The concentration and velocity fields of two refractive index matched miscible shear-thinning fluids in a lid-driven cavity were investigated by using planar laser-induced fluorescence and particle image velocimetry,a...The concentration and velocity fields of two refractive index matched miscible shear-thinning fluids in a lid-driven cavity were investigated by using planar laser-induced fluorescence and particle image velocimetry,as well by computational fluid dynamics.Quantitative analyses show that the results obtained by flow simulations with the species transport model are in good agreement with the experimental results.The effects of different parameters were studied by using the intensity of segregation.For two fluids with the same rheological parameters,the relative amounts of liquids H_(1)/H and the power-law index n dominate the mixing process while the Reynolds number Re plays a marginal role.As for two fluids with density difference,buoyancy has significant influence on the mixing process.The dimensionless group Ar/Re(redefined such as to include shear thinning behavior)is proposed for assessing the effect of buoyancy and rheological properties on the mixing of miscible shear-thinning fluids.展开更多
In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements.Three generations of pyrite(PyⅠ,PyⅡ,...In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements.Three generations of pyrite(PyⅠ,PyⅡ,and PyⅢ)in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central,western,and northern(C_Py,W_Py,and N_Py)mining districts are selected for comparison.Compared with PyⅠand PyⅢ,the contents of most elements in PyⅡare apparently higher.The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py.The highest As,Se,and Pb contents were found in W_Py and N_Py.These results indicate the drastic changes in the temperature and fluid mixing during the mineralization.The occurrence of fluctuation and change in temperature and f(O_(2))was triggered by intermittent pulses of magmatic-hydrothermal fluids,mixing with meteoric water,and water-rock interactions.The sulfur isotopes of all species of pyrite indicated the magmatic source.The change in the f(O_(2))conditions caused slight differences in the sulfur isotope compositions.Consequently,a metallogenic model was proposed to explain the ore-forming processes.展开更多
The underlying effect of vortex interaction characterized by the merging and non-merging on mixing enhancement is of fundamental significance to understand the flow dynamics of strut injectors in scramjets.Starting fr...The underlying effect of vortex interaction characterized by the merging and non-merging on mixing enhancement is of fundamental significance to understand the flow dynamics of strut injectors in scramjets.Starting from a simplified configuration of a vortex generator,this study focuses on the influence of geometric parameters on vortex structures and fluid mixing through compressible Navier-Stokes(NS)simulations.By adjusting the induction of outer vortices,the inner co-rotating vortex pair exhibits two modes of interaction(merging/separation regime)reflected by closer/farther vortex centers.Defined by the zero variation rate of the inner vortex spacing,the critical state of equilibrium is determined.The critical condition is well predicted by a theoretical model based on the Biot-Savart law.Through the introduction of mixedness and mixing time,the intrinsic impact of interaction modes on fluid mixing is revealed.Compared with the vortex dynamics in the merging regime,the one in the separation regime is more effective for passive scalar mixing augmentation.With efficient material stretching characterized by the higher interface stretching factor and averaging finite-time Lyapunov exponent(FTLE),the mixing time is shortened by as much as 2.5 times in the separation regime.The implication of the present two interaction regimes in mixing enhancement physically reflected by the averaging FTLE has the potential to improve the combustion performance and shorten the combustor chamber.展开更多
The Huize Pb-Zn deposits of Yunnan Province, located in the south-central part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn multimetal mineralization district (MMD), are strictly controlled by fault zones. The sources of...The Huize Pb-Zn deposits of Yunnan Province, located in the south-central part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn multimetal mineralization district (MMD), are strictly controlled by fault zones. The sources of ore-forming fluid in the deposits have been debated for a long time. Calcite, a gangue mineral, has uniform C and O isotopes. The δ~13C_PDB and δ~18O_SMOW values vary respectively from -2.1×10^-3 to -3.5×10^-3 (mean -2.8×10^-3) and 16.7×10^-3-18.6×10^-3 (mean 17.7×10^-3). No obvious difference can be found in C and O isotopes among occurrences and elevations and even ore-bodies. Types of inclusions include those of pure liquid (L), liquid-rich gas-liquid (L+V), and three-phase ones containing a daughter mineral (S+L+V) and immiscible CO_2 with three-phases (V_CO_2+L_CO_2+L_H_2O). Their homogenization temperatures vary from 110 to 400 ℃, and two peaks are shown. (~87Sr/~86Sr)_0 ratios of calcite in the deposits are higher than those in the mantle and Emeishan basalts, and slightly higher than those in the Baizuo Formation, which the Huize lead-zinc deposits are found in. All of the (~87Sr/~86Sr)_0 are low relative to those in the basement rocks. Fractionation of Sr isotope did not occur in the ore-forming fluid during the precipitation of minerals. The results indicate that the ore-forming fluid is homogeneous and derived from the mixing of different fluids. Gas-liquid inclusions can be separated into two groups in 300-400 ℃ with a salinity of 5 %-6 % and 12 %-16 % NaCl respectively. However, the salinities of inclusions vary from 7 % to 23 % NaCl in 100-300 ℃, especially in 150-250 ℃. The formation pressures of faulted zones are (50-320)×105 Pa. The estimated pressures of the overlying rocks on the ore bodies are 574×105-640×105 Pa. The pressures of ore-forming processes would be 145×105 to 754×105 Pa. Therefore, pressure sharply reduced and boiling occurred when the ore-forming fluid flew into the fault zones. As a result, the ore-forming fluid was highly concentrated, and metallic minerals began to precipitate from the fluid on a great scale. The high-grade lead-zinc deposits were formed when the fluid was under saturation or over-saturation conditions.展开更多
Strategy of the shaft eccentricity is introduced to enhance the mixing characteristics in a flat bottomed cylindrical vessel without baffles. The mixing is ensured by a six-curved blade impeller. Three solutions which...Strategy of the shaft eccentricity is introduced to enhance the mixing characteristics in a flat bottomed cylindrical vessel without baffles. The mixing is ensured by a six-curved blade impeller. Three solutions which are models of food emulsions are used as working fluids. These solutions have a shear thinning behavior modeled by the power-law. The effects of fluid properties, stirring rates, impeller rotational direction and impeller eccentricity on the 3D flow fields and power consumption are investigated. Three values of impeller eccentricity are considered, namely 0%, 24% and 48% of the vessel diameter. It is found that the opposite clockwise rotational direction reduces the power consumption, compared with the clockwise rotational direction. Also, the obtained results show that an impeller placed at an eccentric position between 24% and 48% of the vessel diameter and at the third of the vessel height may ensure the best mixing characteristics.展开更多
A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of a stable system, and it is used to describe the ingredient distribution of a mixed fluid in a non-unifor...A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of a stable system, and it is used to describe the ingredient distribution of a mixed fluid in a non-uniform stress field and to analyse its phase drift phenomenon. In the model, the drift-inhibition angle and the expansion-inhibition angle are also deduced and used as evaluating indexes to describe the drifting trend of different ingredients among the mixed fluids. For solving above two indexes of the model, a new calculation method is developed and used to compute the phase distributions of multiphase fluid at peak stress and gradient area stress, respectively. As an example, the flow process of grease in a pipe is analysed by simulation method and used to verify the validity of the model.展开更多
Constant-volume heat capacities of supercritical (SC) CO2, SC CO2-n-pentane, and SC CO2-n-heptane mixtures were determined at 308.15 K in the pressure range from 6 to 12 MPa. It was found that there is a maximum in ea...Constant-volume heat capacities of supercritical (SC) CO2, SC CO2-n-pentane, and SC CO2-n-heptane mixtures were determined at 308.15 K in the pressure range from 6 to 12 MPa. It was found that there is a maximum in each heat capacity vs pressure curve. Intermolecular interaction in the fluids was studied.展开更多
A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whet...A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.展开更多
Drilling fluids and mud additives are generally acknowledged as potential sources of contamination in deep drilling programs, as they may contain high concentration of nutrients for subsurface microorganisms. Microorg...Drilling fluids and mud additives are generally acknowledged as potential sources of contamination in deep drilling programs, as they may contain high concentration of nutrients for subsurface microorganisms. Microorganisms introduced into drilling process cause a number of problems that can lead to significant costs for the industry. Numerous studies have shown that biogenic sulfide production in oil and natural gas fields have led to a number of problems, including reservoir plugging, reservoir souring, reduced product quality, and corrosion of metal-containing equipment. The aim of this study is to determine the microbial contamination of water drilling mud and cement Mix fluid at two Saudi Aramco well SA-10 ＆ SA-12 and to adequately perform microbial assessment for the well both wells. Microbiological analyses were conducted to evaluate the level of contamination by TB （total bacterial） and SRB （sulfate reducing bacteria） using and q-PCR （quantitative poly chain reaction） technique. Microbial results for SA-10 indicated that total bacteria were 2.21 × 103/mL for mix fluid sample and 1.22 × 105/mL for drilling water sample. In addition, microbial results for total SRB were 1.65 × 102/mL and 1.34 × 102 mL, respectively. Moreover, microbial results for SA-12 indicated 5.89 × 105/mL of total bacteria and 98/mL of SRB in the sample.展开更多
Electrical tomography is, in certain cases, the most attractive method for real imaging of industrial processes, because of its inherent simplicity, rugged construction of the tomographer and high-speed capability. Th...Electrical tomography is, in certain cases, the most attractive method for real imaging of industrial processes, because of its inherent simplicity, rugged construction of the tomographer and high-speed capability. This paper presents examples illus- trating applications of electrical tomography for imaging fluidized beds, bubble columns and pneumatic conveyors. Electrical tomography opens up new ways for processing, imaging and modelling multi-phase flows as shown by 2D and 3D images illus- trating the various types of flow morphology.展开更多
In this work,numerical simulations for the flow characteristics in a tank of KR mechanical stirring or/and gas injection are performed using the Fluent software.The Eulerian multi-fluid model is employed along with th...In this work,numerical simulations for the flow characteristics in a tank of KR mechanical stirring or/and gas injection are performed using the Fluent software.The Eulerian multi-fluid model is employed along with the standard k-εturbulence model to simulate the gas-liquid flow in the stirring tank.A multiple reference frame approach is used to model the impeller rotation.Combined the KR mechanical stirring method and gas injection method,a new gas injection plus mechanical stirring method is proposed.The present results show that the gas phase distributes widely in the eccentric gas injection plus mechanical stirring tank.Therefore,the gas holdup would be increased and the better gas-liquid mixing effect can be obtained in the gas injection plus mechanical stirring case.展开更多
Body-scanning exploiting 3-D imaging has revolutionised diagnostics and treatment in medicine. Process engineers would like to be similarly able to image chemical process units in 3-D, but without the Lmulti-million p...Body-scanning exploiting 3-D imaging has revolutionised diagnostics and treatment in medicine. Process engineers would like to be similarly able to image chemical process units in 3-D, but without the Lmulti-million price tag. UMIST and Leeds University have together, through the Virtual Centre for Industrial Process Tomography （http：//www.vcipt.org）, pioneered several electrical process tomography techniques and used them in a variety of applications. Illustrations are presented to show how electrical resistance tomography （ERT） has been developed for typical stirred vessels widely encountered in batch process manufacturing. The technique is potentially fast and inexpensive and capable of imaging both dynamic and pseudo-stationary processes. Examples from UMIST＇s two-tonne vessel will be presented for miscible tracer mixing, as well as gas-liquid and solid-liquid mixing.展开更多
The exceptionally rapid fluid mixing that is achievable in confined mixing layers through external excitation is studied through both flow visualization and particle image velocimetry at a moderate Reynolds number.Com...The exceptionally rapid fluid mixing that is achievable in confined mixing layers through external excitation is studied through both flow visualization and particle image velocimetry at a moderate Reynolds number.Compared with free mixing layers,confined mixing layers exhibit a twofold larger spreading rate in the absence of excitation.When they are excited,a significantly larger V component of the mean velocity can be generated.This broadens the mixing layer on large scales,meanwhile generating a large∣∂V/∂y∣around the centerline.This large∣∂V/∂y∣further stretches the spanwise vortices,induces earlier collapse,and indirectly promotes small-scale mixing.Thus,the mean flow field plays an important role in the evolution of a confined mixing layer with excitation.Under the optimal excitation frequency,the turbulent kinetic energy primarily attributed to acoustical excitation is rapidly consumed by inverse energy transport.This further explains the formation of the mean field from the perspective of kinetic energy transfer.The results obtained here can be potentially applied to the design of high-efficiency and compact active mixers/reactors for chemical engineering and biomedical applications.展开更多
The available studies in the literature on physical and mathematical modeling of the argon oxygen decarburization (AOD) process of stainless steel have briefly been reviewed. The latest advances made by the author wi...The available studies in the literature on physical and mathematical modeling of the argon oxygen decarburization (AOD) process of stainless steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was used to investigate the fluid flow and mixing characteristics in the bath of an 18 t AOD vessel, as well as the 'back attack' action of gas jets and its effects on the erosion and wear of the refractory lining, with sufficiently full kinematic similarity. The non rotating and rotating gas jets blown through two annular tuyeres, respectively of straight tube and spiral flat tube type, were employed in the experiments. The geometric similarity ratio between the model and its prototype (including the straight tube type tuyeres) was 1:3. The influences of the gas flow rate, the angle included between the two tuyeres and other operating parameters, and the suitability of the spiral tuyere as a practical application, were examined. These latest studies have clearly and successfully brought to light the fluid flow and mixing characteristics in the bath and the overall features of the back attack phenomena of gas jets during the blowing, and have offered a better understanding of the refining process. Besides, mathematical modeling for the refining process of stainless steel was carried out and a new mathematical model of the process was proposed and developed. The model performs the rate calculations of the refining and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and scrap, and alloy agents; the non isothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors were all considered. The model was used to deal with and analyze the austenitic stainless steel making (including ultra low carbon steel) and was tested on data of 32 heats obtained in producing 304 grade steel in an 18 t AOD vessel. The changes in the bath composition and temperature during the refining process with time can be accurately predicted using this model. The model can provide some very useful information and a reliable basis for optimizing the process practice of the refining of stainless steel and control of the process in real time and online.展开更多
Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence(VIT) is a significant factor that controls the initial dilution, dispersion, and ultima...Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence(VIT) is a significant factor that controls the initial dilution, dispersion, and ultimately the chemical and physical fate of pollutants by altering the conditions in the microenvironment. This study used a computational fluid dynamics(CFD) software FLUENT to model the vehicle-induced turbulence(VIT) generated on roadways, with a focus on impact of vehicle-vehicle interactions, traffic density and vehicle composition on turbulent kinetic energy(TKE). We show, for the first time, that the overall TKE from multiple vehicles traveling in series can be estimated by superimposing the TKE of each vehicle, without considering the distance between them while the distance is greater than one vehicle length. This finding is particularly significant since it enables a new approach to VIT simulations where the overall TKE is calculated as a function of number of vehicles. We found that the interactions between vehicles traveling next to each other in adjacent lanes are insignificant,regardless the directions of the traffic flow. Consequently, simulations of different traffic scenarios can be substantially simplified by treating two-way traffic as one-way traffic, with less than 5% difference in the overall volume-averaged TKE. We also developed equations that allow the estimation of the overall volume-averaged TKE as a function of the number and the type of vehicles.展开更多
We present a three dimensional model of an open elastic tube immersed in fluid to understand valveless pumping mechanism.A fluid-tube interaction problem is simulated by the volume conserved immersed boundarymethodwhi...We present a three dimensional model of an open elastic tube immersed in fluid to understand valveless pumping mechanism.A fluid-tube interaction problem is simulated by the volume conserved immersed boundarymethodwhich prevents the generation of spurious velocity field near the tube and local cluster of the tube surface.In order to explain pumping phenomena without valves,average net flow ismeasured by changing parameter values such as pumping frequency,compression duration,and pumping amplitude.Some frequencies that make the system reach maximal or minimal net flow are selected to study case by case.We also study the effectiveness of fluid mixing using the Shannon entropy increase rate.展开更多
Experimentalists, numerical modellers and reactor modellers need to work together, not only just for validation of numerical codes, but also to shed fundamental light on each other＇s problems and underlying assumptio...Experimentalists, numerical modellers and reactor modellers need to work together, not only just for validation of numerical codes, but also to shed fundamental light on each other＇s problems and underlying assumptions. Several examples are given, Experimental gas axial dispersion data provide a means of choosing the most appropriate boundary condition （no slip, partial slip or full slip） for particles at the wall of fluidized beds. CFD simulations help to identify how close ＂two-dimensional＂ experimental columns are to being truly two-dimensional and to representing three-dimensional columns. CFD also can be used to provide a more rational means of establishing assumptions needed in the modelling of two-phase fluidized bed reactors, for example how to deal with cases where there is a change in molar flow （and hence volumetric flow） as a result of chemical reactions.展开更多
A magnetorheological fluid(MRF)is a smart composite suspension composed of nonmagnetic liquid and soft magnetic particles.Carrier fluids can considerably influence the performance of MRFs;therefore,to investigate the ...A magnetorheological fluid(MRF)is a smart composite suspension composed of nonmagnetic liquid and soft magnetic particles.Carrier fluids can considerably influence the performance of MRFs;therefore,to investigate the effect of carrier fluids on MRFs,an SO/IL-MRF was prepared by mixing an ionic liquid(IL)with silicone oil(SO)in this study.Three types of MRF samples were prepared for experiments(pure SO,pure IL,and SO/IL).According to the experi-mental results,the SO/IL-MRF has better sedimentation stability than those based on pure SO and pure IL.Further,three methods were used to determine the shear yield stresses of the MRFs.The SO/IL-MRF achieved a higher shear yield stress than those of the other two because a network structure is formed between the ionic fragments and the molecular chains of the SO in the SO/IL-MRF.This increases the movement resistance of the particles in the carrier fluid,and it is unlike the mechanism of the IL-enhanced MRF.This work provides new ideas for improving the MRF performance.展开更多
Numerical simulation of fully developed hydrodynamics of a riser and a downer was carried out using an Eulerian-Lagrangian model, where the particles are modeled by the discrete element method （DEM） and the gas by t...Numerical simulation of fully developed hydrodynamics of a riser and a downer was carried out using an Eulerian-Lagrangian model, where the particles are modeled by the discrete element method （DEM） and the gas by the Navier-Stokes equations. Periodic flow domain with two side walls was adopted to simulate the fully developed dynamics in a 2D channel of 10 cm in width. All the simulations were carried out under the same superficial gas velocity and solids holdup in the domain, starting with a homogenous state for both gas and solids, and followed by the evolution of the dynamics to the heterogeneous state with distinct clustering in the riser and the downer. In the riser, particle clusters move slowly, tending to suspend along the wall or to flow downwards, which causes wide residence time distribution of the particles. In the downer, clusters still exist, but they have faster velocities than the discrete particles. Loosely collected particles in the clusters move in the same direction as the bulk flow, resulting in plug flow in the downer. The residence time distribution （RTD） of solids was computed by tracking the displacements of all particles in the flow direction. The results show a rather wide RTD for the solids in the riser hut a sharp peak RTD in the downer, much in agreement with the experimental findings in the literature. The ensemble average of transient dynamics also shows reasonable profiles of solids volume fraction and solids velocity, and their dependence on particle density.展开更多
In this paper, the efficient utilization of liquefied natural gas(LNG) vaporization cold energy in offshore liquefied natural gas floating storage regasification unit(FSRU) is studied. On the basis of considering diff...In this paper, the efficient utilization of liquefied natural gas(LNG) vaporization cold energy in offshore liquefied natural gas floating storage regasification unit(FSRU) is studied. On the basis of considering different boil-off gas(BOG) practical treatment processes, a cascade comprehensive utilization scheme of cold energy of LNG based on the longitudinal three-stage organic Rankine cycle power generation and the low-grade cold energy used to frozen seawater desalination was proposed. Through the comparative analysis of the effects of the pure working fluid and eight mixed working fluids on the performance of the new system, the combination scheme of system mixed working fluid with the highest exergy efficiency of the system was determined. Then, the genetic algorithm was used to optimize the parameters of the new system. After optimization, the net output power of the LNG cold energy comprehensive utilization system proposed in this paper was 5186 kW, and the exergy efficiency is 30.6%. Considering the power generation and freshwater revenue, the annual economic benefit of the system operating is 18.71 million CNY.展开更多
基金The financial supports from the National Natural Science Foundation of China(22178014)。
文摘The concentration and velocity fields of two refractive index matched miscible shear-thinning fluids in a lid-driven cavity were investigated by using planar laser-induced fluorescence and particle image velocimetry,as well by computational fluid dynamics.Quantitative analyses show that the results obtained by flow simulations with the species transport model are in good agreement with the experimental results.The effects of different parameters were studied by using the intensity of segregation.For two fluids with the same rheological parameters,the relative amounts of liquids H_(1)/H and the power-law index n dominate the mixing process while the Reynolds number Re plays a marginal role.As for two fluids with density difference,buoyancy has significant influence on the mixing process.The dimensionless group Ar/Re(redefined such as to include shear thinning behavior)is proposed for assessing the effect of buoyancy and rheological properties on the mixing of miscible shear-thinning fluids.
基金funded by the National Key Research and Development Program of China (Nos. 2018YFC0603904, 2018YFC0603901)。
文摘In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements.Three generations of pyrite(PyⅠ,PyⅡ,and PyⅢ)in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central,western,and northern(C_Py,W_Py,and N_Py)mining districts are selected for comparison.Compared with PyⅠand PyⅢ,the contents of most elements in PyⅡare apparently higher.The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py.The highest As,Se,and Pb contents were found in W_Py and N_Py.These results indicate the drastic changes in the temperature and fluid mixing during the mineralization.The occurrence of fluctuation and change in temperature and f(O_(2))was triggered by intermittent pulses of magmatic-hydrothermal fluids,mixing with meteoric water,and water-rock interactions.The sulfur isotopes of all species of pyrite indicated the magmatic source.The change in the f(O_(2))conditions caused slight differences in the sulfur isotope compositions.Consequently,a metallogenic model was proposed to explain the ore-forming processes.
基金Project supported by the National Natural Science Foundation of China(Nos.91741113,91841303,and 91941301)。
文摘The underlying effect of vortex interaction characterized by the merging and non-merging on mixing enhancement is of fundamental significance to understand the flow dynamics of strut injectors in scramjets.Starting from a simplified configuration of a vortex generator,this study focuses on the influence of geometric parameters on vortex structures and fluid mixing through compressible Navier-Stokes(NS)simulations.By adjusting the induction of outer vortices,the inner co-rotating vortex pair exhibits two modes of interaction(merging/separation regime)reflected by closer/farther vortex centers.Defined by the zero variation rate of the inner vortex spacing,the critical state of equilibrium is determined.The critical condition is well predicted by a theoretical model based on the Biot-Savart law.Through the introduction of mixedness and mixing time,the intrinsic impact of interaction modes on fluid mixing is revealed.Compared with the vortex dynamics in the merging regime,the one in the separation regime is more effective for passive scalar mixing augmentation.With efficient material stretching characterized by the higher interface stretching factor and averaging finite-time Lyapunov exponent(FTLE),the mixing time is shortened by as much as 2.5 times in the separation regime.The implication of the present two interaction regimes in mixing enhancement physically reflected by the averaging FTLE has the potential to improve the combustion performance and shorten the combustor chamber.
文摘The Huize Pb-Zn deposits of Yunnan Province, located in the south-central part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn multimetal mineralization district (MMD), are strictly controlled by fault zones. The sources of ore-forming fluid in the deposits have been debated for a long time. Calcite, a gangue mineral, has uniform C and O isotopes. The δ~13C_PDB and δ~18O_SMOW values vary respectively from -2.1×10^-3 to -3.5×10^-3 (mean -2.8×10^-3) and 16.7×10^-3-18.6×10^-3 (mean 17.7×10^-3). No obvious difference can be found in C and O isotopes among occurrences and elevations and even ore-bodies. Types of inclusions include those of pure liquid (L), liquid-rich gas-liquid (L+V), and three-phase ones containing a daughter mineral (S+L+V) and immiscible CO_2 with three-phases (V_CO_2+L_CO_2+L_H_2O). Their homogenization temperatures vary from 110 to 400 ℃, and two peaks are shown. (~87Sr/~86Sr)_0 ratios of calcite in the deposits are higher than those in the mantle and Emeishan basalts, and slightly higher than those in the Baizuo Formation, which the Huize lead-zinc deposits are found in. All of the (~87Sr/~86Sr)_0 are low relative to those in the basement rocks. Fractionation of Sr isotope did not occur in the ore-forming fluid during the precipitation of minerals. The results indicate that the ore-forming fluid is homogeneous and derived from the mixing of different fluids. Gas-liquid inclusions can be separated into two groups in 300-400 ℃ with a salinity of 5 %-6 % and 12 %-16 % NaCl respectively. However, the salinities of inclusions vary from 7 % to 23 % NaCl in 100-300 ℃, especially in 150-250 ℃. The formation pressures of faulted zones are (50-320)×105 Pa. The estimated pressures of the overlying rocks on the ore bodies are 574×105-640×105 Pa. The pressures of ore-forming processes would be 145×105 to 754×105 Pa. Therefore, pressure sharply reduced and boiling occurred when the ore-forming fluid flew into the fault zones. As a result, the ore-forming fluid was highly concentrated, and metallic minerals began to precipitate from the fluid on a great scale. The high-grade lead-zinc deposits were formed when the fluid was under saturation or over-saturation conditions.
文摘Strategy of the shaft eccentricity is introduced to enhance the mixing characteristics in a flat bottomed cylindrical vessel without baffles. The mixing is ensured by a six-curved blade impeller. Three solutions which are models of food emulsions are used as working fluids. These solutions have a shear thinning behavior modeled by the power-law. The effects of fluid properties, stirring rates, impeller rotational direction and impeller eccentricity on the 3D flow fields and power consumption are investigated. Three values of impeller eccentricity are considered, namely 0%, 24% and 48% of the vessel diameter. It is found that the opposite clockwise rotational direction reduces the power consumption, compared with the clockwise rotational direction. Also, the obtained results show that an impeller placed at an eccentric position between 24% and 48% of the vessel diameter and at the third of the vessel height may ensure the best mixing characteristics.
基金Project supported by the National Natural Science Foundation of China (Grant No. 51075311)
文摘A two-phase wedge-sliding model is developed based on the micro-cellular structure and minimum entropy theory of a stable system, and it is used to describe the ingredient distribution of a mixed fluid in a non-uniform stress field and to analyse its phase drift phenomenon. In the model, the drift-inhibition angle and the expansion-inhibition angle are also deduced and used as evaluating indexes to describe the drifting trend of different ingredients among the mixed fluids. For solving above two indexes of the model, a new calculation method is developed and used to compute the phase distributions of multiphase fluid at peak stress and gradient area stress, respectively. As an example, the flow process of grease in a pipe is analysed by simulation method and used to verify the validity of the model.
文摘Constant-volume heat capacities of supercritical (SC) CO2, SC CO2-n-pentane, and SC CO2-n-heptane mixtures were determined at 308.15 K in the pressure range from 6 to 12 MPa. It was found that there is a maximum in each heat capacity vs pressure curve. Intermolecular interaction in the fluids was studied.
文摘A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.
文摘Drilling fluids and mud additives are generally acknowledged as potential sources of contamination in deep drilling programs, as they may contain high concentration of nutrients for subsurface microorganisms. Microorganisms introduced into drilling process cause a number of problems that can lead to significant costs for the industry. Numerous studies have shown that biogenic sulfide production in oil and natural gas fields have led to a number of problems, including reservoir plugging, reservoir souring, reduced product quality, and corrosion of metal-containing equipment. The aim of this study is to determine the microbial contamination of water drilling mud and cement Mix fluid at two Saudi Aramco well SA-10 ＆ SA-12 and to adequately perform microbial assessment for the well both wells. Microbiological analyses were conducted to evaluate the level of contamination by TB （total bacterial） and SRB （sulfate reducing bacteria） using and q-PCR （quantitative poly chain reaction） technique. Microbial results for SA-10 indicated that total bacteria were 2.21 × 103/mL for mix fluid sample and 1.22 × 105/mL for drilling water sample. In addition, microbial results for total SRB were 1.65 × 102/mL and 1.34 × 102 mL, respectively. Moreover, microbial results for SA-12 indicated 5.89 × 105/mL of total bacteria and 98/mL of SRB in the sample.
文摘Electrical tomography is, in certain cases, the most attractive method for real imaging of industrial processes, because of its inherent simplicity, rugged construction of the tomographer and high-speed capability. This paper presents examples illus- trating applications of electrical tomography for imaging fluidized beds, bubble columns and pneumatic conveyors. Electrical tomography opens up new ways for processing, imaging and modelling multi-phase flows as shown by 2D and 3D images illus- trating the various types of flow morphology.
基金supported financially by the Natural Science Foundation of Liaoning Province under the grant of 20092002the Program of Introducing Talents of Discipline to Universities under the grant of B07015
文摘In this work,numerical simulations for the flow characteristics in a tank of KR mechanical stirring or/and gas injection are performed using the Fluent software.The Eulerian multi-fluid model is employed along with the standard k-εturbulence model to simulate the gas-liquid flow in the stirring tank.A multiple reference frame approach is used to model the impeller rotation.Combined the KR mechanical stirring method and gas injection method,a new gas injection plus mechanical stirring method is proposed.The present results show that the gas phase distributes widely in the eccentric gas injection plus mechanical stirring tank.Therefore,the gas holdup would be increased and the better gas-liquid mixing effect can be obtained in the gas injection plus mechanical stirring case.
文摘Body-scanning exploiting 3-D imaging has revolutionised diagnostics and treatment in medicine. Process engineers would like to be similarly able to image chemical process units in 3-D, but without the Lmulti-million price tag. UMIST and Leeds University have together, through the Virtual Centre for Industrial Process Tomography （http：//www.vcipt.org）, pioneered several electrical process tomography techniques and used them in a variety of applications. Illustrations are presented to show how electrical resistance tomography （ERT） has been developed for typical stirred vessels widely encountered in batch process manufacturing. The technique is potentially fast and inexpensive and capable of imaging both dynamic and pseudo-stationary processes. Examples from UMIST＇s two-tonne vessel will be presented for miscible tracer mixing, as well as gas-liquid and solid-liquid mixing.
基金supported by a North American Mixing Forum Startup Grant Award,NAMF/AIChE 2009the NSF of the USA(EPSCoR Award,EPS-1317771).
文摘The exceptionally rapid fluid mixing that is achievable in confined mixing layers through external excitation is studied through both flow visualization and particle image velocimetry at a moderate Reynolds number.Compared with free mixing layers,confined mixing layers exhibit a twofold larger spreading rate in the absence of excitation.When they are excited,a significantly larger V component of the mean velocity can be generated.This broadens the mixing layer on large scales,meanwhile generating a large∣∂V/∂y∣around the centerline.This large∣∂V/∂y∣further stretches the spanwise vortices,induces earlier collapse,and indirectly promotes small-scale mixing.Thus,the mean flow field plays an important role in the evolution of a confined mixing layer with excitation.Under the optimal excitation frequency,the turbulent kinetic energy primarily attributed to acoustical excitation is rapidly consumed by inverse energy transport.This further explains the formation of the mean field from the perspective of kinetic energy transfer.The results obtained here can be potentially applied to the design of high-efficiency and compact active mixers/reactors for chemical engineering and biomedical applications.
文摘The available studies in the literature on physical and mathematical modeling of the argon oxygen decarburization (AOD) process of stainless steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was used to investigate the fluid flow and mixing characteristics in the bath of an 18 t AOD vessel, as well as the 'back attack' action of gas jets and its effects on the erosion and wear of the refractory lining, with sufficiently full kinematic similarity. The non rotating and rotating gas jets blown through two annular tuyeres, respectively of straight tube and spiral flat tube type, were employed in the experiments. The geometric similarity ratio between the model and its prototype (including the straight tube type tuyeres) was 1:3. The influences of the gas flow rate, the angle included between the two tuyeres and other operating parameters, and the suitability of the spiral tuyere as a practical application, were examined. These latest studies have clearly and successfully brought to light the fluid flow and mixing characteristics in the bath and the overall features of the back attack phenomena of gas jets during the blowing, and have offered a better understanding of the refining process. Besides, mathematical modeling for the refining process of stainless steel was carried out and a new mathematical model of the process was proposed and developed. The model performs the rate calculations of the refining and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and scrap, and alloy agents; the non isothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors were all considered. The model was used to deal with and analyze the austenitic stainless steel making (including ultra low carbon steel) and was tested on data of 32 heats obtained in producing 304 grade steel in an 18 t AOD vessel. The changes in the bath composition and temperature during the refining process with time can be accurately predicted using this model. The model can provide some very useful information and a reliable basis for optimizing the process practice of the refining of stainless steel and control of the process in real time and online.
基金financial support from Environment Canada and the Government of Ontario (72021622) for a scholarship to YK
文摘Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence(VIT) is a significant factor that controls the initial dilution, dispersion, and ultimately the chemical and physical fate of pollutants by altering the conditions in the microenvironment. This study used a computational fluid dynamics(CFD) software FLUENT to model the vehicle-induced turbulence(VIT) generated on roadways, with a focus on impact of vehicle-vehicle interactions, traffic density and vehicle composition on turbulent kinetic energy(TKE). We show, for the first time, that the overall TKE from multiple vehicles traveling in series can be estimated by superimposing the TKE of each vehicle, without considering the distance between them while the distance is greater than one vehicle length. This finding is particularly significant since it enables a new approach to VIT simulations where the overall TKE is calculated as a function of number of vehicles. We found that the interactions between vehicles traveling next to each other in adjacent lanes are insignificant,regardless the directions of the traffic flow. Consequently, simulations of different traffic scenarios can be substantially simplified by treating two-way traffic as one-way traffic, with less than 5% difference in the overall volume-averaged TKE. We also developed equations that allow the estimation of the overall volume-averaged TKE as a function of the number and the type of vehicles.
基金supported by a Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology(No.2009-0077511)S.Lim acknowledges the support from Charles Phelps Taft Research Center,University of Cincinnatisupported by the Korea Student Aid Foundation(KOSAF)grant funded by the Korea government(MEST)(No.S2-2009-000-00256-1).
文摘We present a three dimensional model of an open elastic tube immersed in fluid to understand valveless pumping mechanism.A fluid-tube interaction problem is simulated by the volume conserved immersed boundarymethodwhich prevents the generation of spurious velocity field near the tube and local cluster of the tube surface.In order to explain pumping phenomena without valves,average net flow ismeasured by changing parameter values such as pumping frequency,compression duration,and pumping amplitude.Some frequencies that make the system reach maximal or minimal net flow are selected to study case by case.We also study the effectiveness of fluid mixing using the Shannon entropy increase rate.
文摘Experimentalists, numerical modellers and reactor modellers need to work together, not only just for validation of numerical codes, but also to shed fundamental light on each other＇s problems and underlying assumptions. Several examples are given, Experimental gas axial dispersion data provide a means of choosing the most appropriate boundary condition （no slip, partial slip or full slip） for particles at the wall of fluidized beds. CFD simulations help to identify how close ＂two-dimensional＂ experimental columns are to being truly two-dimensional and to representing three-dimensional columns. CFD also can be used to provide a more rational means of establishing assumptions needed in the modelling of two-phase fluidized bed reactors, for example how to deal with cases where there is a change in molar flow （and hence volumetric flow） as a result of chemical reactions.
基金This work was supported by the National Natural Science Foundation of China[52002264,52178459].
文摘A magnetorheological fluid(MRF)is a smart composite suspension composed of nonmagnetic liquid and soft magnetic particles.Carrier fluids can considerably influence the performance of MRFs;therefore,to investigate the effect of carrier fluids on MRFs,an SO/IL-MRF was prepared by mixing an ionic liquid(IL)with silicone oil(SO)in this study.Three types of MRF samples were prepared for experiments(pure SO,pure IL,and SO/IL).According to the experi-mental results,the SO/IL-MRF has better sedimentation stability than those based on pure SO and pure IL.Further,three methods were used to determine the shear yield stresses of the MRFs.The SO/IL-MRF achieved a higher shear yield stress than those of the other two because a network structure is formed between the ionic fragments and the molecular chains of the SO in the SO/IL-MRF.This increases the movement resistance of the particles in the carrier fluid,and it is unlike the mechanism of the IL-enhanced MRF.This work provides new ideas for improving the MRF performance.
基金supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 20306012 and 20806045the National Foundation of PR China for Authors of Excellent Doctoral Dissertations (No. 200245)Specialized Research Fund for Doctoral Program of Higher Education (No.20050003028)
文摘Numerical simulation of fully developed hydrodynamics of a riser and a downer was carried out using an Eulerian-Lagrangian model, where the particles are modeled by the discrete element method （DEM） and the gas by the Navier-Stokes equations. Periodic flow domain with two side walls was adopted to simulate the fully developed dynamics in a 2D channel of 10 cm in width. All the simulations were carried out under the same superficial gas velocity and solids holdup in the domain, starting with a homogenous state for both gas and solids, and followed by the evolution of the dynamics to the heterogeneous state with distinct clustering in the riser and the downer. In the riser, particle clusters move slowly, tending to suspend along the wall or to flow downwards, which causes wide residence time distribution of the particles. In the downer, clusters still exist, but they have faster velocities than the discrete particles. Loosely collected particles in the clusters move in the same direction as the bulk flow, resulting in plug flow in the downer. The residence time distribution （RTD） of solids was computed by tracking the displacements of all particles in the flow direction. The results show a rather wide RTD for the solids in the riser hut a sharp peak RTD in the downer, much in agreement with the experimental findings in the literature. The ensemble average of transient dynamics also shows reasonable profiles of solids volume fraction and solids velocity, and their dependence on particle density.
基金supported by special project of R&D and industrialization of Marine equipment of national development and reform commission of China(National Development and Reform Commission High Technology[2015]No.1409)。
文摘In this paper, the efficient utilization of liquefied natural gas(LNG) vaporization cold energy in offshore liquefied natural gas floating storage regasification unit(FSRU) is studied. On the basis of considering different boil-off gas(BOG) practical treatment processes, a cascade comprehensive utilization scheme of cold energy of LNG based on the longitudinal three-stage organic Rankine cycle power generation and the low-grade cold energy used to frozen seawater desalination was proposed. Through the comparative analysis of the effects of the pure working fluid and eight mixed working fluids on the performance of the new system, the combination scheme of system mixed working fluid with the highest exergy efficiency of the system was determined. Then, the genetic algorithm was used to optimize the parameters of the new system. After optimization, the net output power of the LNG cold energy comprehensive utilization system proposed in this paper was 5186 kW, and the exergy efficiency is 30.6%. Considering the power generation and freshwater revenue, the annual economic benefit of the system operating is 18.71 million CNY.
