This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ...This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.展开更多
Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has bee...Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has been applied in the petrochemical industry since 1968,the JCPT has lower pressure drop, higher capacity and higher masstransfer efficiency, and seems promising in commercial application.展开更多
Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the perf...Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the performance of these applications and network utilization of data centers. Previous studies have addressed this issue by scheduling network flows with coflow semantics or optimizing VM placement with traffic considerations.However, coflow scheduling and VM placement have been conducted orthogonally. In fact, these two mechanisms are mutually dependent, and optimizing these two complementary degrees of freedom independently turns out to be suboptimal. In this paper, we present VirtCO, a practical framework that jointly schedules coflows and places VMs ahead of VM launch to optimize the overall performance of data center applications. We model the joint coflow scheduling and VM placement optimization problem, and propose effective heuristics for solving it. We further implement VirtCO with OpenStack and deploy it in a testbed environment. Extensive evaluation of real-world traces shows that compared with state-of-the-art solutions, VirtCO greatly reduces the average coflow completion time by up to 36.5%. This new framework is also compatible with and readily deployable within existing data center architectures.展开更多
The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a...The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a jet in a coflowing environment. As a typical length-scale model, the jet was divided into a number of distinct regimes in which a single parameter formed from a combination of the governing parameters dominates over the behaviour of a jet. In each of these regions we gave an integral solution which adequately describes the behavior of the jet. A set of length-scales was then defined for the transitions between each of the regions. It was found that the hybrid model could predict the velocity decay and radial growth of a jet as it moves downstream from the source and merges with ambient fluid in a coflowing environment. Comparisons computational results with the laboratory data for merging jet in a coflow indicate that the hybrid model predicts the behavior of the jet in each of the regimes well.展开更多
Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which i...Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which is newly used for the fundamental research into turbulent combustion. The characteristics of controllable active thermo-atmosphere (CATA) of a vitiated coflow combustor are investigated. The results show that the oxygen mole frac- tion of vitiated coflow flames between 0% and 21% yield coflow temperature between 700 and 1500 K, and there is a constant temperature space as a cylinder with a radius of 40 mm. These features of the vitiated coflow indicate the exis- tence of a controllable active thermo-atmosphere, which benefits the basic study on the autoignition of a combustible mixture in a homogeneous charge compression ignition (HCCI) combustion.展开更多
A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence m...A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence model is used in the mathematical model. The wall-function method is employed to treat the wall boundary condition at the bottom plane. The closed control equations are discretized by using Hybrid Finite Analytic Method (HFAM) on a non-uniform staggered grid system. The numerical results are obtained for different ratio of the jet velocity to the coflowing velocity. The comparison with experimental data shows good agreement.展开更多
The direct numerical simulation (DNS) method with 16 steps detailed chemical kinetics was applied to a lifted turbulent jet flame with H2/N2 fuel issuing into a wide hot coflow of lean combustion products,at temperatu...The direct numerical simulation (DNS) method with 16 steps detailed chemical kinetics was applied to a lifted turbulent jet flame with H2/N2 fuel issuing into a wide hot coflow of lean combustion products,at temperature of 1045 K and low oxygen concentrations. The chemical reactions were handled by the library function of CHEMKIN which was called by the main program in every time step. Parallel com-putational technology based on message passing interface method (MPI) was used in the simulation. All the cases were run by 12 CPUs on a high performance computer system. Faver-averaged DNS re-sults were obtained by long time averaging the transient profile and compared with the experimental data. The roll-up and evolution of the vortices in jet flame were well captured. The vortices in the same rotating direction attracted each other and those in different rotating directions repulsed each other. Through complex interactions between vortices,the original symmetrical vortex structure could be converted into nonsymmetrical and more complex structures by combination,distortion and splitting of the vortices. The transient profiles of H,OH and H2O mass fraction at 5.76 ms showed the flame structure in jet flame,especially the autoignition regions clearly. The lift-off height was about 9 d―11 d,in agreement with the experimental observation. At the corner point of the flame sheet indicated by OH and H profiles,the combustion was always enhanced by the flame curvature and extended resident time. The profiles of turbulence intensities show that the flames were diffused from the original two outside flame sheets into the core. The DNS results can be considered in developing more accurate and more universal turbulence models.展开更多
基金Supported by the National Natural Science Foundation of China （51276002）, and the Specific Research Fund for the Doctoral Program of Higher Education of China （20110001130014）.
文摘This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.
文摘Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has been applied in the petrochemical industry since 1968,the JCPT has lower pressure drop, higher capacity and higher masstransfer efficiency, and seems promising in commercial application.
基金supported by the National Key R&D Program of China(No.2017YFB1003000)the National Natural Science Foundation of China(Nos.61572129,61602112,61502097,61702096,61320106007,and 61632008)+4 种基金the International S&T Cooperation Program of China(No.2015DFA10490)the National Science Foundation of Jiangsu Province(Nos.BK20160695 and BK20170689)the Jiangsu Provincial Key Laboratory of Network and Information Security(No.BM2003201)the Key Laboratory of Computer Network and InformationIntegration of Ministry of Education of China(No.93K-9)supported by the Collaborative Innovation Center of Novel Software Technology and Industrialization and Collaborative Innovation Center of Wireless Communications Technology
文摘Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the performance of these applications and network utilization of data centers. Previous studies have addressed this issue by scheduling network flows with coflow semantics or optimizing VM placement with traffic considerations.However, coflow scheduling and VM placement have been conducted orthogonally. In fact, these two mechanisms are mutually dependent, and optimizing these two complementary degrees of freedom independently turns out to be suboptimal. In this paper, we present VirtCO, a practical framework that jointly schedules coflows and places VMs ahead of VM launch to optimize the overall performance of data center applications. We model the joint coflow scheduling and VM placement optimization problem, and propose effective heuristics for solving it. We further implement VirtCO with OpenStack and deploy it in a testbed environment. Extensive evaluation of real-world traces shows that compared with state-of-the-art solutions, VirtCO greatly reduces the average coflow completion time by up to 36.5%. This new framework is also compatible with and readily deployable within existing data center architectures.
文摘The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a jet in a coflowing environment. As a typical length-scale model, the jet was divided into a number of distinct regimes in which a single parameter formed from a combination of the governing parameters dominates over the behaviour of a jet. In each of these regions we gave an integral solution which adequately describes the behavior of the jet. A set of length-scales was then defined for the transitions between each of the regions. It was found that the hybrid model could predict the velocity decay and radial growth of a jet as it moves downstream from the source and merges with ambient fluid in a coflowing environment. Comparisons computational results with the laboratory data for merging jet in a coflow indicate that the hybrid model predicts the behavior of the jet in each of the regimes well.
基金supported by the National Basic Research Priorities Programme(973)(Grant No.2001CB209203)
文摘Turbulent combustion remains to be one of most complicated technologies due to the complexities of turbulence and combustion as well as the interaction of both. This paper presents a vitiated coflow combustor, which is newly used for the fundamental research into turbulent combustion. The characteristics of controllable active thermo-atmosphere (CATA) of a vitiated coflow combustor are investigated. The results show that the oxygen mole frac- tion of vitiated coflow flames between 0% and 21% yield coflow temperature between 700 and 1500 K, and there is a constant temperature space as a cylinder with a radius of 40 mm. These features of the vitiated coflow indicate the exis- tence of a controllable active thermo-atmosphere, which benefits the basic study on the autoignition of a combustible mixture in a homogeneous charge compression ignition (HCCI) combustion.
文摘A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence model is used in the mathematical model. The wall-function method is employed to treat the wall boundary condition at the bottom plane. The closed control equations are discretized by using Hybrid Finite Analytic Method (HFAM) on a non-uniform staggered grid system. The numerical results are obtained for different ratio of the jet velocity to the coflowing velocity. The comparison with experimental data shows good agreement.
基金China Postdoctoral Science Foundation (20060391042), the Key Project of Chinese National Programs for Fundamental Research and Development (2006CB200303)the National Natural Science Foundation for Distinguished Young Scholars (Grant No. 50525620)Natural Science Foundation of Zhejiang Prov-ince (Grant No. Z104314)
文摘The direct numerical simulation (DNS) method with 16 steps detailed chemical kinetics was applied to a lifted turbulent jet flame with H2/N2 fuel issuing into a wide hot coflow of lean combustion products,at temperature of 1045 K and low oxygen concentrations. The chemical reactions were handled by the library function of CHEMKIN which was called by the main program in every time step. Parallel com-putational technology based on message passing interface method (MPI) was used in the simulation. All the cases were run by 12 CPUs on a high performance computer system. Faver-averaged DNS re-sults were obtained by long time averaging the transient profile and compared with the experimental data. The roll-up and evolution of the vortices in jet flame were well captured. The vortices in the same rotating direction attracted each other and those in different rotating directions repulsed each other. Through complex interactions between vortices,the original symmetrical vortex structure could be converted into nonsymmetrical and more complex structures by combination,distortion and splitting of the vortices. The transient profiles of H,OH and H2O mass fraction at 5.76 ms showed the flame structure in jet flame,especially the autoignition regions clearly. The lift-off height was about 9 d―11 d,in agreement with the experimental observation. At the corner point of the flame sheet indicated by OH and H profiles,the combustion was always enhanced by the flame curvature and extended resident time. The profiles of turbulence intensities show that the flames were diffused from the original two outside flame sheets into the core. The DNS results can be considered in developing more accurate and more universal turbulence models.
