Relaxation Effects in Small Critical Nozzles

We computed the flow of four gases (He, N2, CO2, and SF6) through a critical flow venturi (CFV) by augmenting traditional computational fluid dynamics (CFD) with a rate equation that accounts for τrelax, a species-dependent relaxation time that characterizes the equilibration of the vibrational degrees of freedom with the translational and rotational degrees of freedom. Conventional CFD (τrelax=0) underpredicts the flow through small CFVs (throat diameter d=0.593mm) by up to 2.3% for CO2 and by up to 1.2% for SF6. When we used values of τrelax from the acoustics literature, the augmented CFD underpredicted the flow for SF6 by only 0.3%, in the worst case. The augmented predictions for CO2 were within the scatter of previously published experimental data (±0.1%). As expected, both conventional and augmented CFD agree with experiments for He and N2. Thus, augmented CFD enables one to calibrate a small CFV with one gas (e.g., N2) and to use these results as a flow standard with other gases (e.g., CO2) for which reliable values of τrelax and the relaxing heat capacity are available.

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Elastically Mounted Double Aerodynamic Pendulum

International Journal of Structural Stability and Dynamics ◽

10.1142/s0219455419410074 ◽

2019 ◽

Vol 19 (05) ◽

pp. 1941007 ◽

Cited By ~ 1

Author(s):

Yury D. Selyutskiy ◽

Andrei P. Holub ◽

Marat Z. Dosaev

Keyword(s):

Experimental Data ◽

Numerical Simulation ◽

Degrees Of Freedom ◽

State University ◽

Periodic Motions ◽

Aeroelastic System ◽

Subsonic Wind Tunnel ◽

Trivial Equilibrium ◽

Rotational Degrees Of Freedom ◽

Moscow State University

Elastically mounted double aerodynamic pendulum is an aeroelastic system with two rotational degrees of freedom. A wing is attached to the second link of the pendulum. It is shown that it is possible to select values of parameters in such a way as to make the trivial equilibrium (where both links of the pendulum are stretched along the flow) unstable. Numerical simulation of behavior of the system in such situations is performed, and arising limit cycles are studied. Experimental investigation of such aerodynamic pendulum is performed in the subsonic wind tunnel of the Institute of Mechanics of Lomonosov Moscow State University. Characteristics of periodic motions are registered for different values of parameters of the system. It is shown that experimental data are in qualitative agreement with results of numerical simulation.

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Swirling Flow Through Venturi Tubes of Convergent Angle 10.5° and 21°

Volume 2: Fora ◽

10.1115/fedsm2006-98229 ◽

2006 ◽

Cited By ~ 2

Author(s):

Jeff Gibson ◽

Michael Reader-Harris

Keyword(s):

Fluid Dynamics ◽

Experimental Data ◽

Computational Fluid Dynamics ◽

Reynolds Number ◽

Swirling Flow ◽

Computational Fluid Dynamics Cfd ◽

Flow Through ◽

Good Agreement

Computational Fluid Dynamics (CFD) was used to compute the effect of two bends in perpendicular planes on the performance of 4-inch Venturi tubes with β = 0.4, 0.6 and 0.75 for water at a Reynolds number of 350,000 and at various distances from the bend. Two types of Venturi tubes were analysed, the first having a standard convergent angle of 21°, the second having a non-standard convergent angle of 10.5°. Good agreement with experiment was obtained. Swirling axisymmetric flows were computed to help interpret experimental data.

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A computational study on airflow balancing in a horticultural drying chamber

Transactions of the Canadian Society for Mechanical Engineering ◽

10.1139/tcsme-2019-0016 ◽

2020 ◽

Vol 44 (2) ◽

pp. 189-201 ◽

Cited By ~ 1

Author(s):

Mahmoud Elhalwagy ◽

Anthony Straatman ◽

Bernard Goyette ◽

Gideon Avigad

Keyword(s):

Fluid Dynamics ◽

Experimental Data ◽

Computational Fluid Dynamics ◽

Computational Study ◽

Additional Variable ◽

Variable Resistance ◽

Computational Fluid Dynamics Cfd ◽

Flow Through ◽

Resistance Coefficients ◽

Drying Chamber

Simulations were conducted to study the airflow across skids of grapes in a horticultural grape drying chamber for the purpose of balancing the airflow to produce a uniform drying environment. The focus of the study was on the approach taken to provide balanced airflow using a computational fluid dynamics (CFD) tool combined with experimental data. The process was to first characterize the crate stacks by comparison of airflow simulations across a single crate stack to experimental data to establish resistance coefficients. The next step was to use these coefficients to simulate a row of stacked skids to establish corrections in terms of additional (variable) resistance that would result in balanced airflow. The corrected model was then used to simulate flow through the entire horticultural chamber to confirm that under the conditions of fan operation, the balance of airflow persists. The study shows that while the unmodified stacks had nearly 20% imbalance from the first to the last stack, the stack with resistance modifiers corrected this imbalance to within 5%, which is considered suitable for operation of the chamber.

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On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

10.26434/chemrxiv.8870594.v2 ◽

2019 ◽

Author(s):

Riccardo Spezia ◽

Hichem Dammak

Keyword(s):

Degrees Of Freedom ◽

Molecular Simulations ◽

Zero Point ◽

Thermal Bath ◽

Unimolecular Dissociation ◽

Point Energy ◽

Rotational Degrees Of Freedom ◽

The Difference ◽

Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

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Comparison of Aerobic and Anoxic-Aerobic Digestion of Waste Activated Sludge

Water Science & Technology ◽

10.2166/wst.1985.0068 ◽

1985 ◽

Vol 17 (8) ◽

pp. 1475-1478 ◽

Cited By ~ 6

Author(s):

A P. C. Warner ◽

G. A. Ekama ◽

G v. R. Marais

Keyword(s):

Experimental Data ◽

Activated Sludge ◽

Waste Activated Sludge ◽

Activated Sludge Process ◽

Cycle Times ◽

Waste Sludge ◽

Volatile Solids ◽

In Series ◽

Flow Through ◽

Theoretical Simulations

The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge of which was fed to a number of digesters operated as follows: single reactor flow through digesters at 4 or 6 days sludge age, under aerobic and anoxic-aerobic conditions (with 1,5 and 4 h cycle times) and 3-in-series flow through aerobic digesters each at 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model for the aerobic activated sludge process set out by Dold et al., (1980) and extended to the anoxic-aerobic process by van Haandel et al., (1981) simulated accurately all the experimental data (Figs 1 to 4) without the need for adjusting the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate is independent of sludge age and is K4T = 0,046(l,029)(T-20) mgNO3-N/(mg active VSS. d) i.e. about 2/3 of that in the secondary anoxic of the single sludge activated sludge stystem. An important consequence of (i) and (ii) above is that denitrification can be integrated easily in the steady state digester model of Marais and Ekama (1976) and used for design (Warner et al., 1983).

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Two-phase countercurrent flow through a bed of packing. VII. Pressure drop at flooding and critical flow rates of both phases in packed bed of spheres

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19721666 ◽

1972 ◽

Vol 37 (5) ◽

pp. 1666-1670

Author(s):

V. Kolář ◽

Z. Brož

Keyword(s):

Pressure Drop ◽

Packed Bed ◽

Critical Flow ◽

Countercurrent Flow ◽

Two Phase ◽

Flow Rates ◽

Flow Through

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Effects of Over Fire Air on the Combustion and NOx Emission Characteristics of a 600 MW Opposed Swirling Fired Boiler

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.512-515.2135 ◽

2012 ◽

Vol 512-515 ◽

pp. 2135-2142 ◽

Cited By ~ 5

Author(s):

Yu Peng Wu ◽

Zhi Yong Wen ◽

Yue Liang Shen ◽

Qing Yan Fang ◽

Cheng Zhang ◽

...

Keyword(s):

Fluid Dynamics ◽

Experimental Data ◽

Empirical Method ◽

Nox Emission ◽

Emission Characteristics ◽

Cfd Model ◽

Nitrogen Release ◽

Computational Fluid Dynamics Cfd ◽

Low Nox Emission

A computational fluid dynamics (CFD) model of a 600 MW opposed swirling coal-fired utility boiler has been established. The chemical percolation devolatilization (CPD) model, instead of an empirical method, has been adapted to predict the nitrogen release during the devolatilization. The current CFD model has been validated by comparing the simulated results with the experimental data obtained from the boiler for case study. The validated CFD model is then applied to study the effects of ratio of over fire air (OFA) on the combustion and nitrogen oxides (NOx) emission characteristics. It is found that, with increasing the ratio of OFA, the carbon content in fly ash increases linearly, and the NOx emission reduces largely. The OFA ratio of 30% is optimal for both high burnout of pulverized coal and low NOx emission. The present study provides helpful information for understanding and optimizing the combustion of the studied boiler

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Three-dimensional asymmetric maximum weight lifting prediction considering dynamic joint strength

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1177/0954411920987035 ◽

2021 ◽

pp. 095441192098703

Author(s):

Rahid Zaman ◽

Yujiang Xiang ◽

Jazmin Cruz ◽

James Yang

Keyword(s):

Experimental Data ◽

Degrees Of Freedom ◽

Inverse Dynamics ◽

Three Dimensional ◽

Optimization Method ◽

Weight Lifting ◽

Joint Torque ◽

Maximum Weight ◽

Angular Velocities ◽

Asymmetric Lifting

In this study, the three-dimensional (3D) asymmetric maximum weight lifting is predicted using an inverse-dynamics-based optimization method considering dynamic joint torque limits. The dynamic joint torque limits are functions of joint angles and angular velocities, and imposed on the hip, knee, ankle, wrist, elbow, shoulder, and lumbar spine joints. The 3D model has 40 degrees of freedom (DOFs) including 34 physical revolute joints and 6 global joints. A multi-objective optimization (MOO) problem is solved by simultaneously maximizing box weight and minimizing the sum of joint torque squares. A total of 12 male subjects were recruited to conduct maximum weight box lifting using squat-lifting strategy. Finally, the predicted lifting motion, ground reaction forces, and maximum lifting weight are validated with the experimental data. The prediction results agree well with the experimental data and the model’s predictive capability is demonstrated. This is the first study that uses MOO to predict maximum lifting weight and 3D asymmetric lifting motion while considering dynamic joint torque limits. The proposed method has the potential to prevent individuals’ risk of injury for lifting.

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