Computational Fluid Dynamics （CFD） has become an alternative method to experiments for understanding the fluid dynamics of multiphase flow. A two-fluid model, which contains additional terms in both the gas- and sol...Computational Fluid Dynamics （CFD） has become an alternative method to experiments for understanding the fluid dynamics of multiphase flow. A two-fluid model, which contains additional terms in both the gas- and solid-phase momentum equations, is used to investigate the fluidization quality in a fluidized bed. A case study for quartz sand with a density of 2,660 kg/m^3 and a diameter of 500 μm, whose physical property is similar to a new kind of catalyst for producing clean fuels through the residue fluid catalytic cracking process, is simulated in a two-dimensional fluidized bed with 0.57 m width and 1.00 m height. Transient bubbling and collapsing characteristics are numerically investigated in the platform of CFX 4.4 by integrating user-defined Fortran subroutines. The results show that the fluidization and collapse process is in fair agreement with the classical theory of Geldart B classification, but the collapse time is affected by bubbles at the interface between the dense phase and freeboard.展开更多
Turbidity currents represent a major agent for sediment transport in lakes, seas and oceans. In particu-lar, they formulate the most significant clastic accumulations in the deep sea, which become many of the world＇s...Turbidity currents represent a major agent for sediment transport in lakes, seas and oceans. In particu-lar, they formulate the most significant clastic accumulations in the deep sea, which become many of the world＇s most important hydrocarbon reservoirs. Several boreholes in the Qiongdongnan Basin, the north-western South China Sea, have recently revealed turbidity current deposits as significant hydrocarbon res-ervoirs. However, there are some arguments for the potential provenances. To solve this problem, it is es-sential to delineate their sedimentary processes as well as to evaluate their qualities as reservoir. Numerical simulations have been developed rapidly over the last several years, offering insights into turbidity current behaviors, as geologically significant turbidity currents are difficult to directly investigate due to their large scale and often destructive nature. Combined with the interpretation of the turbidity system based on high-resolution 3D seismic data, the paleotophography is acquired via a back-stripping seismic profile integrated with a borehole, i.e., Well A, in the western Qiongdongnan Basin; then a numerical model is built on the basis of this back-stripped profile. After defining the various turbidity current initial boundary conditions, includ-ing grain size, velocity and sediment concentration, the structures and behaviors of turbidity currents are investigated via numerical simulation software ANSYS FLUENT. Finally, the simulated turbidity deposits are compared with the interpreted sedimentary bodies based on 3D seismic data and the potential provenances of the revealed turbidites by Well A are discussed in details. The simulation results indicate that a sedimen-tary body develops far away from its source with an average grain size of 0.1 mm, i.e., sand-size sediment. Taking into account the location and orientation of the simulated seismic line, the consistence between normal forward simulation results and the revealed cores in Well A indicates that the turbidites should have been transported from Vietnam instead of Hainan Island. This interpretation has also been verified by the planar maps of sedimentary systems based on integration of boreholes and seismic data. The identification of the turbidity provenance will benefit the evaluation of extensively distributed submarine fans for hydro-carbon exploration in the deepwater areas.展开更多
A simple hydrodynamic model based on two-fluid theory, taking into account the effect of discrete particles on both the gas- and solid-phase momentum equations, was used to numerically investigate the pressure fluctua...A simple hydrodynamic model based on two-fluid theory, taking into account the effect of discrete particles on both the gas- and solid-phase momentum equations, was used to numerically investigate the pressure fluctuation characteristics in a gas-solid fluidized bed with the aid of CFX 4.4, a commercial CFD software package, by adding user-defined Fortran subroutines. Numerical simulations together with typical experimental measurements show that pressure fluctuations originate above the distributor when a gas pulse is injected into the fluidized bed. The pressure above the bubble gradually increases due to the presence of a rising bubble. When the bubble passes through the bed surface, the pressure near the bed surface gradually decreases to a lower value. Moreover, the pressure signals in the bubbling fluidized beds show obviously periodic characteristics. The major frequency of pressure fluctuations at the same vertical position is affected slightly by the operating gas velocity, and the amplitude of pressure fluctuations is related to both the operating gas velocity and the vertical height. In this study, the influence of the operating gas velocity on the pressure wave propagation velocity can be ignored, and only two peak frequencies in the power spectrum of the pressure fluctuations are observed which are associated with the bubble formation above the distributor and its eruption at the bed surface.展开更多
Heat exchangers play an important role in supercritical water coal gasification systems for heating feed and cooling products. However, serious deposition and plugging problems always exist in heat exchangers. CFD mod...Heat exchangers play an important role in supercritical water coal gasification systems for heating feed and cooling products. However, serious deposition and plugging problems always exist in heat exchangers. CFD modeling was used to simulate the transport characteristics of solid particles in supercdtical water through the shell and tube of heat exchangers to alleviate the problems. In this paper, we discuss seven types of exchangers CA, B, C D, E, F and G）, which vary in inlet nozzle configuration, header height, inlet pipe diameter and tube pass distribution. In the modeling, the possibility of deposition in the header was evaluated by accumulated mass of particles; we used the velocity contour of supercritical water （SCW） to evaluate the uniformity of the velocity dis- tribution among the tube passes. Simulation results indicated that the optimum heat exchanger had structure F, which had a rectangular configuration of tube pass distractions, a bottom inlet, a 200-mm header height and a 10-ram inlet pipe diameter.展开更多
A new quenching process using the cold pyrolysis gas has been proposed for the partial oxidation(POX) of methane to recover the heat. The mixing of hot product gas and cold pyrolysis gas in milliseconds is critical to...A new quenching process using the cold pyrolysis gas has been proposed for the partial oxidation(POX) of methane to recover the heat. The mixing of hot product gas and cold pyrolysis gas in milliseconds is critical to this new approach. Two most widely-used rapid mixing configurations, i.e. the jet-in-cross-flow(JICF) and impinging flow configurations, are compared in terms of mixing and quenching performances using computational fluid dynamics(CFD) coupled with detailed reaction mechanism Leeds 1.5. The mixedness, residence time distribution, temperature decreasing rate and loss ratio of acetylene during the quenching are systematically studied. The results show that the impinging flow has a more uniform mixing and narrower residence time distribution than the JICF.However, the temperature decreasing rate of the mainstream is faster in the JICF than in the impinging flow. The loss ratio of acetylene in the quenching process is 2.89% for the JICF and 1.45% for the impinging flow, showing that the impinging flow configuration is better and feasible for the quenching of POX of methane.展开更多
Flow passages in vortex pumps usually have rough walls.Precise consideration of wall roughness is an important issue in pump flow simulations.Numerical studies of the effects of wall roughness on the performance of vo...Flow passages in vortex pumps usually have rough walls.Precise consideration of wall roughness is an important issue in pump flow simulations.Numerical studies of the effects of wall roughness on the performance of vortex pumps are quite rare,especially with different interface models.Turbulent flows of water in a vortex pump with a specific speed of 76 are simulated using 1/8 and whole impeller fluid domains with rough walls,using the three-dimensional Reynolds-averaged Navier-Stokes equations,the standard k-εmodel,and a scalable wall function in Ansys CFX 2019 R2.Equivalent sand grain roughnesses k_(s)=0.586 and 9.38μm are determined for the chamber casing,volute,and suction pipe,and k_(s)=18.47 and 36.94μm for the impeller by using the arithmetic average roughness Ra of the materials used in the pump and the correlation between k_(s)and Ra given in the literature.The mixing loss along the interface between impeller and volute in the transient rotor model is determined.The rates of change of the head,shaft-power,and efficiency of the pump due to wall roughness are calculated.The transient rotor model with whole impeller domain and the frozen rotor model with 1/8 impeller domain for rough walls with Ra=0.1μm in the suction pipe,volute,and chamber and 3.2μm in the impeller give the most accurate predictions of pump performance compared with experimental data.The transient rotor model with whole impeller domain gives more accurate predictions of pump performance than the frozen rotor model with 1/8 impeller domain.The mixing loss rises quickly at high flow rates.The transient rotor model with whole impeller domain gives plausible predictions of the rates of change.展开更多
The internal structure of electric desalting vessels is an important factor affecting the performance of crude oil dehydration and desalination.The flow and distribution of oil-water emulsions are generally not fully ...The internal structure of electric desalting vessels is an important factor affecting the performance of crude oil dehydration and desalination.The flow and distribution of oil-water emulsions are generally not fully considered in the traditional design of a desalter.Computational fluid dynamics(CFD)simulations enable a deep understanding of oil-water two-phase flows,thereby providing a scientific basis for optimizing structural design of desalters.In this paper,CFD simulations are used to study the flow of oil-water two-phase fluid in a desalting vessel with advection squirrel-cage structure in a SINOPEC refinery,revealing the defects in its electric field layout.A structural improvement scheme is then proposed,and a medium-scale bypass test is conducted.The test results show that the single-stage salt removal rate is increased from 85.4%to 92.1%.The water and salt contents in desalted oil and the oil content in brine are also significantly improved,providing a solid foundation for transformation of the related industrial equipment.展开更多
As a renewable energy source,the thermal conversion of poultry manure,is a promising waste treatment solution that can generate circular economic outputs such as energy and reduce greenhouse gas emissions.Currently,pr...As a renewable energy source,the thermal conversion of poultry manure,is a promising waste treatment solution that can generate circular economic outputs such as energy and reduce greenhouse gas emissions.Currently,pressurized gasification of poultry manure is still a novel research field,especially when combined with a novel technological route of oxy-fuel gasification.Oxy-fuel gasification is a newly proposed and promising gasification technology for power generation that facilitates future carbon capture and storage.In this work,based on a commercially operated industrial-scale chicken manure gasification power plant in Singapore,we presented an interesting first exploration of the coupled pressurization technology for oxy-fuel gasification of poultry manure using CFD numerical simulation,analyzed the effects of pressure and oxygen enrichment concentration as well as the coupling mechanism between them,and discussed the conversion and emission of nitrogen-and sulfur-containing pollutants.The results indicate that under oxy-fuel gasification condition(Oxy-30,i.e.,30%O_(2)/70%CO_(2)),as the pressure increases from 0.1 to 0.5 MPa,the CO concentration in the syngas increases slightly,the H_(2)concentration increases to approximately 25%,and the CH4 concentration(less than 1%)decreases,resulting in an increase in the calorific value of syngas from 5.2 to 5.6 MJ·m^(-3).Compared to atmospheric pressure conditions,a relatively higher oxygen-enriched concentration interval(Oxy-40 to Oxy-50)under pressurized conditions is advantageous for autothermal gasification.Pressurization increases NO precursors production and also promotes homogeneous and heterogeneous reduction of NO,and provides favorable conditions for self-desulfurization.This work offers reference for the realization of a highly efficient and low-energy-consumption thermochemical treatment of livestock manure coupled with negative carbon emission technology.展开更多
The article is an attempt to compile the results of CFD liquid flow simulation through pipeline section containing hydraulic elbow with the results of ultrasonic flow measurements. To carry out the measurements behind...The article is an attempt to compile the results of CFD liquid flow simulation through pipeline section containing hydraulic elbow with the results of ultrasonic flow measurements. To carry out the measurements behind the flow disturbing element(hydraulic elbow), an ultrasonic flowmeter with applied head set in accordance with the Z-type system was used. For comparative purposes, a flow simulation for 3 different turbulence models(k-epsilon, SST and SSG) was performed. It was found that with a proper ultrasonic flowmeter heads configurations, it is possible to measure the flow rate disturbed by the hydraulic elbow at any distance from the source of the disturbance. It has to use appropriate correction factor that can be determined by knowing the flow velocity profile equation. Based on comparison of CFD simulation results with experimental data, the accuracy/purposefulness of using individual turbulence models in the case of discussed hydraulic installation was evaluated.展开更多
Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of orien...Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes.The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data,and built in UDF for simulation.The flow pattern of oriented valve tray under different operating conditions was simulated under Eulerian-Eulerian framework with realizable k-ε model.The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations.Meanwhile,the velocity distribution and volume fraction of the two phases were demonstrated and analyzed,which are useful in design and analysis of the column trays.展开更多
Particle suspension characteristics are predicted computationally in a stirred tank driven by a Smith turbine. In order to verify the hydrodynamic model and numerical method, the predicted power number and flow patter...Particle suspension characteristics are predicted computationally in a stirred tank driven by a Smith turbine. In order to verify the hydrodynamic model and numerical method, the predicted power number and flow pattern are compared with designed values and simulated results from the literature, respectively. The effects of particle density, particle diameter, liquid viscosity and initial solid loading on particle suspension behavior are investigated by using the Eulerian-Eulerian two-fluid model and the standard k-ε turbulence model. The results indicate that solid concentration distribution depends on the flow field in the stirred tank. Higher particle density or larger particle size results in less homogenous distribution of solid particles in the tank. Increasing initial solid loading has an adverse impact on the homogeneous suspension of solid particles in a low-viscosity liquid, whilst more uniform particle distribution is found in a high-viscosity liquid.展开更多
In order to explore the performance of the B-ULV-616A knapsack sprayer,computational fluid dynamics(CFD)was used to simulate the B-ULV-616A knapsack air-assisted device,which features an ultra-low-volume electric spra...In order to explore the performance of the B-ULV-616A knapsack sprayer,computational fluid dynamics(CFD)was used to simulate the B-ULV-616A knapsack air-assisted device,which features an ultra-low-volume electric sprayer.Field experiments were carried out to test the spraying effects,and the KANOMAX anemometer was used to verify the simulated results.First,the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established.The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device.The high-speed airflow(maximum of 83.5 m/s)generates negative pressure(minimum of 0.099 MPa)and causes a rapid increase in the droplet velocity and a secondary droplets spray,allowing droplets to reach a longer distance.Then,the maximum relative error was 20.14%,and its average value was 9.59%,indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device.Finally,based on the greenhouse experiment,the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop,increase the droplet density(maximum of 81/cm2;droplet density of conventional electric sprayer is 64/cm2),and reduce the deposition amount and coefficient of variation(below 20%)within and between regions.Further,it managed to reduce pesticide use(by 69.85%)and rural non-point source pollution.展开更多
This study proposed a comprehensive evaluation system to incorporate the contribution of both numerical simulation and statistical decision theory in ventilation performance assessment.A high-resolution model based on...This study proposed a comprehensive evaluation system to incorporate the contribution of both numerical simulation and statistical decision theory in ventilation performance assessment.A high-resolution model based on the finite volume approach was established to analyze the influence of rotation angles(i.e.,side vent flip angle and roof vent flip angle)of the rack-and-pinion ventilated structure on the greenhouse microclimate.The water circulating system and tomato seeding canopies were considered.Heat removal efficiency and mean age of air were employed as quantitative attributes to reflect the internal thermal environment and the airflow organization in the sliding cover solar greenhouse.The simulation model was verified with the temperature profile measured and the average relative error was 1.74%.The results demonstrate that the rotating angles of ventilation schemes have a substantial impact on the microclimate and inhomogeneity of the tomato seeding canopies.The results suggest the average velocity and its inhomogeneity are the crucial predictors,and their entropy weight values are 0.231 and 0.218,respectively.The relative degree of membership of the side vent flip angle of 45°is 36%and 97%higher than that of the side vent flip angle of 35°and the side vent flip angle of 25°,respectively.This study can provide a reference to evaluate the ventilated strategies of the sliding cover solar greenhouse for the regional and central government.展开更多
The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-in...The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-induced buoyancy.However,the wind effect is not well understood as it is often neglected in previous studies.The present study investigates the properties of such airflows,including the flow pattern,flow regime,and flow rate,using a CFD method.The target building is a large-span commercial building with a low-pitched roof.To study the wind-induced airflows,the onset atmospheric boundary layer wind flow was modelled,and the results were compared with the site-measured data recorded in the literature.To study the thermal-induced buoyancy effects,a roof cavity model found in the literature with experimental data was adopted.The findings show that the flow pattern in the roof cavity varied with the airflow driven factors.The flow separation at the windward eave inlet of the thermally induced flows are more pronounced compared with those of the wind-induced flows.Furthermore,the wind-induced airflows can generate around two times more ventilation flow rate through the roof cavity compared to the thermal-induced airflow.The findings indicate that wind-induced ventilation flows are the dominant factor of the roof cavity ventilation in a large-span,low-pitched building.展开更多
Industrial Flares are important safety devices to bum off the unwanted gas during process startup, shutdown, or upset. However, flaring, especially the associated smoke, is a symbol of emissions from refineries, oil g...Industrial Flares are important safety devices to bum off the unwanted gas during process startup, shutdown, or upset. However, flaring, especially the associated smoke, is a symbol of emissions from refineries, oil gas fields, and chemical processing plants. How to simultaneously achieve high combustion efficiency （CE） and low soot emission is an important issue. Soot emissions are influenced by many factors. Flare operators tend to over-steam or over-air to suppress smoke, which results in low CE. How to achieve optimal flare performance remains a question to the industry and the regulatory agencies. In this paper, regulations in the US regarding flaring were reviewed. In order to determine the optimal operating window for the flare, different combus- tion mechanisms related to soot emissions were summar- ized. A new combustion mechanism （Vsoot） for predicting soot emissions was developed and validated against experimental data. Computational fluid dynamic （CFD） models combined with Vsoot combustion mechanism were developed to simulate the flaring events. It was observed that simulation results agree well with experimental data.展开更多
The study presented hereby investigates experimentally and with CFD simulations the gas distribution effect on the hydrodynamic of a Geldart Group A turbulent fluidized bed. Experiments were carried out on a cold flow...The study presented hereby investigates experimentally and with CFD simulations the gas distribution effect on the hydrodynamic of a Geldart Group A turbulent fluidized bed. Experiments were carried out on a cold flow fluidized bed column with an even and uneven gas distribution. Local solid volume fraction profiles were measured using optical probes at different bed heights and along two radial directions. Optical probe measurements allow catching a clear hydrodynamic difference between both even and uneven gas distributions. These results were then used to assess CFD simulations with the code Barracuda^(TM) (MP-PIC approach). It is noteworthy that the choice of drag correlation and boundary conditions strongly influences the agreement between the experimental and CFD results. Once the correct parameters are chosen, CFD simulations captured the effect of gas distribution changes.展开更多
In this study, a new mass model involving superheat, initial temperature, liquid height, evaporator diameter, and flashing time is established to describe the flash evaporation process of water film. Of 469 sets of fl...In this study, a new mass model involving superheat, initial temperature, liquid height, evaporator diameter, and flashing time is established to describe the flash evaporation process of water film. Of 469 sets of flash experimental data from three previous researches, 305 sets were applied to optimize parameters, and the other 164 sets were used to verify the practicability of the model. The results showed that the mean relative error between the literature data and the model values was less than 16.3%, and the model statistics proved that the model was well-posed. Then, the kinetic model was obtained using the time derivative of the new mass model. Computational fluid dynamics simulation of water film flash evaporation was studied based on a user-defined function program of the new evaporation kinetic model. The new kinetic model shows more consistency with the experimental phenomena in terms of evaporated mass and temperature compared with the evaporation–condensation model in Fluent software and Gopalakrishna's model. This new kinetic model can be extended to describe the flash process of water solution under other conditions.展开更多
The building parameters of Chinese solar greenhouse(CSG)directly affect the front roof lighting and indoor thermal environment.In order to obtain the optimal parameter combination,a building parameter optimization met...The building parameters of Chinese solar greenhouse(CSG)directly affect the front roof lighting and indoor thermal environment.In order to obtain the optimal parameter combination,a building parameter optimization method based on computational fluid dynamics(CFD)simulation and entropy weight method was proposed.Firstly,a three-dimensional thermal and humidity environment model of CSG was constructed considering the coupling effect of soil,crop,and back wall based on CFD.The reliability of the model was validated through experiments in a CSG of Yongqing County,Hebei Province of China.Then,the indoor air temperature rise rate,air temperature and humidity uneven coefficient,and average air temperature and humidity were selected as the evaluation indicators of CSG thermal and humidity environment.The ridge height,back wall height and the horizontal projection of back roof of CSG were selected as the three factors of the orthogonal test plan,and a three-factor and four-level plan was designed,resulting in 16 different parameter combinations.By use of CFD simulation,the thermal and humidity environment evaluation indicators under different parameter combinations were calculated.The entropy weight method was used to assign weights to the evaluation indicators,and the comprehensive evaluation indicators of CSG thermal and humidity environment were obtained based on the linear weighting principle.By comparing comprehensive evaluation indicators,the optimal combination of building parameters was obtained with a ridge height of 5.72 m,a back wall height of 3.2 m,and a horizontal projection of 2.1 m on the back roof.The research results can provide a practical and feasible method for optimizing the building parameters of CSG,and provided theoretical guidance for the structural design and optimization of CSG.展开更多
This paper represents a detailed and systematic review of one of the most ongoing applications of computational fluid dynamics(CFD)in biomedical applications.Beyond its various engineering applications,CFD has started...This paper represents a detailed and systematic review of one of the most ongoing applications of computational fluid dynamics(CFD)in biomedical applications.Beyond its various engineering applications,CFD has started to establish a presence in the biomedical field.Cardiac abnormality,a familiar health issue,is an essential point of investigation by research analysts.Diagnostic modalities provide cardiovascular structural information but give insufficient information about the hemodynamics of blood.The study of hemodynamic parameters can be a potential measure for determining cardiovascular abnormalities.Numerous studies have explored the rheological behavior of blood experimentally and numerically.This paper provides insight into how researchers have incorporated the pulsatile nature of the blood experimentally,numerically,or through various simulations over the years.It focuses on how machine learning platforms derive outputs based on mass and momentum conservation to predict the velocity and pressure profile,analyzing various cardiac diseases for clinical applications.This will pave the way toward responsive AI in cardiac healthcare,improving productivity and quality in the healthcare industry.The paper shows how CFD is a vital tool for efficiently studying the flow in arteries.The review indicates this biomedical simulation and its applications in healthcare using machine learning and AI.Developing AI-based CFD models can impact society and foster the advancement towards responsive AI.展开更多
Field emission electric propulsion(FEEP) thrusters possess excellent characteristics, such as high specific impulse, low power requirements, compact size and precise pointing capabilities,making them ideal propulsion ...Field emission electric propulsion(FEEP) thrusters possess excellent characteristics, such as high specific impulse, low power requirements, compact size and precise pointing capabilities,making them ideal propulsion devices for micro-nano satellites. However, the detection of certain aspects, such as the evolution process of the liquid cone and the physical quantities at the cone apex, proves challenging due to the minute size of the needle tip and the vacuum environment in which they operate. Consequently, this paper introduces a computational fluid dynamics(CFD) model to gain insight into the formation process of the liquid cone on the tip apex of indium FEEP. The CFD model is based on electrohydrodynamic(EHD) equations and the volume of fluid(VOF) method. The entire cone formation process can be divided into three stages, and the time-dependent characteristics of the physical quantities at the cone apex are investigated. The influences of film thickness, apex radius size and applied voltage are compared.The results indicate a gradual increase in the values of electrostatic stress and surface tension stress at the cone apex over an initial period, followed by a rapid escalation within a short duration.Apex configurations featuring a small radius, thick film and high voltage exhibit a propensity for liquid cone formation, and the cone growth time decreases as the film thickness increases.Moreover, some unstable behavior is observed during the cone formation process.展开更多
基金support from the Major State Basic Research Development Program of China (973 Program,2005CB221205)National Natural Science Foundation of China (No.20490200 and 20576076)
文摘Computational Fluid Dynamics （CFD） has become an alternative method to experiments for understanding the fluid dynamics of multiphase flow. A two-fluid model, which contains additional terms in both the gas- and solid-phase momentum equations, is used to investigate the fluidization quality in a fluidized bed. A case study for quartz sand with a density of 2,660 kg/m^3 and a diameter of 500 μm, whose physical property is similar to a new kind of catalyst for producing clean fuels through the residue fluid catalytic cracking process, is simulated in a two-dimensional fluidized bed with 0.57 m width and 1.00 m height. Transient bubbling and collapsing characteristics are numerically investigated in the platform of CFX 4.4 by integrating user-defined Fortran subroutines. The results show that the fluidization and collapse process is in fair agreement with the classical theory of Geldart B classification, but the collapse time is affected by bubbles at the interface between the dense phase and freeboard.
基金The National Science and Technology Major Project of China under contract No.2011ZX05025-002-02the National Natural Science Foundation of China under contract Nos 41476032,91028009 and 40806019
文摘Turbidity currents represent a major agent for sediment transport in lakes, seas and oceans. In particu-lar, they formulate the most significant clastic accumulations in the deep sea, which become many of the world＇s most important hydrocarbon reservoirs. Several boreholes in the Qiongdongnan Basin, the north-western South China Sea, have recently revealed turbidity current deposits as significant hydrocarbon res-ervoirs. However, there are some arguments for the potential provenances. To solve this problem, it is es-sential to delineate their sedimentary processes as well as to evaluate their qualities as reservoir. Numerical simulations have been developed rapidly over the last several years, offering insights into turbidity current behaviors, as geologically significant turbidity currents are difficult to directly investigate due to their large scale and often destructive nature. Combined with the interpretation of the turbidity system based on high-resolution 3D seismic data, the paleotophography is acquired via a back-stripping seismic profile integrated with a borehole, i.e., Well A, in the western Qiongdongnan Basin; then a numerical model is built on the basis of this back-stripped profile. After defining the various turbidity current initial boundary conditions, includ-ing grain size, velocity and sediment concentration, the structures and behaviors of turbidity currents are investigated via numerical simulation software ANSYS FLUENT. Finally, the simulated turbidity deposits are compared with the interpreted sedimentary bodies based on 3D seismic data and the potential provenances of the revealed turbidites by Well A are discussed in details. The simulation results indicate that a sedimen-tary body develops far away from its source with an average grain size of 0.1 mm, i.e., sand-size sediment. Taking into account the location and orientation of the simulated seismic line, the consistence between normal forward simulation results and the revealed cores in Well A indicates that the turbidites should have been transported from Vietnam instead of Hainan Island. This interpretation has also been verified by the planar maps of sedimentary systems based on integration of boreholes and seismic data. The identification of the turbidity provenance will benefit the evaluation of extensively distributed submarine fans for hydro-carbon exploration in the deepwater areas.
基金support from National Basic Research Program of China(No.2009CB219801)National Natural Science Foundation of China(No.20976191)+1 种基金International Cooperative Program of Guizhou Province([2009]700110)Program for New Century Excellent Talents in University(NCET-09-0342)
文摘A simple hydrodynamic model based on two-fluid theory, taking into account the effect of discrete particles on both the gas- and solid-phase momentum equations, was used to numerically investigate the pressure fluctuation characteristics in a gas-solid fluidized bed with the aid of CFX 4.4, a commercial CFD software package, by adding user-defined Fortran subroutines. Numerical simulations together with typical experimental measurements show that pressure fluctuations originate above the distributor when a gas pulse is injected into the fluidized bed. The pressure above the bubble gradually increases due to the presence of a rising bubble. When the bubble passes through the bed surface, the pressure near the bed surface gradually decreases to a lower value. Moreover, the pressure signals in the bubbling fluidized beds show obviously periodic characteristics. The major frequency of pressure fluctuations at the same vertical position is affected slightly by the operating gas velocity, and the amplitude of pressure fluctuations is related to both the operating gas velocity and the vertical height. In this study, the influence of the operating gas velocity on the pressure wave propagation velocity can be ignored, and only two peak frequencies in the power spectrum of the pressure fluctuations are observed which are associated with the bubble formation above the distributor and its eruption at the bed surface.
基金Supported by the National Basic Research Program of China(2014CB745100)the National Natural Science Foundation of China(21576197)+1 种基金Tianjin Research Program of Application Foundation and Advanced Technology(14JCQNJC06700)Tianjin Penglai 19-3 Oil Spill Accident Compensation Project(19-3 BC2014-03)
文摘Heat exchangers play an important role in supercritical water coal gasification systems for heating feed and cooling products. However, serious deposition and plugging problems always exist in heat exchangers. CFD modeling was used to simulate the transport characteristics of solid particles in supercdtical water through the shell and tube of heat exchangers to alleviate the problems. In this paper, we discuss seven types of exchangers CA, B, C D, E, F and G）, which vary in inlet nozzle configuration, header height, inlet pipe diameter and tube pass distribution. In the modeling, the possibility of deposition in the header was evaluated by accumulated mass of particles; we used the velocity contour of supercritical water （SCW） to evaluate the uniformity of the velocity dis- tribution among the tube passes. Simulation results indicated that the optimum heat exchanger had structure F, which had a rectangular configuration of tube pass distractions, a bottom inlet, a 200-mm header height and a 10-ram inlet pipe diameter.
基金Supported by the National Natural Science Foundation of China(21276135)the Project of Chinese Ministry of Education(113004A)
文摘A new quenching process using the cold pyrolysis gas has been proposed for the partial oxidation(POX) of methane to recover the heat. The mixing of hot product gas and cold pyrolysis gas in milliseconds is critical to this new approach. Two most widely-used rapid mixing configurations, i.e. the jet-in-cross-flow(JICF) and impinging flow configurations, are compared in terms of mixing and quenching performances using computational fluid dynamics(CFD) coupled with detailed reaction mechanism Leeds 1.5. The mixedness, residence time distribution, temperature decreasing rate and loss ratio of acetylene during the quenching are systematically studied. The results show that the impinging flow has a more uniform mixing and narrower residence time distribution than the JICF.However, the temperature decreasing rate of the mainstream is faster in the JICF than in the impinging flow. The loss ratio of acetylene in the quenching process is 2.89% for the JICF and 1.45% for the impinging flow, showing that the impinging flow configuration is better and feasible for the quenching of POX of methane.
文摘Flow passages in vortex pumps usually have rough walls.Precise consideration of wall roughness is an important issue in pump flow simulations.Numerical studies of the effects of wall roughness on the performance of vortex pumps are quite rare,especially with different interface models.Turbulent flows of water in a vortex pump with a specific speed of 76 are simulated using 1/8 and whole impeller fluid domains with rough walls,using the three-dimensional Reynolds-averaged Navier-Stokes equations,the standard k-εmodel,and a scalable wall function in Ansys CFX 2019 R2.Equivalent sand grain roughnesses k_(s)=0.586 and 9.38μm are determined for the chamber casing,volute,and suction pipe,and k_(s)=18.47 and 36.94μm for the impeller by using the arithmetic average roughness Ra of the materials used in the pump and the correlation between k_(s)and Ra given in the literature.The mixing loss along the interface between impeller and volute in the transient rotor model is determined.The rates of change of the head,shaft-power,and efficiency of the pump due to wall roughness are calculated.The transient rotor model with whole impeller domain and the frozen rotor model with 1/8 impeller domain for rough walls with Ra=0.1μm in the suction pipe,volute,and chamber and 3.2μm in the impeller give the most accurate predictions of pump performance compared with experimental data.The transient rotor model with whole impeller domain gives more accurate predictions of pump performance than the frozen rotor model with 1/8 impeller domain.The mixing loss rises quickly at high flow rates.The transient rotor model with whole impeller domain gives plausible predictions of the rates of change.
基金supported by the SINOPEC research project“Research and development of electric desalting technology and equipment for heavy crude oil”(Project No.318020-9).
文摘The internal structure of electric desalting vessels is an important factor affecting the performance of crude oil dehydration and desalination.The flow and distribution of oil-water emulsions are generally not fully considered in the traditional design of a desalter.Computational fluid dynamics(CFD)simulations enable a deep understanding of oil-water two-phase flows,thereby providing a scientific basis for optimizing structural design of desalters.In this paper,CFD simulations are used to study the flow of oil-water two-phase fluid in a desalting vessel with advection squirrel-cage structure in a SINOPEC refinery,revealing the defects in its electric field layout.A structural improvement scheme is then proposed,and a medium-scale bypass test is conducted.The test results show that the single-stage salt removal rate is increased from 85.4%to 92.1%.The water and salt contents in desalted oil and the oil content in brine are also significantly improved,providing a solid foundation for transformation of the related industrial equipment.
基金supported by the National Natural Science Foundation of China(52306131)the Natural Science Foundation of Jiangsu Province(BK20230847)+2 种基金the Key Project of the National Natural Science Foundation of China(52336005)the Fundamental Research Funds for the Central Universities(2242024RCB0036)the Open Project Program of State Key Laboratory of Low-carbon Smart Coal-fired Power Generation and Ultra-clean Emission(D2024FK156).
文摘As a renewable energy source,the thermal conversion of poultry manure,is a promising waste treatment solution that can generate circular economic outputs such as energy and reduce greenhouse gas emissions.Currently,pressurized gasification of poultry manure is still a novel research field,especially when combined with a novel technological route of oxy-fuel gasification.Oxy-fuel gasification is a newly proposed and promising gasification technology for power generation that facilitates future carbon capture and storage.In this work,based on a commercially operated industrial-scale chicken manure gasification power plant in Singapore,we presented an interesting first exploration of the coupled pressurization technology for oxy-fuel gasification of poultry manure using CFD numerical simulation,analyzed the effects of pressure and oxygen enrichment concentration as well as the coupling mechanism between them,and discussed the conversion and emission of nitrogen-and sulfur-containing pollutants.The results indicate that under oxy-fuel gasification condition(Oxy-30,i.e.,30%O_(2)/70%CO_(2)),as the pressure increases from 0.1 to 0.5 MPa,the CO concentration in the syngas increases slightly,the H_(2)concentration increases to approximately 25%,and the CH4 concentration(less than 1%)decreases,resulting in an increase in the calorific value of syngas from 5.2 to 5.6 MJ·m^(-3).Compared to atmospheric pressure conditions,a relatively higher oxygen-enriched concentration interval(Oxy-40 to Oxy-50)under pressurized conditions is advantageous for autothermal gasification.Pressurization increases NO precursors production and also promotes homogeneous and heterogeneous reduction of NO,and provides favorable conditions for self-desulfurization.This work offers reference for the realization of a highly efficient and low-energy-consumption thermochemical treatment of livestock manure coupled with negative carbon emission technology.
文摘The article is an attempt to compile the results of CFD liquid flow simulation through pipeline section containing hydraulic elbow with the results of ultrasonic flow measurements. To carry out the measurements behind the flow disturbing element(hydraulic elbow), an ultrasonic flowmeter with applied head set in accordance with the Z-type system was used. For comparative purposes, a flow simulation for 3 different turbulence models(k-epsilon, SST and SSG) was performed. It was found that with a proper ultrasonic flowmeter heads configurations, it is possible to measure the flow rate disturbed by the hydraulic elbow at any distance from the source of the disturbance. It has to use appropriate correction factor that can be determined by knowing the flow velocity profile equation. Based on comparison of CFD simulation results with experimental data, the accuracy/purposefulness of using individual turbulence models in the case of discussed hydraulic installation was evaluated.
文摘Computational fluid dynamics(CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers.The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes.The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data,and built in UDF for simulation.The flow pattern of oriented valve tray under different operating conditions was simulated under Eulerian-Eulerian framework with realizable k-ε model.The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations.Meanwhile,the velocity distribution and volume fraction of the two phases were demonstrated and analyzed,which are useful in design and analysis of the column trays.
基金Financial support from National Natural Science Foundationof China(20976191 and 51025624)Program for New Century Excellent Talents in University(NCET-09-0342)111 Project(B12034)
文摘Particle suspension characteristics are predicted computationally in a stirred tank driven by a Smith turbine. In order to verify the hydrodynamic model and numerical method, the predicted power number and flow pattern are compared with designed values and simulated results from the literature, respectively. The effects of particle density, particle diameter, liquid viscosity and initial solid loading on particle suspension behavior are investigated by using the Eulerian-Eulerian two-fluid model and the standard k-ε turbulence model. The results indicate that solid concentration distribution depends on the flow field in the stirred tank. Higher particle density or larger particle size results in less homogenous distribution of solid particles in the tank. Increasing initial solid loading has an adverse impact on the homogeneous suspension of solid particles in a low-viscosity liquid, whilst more uniform particle distribution is found in a high-viscosity liquid.
基金This work was financially supported by the National Key Research and Development Program of China(Grant No.2017YFD0200303)the National Key Research and Development Program of China(Grant No.2018YFD0201304)the China Agriculture Research System(Grant No.CARS-25).
文摘In order to explore the performance of the B-ULV-616A knapsack sprayer,computational fluid dynamics(CFD)was used to simulate the B-ULV-616A knapsack air-assisted device,which features an ultra-low-volume electric sprayer.Field experiments were carried out to test the spraying effects,and the KANOMAX anemometer was used to verify the simulated results.First,the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established.The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device.The high-speed airflow(maximum of 83.5 m/s)generates negative pressure(minimum of 0.099 MPa)and causes a rapid increase in the droplet velocity and a secondary droplets spray,allowing droplets to reach a longer distance.Then,the maximum relative error was 20.14%,and its average value was 9.59%,indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device.Finally,based on the greenhouse experiment,the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop,increase the droplet density(maximum of 81/cm2;droplet density of conventional electric sprayer is 64/cm2),and reduce the deposition amount and coefficient of variation(below 20%)within and between regions.Further,it managed to reduce pesticide use(by 69.85%)and rural non-point source pollution.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFD1000305).
文摘This study proposed a comprehensive evaluation system to incorporate the contribution of both numerical simulation and statistical decision theory in ventilation performance assessment.A high-resolution model based on the finite volume approach was established to analyze the influence of rotation angles(i.e.,side vent flip angle and roof vent flip angle)of the rack-and-pinion ventilated structure on the greenhouse microclimate.The water circulating system and tomato seeding canopies were considered.Heat removal efficiency and mean age of air were employed as quantitative attributes to reflect the internal thermal environment and the airflow organization in the sliding cover solar greenhouse.The simulation model was verified with the temperature profile measured and the average relative error was 1.74%.The results demonstrate that the rotating angles of ventilation schemes have a substantial impact on the microclimate and inhomogeneity of the tomato seeding canopies.The results suggest the average velocity and its inhomogeneity are the crucial predictors,and their entropy weight values are 0.231 and 0.218,respectively.The relative degree of membership of the side vent flip angle of 45°is 36%and 97%higher than that of the side vent flip angle of 35°and the side vent flip angle of 25°,respectively.This study can provide a reference to evaluate the ventilated strategies of the sliding cover solar greenhouse for the regional and central government.
文摘The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-induced buoyancy.However,the wind effect is not well understood as it is often neglected in previous studies.The present study investigates the properties of such airflows,including the flow pattern,flow regime,and flow rate,using a CFD method.The target building is a large-span commercial building with a low-pitched roof.To study the wind-induced airflows,the onset atmospheric boundary layer wind flow was modelled,and the results were compared with the site-measured data recorded in the literature.To study the thermal-induced buoyancy effects,a roof cavity model found in the literature with experimental data was adopted.The findings show that the flow pattern in the roof cavity varied with the airflow driven factors.The flow separation at the windward eave inlet of the thermally induced flows are more pronounced compared with those of the wind-induced flows.Furthermore,the wind-induced airflows can generate around two times more ventilation flow rate through the roof cavity compared to the thermal-induced airflow.The findings indicate that wind-induced ventilation flows are the dominant factor of the roof cavity ventilation in a large-span,low-pitched building.
文摘Industrial Flares are important safety devices to bum off the unwanted gas during process startup, shutdown, or upset. However, flaring, especially the associated smoke, is a symbol of emissions from refineries, oil gas fields, and chemical processing plants. How to simultaneously achieve high combustion efficiency （CE） and low soot emission is an important issue. Soot emissions are influenced by many factors. Flare operators tend to over-steam or over-air to suppress smoke, which results in low CE. How to achieve optimal flare performance remains a question to the industry and the regulatory agencies. In this paper, regulations in the US regarding flaring were reviewed. In order to determine the optimal operating window for the flare, different combus- tion mechanisms related to soot emissions were summar- ized. A new combustion mechanism （Vsoot） for predicting soot emissions was developed and validated against experimental data. Computational fluid dynamic （CFD） models combined with Vsoot combustion mechanism were developed to simulate the flaring events. It was observed that simulation results agree well with experimental data.
基金the Project“Programma di scambi internazionali con Universitàe Istituti di Ricerca Stranieri per la Mobilitàdi breve durata di Docenti,Studiosi e Ricercatori”promoted and funded by Universitàdegli Studi di Napoli Federico II.
文摘The study presented hereby investigates experimentally and with CFD simulations the gas distribution effect on the hydrodynamic of a Geldart Group A turbulent fluidized bed. Experiments were carried out on a cold flow fluidized bed column with an even and uneven gas distribution. Local solid volume fraction profiles were measured using optical probes at different bed heights and along two radial directions. Optical probe measurements allow catching a clear hydrodynamic difference between both even and uneven gas distributions. These results were then used to assess CFD simulations with the code Barracuda^(TM) (MP-PIC approach). It is noteworthy that the choice of drag correlation and boundary conditions strongly influences the agreement between the experimental and CFD results. Once the correct parameters are chosen, CFD simulations captured the effect of gas distribution changes.
基金supported by the Scientific Research Special Fund of Marine Public Welfare Industry(No.20140508)National Natural Science Foundation of China(No.51478308)Natural Science Foundation of Tianjin(No.14JCYBJC23300)
文摘In this study, a new mass model involving superheat, initial temperature, liquid height, evaporator diameter, and flashing time is established to describe the flash evaporation process of water film. Of 469 sets of flash experimental data from three previous researches, 305 sets were applied to optimize parameters, and the other 164 sets were used to verify the practicability of the model. The results showed that the mean relative error between the literature data and the model values was less than 16.3%, and the model statistics proved that the model was well-posed. Then, the kinetic model was obtained using the time derivative of the new mass model. Computational fluid dynamics simulation of water film flash evaporation was studied based on a user-defined function program of the new evaporation kinetic model. The new kinetic model shows more consistency with the experimental phenomena in terms of evaporated mass and temperature compared with the evaporation–condensation model in Fluent software and Gopalakrishna's model. This new kinetic model can be extended to describe the flash process of water solution under other conditions.
基金support provided by Hebei Province Key Research and Development Program (Grant No.22327214D)Independent Research and Development Plan of Academy of Agricultural Planning and Engineering,Ministry of Agriculture and Rural Affairs (Grant No.SP202101).
文摘The building parameters of Chinese solar greenhouse(CSG)directly affect the front roof lighting and indoor thermal environment.In order to obtain the optimal parameter combination,a building parameter optimization method based on computational fluid dynamics(CFD)simulation and entropy weight method was proposed.Firstly,a three-dimensional thermal and humidity environment model of CSG was constructed considering the coupling effect of soil,crop,and back wall based on CFD.The reliability of the model was validated through experiments in a CSG of Yongqing County,Hebei Province of China.Then,the indoor air temperature rise rate,air temperature and humidity uneven coefficient,and average air temperature and humidity were selected as the evaluation indicators of CSG thermal and humidity environment.The ridge height,back wall height and the horizontal projection of back roof of CSG were selected as the three factors of the orthogonal test plan,and a three-factor and four-level plan was designed,resulting in 16 different parameter combinations.By use of CFD simulation,the thermal and humidity environment evaluation indicators under different parameter combinations were calculated.The entropy weight method was used to assign weights to the evaluation indicators,and the comprehensive evaluation indicators of CSG thermal and humidity environment were obtained based on the linear weighting principle.By comparing comprehensive evaluation indicators,the optimal combination of building parameters was obtained with a ridge height of 5.72 m,a back wall height of 3.2 m,and a horizontal projection of 2.1 m on the back roof.The research results can provide a practical and feasible method for optimizing the building parameters of CSG,and provided theoretical guidance for the structural design and optimization of CSG.
文摘This paper represents a detailed and systematic review of one of the most ongoing applications of computational fluid dynamics(CFD)in biomedical applications.Beyond its various engineering applications,CFD has started to establish a presence in the biomedical field.Cardiac abnormality,a familiar health issue,is an essential point of investigation by research analysts.Diagnostic modalities provide cardiovascular structural information but give insufficient information about the hemodynamics of blood.The study of hemodynamic parameters can be a potential measure for determining cardiovascular abnormalities.Numerous studies have explored the rheological behavior of blood experimentally and numerically.This paper provides insight into how researchers have incorporated the pulsatile nature of the blood experimentally,numerically,or through various simulations over the years.It focuses on how machine learning platforms derive outputs based on mass and momentum conservation to predict the velocity and pressure profile,analyzing various cardiac diseases for clinical applications.This will pave the way toward responsive AI in cardiac healthcare,improving productivity and quality in the healthcare industry.The paper shows how CFD is a vital tool for efficiently studying the flow in arteries.The review indicates this biomedical simulation and its applications in healthcare using machine learning and AI.Developing AI-based CFD models can impact society and foster the advancement towards responsive AI.
基金supported by National Natural Science Foundation of China(No.52075334)。
文摘Field emission electric propulsion(FEEP) thrusters possess excellent characteristics, such as high specific impulse, low power requirements, compact size and precise pointing capabilities,making them ideal propulsion devices for micro-nano satellites. However, the detection of certain aspects, such as the evolution process of the liquid cone and the physical quantities at the cone apex, proves challenging due to the minute size of the needle tip and the vacuum environment in which they operate. Consequently, this paper introduces a computational fluid dynamics(CFD) model to gain insight into the formation process of the liquid cone on the tip apex of indium FEEP. The CFD model is based on electrohydrodynamic(EHD) equations and the volume of fluid(VOF) method. The entire cone formation process can be divided into three stages, and the time-dependent characteristics of the physical quantities at the cone apex are investigated. The influences of film thickness, apex radius size and applied voltage are compared.The results indicate a gradual increase in the values of electrostatic stress and surface tension stress at the cone apex over an initial period, followed by a rapid escalation within a short duration.Apex configurations featuring a small radius, thick film and high voltage exhibit a propensity for liquid cone formation, and the cone growth time decreases as the film thickness increases.Moreover, some unstable behavior is observed during the cone formation process.
