Particle resuspension velocity

The Oroskar-Turian s correlation and previous ones were developed to determine the critical deposit velocity of Newtonian carrier fluids with various particle sizes and concentrations. Shah and Lord (7) generalized equation 2 to extend its capability to correlate the critical deposit velocity for non-Newtonian carrier fluids (power law). The parameter X was eliminated from equation 2 because of its insignificant contribution to the correlation results and because it would be undefined for the laminar flow regime of non-Newtonian fluids. The generalized form of equation 2, which can be applied to either critical deposit (VD) or resuspension velocity (Vs), is as follows ... 

The slurry velocity at which a particle bed forms is defined as critical deposition velocity, VD, and represents the lower pump rate limit for minimum particle settling. A further decrease in slurry velocity leads to increased friction loss, as indicated by a characteristic hook upward of curve A, and may also lead to pipe plugging. After shutdown, if flow rate over the settled solids is gradually increased, a response similar to curve A of Figure 16 is once again obtained. With increasing nominal shear rate, wall shear stress decreases until a minimum is reached and then increases rapidly thereafter. The fluid velocity that corresponds to this minimum stress value is the critical resuspension velocity, Vs. 

An empirical correlation has been proposed by Shah and Lord [10] for predicting deposition and resuspension velocities for slurries of relatively coarse particles ( d = 0.63 and 1 mm) in power law fluids of the type sometimes employed as drilling fluids. In these experiments, a minimum pressure gradient criterion was used to determine the deposition or resusjjension velocity. The pipe diameters used in the experiments ranged between 38 amd 70 mm and because most of the fluids were viscous, many of the flows were laminar. The correlation does not distinguish between turbulent and laminar flows and is not applicable to other fluids. 

The experiments showed that the deposition and resuspension velocities increased with pipe diameter and density difference, decreased as the fluid became more viscous and were insensitive to solids concentration in the range (0.08 < C < 0.31). Further research would be desirable to generalize these observations to finer particles, larger pipes and other fluids or slurries. 

The dispersion term is absent since dividing the reach into Ax completely mixed segments accomplishes dispersion numerically. In equation 1 t is time (t), Ct is soluble, particulate, and colloidal, concentration (M/L ), U is average water velocity (M/t), Ds is particle deposition flux (M/L t), h is water column depth (L), m v is suspended solids concentration (M/L ), fp and fd are fractions chemical on particles and in solution, kf is the soluble fraction bed release mass-transfer coefficient (L/t), Cs is the total, soluble and colloidal, concentration at the sediment-water interface (M/L ), Rs is particle resuspension flux (M/L t), ms is the particulate chemical concentration in the surface sediment (M/L ), fps Cts is the fraction on particles and total chemical concentration in the surface sediment (M/L ), Kl is the evaporation mass-transfer coefficient (L/t), Ca is chemical vapor concentration in air (M/L ), H is Henry s constant (L / L ) and Sx is the chemical lost by reaction (M/L t). It is conventional to use the local or instantaneous equilibrium theory to quantify the dissolved fraction, fd, particulate fraction, fp, and colloidal fraction, fooM in both the water column and bed. The equations needed to quantify these fractions appear elsewhere (4, 5, 6) and are omitted here for brevity. 

Including the particle resuspenion velocity, the details of five individual mass-transfer coefficients were presented above. These appear in Table I normalized to the chemical concentration on solid particles in the bed. Although the particle resuspension and particle biodiffusion transport coefficients remain unchanged the ones defined with solute concentrations require the msKo term for conversions to the equivalent particle concentration form. The Kd is the particle-to-porewater chemical partition coefficient (L /M). In doing so all can be compared on the same numerical basis. 

CFaT riverine models were presented for both the water column and bed sediment. They were then simplified to focus onto the non-flow resuspension soluble fraction using the quasi-steady state assumption to isolate the key water-side and sediment-side process elements. Field evidence of soluble release based on CFaT model derived data was reviewed for three rivers. Both the traditional particle background resuspension process and more recent soluble fraction process algorithms data interpretation were covered. Numerical field calibrated resuspension velocities and soluble mass-transfer coefficients were presented. Candidate water-side and sediment-side transport processes, selected from the literature were reviewed. Those that provided the best theoretical explanation and contained laboratory and/or field data support were selected. Finally, the flux and the overall transport coefficient which captures the essential features of the framework were presented. Following this the theoretical mass-transfer coefficients were applied to a site on the Fox River below De Pere Dam. Numerical calculations were made for the transport coefficients for both individual and combined processes. 

The negative sign indicates that the resuspension velocity is in the opposite direction of both deposition velocities. The dust-to-air partition coefficient is similar to that for the airborne solid particles. The dust resuspension rate parameter defined by Equation 4.8 appears in Table 4.2 in the PsCs column. All three of the advective rate parameters that were presented in this section were converted to their equivalent air concentration forms by using the appropriate equilibrium or phase partition coefficient. The final result appears in Equation 4.9. These converted forms are also presented individually in Table 4.2 and appear under the Ca column. 

Leighton, D. Acrivos, A. Viscous resuspension. Chem. Eng. Sci. 1986, 41 (6), 1377-1384. Leighton, D. Acrivos, A. Measurement of shear-induced self-diffusion in concentrated suspensions of spheres. J. Fluid Mech. 1987, 177, 109-131. Leighton, D. Acrivos, A. The shear-induced migration of particles in concentrated suspensions. J. Fluid Mech. 1987, 181, 415-439. Altobelli, S.A. Givler, R.C. Fukushima, E. Velocity and concentration measurements of... 

If the skin friction exceeds the critical threshold for resuspension, sedimentary material is I ifted off from the bottom and is transported into the water body. Grainy particles may also be moved by the so-called bed-load transport that occurs already at a lower threshold. Deposition results from the settling of the sediment particles, if the shear stress falls below a certain limit. The critical thresholds, the settling velocities, and the erosion and deposition rates are material constants derived from experiments (Soulsby, 1997). 

In the following, concentrations of HHCB and AHTN in pg/g (normalized to TOC) along a river section from the source to the river mouth are discussed (Fig. 5). Sedimentation in river systems is a dynamic process with permanent settling and resuspension of particles depending on flow velocities and particle size. Thus, sediment samples do not necessarily represent the local pollution histoiy of the river at the sampling sites. Additionally, sediments were not collected at representative cross sections, but only one hopefully representative sample at each site. This has to be considered in the following discussion. 

It was estimated from wave data that only in a zone around the margins of the Sound where the water is less than 18 m deep are the particle velocities of waves a significant fraction of the tidal stream speed. Direct evidence of excitation of sediment by waves in this zone is found in turbidity measurements and in the structure of surficial sediment layers. For example. Fig. 11 shows a turbidity track made from deep to shallow water in an area where the bottom is mud and the tidal stream weak. There is resuspension of mud through the water column where the depth is less than about half the wavelength of the waves present at the time the track... 

They are greater in the winter months because of the broadening of the distributions of and v under storm conditions ( and v are E-W and N-S velocity components). In Long Island Sound the pellets at the sediment-water interface undergo frequent resuspension before their incorporation into the permanent sediment. Dispersion of resuspended pellets by both advection and diffusion is rapid. New silt-clay-size mineral matter Introduced into the Sound will be rapidly distributed throughout the layer of pellets mantling the mud buttom. Chemical species adsorbed on silt-clay particles will be similarly dispersed. 

Resuspension of bottom sediments into the water column of aquatic systems represents an important source of particles and particle-associated contaminants into the water column. Unlike deposition, the resuspension process is very sporadic and short-lived, but when it does occur, the flux is generally quite large. Sediment resuspension occurs when hydraulic shear stress at the sediment-water interface rises above a critical level, sufficient to dislodge particles. Shear stress (x, dyn/cm ) is calculated as a function of shear velocity ( , cm/s) and water density (p, g/cm ) ... 

Resuspension and scour of noncohesive sediments are well understood as functions of particle diameter, and reasonable estimates of resuspension rates can be determined for noncohesive sediments with information about the system hydraulics and physical properties of the sediment. However, widely applicable relationships predicting cohesive sediment erosion have not yet been developed. Quantifying resuspension of cohesive sediments usually requires development of site-specific data and experimentation. Cohesive sediment resuspension has been observed to depend on sediment bulk density (or porosity), particle size, surface and porewater chemistry, algal colonization, bioturbation and gas formation within the sediments, in addition to bottom shear velocity. 

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