Numerical Investigation of Delft-Jet-in-Hot-Coflow (DJHC) Burner Using Probability Density Function (PDF) Transport Modeling

2013 ◽  
Author(s):  
Ashoke De ◽  
Akshay Dongre ◽  
Rakesh Yadav
Keyword(s):  
Reynolds Number ◽  
Molecular Diffusion ◽  
Minimum Spanning Tree ◽  
Transport Modeling ◽  
Low Oxygen ◽  
Energy Profiles ◽  
Numerical Predictions ◽  
Model Predictions ◽  
Solution Methods ◽  
Good Agreement

In the present paper, the flames from DJHC burner, imitating MILD (Moderate and Intense Low Oxygen Dilution) combustion, are simulated using PDF transport modeling. Two different solution approaches have been used to resolve the joint composition PDF. First, a Lagrangian approach is used to solve the joint composition PDF, while in the second approach, the approximate solution is achieved by using presumed shape PDF and DQMOM-IEM modeling known as Multi-Environment Eulerian PDF (MEPDF). A quantitative comparison of the predictions from these two solution methods has been performed for two different jet Reynolds number, i.e. Re = 4100 & 8800. Moreover, the effect of molecular diffusion is also explored by comparing the predictions using different micro-mixing models such as Coalescence Dispersion (CD), Euclidean Minimum Spanning Tree (EMST), and Interaction-by-Exchange-with-Mean (IEM) model. The obtained numerical predictions from both approaches are compared with the experimental data to highlight the accuracy as well as the predictive capability of these models. In the case of low Reynolds number (Re = 4100), it is observed that the mean axial velocity and turbulent kinetic energy profiles are in good agreement with the measurements while the temperature profiles are slightly over-predicted in the downstream region. Although MEPDF results are in good agreement with the LPDF results, both the model predictions tend to exhibit discrepancies at higher Reynolds number.

3D Numerical Simulation and PEPT Experimental Investigation of Pressurized Gas-Solid Fluidized Bed Hydrodynamic

2009 ◽  
Author(s):  
P. Fede ◽  
G. Moula ◽  
A. Ingram ◽  
T. Dumas ◽  
O. Simonin
Keyword(s):  
Numerical Model ◽  
Fluidized Bed ◽  
Particle Velocity ◽  
Particle Trajectory ◽  
Wall Region ◽  
3 Dimensional ◽  
The Core ◽  
Numerical Predictions ◽  
Model Predictions ◽  
Good Agreement

The present paper is dedicated to numerical and experimental study of the hydrodynamic of a non-reactive isothermal pressurized fluidized bed. Experimental data have been obtained using PEPT technique allowing to track a particle trajectory inside a dense fluidized bed. A specific post-processing approach has been developed to compute the Eulerian time-averaged particle velocity field. The comparison with 3-dimensional numerical model predictions shows a good agreement in the core of the fluidized bed. In contrast, in the near wall region the numerical model overestimate the downward particle velocity. The modification of particle phase wall boundary condition improves the numerical predictions.

Effect of microgravity and hypergravity on deposition of 0.5- to 3-μm-diameter aerosol in the human lung

1997 ◽  
Vol 83 (6) ◽  
pp. 2029-2036 ◽  
Author(s):  
Chantal Darquenne ◽  
Manuel Paiva ◽  
John B. West ◽  
G. Kim Prisk
Keyword(s):  
Particle Size ◽  
Tidal Volume ◽  
Flow Rate ◽  
Human Lung ◽  
Constant Flow ◽  
Parabolic Flights ◽  
Constant Flow Rate ◽  
Numerical Predictions ◽  
Model Predictions ◽  
Good Agreement

Darquenne, Chantal, Manuel Paiva, John B. West, and G. Kim Prisk. Effect of microgravity and hypergravity on deposition of 0.5- to 3-μm-diameter aerosol in the human lung. J. Appl. Physiol. 83(6): 2029–2036, 1997.—We measured intrapulmonary deposition of 0.5-, 1-, 2-, and 3-μm-diameter particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (μG) and at ∼1.6 G. Subjects breathed aerosols at a constant flow rate (0.4 l/s) and tidal volume (0.75 liter). At 1 G and ∼1.6 G, deposition increased with increasing particle size. In μG, differences in deposition as a function of particle size were almost abolished. Deposition was a nearly linear function of the G level for 2- and 3-μm-diameter particles, whereas for 0.5- and 1.0-μm-diameter particles, deposition increased less between μG and 1 G than between 1 G and ∼1.6 G. Comparison with numerical predictions showed good agreement for 1-, 2-, and 3-μm-diameter particles at 1 and ∼1.6 G, whereas the model consistently underestimated deposition in μG. The higher deposition observed in μG compared with model predictions might be explained by a larger deposition by diffusion because of a higher alveolar concentration of aerosol in μG and to the nonreversibility of the flow, causing additional mixing of the aerosols.

Heat Transfer Committee and Turbomachinery Committee Best Paper of 1996 Award: The Path to Predicting Bypass Transition

1997 ◽  
Vol 119 (3) ◽  
pp. 405-411 ◽  
Author(s):  
R. E. Mayle ◽  
A. Schulz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Energy Equation ◽  
Free Stream ◽  
Bypass Transition ◽  
Turbulence Level ◽  
Free Stream Turbulence ◽  
Energy Profiles ◽  
Computer Codes ◽  
Good Agreement

A theory is presented for calculating the fluctuations in a laminar boundary layer when the free stream is turbulent. The kinetic energy equation for these fluctuations is derived and a new mechanism is revealed for their production. A methodology is presented for solving the equation using standard boundary layer computer codes. Solutions of the equation show that the fluctuations grow at first almost linearly with distance and then more slowly as viscous dissipation becomes important. Comparisons of calculated growth rates and kinetic energy profiles with data show good agreement. In addition, a hypothesis is advanced for the effective forcing frequency and free-stream turbulence level that produce these fluctuations. Finally, a method to calculate the onset of transition is examined and the results compared to data.

Rigid-Plastic Impact of Single Angular Particles

2021 ◽  
Author(s):  
Sandeep Dhar
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Orientation Dependence ◽  
Particle Orientation ◽  
Rigid Plastic ◽  
Plastic Model ◽  
Model Predictions ◽  
Good Agreement ◽  
Angular Particles

The trajectory of an angular particle as it cuts a ductile target is, in general, complicated because of its dependence not only on particle shape, but also on particle orientation at the initial instant of impact. This orientation dependence has also made experimental measurement of impact parameters of single angular particles very difficult, resulting in a relatively small amount of available experimental data in the literature. The current work is focused on obtaining measurements of particle kinematics for comparison to rigid plastic model developed by Papini and Spelt. Fundamental mechanisms of material removal are identified, and measurements of rebound parameters and corresponding crater dimensions of single hardened steel particles launched against flat aluminium alloy targets are presented. Also a 2-D finite element model is developed and a dynamic analysis is performed to predict the erosion mechanism. Overall, a good agreement was found among the experimental results, rigid-plastic model predictions and finite element model predictions.

Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings

2017 ◽  
Author(s):  
Marcel Mahner ◽  
Pu Li ◽  
Andreas Lehn ◽  
Bernhard Schweizer
Keyword(s):  
Reynolds Equation ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Compressible Fluids ◽  
Experimental Investigations ◽  
Hysteresis Curves ◽  
Numerical Predictions ◽  
Bearing Stiffness ◽  
Gasdynamic Model ◽  
Good Agreement

A detailed elasto-gasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The 2D pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the bearing stiffness (in particular for moderate shaft displacements) and the bearing damping.

Viscosity Models Based on Network Theory for Polymer Melts

2010 ◽  
Vol 129-131 ◽  
pp. 1244-1247
Author(s):  
Hai Hang Xu ◽  
Lei Zhong
Keyword(s):  
Experimental Data ◽  
Kinetic Equation ◽  
Constitutive Equation ◽  
Polymer Composites ◽  
Network Theory ◽  
Polymer Melts ◽  
Structure Parameter ◽  
Viscosity Models ◽  
Model Predictions ◽  
Good Agreement

New shear and extensional viscosity models based on Fredrickson kinetic equation coupled with Dewitt constitutive equation were established to predict viscosities of polymer melts. The experimental data of 125°C LDPE and LDPE filled with 35% glass beads reported from references were compared with the model predictions. The predictions showed good agreement with the measurements. The models are simple and easy to use. Because they contain no structure parameter, they are capable to describe the viscosities of pure polymer and polymer composites.

Comparison of Four Friction Models: Feature Prediction

2015 ◽  
Vol 11 (3) ◽  
Author(s):  
Yun-Hsiang Sun ◽  
Tao Chen ◽  
Christine Qiong Wu ◽  
Cyrus Shafai
Keyword(s):  
Numerical Model ◽  
Viscous Friction ◽  
Friction Model ◽  
Dynamic Features ◽  
Numerical Predictions ◽  
Wide Range ◽  
Model Predictions ◽  
Friction Models ◽  
Parameter Identifications ◽  
Model Structures

In this paper, we provide not only key knowledge for friction model selection among candidate models but also experimental friction features compared with numerical predictions reproduced by the candidate models. A motor-driven one-dimensional sliding block has been designed and fabricated in our lab to carry out a wide range of control tasks for the friction feature demonstrations and the parameter identifications of the candidate models. Besides the well-known static features such as break-away force and viscous friction, our setup experimentally demonstrates subtle dynamic features that characterize the physical behavior. The candidate models coupled with correct parameters experimentally obtained from our setup are taken to simulate the features of interest. The first part of this work briefly introduces the candidate friction models, the friction features of interest, and our experimental approach. The second part of this work is dedicated to the comparisons between the experimental features and the numerical model predictions. The discrepancies between the experimental features and the numerical model predictions help researchers to judge the accuracy of the models. The relation between the candidate model structures and their numerical friction feature predictions is investigated and discussed. A table that summarizes how to select the most optimal friction model among a variety of engineering applications is presented at the end of this paper. Such comprehensive comparisons have not been reported in previous literature.

Low-Reynolds-number flow around an oscillating circular cylinder at low Keulegan–Carpenter numbers

1998 ◽  
Vol 360 ◽  
pp. 249-271 ◽  
Author(s):  
H. DÜTSCH ◽  
F. DURST ◽  
S. BECKER ◽  
H. LIENHART
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Time Step ◽  
Time Resolved ◽  
Reynolds Number Flow ◽  
Line Force ◽  
Number Flow ◽  
Weakly Stable ◽  
Fluid Behaviour ◽  
Good Agreement

Time-averaged LDA measurements and time-resolved numerical flow predictions were performed to investigate the laminar flow induced by the harmonic in-line oscillation of a circular cylinder in water at rest. The key parameters, Reynolds number Re and Keulegan–Carpenter number KC, were varied to study three parameter combinations in detail. Good agreement was observed for Re=100 and KC=5 between measurements and predictions comparing phase-averaged velocity vectors. For Re=200 and KC=10 weakly stable and non-periodic flow patterns occurred, which made repeatable time-averaged measurements impossible. Nevertheless, the experimentally visualized vortex dynamics was reproduced by the two-dimensional computations. For the third combination, Re=210 and KC=6, which refers to a totally different flow regime, the computations again resulted in the correct fluid behaviour. Applying the widely used model of Morison et al. (1950) to the computed in-line force history, the drag and the added-mass coefficients were calculated and compared for different grid levels and time steps. Using these to reproduce the force functions revealed deviations from those originally computed as already noted in previous studies. They were found to be much higher than the deviations for the coarsest computational grid or the largest time step. The comparison of several in-line force coefficients with results obtained experimentally by Kühtz (1996) for β=35 confirmed that force predictions could also be reliably obtained by the computations.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

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