buzz is delayed with application of bleed.

Effects of polymer stiffness on surface tension and pressure in confinement.

We study the effect of chain rigidity on the behavior of semiflexible polymers in the vicinity of flat walls in a slit, and of surfactants at the liquid-liquid interface between immiscible liquids. Using molecular dynamics simulations, it is demonstrated that the impact of bending angle forces is particularly strong within the depletion layer at the phase boundary whereas at distance Re away from the interface, where Re is the mean distance between the ends of a semiflexible chain, the contribution of these non-local triplet interactions to pressure tensor virtually disappears. The present study also demonstrates that growing stiffness of the macromolecules leads to an increase in surface tension and total pressure.