scholarly journals Isotropic-turbulence-induced mass transfer across a severely contaminated water surface

2016 ◽  
Vol 797 ◽  
pp. 665-682 ◽  
Author(s):  
H. Herlina ◽  
J. G. Wissink
Keyword(s):  
Mass Transfer ◽  
Schmidt Number ◽  
Isotropic Turbulence ◽  
Slip Boundary Condition ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Slip Conditions ◽  
Slip Boundary ◽  
Turbulent Reynolds Number ◽  
Solid Liquid

Direct numerical simulations were performed to investigate the effect of severe contamination on interfacial gas transfer in the presence of isotropic turbulence diffusing from below. A no-slip boundary condition was employed at the interface to model the severe contamination effect. The influence of both Schmidt number ($Sc$) and turbulent Reynolds number ($R_{T}$) on the transfer velocity ($K_{L}$) was studied. In the range from $Sc=2$ up to $Sc=500$ it was found that $K_{L}\propto Sc^{-2/3}$, which is in agreement with predictions based on solid–liquid transport models, see e.g. Davies (1972, Turbulence Phenomena, Academic). For similar $R_{T}$, the transfer velocity was observed to reduce significantly compared with the free-slip conditions. The reduction becomes more pronounced with increasing Schmidt number. Similar to the observation for free-slip conditions made by Theofanous et al. (Intl J. Heat Mass Transfer, vol. 19 (6), 1976, pp. 613–624), the normalized $K_{L}$ in the present no-slip case was also found to depend on $R_{T}^{-1/2}$ and $R_{T}^{-1/4}$ for small and large turbulent Reynolds numbers, respectively.

scholarly journals Direct numerical simulation of turbulent scalar transport across a flat surface

2014 ◽  
Vol 744 ◽  
pp. 217-249 ◽  
Author(s):  
H. Herlina ◽  
J. G. Wissink
Keyword(s):  
Mass Transfer ◽  
Isotropic Turbulence ◽  
Reynolds Numbers ◽  
Gas Transfer ◽  
Computational Domain ◽  
Atmospheric Gases ◽  
Transfer Velocity ◽  
Physical Mechanisms ◽  
Schmidt Numbers ◽  
Large Eddies

AbstractTo elucidate the physical mechanisms that play a role in the interfacial transfer of atmospheric gases into water, a series of direct numerical simulations of mass transfer across the air–water interface driven by isotropic turbulence diffusing from below has been carried out for various turbulent Reynolds numbers ($R_T=84,195,507$). To allow a direct (unbiased) comparison of the instantaneous effects of scalar diffusivity, in each of the DNS up to six scalar advection–diffusion equations with different Schmidt numbers were solved simultaneously. As far as the authors are aware this is the first simulation that is capable to accurately resolve the realistic Schmidt number, $\mathit{Sc}=500$, that is typical for the transport of atmospheric gases such as oxygen in water. For the range of turbulent Reynolds numbers and Schmidt numbers considered, the normalized transfer velocity $K_L$ was found to scale with $R_T^{-{1/2}}$ and $\mathit{Sc}^{-{1/2}}$, which indicates that the largest eddies present in the isotropic turbulent flow introduced at the bottom of the computational domain tend to determine the mass transfer. The $K_L$ results were also found to be in good agreement with the surface divergence model of McCready, Vassiliadou & Hanratty (AIChE J., vol. 32, 1986, pp. 1108–1115) when using a constant of proportionality of 0.525. Although close to the surface large eddies are responsible for the bulk of the gas transfer, it was also observed that for higher $R_T$ the influence of smaller eddies becomes more important.

scholarly journals Effect of surface contamination on interfacial mass transfer rate

2017 ◽  
Vol 830 ◽  
pp. 5-34 ◽  
Author(s):  
J. G. Wissink ◽  
H. Herlina ◽  
Y. Akar ◽  
M. Uhlmann
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Isotropic Turbulence ◽  
Mass Transfer Rate ◽  
Surface Contamination ◽  
Gas Transfer ◽  
Clean Surface ◽  
Transfer Velocity ◽  
Surface Fraction ◽  
Interfacial Mass Transfer

The influence of surface contamination upon the mass transfer rate of a low diffusivity gas across a flat surface is studied using direct numerical simulations. The interfacial mass transfer is driven by isotropic turbulence diffusing from below. Similar to Shen et al. (J. Fluid Mech., vol. 506, 2004, pp. 79–115) the surface contamination is modelled by relating the normal gradient of the horizontal velocities at the top to the horizontal gradients of the surfactant concentrations. A broad range of contamination levels is considered, including clean to severely contaminated conditions. The time-averaged results show a strong correlation between the gas transfer velocity and the clean surface fraction of the surface area. In the presence of surface contamination the mass transfer velocity $K_{L}$ is found to scale as a power of the Schmidt number, i.e. $Sc^{-q}$, where $q$ smoothly transitions from $q=1/2$ for clean surfaces to $q=2/3$ for very dirty interfaces. A power law $K_{L}\propto Sc^{-q}$ is proposed in which both the exponent $q$ and the constant of proportionality become functions of the clean surface fraction.

Friction and the Continuum Limit – Where is the Boundary?

2000 ◽  
Vol 651 ◽  
Author(s):  
Yingxi Zhu ◽  
Steve Granick
Keyword(s):  
Continuum Limit ◽  
Fluid Transport ◽  
Liquid Surface ◽  
Microfluidic Devices ◽  
Slip Boundary Condition ◽  
Surface Interactions ◽  
Slip Boundary ◽  
Low Viscosity ◽  
Solid Liquid ◽  
The Continuum

AbstractThe no-slip boundary condition, believed to describe macroscopic flow of low-viscosity fluids, overestimates hydrodynamic forces starting at lengths corresponding to hundreds of molecular dimensions when water or tetradecane is placed between smooth nonwetting surfaces whose spacing varies dynamically. When hydrodynamic pressures exceed 0.1-1 atmospheres (this occurs at spacings that depend on the rate of spacing change), flow becomes easier than expected. Therefore solid-liquid surface interactions influence not just molecularly-thin confined liquids but also flow at larger length scales. This points the way to strategies for energy-saving during fluid transport and may be relevant to filtration, colloidal dynamics, and microfluidic devices, and shows a hitherto-unappreciated dependence of slip on velocity.

On Stability Analysis of a Flexible Cylinder in an Array of Rigid Cylinders

1992 ◽  
Vol 114 (1) ◽  
pp. 12-19 ◽  
Author(s):  
J. Marn ◽  
I. Catton
Keyword(s):  
Experimental Data ◽  
Boundary Condition ◽  
First Principles ◽  
Control Volume ◽  
Slip Boundary Condition ◽  
Flexible Cylinder ◽  
Slip Boundary ◽  
Advantages And Disadvantages ◽  
Solid Liquid Interface ◽  
Solid Liquid

The concept of an unsteady control volume is used to predict the onset of instability for a simple array of cylinders. The array consists of a flexible cylinder placed amidst rigid cylinders. The fluid is assumed to be incompressible with a “slip” boundary condition used on the solid/liquid interface. The equations derived for the model from first principles are solved in the complex plane. The results are compared to experimental data. The paper is concluded with a discussion of the advantages and disadvantages of the model and an assessment of the accuracy of the predictions.

No-Slip Boundary Condition for Weak Solid−Liquid Interactions

2011 ◽  
Vol 115 (17) ◽  
pp. 8613-8621 ◽  
Author(s):  
Adam P. Bowles ◽  
Christopher D. F. Honig ◽  
William A. Ducker
Keyword(s):  
Boundary Condition ◽  
Slip Boundary Condition ◽  
Slip Boundary ◽  
Solid Liquid

scholarly journals Scale effect of slip boundary condition at solid–liquid interface

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Gyoko Nagayama ◽  
Takenori Matsumoto ◽  
Kohei Fukushima ◽  
Takaharu Tsuruta
Keyword(s):  
Boundary Condition ◽  
Scale Effect ◽  
Slip Boundary Condition ◽  
Liquid Interface ◽  
Slip Boundary ◽  
Solid Liquid Interface ◽  
Solid Liquid

Fully Resolved Simulations of Stationary Particles in Turbulent Flow

2003 ◽  
Author(s):  
Tristan M. Burton ◽  
John K. Eaton
Keyword(s):  
Gas Flow ◽  
Isotropic Turbulence ◽  
Numerical Models ◽  
Particle Surface ◽  
Particle Diameter ◽  
Grid Method ◽  
Slip Boundary Condition ◽  
Slip Boundary ◽  
Kolmogorov Length Scale ◽  
Turbulence Modification

Gas flows containing a dilute loading of solid particle constitute an important class of multiphase flows. In most cases the gas flow is turbulent, and the interactions between the particles and the turbulence offer major modeling challenges. Many numerical models implicitly assume that the particles are significantly smaller than all turbulence length scales. Simple particle drag laws derived for uniform steady flow around a sphere are used to compute the motion of point-particles, and to determine the magnitude of the point-forces that are applied to the gas phase in order to produce turbulence modification. This technique may be appropriate if the particle is small relative to any turbulent eddies, but in many practical problems the particle diameter, d, is of the same order as the flow Kolmogorov scale, η. Here we perform fully-resolved simulations of a fixed particle in decaying homogeneous isotropic turbulence using an overset grid method. All flow scales are accurately resolved with this technique including the effect of the no-slip boundary condition at the particle surface. A set of 29 simulations with an initial Taylor microscale Reynolds number, Reλ = 32.2, and Kolmogorov length scale, η = 0.45d are computed to obtain a useful statistical sample. The turbulent kinetic energy and viscous dissipation near the particle surface in laden and unladen simulations are compared to provide understanding of the turbulence modification process. We anticipate that these results will provide direction for the development of turbulence modification models suitable for larger scale simulations where the flow cannot be resolved to the particle surface.

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