Modeling Exposure Close to Air Pollution Sources in Naturally Ventilated Residences: Association of Turbulent Diffusion Coefficient with Air Change Rate

2011 ◽  
Vol 45 (9) ◽  
pp. 4016-4022 ◽  
Author(s):  
Kai-Chung Cheng ◽  
Viviana Acevedo-Bolton ◽  
Ruo-Ting Jiang ◽  
Neil E. Klepeis ◽  
Wayne R. Ott ◽  
...  
Keyword(s):  
Air Pollution ◽  
Diffusion Coefficient ◽  
Turbulent Diffusion ◽  
Pollution Sources ◽  
Turbulent Diffusion Coefficient ◽  
Change Rate ◽  
Air Change Rate

Optical studies on the turbulent motion of solid particles in a pipe flow

1991 ◽  
Vol 231 ◽  
pp. 665-688 ◽  
Author(s):  
James B. Young ◽  
Thomas J. Hanratty
Keyword(s):  
Diffusion Coefficient ◽  
Particle Velocity ◽  
Turbulent Diffusion ◽  
Slip Velocity ◽  
Rate Of Change ◽  
Solid Particles ◽  
Mean Square ◽  
Turbulent Diffusion Coefficient ◽  
Fluid Turbulence ◽  
The Mean

An extension of an axial viewing optical technique (first used by Lee, Adrian & Hanratty) is described which allows the determination of the turbulence characteristics of solid particles being transported by water in a pipe. Measurements are presented of the mean radial velocity, the mean rate of change radial velocity, the mean-square of the radial and circumferential fluctuations, the Eulerian turbulent diffusion coefficient, and the Lagrangian turbulent diffusion coefficient. A particular focus is to explore the influence of slip velocity for particles which have small time constants. It is found that with increasing slip velocity the magnitude of the turbulent velocity fluctuations remains unchanged but that the turbulent diffusivity decreases. The measurements of the average rate of change of particle velocity are consistent with the notion that particles move from regions of high fluid turbulence to regions of low fluid turbulence. Measurements of the root-mean-square of the fluctuations of the rate of change of particle velocity allow an estimation of the average magnitude of the particle slip in a highly turbulent flow, which needs to be known to analyse the motion of particles not experiencing a Stokes drag.

scholarly journals Evolution of the sun with mixing by hydrodynamic instabilities

1984 ◽  
Vol 105 ◽  
pp. 523-524
Author(s):  
Wai-Yuen Law ◽  
E. Knobloch ◽  
H.C. Spruit
Keyword(s):  
Diffusion Coefficient ◽  
Turbulent Diffusion ◽  
The Sun ◽  
Hydrodynamic Instabilities ◽  
Constant Multiple ◽  
Turbulent Diffusion Coefficient

Following Schatzman and Maeder (1981) we compute the evolution of the sun with partial mixing by hydrodynamic instabilities. Instead of simply assuming a turbulent diffusion coefficient which is a constant multiple of the viscosity, we incorporate some of the properties of hydrodynamic instabilities. This puts limits on the amount of diffusion that can be obtained, and makes it dependent on time and position in the star.

scholarly journals SOLUÇÃO DA EQUAÇÃO DE ADVECÇÃO-DIFUSÃO TRIDIMENSIONAL PELO MÉTODO GIADMT PARA DOIS TERMOS DE CONTRAGRADIENTE

2016 ◽  
Vol 38 ◽  
pp. 53
Author(s):  
Karine Rui ◽  
Camila Pinto da Costa
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Equation ◽  
Turbulent Flow ◽  
Turbulent Diffusion ◽  
Three Dimensional ◽  
Turbulent Diffusion Coefficient ◽  
Advection Diffusion Equation ◽  
Advection Diffusion

In this work, we present the resolution of the three-dimensional stationary advection-diffusion equation, through the GIADMT technique, considering the nonlocal closure for turbulent flow, using two different parameterization for the countergradient, one proposal by Cuijpers e Holtslag (1998) and another proposed by Roberti et al. (2004). The concentration of pollutants is estimated and compared with the observed data in Copenhagen experiment using different parameterization for the vertical turbulent diffusion coefficient.

Spatially varying mixing of a passive scalar in a buoyancy-driven turbulent flow

2014 ◽  
Vol 742 ◽  
pp. 701-719
Author(s):  
Daan D. J. A. van Sommeren ◽  
C. P. Caulfield ◽  
Andrew W. Woods
Keyword(s):  
Diffusion Coefficient ◽  
Turbulent Flow ◽  
Turbulent Diffusion ◽  
Saline Solution ◽  
Passive Scalar ◽  
Eddy Diffusion ◽  
Turbulent Diffusion Coefficient ◽  
Advection Diffusion Equation ◽  
Eddy Diffusion Coefficient ◽  
Spatially Varying

AbstractWe perform experiments to study the mixing of passive scalar by a buoyancy-induced turbulent flow in a long narrow vertical tank. The turbulent flow is associated with the downward mixing of a small flux of dense aqueous saline solution into a relatively large upward flux of fresh water. In steady state, the mixing region is of finite extent, and the intensity of the buoyancy-driven mixing is described by a spatially varying turbulent diffusion coefficient $\kappa _v(z)$ which decreases linearly with distance $z$ from the top of the tank. We release a pulse of passive scalar into either the fresh water at the base of the tank, or the saline solution at the top of the tank, and we measure the subsequent mixing of the passive scalar by the flow using image analysis. In both cases, the mixing of the passive scalar (the dye) is well-described by an advection–diffusion equation, using the same turbulent diffusion coefficient $\kappa _v(z)$ associated with the buoyancy-driven mixing of the dynamic scalar. Using this advection–diffusion equation with spatially varying turbulent diffusion coefficient $\kappa _v(z)$, we calculate the residence time distribution (RTD) of a unit mass of passive scalar released as a pulse at the bottom of the tank. The variance in this RTD is equivalent to that produced by a uniform eddy diffusion coefficient with value $\kappa _e= 0.88 \langle \kappa _v \rangle $, where $\langle \kappa _v \rangle $ is the vertically averaged eddy diffusivity. The structure of the RTD is also qualitatively different from that produced by a flow with uniform eddy diffusion coefficient. The RTD using $\kappa _v$ has a larger peak value and smaller values at early times, associated with the reduced diffusivity at the bottom of the tank, and manifested mathematically by a skewness $\gamma _1\approx 1.60$ and an excess kurtosis $\gamma _2\approx 4.19 $ compared to the skewness and excess kurtosis of $\gamma _1\approx 1.46$, $\gamma _2 \approx 3.50$ of the RTD produced by a constant eddy diffusion coefficient with the same variance.

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