Numerical Analysis of the Liquid-Gas-Solid Three Phase Flow Inside AWJ Nozzle

The multiphase flows inside the two abrasive waterjet (AWJ) nozzles with different abrasive inlet tube angles are simulated using the standard k-ε turbulence model based on the Euler-Lagrangian approach. The volume of fluid (VOF) method is employed to simulate the water-air multiphase flows. And, the abrasive particles are treated as dilute dispersed phase and tracked with the discrete particle method (DPM). The results indicate that the abrasive inlet tube angle has little impact on the water-phase flows. Further analysis shows that a larger abrasive inlet tube angle can enhance the particle accelerations. The particle number independence analysis is conducted, and the results indicate that sufficient particles should be tracked in order to obtain statistically representative results. The effects of particle initial velocities, particle shape factors, and the restitution coefficients on the predicted particle movements are further analyzed for the two nozzles with abrasive inlet tube angles of 45° and 60°. The results reveal that at the current velocity range, the particle initial velocities have little impact on the predicted particle velocities. However, both the shape factors and the restitution coefficients play an important role on the calculated particle velocities. The results provide a deeper understanding of particle acceleration performance inside the AWJ nozzles with different abrasive inlet tube angles

Simulation and Analysis of Cavitating Flow in the Draft Tube of the Francis Turbine with Splitter Blades at Off-Design Condition

Hydraulic plants are required to operate with wider operating range to cover the variants of power outputs into the electrical grid. Although there have been many studies of off-design conditions, studies of cavitating draft tube vortices at the Francis turbine with splitter blades are limited, and the cavitating property is not yet well comprehended. This study presents a prediction of the cavitating characteristics in the Francis-99 draft tube obtained by numerical analysis using the Zwart mass transfer model and shear-stress transport (SST) model. The shape characteristics of two types of cavitating vortex rope (spiral and columnar) and its influence on the cavitation development in the runner blades are analyzed. The link between cavitation with the vorticity is further highlighted by the vorticity transport equation (VTE). The result indicates that the runner cavitating is symmetric for both types of cavitating vortex ropes, and cavitation is significantly improved when a runner with splitter blade is used

DEVELOPMENT OF WORKFLOW FOR GREENERY PLACEMENT AND SELECTION ON BUILDING SURFACES

Master'sMASTER OF SCIENCE (RSH-BDG

Verification and validation of large eddy simulations of turbulent cavitating flow around two marine propellers with emphasis on the skew angle effects

Large eddy simulation (LES) was used to simulate turbulent cavitating flow around a conventional marine propeller (CP) and a highly skewed marine propeller (HSP) with emphasis on the skew angles effects. The LES verification and validation (V&V) analysis was carried out with cavitation influence on the flow structures. The current numerical results demonstrate that LES can give excellent predictions of the transient complex cavitating flows around a CP and a HSP with the numerical results agreeing well with experimental data. This study applies the LES V&V to the cavitating flow around two propellers with a simplified three-equation method. The results show that the LES errors for HSP are smaller than for CP, which is mainly resulted by more skewed blade of HSP than CP. In addition, the cavitation-vortex interactions around the propellers were studied using the relative vorticity transport equation. The results indicate that both the baroclinic torque term and the Coriolis force term have important influences on the vorticity generation and transport in the cavity closure region. Further analyses indicate that most of the important flow structures including the tip vortex, leading edge vortex, trailing vortex and internal jet are reproduced by the current LES simulations. Due to the different geometry features (less skewed blade of CP than HSP), significantly more intense and violent vortical structures and cavitation phenomena are observed on the CP than on the HSP

Prediction of H2O PVT relations at high temperatures by VHL equation of state

Based on the VHL equation of state(EOS) described by the L-J potential function, the water in the high-temperature situation is depicted by medium-high pressure thermodynamic states. The L-J potential function parameters of water adopt a temperature-dependent function form, and by using complex configuration optimization method, the specific value is obtained from the date in NIST during the range of 800K-1275K and 0.1GPa-1.0GPa. In order to test the suitability of VHL equation of state in high -temperature and medium-high pressure state, the theoretical and experimental data of higher temperature and pressure range are investigated. What’s more, the theoretical calculation results of VLW, DMW, BS and TIP4P equations of state are compared. The results show that, during the high-temperature and medium-high pressure section, the volumetric error of water calculated by VHL equation of state is less than 7%. Considering the uncertainty of the experimental data, it can be thought that the VHL equation of state and the temperature-dependent potential function form proposed in this paper can describe the state of water in high temperature, medium-high pressure better

Selective Oxidation of Toluene to Benzaldehyde Using Co-ZIF Nano-Catalyst

Nanometer-size Co-ZIF (zeolitic imidazolate frameworks) catalyst was prepared for selective oxidation of toluene to benzaldehyde under mild conditions. The typical characteristics of the metal-organic frameworks (MOFs) material were affirmed by the XRD, SEM, and TEM, the BET surface area of this catalyst was as high as 924.25 m2/g, and the diameter of particles was near 200 nm from TEM results. The Co metal was coated with 2-methyl glyoxaline, and the crystalline planes were relatively stable. The reaction temperatures, oxygen pressure, mass amount of N-hydroxyphthalimide (NHPI), and reaction time were discussed. The Co-ZIF catalyst gave the best result of 92.30% toluene conversion and 91.31% selectivity to benzaldehyde under 0.12 MPa and 313 K. The addition of a certain amount of NHPI and the smooth oxidate capacity of the catalyst were important factors in the high yield of benzaldehyde. This nanometer-size catalyst showed superior performance for recycling use in the oxidation of toluene. Finally, a possible reaction mechanism was proposed. This new nanometer-size Co-ZIF catalyst will be applied well in the selective oxidation of toluene to benzaldehyde