scholarly journals Mixing characterization in different helically coiled configurations by laser-induced fluorescence

2020 ◽  
Vol 61 (9) ◽  
Author(s):  
P. Kováts ◽  
C. Velten ◽  
M. Mansour ◽  
D. Thévenin ◽  
K. Zähringer
Keyword(s):  
Cross Sections ◽  
Quantitative Measure ◽  
Laser Induced Fluorescence ◽  
Helical Coil ◽  
Mixing Coefficient ◽  
Dean Vortices ◽  
Flow Mixing ◽  
Mixing Coefficients ◽  
Mass Fractions ◽  
Miscible Liquids

AbstractFlow Mixing of two miscible liquids has been characterized experimentally in three different helically coiled reactor configurations of two different lengths in the laminar flow regime at Re = 50…1000. A straight helical coil, a coiled flow inverter, and a new coiled flow reverser have been built, each in a 3-turn and a 6-turn configuration. Laser-induced fluorescence of resorufin has been used to visualize and quantify mixing in cross-sections throughout the reactors. A mixing coefficient is derived from the fluorescence images to allow for a quantitative measure and comparison of the six configurations. It becomes obvious from these experimental results, that an early flow redirection in the helical configuration is beneficial to mixing. The 3-turn reactors achieve nearly the same mixing coefficients as the 6-turn reactors with the double length. This can be explained by the stabilizing effect of the Dean vortices in the helix, which develop during the first two turns. After that, the liquid is trapped inside the vortices and further mixing is inhibited. Accordingly, the coiled flow inverter and coiled flow reverser configurations lead to much higher mixing coefficients than the straight helical coil. The results of these measurements are now used for validation of numerical simulations, which reproduce the geometrical and flow conditions of the experiments. Some exemplary results of these calculations are also shown in this article. Graphic abstract Mass fractions of tracer fluid at Re = 500 in the six examined helix configurations.

scholarly journals Experimental characterization of mixing and flow field in the liquid plugs of gas–liquid flow in a helically coiled reactor

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Conrad Müller ◽  
Péter Kováts ◽  
Katharina Zähringer
Keyword(s):  
Flow Field ◽  
Mixing Efficiency ◽  
Air Bubbles ◽  
Time Resolved ◽  
Liquid Plug ◽  
Mixing Coefficient ◽  
Flow Mixing ◽  
Miscible Liquids ◽  
Secondary Vortices ◽  
Liquid Flows

Abstract Flow mixing of two miscible liquids with the addition of gas bubbles is a process often found in industrial chemical apparatus for the production of primary matter. The ongoing optimization of such processes also involves the transformation of batch to continuous mode operation. In that case, the use of helically coiled tubes is an interesting alternative, since those reactors have narrow residence time distributions, very good radial mixing properties and excellent mass transfer can be realized between gases and liquids. For these reasons, in this study the mixing of two miscible liquids with addition of air bubbles in gas–liquid flows has been characterized in a horizontal helically coiled reactor in the laminar flow regime at $${\text{Re}}_{{{\text{total}}}} = 300 \ldots 1088$$ Re total = 300 … 1088 . Eight different superficial liquid velocities and five superficial gas velocities were investigated. In order to characterize mixing in the liquid plugs between two bubbles, laser-induced fluorescence of resorufin was used and particle image velocimetry has been employed to characterize the flow field. Pseudo-3D-visualizations of the resorufin concentration and the Q-criterion, representing the mixing efficiency and vorticity, respectively, were established for individual liquid plugs from the time-resolved measurement results. A time-resolved mixing coefficient, as well as a mean mixing coefficient obtained from multiple liquid plugs, is calculated from the fluorescence images for all examined flow conditions. The experimental results clearly show an increase in the mixing coefficient compared to single-phase conditions, caused by the bubbles. However, distinct mixing pattern, depending on the flow structure, can be recognized on different locations inside the liquid plug. Compared to a stationary case without air bubbles, mixing is worse behind the bubbles and increases inside the plug, reaching a maximum mixing coefficient in front of the next bubble. Overall the mixing coefficient is always increased by the presence of the bubbles. Pseudo-3D-visualizations of the Q-criterion and the vorticity show the presence of secondary vortices right in front of the bubbles, shifted to the outer tube walls, and in addition to the steady Dean vortices. In small plugs, these secondary vortices appear in the whole plug and increase the mixing coefficient drastically. Graphical Abstract

Three-dimensionality of organized structures in a plane turbulent wake

1989 ◽  
Vol 206 ◽  
pp. 375-404 ◽  
Author(s):  
Michio Hayakawa ◽  
Fazle Hussain
Keyword(s):  
Cross Sections ◽  
Coherent Structures ◽  
Near Field ◽  
Spatial Coherence ◽  
Three Dimensional ◽  
Quantitative Measure ◽  
Turbulent Wake ◽  
Topological Features ◽  
Plane Wake ◽  
Plane Turbulent Wake

This paper describes a quantitative study of the three-dimensional nature of organized motions in a turbulent plane wake. Coherent structures are detected from the instantaneous, spatially phase-correlated vorticity field using certain criteria based on size, strength and geometry of vortical structures. With several combinations of X-wire rakes, vorticity distributions in the spanwise and transverse planes are measured in the intermediate region (10d [les ] x [les ] 40d) of the plane turbulent wake of a circular cylinder at a Reynolds number of 13000 based on the cylinder diameter d. Spatial correlations of smoothed vorticity signals as well as phase-aligned ensemble-averaged vorticity maps over structure cross-sections yield a quantitative measure of the spatial coherence and geometry of organized structures in the fully turbulent field. The data demonstrate that the organized structures in the nominally two-dimensional wake exhibit significant three-dimensionality even in the near field. Using instantaneous velocity and vorticity maps as well as correlations of vorticity distributions in different planes, some topological features of the dominant coherent structures in a plane wake are inferred.

Continuous flow mixing of two miscible liquids of different densities

1970 ◽  
Vol 48 (5) ◽  
pp. 484-490 ◽  
Author(s):  
Martin Pelletier ◽  
Leonce Cloutier
Keyword(s):  
Continuous Flow ◽  
Flow Mixing ◽  
Miscible Liquids

scholarly journals Doppler Measurement of Differential Cross Sections in Crossed Beam Experiments: Dependence of the Detection Sensitivity With the Product Velocity

1990 ◽  
Vol 10 (5-6) ◽  
pp. 319-332 ◽  
Author(s):  
N. Billy ◽  
B. Girard ◽  
G. Gouédard ◽  
J. Vigué
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Differential Cross ◽  
Internal State ◽  
Laser Induced Fluorescence ◽  
Detection Sensitivity ◽  
Differential Cross Sections ◽  
Doppler Measurement ◽  
Laser Induced Fluorescence Detection ◽  
Doppler Profile

Differential cross sections can be measured as a function of the internal state of a reaction product thanks to the analysis of the Doppler profile of the laser induced fluorescence detection line. This analysis is complicated by two effects: first, the LIF signal intensity depends on the interaction time of the molecule with the laser, and this time depends on the scattering angle, second, the angular and velocity distributions of the beams have non negligible widths. We present here a treatment of these effects in the case of the F+I2 reaction for which we have measured the differential cross section by this technique. The same formalism is also applied to the deduction of the rovibrational distribution of the products from the relative intensities of the LIF lines.

Gravity segregation during miscible displacement—re-investigation and re-interpretation

Soil Research ◽  
2007 ◽  
Vol 45 (5) ◽  
pp. 319 ◽  
Author(s):  
D. A. Rose ◽  
F. Abbas
Keyword(s):  
Cross Sections ◽  
Formal Analysis ◽  
Safety Margin ◽  
Breakthrough Curves ◽  
Hydrodynamic Dispersion ◽  
Immiscible Liquids ◽  
Saline Groundwater ◽  
Gravity Segregation ◽  
Dimensional Gravity ◽  
Miscible Liquids

When the liquid residing in a horizontal bed of porous material is displaced by another liquid of different density, the resulting hydrodynamic dispersion is modified by the formation of a tongue of denser liquid undershooting the less dense liquid, a phenomenon known as gravity segregation. An earlier account of gravity segregation contained a substantial error (that of an incorrect frame of reference for flow) and several printing mistakes. In this paper we (i) correct these errors, (ii) extend the analysis to describe the course of breakthrough in beds of rectangular and circular cross-sections, (iii) re-interpret the existing experimental evidence, and (iv) present new experimental results on the vertical and horizontal transport of ionic solutions of different concentrations and densities through inert and reactive porous materials, ballotini, and sepiolite, respectively. The behaviour of immiscible liquids is predicted by the non-dimensional gravity segregation number, β, segregation becoming more extreme as β increases. With miscible liquids, however, breakthrough starts later and ends earlier then predicted for immiscible liquids, mixing by hydrodynamic dispersion moderating the effect of segregation. Breakthrough curves are well fitted by CXTFIT 2.0; apparent coefficients of hydrodynamic dispersion vary much less with pore-water velocity in horizontal than in vertical flow, but retardation factors are not influenced by orientation. Although a formal analysis of the combined effect of gravity segregation and hydrodynamic dispersion was not possible, the statistically significant inverse relation between β and column Peclet number was explained qualitatively. Gravity segregation occurs during the intrusion of saline groundwater into coastal aquifers. The simple theory for immiscible displacement overestimates the actual intrusion that occurs with miscible liquids and so provides an effective safety margin.

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