In ocean engineering, the applications are usually related to a free surface which brings so many interesting physical phenomena （e.g. water waves, impacts, splashing jets, etc.）. To model these complex free surface...In ocean engineering, the applications are usually related to a free surface which brings so many interesting physical phenomena （e.g. water waves, impacts, splashing jets, etc.）. To model these complex free surface flows is a tough and challenging task for most computational fluid dynamics （CFD） solvers which work in the Eulerian framework. As a Lagrangian and meshless method, smoothed particle hydrodynamics （SPH） offers a convenient tracking for different complex boundaries and a straightforward satisfaction for different boundary conditions. Therefore SPH is robust in modeling complex hydrodynamic problems characterized by free surface boundaries, multiphase interfaces or material discontinuities. Along with the rapid development of the SPH theory, related numerical techniques and high-performance computing technologies, SPH has not only attracted much attention in the academic community, but also gradually gained wide applications in industrial circles. This paper is dedicated to a review of the recent developments of SPH method and its typical applications in fluid-structure interactions in ocean engineering. Different numerical techniques for improving numerical accuracy, satisfying different boundary conditions, improving computational efficie- ncy, suppressing pressure fluctuations and preventing the tensile instability, etc., are introduced. In the numerical results, various typical fluid-structure interaction problems or multiphase problems in ocean engineering are described, modeled and validated. The prospective developments of SPH in ocean engineering are also discussed.展开更多
The present study summarizes the results of macro-and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio(H/D≤5) using the electrolytic tracer response technique and the method of p...The present study summarizes the results of macro-and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio(H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.展开更多
Experiments and simulations were conducted for bubble columns with diameter of 0.2 m(180 mm i.d.), 0.5 m(476 mm i.d.) and 0.8 m(760 mm i.d.) at high superficial gas velocities(0.12–0.62 m·s-1) and high solid con...Experiments and simulations were conducted for bubble columns with diameter of 0.2 m(180 mm i.d.), 0.5 m(476 mm i.d.) and 0.8 m(760 mm i.d.) at high superficial gas velocities(0.12–0.62 m·s-1) and high solid concentrations(0–30 vol%). Radial profiles of time-averaged gas holdup, axial liquid velocity, and turbulent kinetic energy were measured by using in-house developed conductivity probes and Pavlov tubes. Effects of column diameter, superficial gas velocity, and solid concentration were investigated in a wide range of operating conditions. Experimental results indicated that the average gas holdup remarkably increases with superficial gas velocity, and the radial profiles of investigated flow properties become steeper at high superficial gas velocities. The axial liquid velocities significantly increase with the growth of the column size, whereas the gas holdup was slightly affected. The presence of solid in bubble columns would inhibit the breakage of bubbles, which results in an increase in bubble rise velocity and a decrease in gas holdup, but time-averaged axial liquid velocities remain almost the same as that of the hollow column. Furthermore, a 2-D axisymmetric k–ε model was used to simulate heterogeneous bubbly flow using commercial code FLUENT 6.2. The lateral lift force and the turbulent diffusion force were introduced for the determination of gas holdup profiles and the effects of solid concentration were considered as the variation of average bubble diameter in the model. Results predicted by the CFD simulation showed good agreement with experimental data.展开更多
A slug flow model considering the dispersed bubbles entrained from the tail of Taylor bubble(TB) and recoalesced with the successive TB was proposed. Experiment was conducted to test the validity of this model by usin...A slug flow model considering the dispersed bubbles entrained from the tail of Taylor bubble(TB) and recoalesced with the successive TB was proposed. Experiment was conducted to test the validity of this model by using a high-speed camcorder and particle image velocimetry(PIV). It was found that the model was valid for predicting the characteristics of slug flow in airlift pump within average error of 14%. Moreover, large pipe diameter was found to accelerate the rise velocity of TB and decreases void fraction in liquid slug by a small margin.展开更多
Xenon was used as the gas phase to investigate the hydrodynamic characteristics in a bubble column.It was found that the flow pattern is mainly in the churn-turbulent flow regime through analysing the relationship bet...Xenon was used as the gas phase to investigate the hydrodynamic characteristics in a bubble column.It was found that the flow pattern is mainly in the churn-turbulent flow regime through analysing the relationship between the slip velocity and gas holdup.The influence of operating conditions on the gas holdup and the Sauter mean diameter was studied.The experimental results show that the Sauter mean diameter decreases with the increase of energy dissipation rate.A new correlation was developed to predict the Sauter mean diameter with an average error of less than 15%.展开更多
It is of vital significance to investigate mass transfer enhancements for chemical engineering processes.This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on b...It is of vital significance to investigate mass transfer enhancements for chemical engineering processes.This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas-liquid mass transfer process in a bubble column.Particle image velocimetry(PIV)technology was employed to analyze the flow field and bubble motion behavior,and dynamic oxygen absorption technology was used to measure the gas-liquid volumetric mass transfer coefficient(kLa).The effect of embedding wire mesh,adding solid particles,and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared.The results show that the gas-liquid interface area increases by 33%-72%when using the wire mesh coupling solid particles strategy compared to the gas-liquid two-phase flow,which is superior to the other two strengthening methods.Compared with the system without reinforcement,kLa in the bubble column increased by 0.5-1.8 times with wire mesh coupling solid particles method,which is higher than the sum of kLa increases with inserting wire mesh and adding particles,and the coupling reinforcement mechanism for affecting gas-liquid mass transfer process was discussed to provide a new idea for enhancing gas-liquid mass transfer.展开更多
Two kinds of gases were used to investigate the influence of gas density on the hydrodynamic characteristics in a bubble column. It can be found out that higher gas density leads to smaller bubble diameter and the flo...Two kinds of gases were used to investigate the influence of gas density on the hydrodynamic characteristics in a bubble column. It can be found out that higher gas density leads to smaller bubble diameter and the flow patterns are different for the both gases. Energy balance mechanisms are analyzed by considering the gas density difference. Models were developed to predict the average bubble diameter with good accuracy.展开更多
Three different types of gas distributors were used in an external loop airlift slurry reactor to investigate the hydrodynamic characteristics. To predict the important hydrodynamic parameters, such as the total gas h...Three different types of gas distributors were used in an external loop airlift slurry reactor to investigate the hydrodynamic characteristics. To predict the important hydrodynamic parameters, such as the total gas holdup, the slurry circulating velocity, the bubble size distribution, and the slip velocity between the gas phase and the slurry phase, the correlations are developed. The calculated results fit the experimental data very well. According to the influence of the solid holdup on the bubble size, the fluid flow in the reactor can be divided into two regimes, while a 10% value is regarded as the critical solid holdup value. When εs is≤10%, the bubble size is determined by both the gas phase and the slurry phase. When εs is ≥10%, the bubble size is determined mainly by the slurry phase. By analyzing the relationship between the slip velocity and the gas holdup, the bubble coalescence plays a key role in the slurry reactor.展开更多
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.U1430236,51609049)the China Postdoctoral Science Foundation(Grant No.2015M581432)the China Scholarship Council(CSC,Grant No.201506680004)
文摘In ocean engineering, the applications are usually related to a free surface which brings so many interesting physical phenomena （e.g. water waves, impacts, splashing jets, etc.）. To model these complex free surface flows is a tough and challenging task for most computational fluid dynamics （CFD） solvers which work in the Eulerian framework. As a Lagrangian and meshless method, smoothed particle hydrodynamics （SPH） offers a convenient tracking for different complex boundaries and a straightforward satisfaction for different boundary conditions. Therefore SPH is robust in modeling complex hydrodynamic problems characterized by free surface boundaries, multiphase interfaces or material discontinuities. Along with the rapid development of the SPH theory, related numerical techniques and high-performance computing technologies, SPH has not only attracted much attention in the academic community, but also gradually gained wide applications in industrial circles. This paper is dedicated to a review of the recent developments of SPH method and its typical applications in fluid-structure interactions in ocean engineering. Different numerical techniques for improving numerical accuracy, satisfying different boundary conditions, improving computational efficie- ncy, suppressing pressure fluctuations and preventing the tensile instability, etc., are introduced. In the numerical results, various typical fluid-structure interaction problems or multiphase problems in ocean engineering are described, modeled and validated. The prospective developments of SPH in ocean engineering are also discussed.
基金Supported by the National Basic Research Program of China(2012CB224806)the National Science Fund for Distinguished Young Scholars(21025627)+2 种基金the National Natural Science Foundation of China(21206166,20990224)the National High Technology Research and Development Program of China(2012AA03A606)Beijing Natural Science Foundation(2112038)
文摘The present study summarizes the results of macro-and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio(H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.
基金Supported by the National High Technology Research and Development Program of China(2011AA05A205)the National Natural Science Foundation of China(U1162125,U1361112)
文摘Experiments and simulations were conducted for bubble columns with diameter of 0.2 m(180 mm i.d.), 0.5 m(476 mm i.d.) and 0.8 m(760 mm i.d.) at high superficial gas velocities(0.12–0.62 m·s-1) and high solid concentrations(0–30 vol%). Radial profiles of time-averaged gas holdup, axial liquid velocity, and turbulent kinetic energy were measured by using in-house developed conductivity probes and Pavlov tubes. Effects of column diameter, superficial gas velocity, and solid concentration were investigated in a wide range of operating conditions. Experimental results indicated that the average gas holdup remarkably increases with superficial gas velocity, and the radial profiles of investigated flow properties become steeper at high superficial gas velocities. The axial liquid velocities significantly increase with the growth of the column size, whereas the gas holdup was slightly affected. The presence of solid in bubble columns would inhibit the breakage of bubbles, which results in an increase in bubble rise velocity and a decrease in gas holdup, but time-averaged axial liquid velocities remain almost the same as that of the hollow column. Furthermore, a 2-D axisymmetric k–ε model was used to simulate heterogeneous bubbly flow using commercial code FLUENT 6.2. The lateral lift force and the turbulent diffusion force were introduced for the determination of gas holdup profiles and the effects of solid concentration were considered as the variation of average bubble diameter in the model. Results predicted by the CFD simulation showed good agreement with experimental data.
基金Supported by the National Key Basic Research Development Program of China(2014CB239200)the National Natural Science Foundation of China(51574173,51705372)+1 种基金the Hubei Provincial Natural Science Foundation(2015CFA154)Jiangsu Provincial Natural Science Foundation of China(No.BK20170411)
文摘A slug flow model considering the dispersed bubbles entrained from the tail of Taylor bubble(TB) and recoalesced with the successive TB was proposed. Experiment was conducted to test the validity of this model by using a high-speed camcorder and particle image velocimetry(PIV). It was found that the model was valid for predicting the characteristics of slug flow in airlift pump within average error of 14%. Moreover, large pipe diameter was found to accelerate the rise velocity of TB and decreases void fraction in liquid slug by a small margin.
文摘Xenon was used as the gas phase to investigate the hydrodynamic characteristics in a bubble column.It was found that the flow pattern is mainly in the churn-turbulent flow regime through analysing the relationship between the slip velocity and gas holdup.The influence of operating conditions on the gas holdup and the Sauter mean diameter was studied.The experimental results show that the Sauter mean diameter decreases with the increase of energy dissipation rate.A new correlation was developed to predict the Sauter mean diameter with an average error of less than 15%.
基金supported by the Key Research and Development Plan of Shandong Province(the Major Scientific and Technological Innovation Projects,2021ZDSYS13)the Natural Science Foundation of Shandong Province(ZR2021MB135)Natural Science Foundation of Shandong Province(ZR2021ME224).
文摘It is of vital significance to investigate mass transfer enhancements for chemical engineering processes.This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas-liquid mass transfer process in a bubble column.Particle image velocimetry(PIV)technology was employed to analyze the flow field and bubble motion behavior,and dynamic oxygen absorption technology was used to measure the gas-liquid volumetric mass transfer coefficient(kLa).The effect of embedding wire mesh,adding solid particles,and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared.The results show that the gas-liquid interface area increases by 33%-72%when using the wire mesh coupling solid particles strategy compared to the gas-liquid two-phase flow,which is superior to the other two strengthening methods.Compared with the system without reinforcement,kLa in the bubble column increased by 0.5-1.8 times with wire mesh coupling solid particles method,which is higher than the sum of kLa increases with inserting wire mesh and adding particles,and the coupling reinforcement mechanism for affecting gas-liquid mass transfer process was discussed to provide a new idea for enhancing gas-liquid mass transfer.
基金financially supported by the National Key Basic Research Development Program "973" Project (2012CB224806) of China
文摘Two kinds of gases were used to investigate the influence of gas density on the hydrodynamic characteristics in a bubble column. It can be found out that higher gas density leads to smaller bubble diameter and the flow patterns are different for the both gases. Energy balance mechanisms are analyzed by considering the gas density difference. Models were developed to predict the average bubble diameter with good accuracy.
文摘Three different types of gas distributors were used in an external loop airlift slurry reactor to investigate the hydrodynamic characteristics. To predict the important hydrodynamic parameters, such as the total gas holdup, the slurry circulating velocity, the bubble size distribution, and the slip velocity between the gas phase and the slurry phase, the correlations are developed. The calculated results fit the experimental data very well. According to the influence of the solid holdup on the bubble size, the fluid flow in the reactor can be divided into two regimes, while a 10% value is regarded as the critical solid holdup value. When εs is≤10%, the bubble size is determined by both the gas phase and the slurry phase. When εs is ≥10%, the bubble size is determined mainly by the slurry phase. By analyzing the relationship between the slip velocity and the gas holdup, the bubble coalescence plays a key role in the slurry reactor.
