Effect of Solids Loading, Reynolds Number, and Particle Size Distribution on Velocity Fluctuations in Gas-Particle Flows

2003 ◽  
Author(s):  
Jennifer Sinclair Curtis
Keyword(s):  
Reynolds Number ◽  
Gas Phase ◽  
Single Phase ◽  
Glass Beads ◽  
Coarse Particles ◽  
Single Phase Flow ◽  
Velocity Fluctuations ◽  
Flow Models ◽  
Solids Loading ◽  
Model Predictions

A variety of LDV experiments were conducted to assess the influence of solids loading, Reynolds number and particle size distribution on velocity fluctuations and flow behavior in gas-particle systems. This talk will summarize those experimental findings, as well as show comparisons of experimental results with multiphase CFD model predictions that utilize concepts from kinetic theory to describe particle velocity fluctuations. In order to probe solids loading effects, an axisymmetric particle-laden jet was investigated using LDV for 70 micron glass beads with solids loadings ranging from one to thirty. Dilute conditions are characterized by isotropic particle r.m.s. velocities and decreases in the magnitude of the r.m.s. velocities as the solids loading increases. Particle clustering is observed for dense conditions as well as anisotropy between axial and radial particle r.m.s. velocities. Under dense conditions, increases in the solids loading lead to increases in the axial particle r.m.s. velocity while the radial r.m.s. velocity remains at a constant level. Gas-solids flow models display good agreement between predictions and experimental measurements of mean velocities of the gas and solids as well as modulation of the gas turbulent kinetic energy by the presence of the particles. However, the gas-solid flow models based on kinetic theory concepts consistently overpredict the particle r.m.s. velocity for the range of solids loadings investigated. In addition, the same axisymmetric particle-laden jet consisting of 70-micron glass beads was investigated for a range of Reynolds numbers with a constant mass loading (m = 0.7). The presence of the solids dampens the gas turbulence intensity at the lowest value of Re investigated (8,300) compared with single-phase flow at the same Re. As the Reynolds number increases, the gas turbulence increases and for Re ≥ 15,200 the turbulence is enhanced compared with the single-phase flow at the same Re. The observed trend in turbulence modulation with Reynolds number is possibly due to the segregation of the solids and their effect on the gas mean velocity profiles. Finally, the particle-laden jet was investigated for binary mixtures of 25 and 70-micron glass beads. Specifically, the effect of a bimodal PSD on the modulation of gas-phase turbulence, the particle rms velocity, and particle segregation patterns was explored in detail. Measurements and model predictions indicate that increasing the mass fraction of the finer particles dampens the gas-phase turbulence. Changes in the random motion of the coarser particles are observed upon the addition of the finer material; clusters of fine particles arise for the largest solids loading investigated, and these clusters increase both the mean and fluctuating velocities of the coarse particles. The particles are also observed to segregate by size and volume fraction, with the coarse particles tending towards the center of the pipe.

Frictional Pressure Drop Correlations for Single-Phase Flow, Condensation, and Evaporation in Microfin Tubes

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Zan Wu ◽  
Bengt Sundén
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Frictional Pressure Drop ◽  
Friction Factors ◽  
Flow Condensation ◽  
Microfin Tubes

Experimental single-phase, condensation, and evaporation (flow boiling) pressure drop data from the literature and our previous studies were collected to evaluate previous frictional pressure drop correlations for horizontal microfin tubes of different geometries. The modified Ravigururajan and Bergles correlation, by adopting the Churchill model to calculate the smooth-tube friction factor and by using the hydraulic diameter in the Reynolds number, can predict single-phase turbulent frictional pressure drop data relatively well. Eleven pressure drop correlations were evaluated by the collected database for condensation and evaporation. Correlations originally developed for condensation and evaporation in smooth tubes can be suitable for microfin tubes if the friction factors in the correlations were calculated by the Churchill model to include microfin effects. The three most accurate correlations were recommended for condensation and evaporation in microfin tubes. The Cavallini et al. correlation and the modified Friedel correlation can give good predictions for both condensation and evaporation. However, some inconsistencies were found, even for the recommended correlations.

scholarly journals Micro-orifice single-phase flow at very high Reynolds number

2018 ◽  
Vol 91 ◽  
pp. 35-40 ◽  
Author(s):  
Andrea Cioncolini ◽  
Stefano Cassineri ◽  
Jonathan Duff ◽  
Michele Curioni ◽  
Fabio Scenini
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Single Phase ◽  
Phase Flow ◽  
Single Phase Flow ◽  
High Reynolds ◽  
Very High

Heat Transfer Augmentation in 3D Inner Finned Helical Tube

Volume 3 ◽  
2004 ◽  
Author(s):  
Longjian Li ◽  
Wenzhi Cui ◽  
Quan Liao ◽  
Mingdao Xin ◽  
Tien-Chien Jen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boiling Heat Transfer ◽  
Flow Resistance ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Helical Tube ◽  
Helical Tubes

Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%∼120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%∼119%.

Capabilities and Challenges of CFD in Multiphase Simulation of Hydraulic Tanks

2014 ◽  
Author(s):  
Thees Vollmer ◽  
Johannes Untch
Keyword(s):  
Multiphase Flow ◽  
Single Phase ◽  
Test Bench ◽  
Cfd Simulation ◽  
Air Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Major Purpose ◽  
Flow Models ◽  
Multiphase Models

A major purpose of hydraulic tanks is the segregation of air, which can be supported by different design measures. To improve these measures CFD multiphase simulation can be used, as it is capable to assess the air flow within the oil. The different possibilities of CFD simulation are presented. Here single-phase flow models, simplified multiphase models as well as full multiphase flow models are discussed and evaluated. An example of each presented method is given and the results are compared. Last the capabilities of validating the simulations on a test bench are briefly discussed.

scholarly journals Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of two-phase volumetrically dilute flow with evaporation

2013 ◽  
Vol 719 ◽  
pp. 230-267 ◽  
Author(s):  
Senthilkumaran Radhakrishnan ◽  
Josette Bellan
Keyword(s):  
Gas Phase ◽  
Single Phase ◽  
Independent Solution ◽  
Phase Flow ◽  
Grid Spacing ◽  
Single Phase Flow ◽  
Two Phase ◽  
Eddy Simulation ◽  
Filter Width ◽  
Spacing Ratio

AbstractPredictions from conventional large-eddy simulation (LES) are known to be grid-spacing and spatial-discretization-order dependent. In a previous article (Radhakrishnan & Bellan, J. Fluid Mech., vol. 697, 2012a, pp. 399–435), we reformulated LES for compressible single-phase flow by explicitly filtering the nonlinear terms in the governing equations so as to render the solution grid-spacing and discretization-order independent. Having shown in Radhakrishnan & Bellan (2012a) that the reformulated LES, which we call EFLES, yields grid-spacing-independent and discretization-order-independent solutions for compressible single-phase flow, we explore here the potential of EFLES for evaporating two-phase flow where the small scales have an additional origin compared to single-phase flow. Thus, we created a database through direct numerical simulation (DNS) that when filtered serves as a template for comparisons with both conventional LES and EFLES. Both conventional LES and EFLES are conducted with two gas-phase SGS models; the drop-field SGS model is the same in all these simulations. For EFLES, we also compared simulations performed with the same SGS model for the gas phase but two different drop-field SGS models. Moreover, to elucidate the influence of explicit filtering versus gas-phase SGS modelling, EFLES with two drop-field SGS models but no gas-phase SGS models were conducted. The results from all these simulations were compared to those from DNS and from the filtered DNS (FDNS). Similar to the single-phase flow findings, the conventional LES method yields solutions which are both grid-spacing and spatial-discretization-order dependent. The EFLES solutions are found to be grid-spacing independent for sufficiently large filter-width to grid-spacing ratio, although for the highest discretization order this ratio is larger in the two-phase flow compared to the single-phase flow. For a sufficiently fine grid, the results are also discretization-order independent. The absence of a gas-phase SGS model leads to build-up of energy near the filter cut-off indicating that while explicit filtering removes energy above the filter width, it does not provide the correct dissipation at the scales smaller than this width. A wider viewpoint leads to the conclusion that although the minimum filter-width to grid-spacing ratio necessary to obtain the unique grid-independent solution might be different for various discretization-order schemes, the grid-independent solution thus obtained is also discretization-order independent.

Liquid Single-Phase Flow in an Array of Micro-Pin-Fins—Part I: Heat Transfer Characteristics

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Weilin Qu ◽  
Abel Siu-Ho
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Single Phase ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pin Fin ◽  
Pin Fins ◽  
Micro Pin Fins

This is Paper I of a two-part study concerning thermal and hydrodynamic characteristics of liquid single-phase flow in an array of micro-pin-fins. This paper reports the heat transfer results of the study. An array of 1950 staggered square micro-pin-fins with 200×200 μm2 cross-section by 670 μm height were fabricated into a copper test section. De-ionized water was used as the cooling liquid. Two coolant inlet temperatures of 30°C and 60°C and six maximum mass velocities for each inlet temperature ranging from 183 to 420 kg/m2 s were tested. The corresponding inlet Reynolds number ranged from 45.9 to 179.6. General characteristics of average and local heat transfer were described. Six previous conventional long and intermediate pin-fin correlations and two micro-pin-fin correlations were examined and were found to overpredict the average Nusselt number data. Two new heat transfer correlations were proposed for the average heat transfer based on the present data, in which the average Nusselt number is correlated with the average Reynolds number by power law. Values of the exponent m of the Reynolds number for the two new correlations are fairly close to those for the two previous micro-pin-fin correlations but substantially higher than those for the previous conventional pin-fin correlations, indicating a stronger dependence of the Nusselt number on the Reynolds number in micro-pin-fin arrays. The correlations developed for the average Nusselt number can adequately predict the local Nusselt number data.

scholarly journals  A Simplified Model of Low Reynolds Number, immiscible, Gas-Liquid Flow and Heat Transfer in Porous Media (Numerical Solution with Experimental Validation)

2021 ◽  
Author(s):  
Gamal B. Abdelaziz ◽  
M. Abdelgaleel ◽  
Z.M. Omara ◽  
A. S. Abdullah ◽  
Emad M.S. El-Said ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Media ◽  
Numerical Solution ◽  
Single Phase ◽  
Energy Equation ◽  
Numerical Results ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase

Abstract This study investigates the thermal-hydraulic characteristics of immiscible two-phase flow (gas/liquid) and heat transfer through porous media. This research topic is interested among others in trickle bed reactors, the reservoirs production of oil, and the science of the earth. Characteristics of two-phase concurrent flow with heat transfer through a vertical, cylindrical, and homogeneous porous medium were investigated both numerically and experimentally. A generalized Darcy model for each phase is applied to derive the momentum equations of a two-phase mixture by appending some constitutive relations. Gravity force is considered through investigation. To promote the system energy equation, the energy equation of solid matrix for each phase are deemed. The test section is exposed to a constant wall temperature after filled with spherical beads. Numerical solution of the model is achieved by the finite volume method. The numerical procedure is generalized such that it can be reduced and applied to single phase flow model. The numerical results are acquired according to, air/water downward flow, spherical beads, ratio of particle diameter to pipe radius D=0.412, porosity φ=0.396, 0.01≤Re≤500, water to air volume ratio 0≤W/A≤∞, and saturation ratio 0≤S1≤1. To validate this model an experimental test rig is designed and constructed, and the corresponding numerical results are compared with its results. Also, the numerical results were compared with other available numerical results. The comparisons show good agreement and validate the numerical model. One of the important results reveals that the heat transfer is influenced by two main parameters; saturation ratios of the two fluids; S1 and S2, and the mixture Reynolds number Re. The thermal entry length is directly dependent on Re, S1, and the thermofluid properties of the fluids. A modified empirical correlation for the entrance length; Xe =0.1 Re.Pr.Rm is predicted, where Rm =Rm(S1, S2, ρ1, ρ2, c1, c2). The predicted correlation is verified by comparing with the supposed correlation of Poulikakos and Ranken (1987) and El-Kady (1997) for a single-phase flow; Xe/Pr=0.1 Re.

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