Simple Model for Gas Holdup and Liquid Velocity of Annular Photocatalytic External-Loop Airlift Reactor Under both Bubble and Developing Slug Flow

Based on the momentum conservation approach, a theoretical model was developed to predict the superficial liquid velocity, and a correlation equation was established to calculate the gas holdup of an annular external-loop airlift reactor(AELAR)in the bubble flow and developing slug flow pattern. Experiments were performed by using tap-water and silicone oil with the viscosity of 2.0 mm^2/s(2cs-SiO)and 5.0 mm^2/s(5cs-SiO)as liquid phases. The effects of liquid viscosity and flow pattern on the AELAR performance were investigated. The predictions of the proposed model were in good agreement with the experimental results of the AELAR. In addition, the comparison of the experimental results shows that the proposed model has good accuracy and could be used to predict the gas holdup and liquid velocity of an AELAR operating in bubble and developing flow pattern.

Annular multiphase flow behavior during deep water drilling and the effect of hydrate phase transition

It is very important to understand the annular multiphase flow behavior and the effect of hydrate phase transition during deep water drilling. The basic hydrodynamic models, including mass, momentum, and energy conservation equations, were established for annular flow with gas hydrate phase transition during gas kick. The behavior of annular multiphase flow with hydrate phase transition was investigated by analyzing the hydrate-forming region, the gas fraction in the fluid flowing in the annulus, pit gain, bottom hole pressure, and shut-in casing pressure. The simulation shows that it is possible to move the hydrate-forming region away from sea floor by increasing the circulation rate. The decrease in gas volume fraction in the annulus due to hydrate formation reduces pit gain, which can delay the detection of well kick and increase the risk of hydrate plugging in lines. Caution is needed when a well is monitored for gas kick at a relatively low gas production rate, because the possibility of hydrate presence is much greater than that at a relatively high production rate. The shut-in casing pressure cannot reflect the gas kick due to hydrate formation, which increases with time.

An integrated approach to study of strata behaviour and gas flow dynamics and its application

This paper presents an advanced and integrated research approach to longwall mining-induced strata move- ment, stress changes, fractures, and gas flow dynamics with actual examples of its application from recent studies for coextraction of coal and methane development at Huainan Mining Group in China, in a deep and multi-seam mining environment. The advanced approach takes advantage of the latest techniques in Australia for mine scale geotechnical characterisation, field measurement, monitoring and numerical modelling. Key techniques described in this paper include coal mine site 3D geotechnical characterisation methods, surface deep downhole multi-point extensometers and piezometers for overburden displacement and pore pressure measurements during mining, tracer gas tests for goal gas flow patterns, and advanced numerical modelling codes for coupled coal mine strata, water and gas simulations, and longwall goaf gas ttow investigations. This integrated approach has resulted in significant insights into the complex dynamic imeraction between strata, groundwater, and gas during mining at Huainan Mining Group in recent years. Based on the lindings from the extensive field monitoring and numerical modelling studies, a three-dimensional annular-shaped over-lying zone along the perimeter of the longwall panel was identified for optimal methane drainage during mining.

Design and Atomization Characteristic of Laval-style Annular Slot Nozzle

Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.

Effects of Gas Flow Field on Clogging Phenomenon in Close-Coupled Vortical Loop Slit Gas Atomization

In order to study the basic characteristics of gas flow field in the atomizing chamber near the nozzle outlet of the vortical loop slit atomizer and its influence mechanism on clogging phenomenon,the computational fluid dynamics(CFD)software Fluent is used to conduct a numerical simulation of the gas flow field in the atomizing chamber near the nozzle outlet of this atomizer under different annular slit widths,different atomization gas pressures and different protrusion lengths of the melt delivery tube. The results show that under atomization gas pressure p=4.5 MPa,the greater the annular slit width D,the lower the static temperature near the central hole outlet at the front end of the melt delivery tube,and the smaller the aspirating pressure at the front end of the melt delivery tube. These features can effectively prevent the occurrence of the clogging phenomenon of metallic melt. Under an annular slit width of D=1.2 mm,when the atomization gas pressure satisfies 1 MPa ≤ p ≤ 2 MPa and increases gradually,the aspirating pressure at the front end of the melt delivery tube will decline rapidly. This can prevent the clogging phenomenon of metallic melt. However,when the atomization gas pressure p >2 MPa,the greater the atomization gas pressure,the lower the static temperature near the central hole outlet at the front end of the melt delivery tube,and the greater the aspirating pressure at the front end of the melt delivery tube. Hence,the effect of preventing the solidification-induced clogging phenomenon of metallic melt is restricted. When atomization gas pressure is p =4.5 MPa and annular slit width is D=1.2 mm,the greater the protrusion length H of the melt delivery tube,and the smaller the aspirating pressure at its front end. The static temperature near the central hole that can be observed in its front end is approximate to effectively prevent the occurrence of clogging phenomenon of metallic melt. However,because of the small aspirating pressure,the metallic melt flows into the atomizing chamber from the central hole at the front end of the melt delivery tube at an increasing speed and the gas-melt ratio in the mass flow rate is reduced,which is not conducive to the improvement of atomization performance.

Rotational Flow in a Narrow Annular Gap Based on Lattice Boltzmann Method

For comprehensive characteristics of flow in a gas bearing,lattice Boltzmann method(LBM)is applied for study of the two-dimensional flow between two eccentric cylinders with the inner one rotating at a high speed.The flow pattern and circumferential pressure distribution are discussed based on critical issues such as eccentricity ranging from 0.2 to 0.9,clearance ratio varying from 0.005 to 0.01 and rotating speed in the range of 3×104—1.8×105 r/min.The analysis and discussion on the circumferential pressure distribution affirmed the quasilinear relation between the extremum pressure and rotating speed.Furthermore,a high eccentricity and small clearance ratio contributes most to the fluctuation of the circumferential pressure distribution.The flow pattern inside the channel exhibits separation vortex under a large eccentricity.The conclusions drawn in this work give rise to prediction of the flow pattern in the gas bearing which is beneficial for evaluating the performance of as well as instructing the design and development.

Numerical analyses and experiment investigations of an annular micro gas turbine power system using fuels with low heating values

This study investigates the effects of using fuels with low heating values on the performance of an annular micro gas turbine(MGT)experimentally and numerically.The MGT used in this study is MW-54, whose original fuel is liquid(Jet A1).Its fuel supply system is re-designed to use biogas fuel with low heating value(LHV).The purpose is to reduce the size of a biogas distributed power supply system and to enhance its popularization.This study assesses the practicability of using fuels with LHVs by using various mixing ratios of methane(CH4)and carbon dioxide(CO2).Prior to experiments,the corresponding simulations,aided by the commercial code CFD-ACE+,were carried out to investigate the cooling effect in a perforated combustion chamber and combustion behavior in an annular MGT when LHV gas was used.The main purposes are to confirm that there are no hot spots occurring in the liners and the exhaust temperatures of combustor are lower than 700°C when MGT is operated under different conditions.In experiments,fuel pressure and mass flow rate,turbine rotational speed,generator power output,and temperature distribution were measured to analyze MGT performance.Experimental results indicate that the presented MGT system operates successfully under each tested condition when the minimum heating value of the simulated fuel is approximately 50%of pure methane.The power output is around 170 W at 85000 r/min as 90%CH4 with 10%CO2 is used and 70 W at 60000 r/min as 70%CH4 with 30%CO2 is used.When a critical limit of 60%CH4 is used,the power output is extremely low. Furthermore,the best theoretical Brayton cycle efficiency for such MGT is calculated as 23%according to the experimental data while LHV fuel is used.Finally,the numerical results and experiment results reveal that MGT performance can be improved further and the possible solutions for performance im- provement are suggested for the future studies.

Design and analysis of annular combustion chamber of a low bypass turbofan engine in a jet trainer aircraft

The design of an annular combustion chamber in a gas turbine engine is thebackbone of this paper.It is specifically designed for a low bypass turbofan engine in a jettrainer aircraft.The combustion chamber is positioned in between the compressor and turbine.lt has to be designed based on the constant pressure,enthalpy addition process.The presentmethodology deals with the computation of the initial design parameters from benchmarking ofreal-time industry standards and arriving at optimized values.It is then studied for feasibilityand finalized.Then the various dimensions of the combustor are calculated based on differentempirical formulas.The air mass flow is then distributed across the zones of the combustor.The cooling requirement is met using the cooling holes.Finally the variations of parameters atdifferent points are calculated.The whole combustion chamber is modeled using Siemens NX8.0,a modeling software and presented.The model is then analyzed using various parametersat various stages and levels to determine the optimized design.The aerodynamic flowcharacteristics is simulated numerically by means of ANSYS 14.5 software suite.The air-fuelmixture,combustion-turbulence,thermal and cooling analysis is carried out.The analysis isperformed at various scenarios and compared.The results are then presented in image outputsand graphs.

Numerical simulation on gas–liquid multiphase flow behavior under coupling effects of annular gas curtain and swirling flow at tundish upper nozzle

A three-dimensional mathematical model has been established for a novel metallurgy process coupling an annular gas curtain with swirling flow at tundish upper nozzle. The discrete phase model and volume of fluid model were applied to simulate the gas–liquid multiphase flow behavior in tundish and nozzle. The effect of argon flow rate on the migration behavior of bubbles and interface behavior between steel and slag was also investigated. The presented results indicate that the novel coupling process can significantly change the flow pattern in the stream zone of a tundish, prolong the average residence time of liquid steel, and reduce the dead fraction. A complete annular gas curtain is formed around the stopper rod of tundish. Under the action of drag force of liquid steel, a part of small bubbles enter the nozzle through the swirling grooves and gather toward the center of the nozzle by centripetal force. As the argon flow rate increases, the volume fraction of argon gas entering the nozzle increases, which enhances the swirl intensity and increases the concentration of bubbles in the nozzle. To avoid the formation of slag open eye in tundish, the argon flow rate should not exceed 8 L min−1.

A simple analytical model to predict liquid unloading in the horizontal gas well

An accurate prediction of the critical gas velocity for the liquid loading is of great importance for operators to select the tubing diameter for the newly drilled gas wells,or to optimize the production rate for production wells.It is clear from previous experimental studies of the liquid entrainment rate in the gas core that the liquid is mainly carried in the form of film under the critical condition of the liquid loading onset.It is more reasonable to establish a mathematical model based on the film reversal rather than based on the droplet reversal.In our previous paper entitled“Prediction of the critical gas velocity of liquid unloading in the horizontal gas well”,a new analytical model was established based on the force balance between the gas-liquid interfacial friction force and the bottom film gravity,but the model is not very convenient to use because of the complexity of calculating the average film thickness.In the present study,a new method is proposed to calculate the average film thickness from the bubble drift velocity in the mixture,so the new analytical model becomes much easier to use.The new analytical model is evaluated against 103 sets of experimental data,the data in 124 vertical gas wells and one horizontal gas well.Meanwhile,the effect ofthe liquid loading on the production of the horizontal gas well is also analyzed.

Comprehensive Mathematical Model for Coal Combustion in a Circulating Fluidized Bed Combustor

Char combustion is on a special reducing condition in the dense bed of a circulating fluidized bed combustor. Experimental findings were used to develop a comprehensive mathematical model to simulate the hydrodynamic and combustion processes in a circulating fluidized bed combustor. In the model, gas solid interaction was used to account for the mass transfer between the bubble phase and the emulsion phase in the dense bed, which contributes to the reducing atmosphere in the dense bed. A core annular structure was assumed in the dilute area rather than a one dimensional model. The submodels were combined to build the comprehensive model to analyze the combustion in a circulating fluidized bed combustor and the effect of operating parameters on the coal combustion. The model predictions agree well with experimental results.