S053035 Eddy Diffusivity and Turbulent Schmidt Number in a Reactive Planar Jet in Liquid Phase

2012 ◽  
Vol 2012 (0) ◽  
pp. _S053035-1-_S053035-3
Author(s):  
Tomoaki WATANABE ◽  
Yasuhiko SAKAI ◽  
Kouji NAGATA ◽  
Osamu TERASHIMA ◽  
Yasumasa ITO
Keyword(s):  
Liquid Phase ◽  
Schmidt Number ◽  
Eddy Diffusivity ◽  
Planar Jet ◽  
Turbulent Schmidt Number

scholarly journals DNS of turbulent Schmidt number and eddy diffusivity for reactive concentrations

2014 ◽  
Vol 80 (809) ◽  
pp. FE0008-FE0008
Author(s):  
Tomoaki WATANABE ◽  
Yasuhiko SAKAI ◽  
Kouji NAGATA ◽  
Osamu TERASHIMA ◽  
Yasumasa ITO ◽  
...  
Keyword(s):  
Schmidt Number ◽  
Eddy Diffusivity ◽  
Turbulent Schmidt Number

Turbulent Schmidt number and eddy diffusivity change with a chemical reaction

2014 ◽  
Vol 754 ◽  
pp. 98-121 ◽  
Author(s):  
Tomoaki Watanabe ◽  
Yasuhiko Sakai ◽  
Kouji Nagata ◽  
Osamu Terashima
Keyword(s):  
Chemical Reaction ◽  
Schmidt Number ◽  
Absorption Spectrometry ◽  
Eddy Diffusivity ◽  
Upstream Region ◽  
Reactive Flow ◽  
Measure Concentration ◽  
Mass Fluxes ◽  
Turbulent Schmidt Number ◽  
The Mean

AbstractWe provide empirical evidence that the eddy diffusivity$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}D_{{t}\alpha }$and the turbulent Schmidt number${\mathit{Sc}}_{{t}\alpha }$of species$\alpha $($\alpha =\mathrm{A}, \mathrm{B}$or$\mathrm{R}$) change with a second-order chemical reaction ($\mathrm{A} + \mathrm{B} \rightarrow \mathrm{R}$). In this study, concentrations of the reactive species and axial velocity are simultaneously measured in a planar liquid jet. Reactant A is premixed into the jet flow and reactant B is premixed into the ambient flow. An optical fibre probe based on light absorption spectrometry is combined with I-type hot-film anemometry to simultaneously measure concentration and velocity in the reactive flow. The eddy diffusivities and the turbulent Schmidt numbers are estimated from the simultaneous measurement results. The results show that the chemical reaction increases${\mathit{Sc}}_{t\mathrm{A}}$;${\mathit{Sc}}_{t\mathrm{B}}$is negative in the region where the mean concentration of reactant B decreases in the downstream direction, and is positive in the non-reactive flow in the entire region on the jet centreline. It is also shown that${\mathit{Sc}}_{t\mathrm{R}}$is positive in the upstream region whereas it is negative in the downstream region. The production terms of axial turbulent mass fluxes of reactant B and product R can produce axial turbulent mass fluxes opposite to the axial gradients of the mean concentrations. The changes in the production terms due to the chemical reaction result in the negative turbulent Schmidt number of these species. These results imply that the gradient diffusion model using a global constant turbulent Schmidt number poorly predicts turbulent mass fluxes in reactive flows.

Verification of micrometeorologically determined nitrous oxide fluxes following controlled release from pasture

2018 ◽  
Vol 58 (6) ◽  
pp. 998
Author(s):  
M. J. Harvey ◽  
S. E. Nichol ◽  
A. M. S. McMillan ◽  
R. J. Martin ◽  
M. J. Evans ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Schmidt Number ◽  
Management Practice ◽  
Flux Measurement ◽  
Surface Flux ◽  
Eddy Diffusivity ◽  
N2o Emissions ◽  
Release Rates ◽  
Air Stream ◽  
Turbulent Schmidt Number

We have developed a high-precision micrometeorological system capable of measuring emissions of nitrous oxide (N2O) from up to four adjacent pasture plots. The system can be used to compare the influence of environmental factors and management practice on N2O emissions at the paddock scale. The system is capable of determining a minimum detectable N2O difference of the order of 40 pmol/mol, with an ability to resolve flux differences among plots of ~26 µg (N2O-N)/m2.h. So as to independently verify the emission estimates of the micrometeorological system, we developed a calibrated N2O-release system and compared known release rates with the micrometeorological flux estimates. Adjustable release rates up to the equivalent average surface flux of ~500 µg (N2O-N)/m2.h were achieved using mass flow-controlled input of pure N2O in a compressed air stream over two 1.5-ha plots upwind of flux-measurement masts. The comparison of network release rate with measured emission rate was quite variable and complicated by a significant and varying background emissions of N2O from the soil. For optimal steady-wind cases, the ratio of uncorrected measured flux to known release, including the estimated background, was of the order of 0.4–0.5; this ratio is likely to be influenced by the turbulent Schmidt number. Flux estimates for uncorrected flux gradient and WindTrax backward Lagrangian Stochastic method (which includes Schmidt correction) agreed well with a ratio of 0.54. The experiment highlighted the need for accurate estimates of gas eddy diffusivity in the micrometeorological gradient or difference-based flux measurement of N2O.

The Enhancement of Turbulent Diffusion in a Parallel-Wall Duct

1970 ◽  
Vol 185 (1) ◽  
pp. 825-835
Author(s):  
C. Betts ◽  
A. P. Hatton
Keyword(s):  
Reynolds Number ◽  
Turbulent Diffusion ◽  
Schmidt Number ◽  
Eddy Diffusivity ◽  
Concentration Profiles ◽  
Blockage Ratio ◽  
Lateral Direction ◽  
Friction Factors ◽  
Turbulent Schmidt Number ◽  
Parallel Wall

Experiments were carried out on the diffusion of nitr ous oxide from a line source in a turbulent flow in a parallel-wall duct over a range of Reynolds number 104to 105. Eddy diffusivity was derived from the concentration profiles in th e lateral direction, with and without obstructions of various shapes in the centre of the duct. Without obstructions the velocity profiles and friction factors agreed well with previous measurements and, for the central portion where the turbulence appears homogeneous, the turbulent Schmidt number was found to be 0·64. Turbulence enhancement caused by obstructions was mainly dependent on the blockage ratio and the shape of the trailing edge.

Analysis of the Mixing and Emission Characteristics in a Model Combustor

2018 ◽  
Author(s):  
Shan Li ◽  
Shanshan Zhang ◽  
Lingyun Hou ◽  
Zhuyin Ren
Keyword(s):  
Gas Turbines ◽  
Schmidt Number ◽  
Numerical Study ◽  
Flame Temperature ◽  
Scalar Dissipation ◽  
Mixing Process ◽  
Nox Formation ◽  
Turbulent Schmidt Number ◽  
Wide Range ◽  
Air Mixing

Modern gas turbines in power systems employ lean premixed combustion to lower flame temperature and thus achieve low NOx emissions. The fuel/air mixing process and its impacts on emissions are of paramount importance to combustor performance. In this study, the mixing process in a methane-fired model combustor was studied through an integrated experimental and numerical study. The experimental results show that at the dump location, the time-averaged fuel/air unmixedness is less than 10% over a wide range of testing conditions, demonstrating the good mixing performance of the specific premixer on the time-averaged level. A study of the effects of turbulent Schmidt number on the unmixedness prediction shows that for the complex flow field involved, it is challenging for Reynolds-Averaged Navier-Stokes (RANS) simulations with constant turbulent Schmidt number to accurately predict the mixing process throughout the combustor. Further analysis reveals that the production and scalar dissipation are the key physical processes controlling the fuel/air mixing. Finally, the NOx formation in this model combustor was analyzed and modelled through a flamelet-based approach, in which NOx formation is characterized through flame-front NOx and its post-flame formation rate obtained from one-dimensional laminar premixed flames. The effect of fuel/air unmixedness on NOx formation is accounted for through the presumed probability density functions (PDF) of mixture fraction. Results show that the measured NOx in the model combustor are bounded by the model predictions with the fuel/air unmixedness being 3% and 5% of the maximum unmixedness. In the context of RANS, the accuracy in NOx prediction depends on the unmixedness prediction which is sensitive to turbulent Schmidt number.

scholarly journals Gas-solid and gas-liquid mass transfer: Effect of turbulent Schmidt number

2007 ◽  
Vol 13 (3) ◽  
pp. 167-168 ◽  
Author(s):  
Aleksandar Dudukovic ◽  
Rada Pjanovic
Keyword(s):  
Mass Transfer ◽  
Eddy Viscosity ◽  
Schmidt Number ◽  
Mass Transfer Rate ◽  
Transfer Effect ◽  
Transfer Coefficients ◽  
Mass Transfer Effect ◽  
Liquid Mass ◽  
Turbulent Schmidt Number ◽  
Liquid Mass Transfer

The scope of this paper is to explain effect of eddy viscosity and turbulent Schmidt number on mass transfer rate. New, theoretically based correlation for gas-liquid mass transfer coefficients are proposed.

Free Turbulent Shear Layers on Plug Nozzles

1977 ◽  
Vol 99 (2) ◽  
pp. 301-308
Author(s):  
C. J. Scott ◽  
D. R. Rask
Keyword(s):  
Turbulent Mixing ◽  
Schmidt Number ◽  
Error Function ◽  
Mixing Layer ◽  
Shear Layers ◽  
Turbulent Shear ◽  
Gas Chromatograph ◽  
Plug Nozzle ◽  
Turbulent Schmidt Number ◽  
Plug Nozzles

Two-dimensional, free, turbulent mixing between a uniform stream and a cavity flow is investigated experimentally in a plug nozzle, a geometry that generates idealized mixing layer conditions. Upstream viscous layer effects are minimized through the use of a sharp-expansion plug nozzle. Experimental velocity profiles exhibit close agreement with both similarity analyses and with error function predictions. Refrigerant-12 was injected into the cavity and concentration profiles were obtained using a gas chromatograph. Spreading factors for momentum and mass were determined. Two methods are presented to determine the average turbulent Schmidt number. The relation Sct = Sc is suggested by the data for Sc < 2.0.

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