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Research Papers: Multiphase Flows

A Computational Fluid Dynamics Study on the Gas Mixing Capabilities of a Multiple Inlet System

[+] Author and Article Information
Gert Lindner

Mathematical Modeling and Data Analysis,
Physikalisch-Technische Bundesanstalt (PTB),
Abbestr. 2-12,
Berlin 10587, Germany
e-mail: Gert.Lindner@ptb.de

Sonja Schmelter

Mathematical Modeling and Data Analysis,
Physikalisch-Technische Bundesanstalt (PTB),
Abbestr. 2-12,
Berlin 10587, Germany
e-mail: Sonja.Schmelter@ptb.de

Regine Model

Mathematical Modeling and Data Analysis,
Physikalisch-Technische Bundesanstalt (PTB),
Abbestr. 2-12,
Berlin 10587, Germany
e-mail: Regine.Model@ptb.de

Andreas Nowak

Analytics and Thermodynamic
State Behaviour of Gases,
Physikalisch-Technische Bundesanstalt (PTB),
Bundesallee 100,
Braunschweig 38116, Germany
e-mail: Andreas.Nowak@ptb.de

Volker Ebert

Analytics and Thermodynamic
State Behaviour of Gases,
Physikalisch-Technische Bundesanstalt (PTB),
Bundesallee 100,
Braunschweig 38116, Germany;
Institute for Reactive Flows and Diagnostics, RSM,
Technische Universität Darmstadt,
Jovanka-Bontschits-Str. 2,
Darmstadt 64287, Germany
e-mail: Volker.Ebert.@ptb.de

Markus Bär

Mathematical Modeling and Data Analysis,
Physikalisch-Technische Bundesanstalt (PTB),
Abbestr. 2-12,
Berlin 10587, Germany
e-mail: Markus.Baer@ptb.de

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 9, 2015; final manuscript received August 18, 2015; published online October 1, 2015. Assoc. Editor: Francine Battaglia.

J. Fluids Eng 138(3), 031302 (Oct 01, 2015) (9 pages) Paper No: FE-15-1154; doi: 10.1115/1.4031380 History: Received March 09, 2015; Revised August 18, 2015

The mixing behavior of three gas streams was investigated numerically by computational fluid dynamics (CFD) for 16 different geometries to gain insight for the construction of soot measuring systems. The overall goal was to find the design that leads to the fastest mixing of all incoming gas components for a given pipe length by numerical simulations. For this purpose, a main pipe with two symmetrically arranged side inlet pipes was considered, where the angle of inclination of the side pipes and the inflow conditions were varied. Upon the change of the angle of inclination, a transition from a conform to a counter flow is observed. As a variant of the simulation setup, the junction of the three pipes was enclosed by a spherical mixing chamber. The dependency on the angle is much less pronounced in the presence of the additional spherical chamber, which, however, in most cases results in a slower mixing of the gas streams. We found, in general, that the required pipe length to reach a sufficiently homogeneous gas mixture decreases with increasing inclination angles exhibiting the best performance at obtuse angles.

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Figures

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Fig. 1

Schematic diagram of the multiple inlet system

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Fig. 2

Contour plots of the mass fraction ξ in ZY-plane for FC5, i.e., Re=30,960 and ξ∞=0.5, with spherical chamber and for three different angles of inclination, α=60 deg, 90 deg, and 120 deg. The flow direction is from left to right.

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Fig. 3

Evolution of both the mass fraction ξ and intensity of segregation Is applied for FC5, i.e., Re=30,960 and ξ∞=0.5 and α=110 deg, without a spherical chamber shown on a two-axis plot. The horizontal line in the middle denotes ξ∞. The second horizontal line at Isl = 0.1 marks the threshold line, which leads to a mixing length lm=0.82 m in this case.

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Fig. 4

Mass fraction ξ along the radial profile x = 0 at position z=0.73 m on the three grids as well as extrapolated value ξext21 for FC4, i.e., Re=23,220 and ξ∞=1/3, with sphere and α=90 deg

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Fig. 5

Mass fraction ξ for grid 2 together with GCIcoarse32 plotted as error bars

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Fig. 6

Velocity magnitude u in YZ-plane for FC5, i.e., Re=30,960 and ξ∞=0.5, without sphere. (a) Plots for α=60 deg, α=90 deg, and α=120 deg. (b) Detailed view of the velocity vector around the mixing area for α=120 deg.

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Fig. 7

Velocity magnitude u in YZ-plane for FC5, i.e., Re=30,960 and ξ∞=0.5, with sphere. (a) Plots for α=60 deg, α=90 deg, and α=120 deg. (b) Detailed view of the velocity vector around the mixing area for α=120 deg.

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Fig. 8

Mass fraction ξ for FC5, i.e., Re=30,960, ξ∞=0.5, with sphere and α=110 deg. (a) Plots of ξ for cross sections at different z-positions z = 0.1 m, z = 0.3 m, z = 0.6 m, and z = 1.0 m. The profile x and profile y positions used in (b) and (c) are marked in the last cross section. (b) Profile x at different z-positions. (c) Profile y at different z-positions.

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Fig. 9

Angle dependence of Is for FC5, i.e., Re=30,960 and ξ∞=0.5, for selected geometries, namely, α=60 deg, 75 deg, 90 deg, 110 deg, and 130 deg. The threshold level Isl is marked at which the mixing length is obtained: (a) without and (b) with spherical chamber.

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Fig. 10

Dependence of Is for flow cases FC3, FC4, and FC5 for α=130 deg : (a) without and (b) with spherical chamber

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Fig. 11

Mixing lengths lm depending on α for the five cases according to Table 1. Circles and squares: ξ=0.5, diamonds: ξ=0.4, and triangles: ξ=1/3. The Reynolds number increases with the number of the flow cases from Re=7740 for FC1 to Re=30,960 for FC5: (a) without and (b) with spherical chamber.

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Fig. 12

Mixing length lm as a function of angle of inclination α evaluated for the three different values of ξ∞: top line ξ∞=0.5, middle line ξ∞=0.4, and bottom line ξ∞=1/3

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