scholarly journals Experimental investigation of turbulent suspensions of spherical particles in a square duct

2018 ◽  
Vol 857 ◽  
pp. 748-783 ◽  
Author(s):  
Sagar Zade ◽  
Pedro Costa ◽  
Walter Fornari ◽  
Fredrik Lundell ◽  
Luca Brandt
Keyword(s):  
Particle Size ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Single Phase ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Spherical Particles ◽  
Particle Sizes ◽  
Duct Flow ◽  
Square Duct

We report experimental observations of turbulent flow with spherical particles in a square duct. Three particle sizes, namely $2H/d_{p}=40$ , 16 and 9 ( $2H$ being the duct full height and $d_{p}$ being the particle diameter), are investigated. The particles are nearly neutrally buoyant with a density ratio of 1.0035 and 1.01 with respect to the suspending fluid. Refractive index matched–particle image velocimetry (RIM–PIV) is used for fluid velocity measurement even at the highest particle volume fraction (20 %) and particle tracking velocimetry (PTV) for the particle velocity statistics for the flows seeded with particles of the two largest sizes, whereas only pressure measurements are reported for the smallest particles. Settling effects are seen at the lowest bulk Reynolds number $Re_{2H}\approx$ 10 000, whereas, at the highest $Re_{2H}\approx 27\,000$ , particles are in almost full suspension. The friction factor of the suspensions is found to be significantly larger than that of single-phase duct flow at the lower $Re_{2H}$ investigated; however, the difference decreases when increasing the flow rate and the total drag approaches the values of the single-phase flow at the higher Reynolds number considered, $Re_{2H}=27\,000$ . The pressure drop is found to decrease with the particle diameter for volume fractions lower than $\unicode[STIX]{x1D719}=10\,\%$ for nearly all $Re_{2H}$ investigated. However, at the highest volume fraction $\unicode[STIX]{x1D719}=20\,\%$ , we report a peculiar non-monotonic behaviour: the pressure drop first decreases and then increases with increasing particle size. The decrease of the turbulent drag with particle size at the lowest volume fractions is related to an attenuation of the turbulence. The drag increase for the two largest particle sizes at $\unicode[STIX]{x1D719}=20\,\%$ , however, occurs despite this large reduction of the turbulent stresses, and it is therefore due to significant particle-induced stresses. At the lowest Reynolds number, the particles reside mostly in the bottom half of the duct, where the mean velocity significantly decreases; the flow is similar to that in a moving porous bed near the bottom wall and to turbulent duct flow with low particle concentration near the top wall.

scholarly journals Suspensions of finite-size neutrally buoyant spheres in turbulent duct flow

2018 ◽  
Vol 851 ◽  
pp. 148-186 ◽  
Author(s):  
Walter Fornari ◽  
Hamid Tabaei Kazerooni ◽  
Jeanette Hussong ◽  
Luca Brandt
Keyword(s):  
Reynolds Number ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Secondary Flows ◽  
Duct Flow ◽  
Turbulent Kinetic Energy Budget ◽  
Square Duct ◽  
The Core ◽  
The Mean ◽  
Neutrally Buoyant

We study the turbulent square duct flow of dense suspensions of neutrally buoyant spherical particles. Direct numerical simulations (DNS) are performed in the range of volume fractions $\unicode[STIX]{x1D719}=0{-}0.2$, using the immersed boundary method (IBM) to account for the dispersed phase. Based on the hydraulic diameter a Reynolds number of 5600 is considered. We observe that for $\unicode[STIX]{x1D719}=0.05$ and 0.1, particles preferentially accumulate on the corner bisectors, close to the corners, as also observed for laminar square duct flows of the same duct-to-particle size ratio. At the highest volume fraction, particles preferentially accumulate in the core region. For plane channel flows, in the absence of lateral confinement, particles are found instead to be uniformly distributed across the channel. The intensity of the cross-stream secondary flows increases (with respect to the unladen case) with the volume fraction up to $\unicode[STIX]{x1D719}=0.1$, as a consequence of the high concentration of particles along the corner bisector. For $\unicode[STIX]{x1D719}=0.2$ the turbulence activity is reduced and the intensity of the secondary flows reduces to below that of the unladen case. The friction Reynolds number increases with $\unicode[STIX]{x1D719}$ in dilute conditions, as observed for channel flows. However, for $\unicode[STIX]{x1D719}=0.2$ the mean friction Reynolds number is similar to that for $\unicode[STIX]{x1D719}=0.1$. By performing the turbulent kinetic energy budget, we see that the turbulence production is enhanced up to $\unicode[STIX]{x1D719}=0.1$, while for $\unicode[STIX]{x1D719}=0.2$ the production decreases below the values for $\unicode[STIX]{x1D719}=0.05$. On the other hand, the dissipation and the transport monotonically increase with $\unicode[STIX]{x1D719}$. The interphase interaction term also contributes positively to the turbulent kinetic energy budget and increases monotonically with $\unicode[STIX]{x1D719}$, in a similar way as the mean transport. Finally, we show that particles move on average faster than the fluid. However, there are regions close to the walls and at the corners where they lag behind it. In particular, for $\unicode[STIX]{x1D719}=0.05,0.1$, the slip velocity distribution at the corner bisectors seems correlated to the locations of maximum concentration: the concentration is higher where the slip velocity vanishes. The wall-normal hydrodynamic and collision forces acting on the particles push them away from the corners. The combination of these forces vanishes around the locations of maximum concentration. The total mean forces are generally low along the corner bisectors and at the core, also explaining the concentration distribution for $\unicode[STIX]{x1D719}=0.2$.

Single Phase and Two-Phase Flow Pressure Drop in Pebble Beds

2010 ◽  
Author(s):  
Bofeng Bai ◽  
Maolong Liu ◽  
Xiaofei Lv ◽  
Wang Su ◽  
Xiao Yan ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Gas Phase ◽  
Single Phase ◽  
Two Phase Flow ◽  
Particle Diameter ◽  
Spherical Particles ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Flow Pressure

An experimental study was conducted on the pressure drop of single phase and air-water two-phase flow in the bed of rectangular cross sections filled with uniform spheres densely. In the present flow-regime model, the bed was subdivided into a near-wall region and a central region. And a new empirical correlation for the prediction of single-phase flow pressure drops was proposed based on the model. The correlation can be used to predict the single phase pressure drop for both great tube-to-particle diameter ratio packed beds and small tube-to-particle diameter ratio packed beds and for the pebble beds packing with spherical particles and non spherical particles. A new empirical correlation for the prediction of two-phase flow pressure drops was proposed based on the gas phase relative permeability as a function of the gas phase saturation and the void fraction. The correlation fit well also for both experimental data points of spherical particles and non spherical particles.

A Parametric Numerical Study of Radiative Transfer in Thermotropic Materials

2013 ◽  
Author(s):  
Adam C. Gladen ◽  
Susan C. Mantell ◽  
Jane H. Davidson
Keyword(s):  
Particle Size ◽  
Radiative Transfer ◽  
Optical Thickness ◽  
Parametric Study ◽  
Volume Fraction ◽  
Numerical Study ◽  
Anisotropic Scattering ◽  
Index Of Refraction ◽  
Spherical Particles ◽  
Size Parameter

A thermotropic material is modeled as an absorbing, thin slab containing anisotropic scattering, monodisperse, spherical particles. Monte Carlo ray tracing is used to solve the governing equation of radiative transfer. Predicted results are validated by comparison to the measured normal-hemispherical reflectance and transmittance of samples with various volume fraction and relative index of refraction. A parametric study elucidates the effects of particle size parameter, scattering albedo, and optical thickness on the normal-hemispherical transmittance, reflectance, and absorptance. The results are interpreted for a thermotropic material used for overheat protection of a polymer solar absorber. For the preferred particle size parameter of 2, the optical thickness should be less than 0.3 to ensure high transmittance in the clear state. To significantly reduce the transmittance and increase the reflectance in the translucent state, the optical thickness should be greater than 2.5 and the scattering albedo should be greater than 0.995. For optical thickness greater than 5, the reflectance is asymptotic and any further reduction in transmittance is through increased absorptance. A case study is used to illustrate how the parametric study can be used to guide the design of thermotropic materials. Low molecular weighted polyethylene in poly(methyl methacrylate) is identified as a potential thermotropic material. For this material and a particle radius of 200 nm, it is determined that the volume fraction and thickness should equal 10% and 1 mm, respectively.

Settling Behavior of Particles in Bubble Containing Newtonian Fluids: Experimental Study and Model Development

2021 ◽  
Author(s):  
Silin Jing ◽  
Xianzhi Song ◽  
Zhaopeng Zhu ◽  
Buwen Yu ◽  
Shiming Duan
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Volume Concentration ◽  
Settling Velocity ◽  
Particle Density ◽  
Particle Diameter ◽  
Newtonian Fluids ◽  
Spherical Particles ◽  
Bubble Volume ◽  
Particle Reynolds Number

Abstract Accurate description of cuttings slippage in the gas-liquid phase is of great significance for wellbore cleaning and the control accuracy of bottom hole pressure during MPD. In this study, the wellbore bubble flow environment was simulated by a constant pressure air pump and the transparent wellbore, and the settling characteristics of spherical particles under different gas volume concentrations were recorded and analyzed by highspeed photography. A total of 225 tests were conducted to analyze the influence of particle diameter (1–12mm), particle density (2700–7860kg/m^3), liquid viscosity and bubble volume concentration on particle settling velocity. Gas drag force is defined to quantitatively evaluate the bubble’s resistance to particle slippage. The relationship between bubble drag coefficient and particle Reynolds number is obtained by fitting the experimental results. An explicit settling velocity equation is established by introducing Archimedes number. This explicit equation with an average relative error of only 8.09% can directly predict the terminal settling velocity of the sphere in bubble containing Newtonian fluids. The models for predicting bubble drag coefficient and the terminal settling velocity are valid with particle Reynolds number ranging from 0.05 to 167 and bubble volume concentration ranging from 3.0% to 20.0%. Besides, a trial-and-error procedure and an illustrative example are presented to show how to calculate bubble drag coefficient and settling velocity in bubble containing fluids. The results of this study will provide the theoretical basis for wellbore cleaning and accurate downhole pressure to further improve the performance of MPD in treating gas influx.

Observations of Precipitation Size and Fall Speed Characteristics within Coexisting Rain and Wet Snow

2006 ◽  
Vol 45 (10) ◽  
pp. 1450-1464 ◽  
Author(s):  
Sandra E. Yuter ◽  
David E. Kingsmill ◽  
Louisa B. Nance ◽  
Martin Löffler-Mang
Keyword(s):  
Particle Size ◽  
Standard Deviation ◽  
Volume Fraction ◽  
Bimodal Distribution ◽  
Particle Sizes ◽  
Large Standard Deviation ◽  
Air Temperatures ◽  
Isothermal Layer ◽  
Wet Snow ◽  
Fall Speed

Abstract Ground-based measurements of particle size and fall speed distributions using a Particle Size and Velocity (PARSIVEL) disdrometer are compared among samples obtained in mixed precipitation (rain and wet snow) and rain in the Oregon Cascade Mountains and in dry snow in the Rocky Mountains of Colorado. Coexisting rain and snow particles are distinguished using a classification method based on their size and fall speed properties. The bimodal distribution of the particles’ joint fall speed–size characteristics at air temperatures from 0.5° to 0°C suggests that wet-snow particles quickly make a transition to rain once melting has progressed sufficiently. As air temperatures increase to 1.5°C, the reduction in the number of very large aggregates with a diameter > 10 mm coincides with the appearance of rain particles larger than 6 mm. In this setting, very large raindrops appear to be the result of aggregrates melting with minimal breakup rather than formation by coalescence. In contrast to dry snow and rain, the fall speed for wet snow has a much weaker correlation between increasing size and increasing fall speed. Wet snow has a larger standard deviation of fall speed (120%–230% relative to dry snow) for a given particle size. The average fall speed for observed wet-snow particles with a diameter ≥ 2.4 mm is 2 m s−1 with a standard deviation of 0.8 m s−1. The large standard deviation is likely related to the coexistence of particles of similar physical size with different percentages of melting. These results suggest that different particle sizes are not required for aggregation since wet-snow particles of the same size can have different fall speeds. Given the large standard deviation of fall speeds in wet snow, the collision efficiency for wet snow is likely larger than that of dry snow. For particle sizes between 1 and 10 mm in diameter within mixed precipitation, rain constituted 1% of the particles by volume within the isothermal layer at 0°C and 4% of the particles by volume for the region just below the isothermal layer where air temperatures rise from 0° to 0.5°C. As air temperatures increased above 0.5°C, the relative proportions of rain versus snow particles shift dramatically and raindrops become dominant. The value of 0.5°C for the sharp transition in volume fraction from snow to rain is slightly lower than the range from 1.1° to 1.7°C often used in hydrological models.

Air Flow Analysis in Square Duct Bend

2014 ◽  
Vol 695 ◽  
pp. 622-626 ◽  
Author(s):  
Mohamad Nor Musa ◽  
Mohd Nurul Hafiz Mukhtar
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Cross Section ◽  
Air Flow ◽  
Flow Analysis ◽  
Maximum Velocity ◽  
Maximum Pressure ◽  
Air Velocity ◽  
Square Duct ◽  
Inlet Velocity

This paper present new result for experimental analysis of air flow velocity and pressure distributions between two ducts bend: (1) 90° duct bend with a single turning vane having 0.03m radius and (2) 90° duct bend with double turning vane, in 0.06 × 0.06 m duct cross section. The experiment used five different Reynolds numbers chosen between the ranges 1 ×104 and 6×104. Each experiment has four point measurements: (1) point 1 and point 2 at cross section A-A and (2) point 3 and point 4 at cross section B-B. The first experimental study used single turning vane radius 0.03m with inlet air velocity from 2.5m/s to 12.2m/s. And for the second experiment that used square turning vane with 0.03m radius. In experiment 2, the inlet air velocity also start from 2.5m/s to 12.2m/s. From analysis results, the pressure drop in experiment 1 is higher than experiment 2. As example the maximum pressure drop at 7.5m/s inlet air velocity between point 1 and 3 was found to be 71.6203 Pa in experiment 1 as compared to 61.8093 Pa in experiment 2. The velocity after duct bend is greater when using double turning vane compare used single turning vane as maximum velocity at point 3 in experiment 2 compare to velocity at point 3 in experiment 1 that is 55.677× 10-4 m/s and 54.221× 10-4 m/s. The velocity at duct wall is equal to zero. When increase the value of Reynolds number or inlet velocity, the maximum velocity and total pressure also increase. For example in experiment 1 at point 1, the velocity is 48.785 × 10-4 m/s at Reynolds number 1 ×104 and velocity 65.115×10-4 m/s at Reynolds number 12.2 ×104 . Velocity flow in duct section are lower than inlet velocity. In experiment 1, the inlet velocity is 2.5m/s meanwhile the maximum velocity in the duct section at point 2 is 73.075×10-4 m/s that is much more lower than inlet velocity.

Effect of Stress Wave Scattering at the Liquid-Particle Interface on Viscosity Calculation of Nanocolloidal Dispersions

2008 ◽  
Author(s):  
Tao Wang ◽  
Xinwei Wang ◽  
Haiping Hong ◽  
Zhongyang Luo ◽  
Kefa Cen
Keyword(s):  
Particle Size ◽  
Autocorrelation Function ◽  
Stress Wave ◽  
Wave Scattering ◽  
Volume Fraction ◽  
Solid Particles ◽  
Spherical Particles ◽  
Computational Domain ◽  
Liquid Particle ◽  
Pressure Tensor

In this work, extensive equilibrium molecular dynamics simulations are conducted to study the shear viscosity of nanocolloidal dispersion. Strong oscillation of the pressure tensor autocorrelation function is observed. The computational domain contains solvent of liquid argon at 143.4 K and spherical particles with volume fraction of 3%. By studying the effect of the particle size, particle density, and acoustic impedance, it is found for the first time that the stress wave scattering/reflecting at the liquid-particle interface due to acoustic mismatch plays a critical important role in the oscillation of pressure tensor autocorrelation function. The Brownian motion/vibration of solid particles is considered to have little effect on the oscillation of pressure tensor autocorrelation function curve except the frequency. And when the particle size is comparable with the wavelength of stress wave, the diffraction of stress wave happens at the interface that will also weaken the oscillation of pressure tensor autocorrelation function.

scholarly journals Fluid Flow and Entropy Generation Analysis of Al2O3–Water Nanofluid in Microchannel Plate Fin Heat Sinks

Entropy ◽  
2019 ◽  
Vol 21 (8) ◽  
pp. 739 ◽  
Author(s):  
Hao Ma ◽  
Zhipeng Duan ◽  
Liangbin Su ◽  
Xiaoru Ning ◽  
Jiao Bai ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Microchannel Plate ◽  
Heat Sinks ◽  
Entropy Generation Rate ◽  
Nanoparticle Volume Fraction ◽  
Channel Aspect Ratio

The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated numerically in this paper. Deionized water and Al2O3–water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.

Effects of Particle Concentration on the Partitioning of Suspensions at Small Divergent Bifurcations

1996 ◽  
Vol 118 (3) ◽  
pp. 287-294 ◽  
Author(s):  
R. Ditchfield ◽  
W. L. Olbricht
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Diameter ◽  
Circular Cross Section ◽  
Experimental Results ◽  
Hydrodynamic Interactions ◽  
Spherical Particles ◽  
Straight Tube ◽  
Particle Volume ◽  
Reynolds Number Flow

Experimental results are reported for the low Reynolds number flow of a suspension of spherical particles through a divergent capillary bifurcation consisting of a straight tube of circular cross-section that splits to form two tubes of equal diameter. The partitioning of particles between the downstream branches of the bifurcation is measured as a function of the partitioning of total volume (particles + suspending fluid) between the branches. Two bifurcation geometries are examined: a symmetric Y-shaped bifurcation and a nonsymmetric T-shaped bifurcation. This experiment focuses on the role of hydrodynamic interactions between particles on the partitioning of particles at the bifurcation. The particle diameter, made dimensionless with respect to the diameter of the branch tubes, ranges from 0.4 to 0.8. Results show that hydrodynamic interactions among the particles are significant at the bifurcation, even for conditions where interactions are unimportant in the straight branches away from the bifurcation. As a result of hydrodynamic interactions among particles at the bifurcation, the partitioning of particles between the branches is affected for particle volume fractions as small as 2 percent. The experimental results show that the effect of particle volume fraction is to diminish the inhomogeneity of particle partitioning at the bifurcation. However, the magnitude of this effect depends strongly on the overall shape of the bifurcation geometry, and, in particular on the angles between the branches.

Oxygen-Enriched Combustion Characteristics of Lignite: A Case Study of the Pingzhuang Lignite from Inner Mongolia, China

2012 ◽  
Vol 550-553 ◽  
pp. 2868-2872
Author(s):  
Xiang Yun Chen ◽  
Yong Feng Zhang ◽  
Qian Cheng Zhang ◽  
Jie Bai ◽  
Fei Wu
Keyword(s):  
Particle Size ◽  
Oxygen Concentration ◽  
Volume Fraction ◽  
Particle Sizes ◽  
Temperature Zone ◽  
Thermogravimetric Method ◽  
Combustion Experiment ◽  
Lower Temperature ◽  
Lower Temperature Zone

Combustion curves of lignite samples from China in four different particle sizes and Oxygen-enriched condition were analyzed using non-isothermal thermogravimetric method. The lignite samples separated into -150+100 μm, -100+75 μm, -75+50 μm, and -50μm sizes. Combustion profiles shift to lower temperature zone as particle size decrease. Combustion profiles have little difference when the particle size below 100 μm in oxygen atmosphere; Oxygen-enriched combustion experiment were carried out in O2/N2 mixture atmospheres with the volume fraction of oxygen was 21%, 30%, 40%, 50%, 60% and 70%, respectively. As oxygen concentration increase profiles shift to lower temperature zone. and gets the proper range of oxygen concentration is about 50%.

Sign in / Sign up

Export Citation Format

Share Document