Coefficient deposition

Figure 5.28 Variation of deposition coefficient with surface tension. (From Whalley et al., 1973. Reprinted with permission.)...

Blunt MJ, Scher H (1995) Pore-level modeling of wetting. Phys Rev E 52 6387-6403 Bolster CH, Hornberger GM, Mills AL, Wilson JL (1998) A method for calculating bacterial deposition coefficients using the fraction of bacteria recovered from laboratory columns. Environ Sci Technol 32 1329-1332... 

Equation (10.30) implies that the particle downward flow rate along the wall decays exponentially with the bed height. The deposition coefficient, kd, can be related to the amplitude of the gas velocity fluctuations as [Pemberton and Davidson, 1986 Bolton and Davidson, 1988] (Problem 10.8)... 

Sea bottom contamination depends on the rate of principal radionuclide deposition. In estimates the deposition coefficient 10" cm/s can be taken. 

Any species involved in the RSGP mechanisms (Fig. 5.3) can deposit on the substrate surface. Deposition occurs when an impinging particle fails to bounce back from a colliding surface. Such a deposition may result from the loss of kinetic energy or from the formation of a chemical bond with a target molecule or atom. The sticking coefficient, or deposition coefficient, can be defined as the number of particles deposited divided by the total number of impinging particles. 

Where, r is radial distance of reaction front e is void fraction is deposition coefficient U is radial diffusion velocity Pj, , Py, and p are... 

FIGURE 15.128 Correlation for deposition coefficient k (from Hewitt and Govan [298], with permission from ASME). 

The deposition coefficient may be further defined by the following equation ... 

The deposition of dust is characterized by the deposition coefficient Kq, which in this particular case is defined as the ratio (expressed as a percentage) between the mass of the particles deposited per running centimeter of duct length and the mass of all particles passing through the given cross section of the duct. 

In the Cora code, the corrosion product layers outside the reactor core are rather arbitrarily subdivided into two layers, a transient one and a permanently deposited one. Supply to the transient layer occurs via deposition of suspended particles from the coolant, release from it includes erosion of particles back to the coolant as well as transport into the permanently deposited layer and partial conversion into dissolved species. In a comparable manner, the supply of nuclides to the permanent layer is assumed to result from transfer from the transient layer and the exchange equilibrium with the dissolved species present in the coolant. The deposition coefficients of suspended solids can be calculated on the basis of particle size and flow characteristics. The coefficients of relevance for the permanently deposited layer, including ionic transfer mechanisms between liquid and solid phases, can be derived from theoretical considerations as well as from laboratory studies of corrosion product solubilities. Finally, diffusion rates of nuclides at the interphase layers are needed, from the oxide layer to the coolant as well as in the reverse direction. These data can be obtained in part by theoretical considerations and by measurements at the plants. 

A scale deposit coefficient based on the reference exchanger s temperatures or a scale meter. 

The deposition coefficient or factor (K ep) is the ratio of the number of adhering particles touching the surface (see 34). 

In the present case, Kdep is the ratio of the number of adhering particles to the total number of particles which have passed through the middle section of the obstacle. The amount of adhering dust and the value of the deposition coefficient depend on tiie conditions governing the flow of the dust-laden air stream around the obstacles, the possible rebounding of particles from the surface, and also the adhesive forces capable of holding these particles. 

The value of the deposition coefficient is usually less than unity. 

Knowing the characteristics of the flow and the obstacle, we may calculate the criterion Cj and determine K ep. Using the deposition coefficient and the number of particles in the flow, we may calculate the number of particles deposited on the obstacle [see (VI.42)]. It is also possible to solve the problem in reverse. From the number of adhering particles N and the value of K j p we may calculate the number of particles in the flow. 

The criteria Cj and C2 are valid for specific conditions [117, 318] (specified dust, surface, and air conduit) and as yet there are no grounds for extending their significance to other cases of dust deposition. In addition to this, the distribution of the dust particles in a flow depends on their dimensions and it is in practice difficult to ensure a uniform concentration of dust in a flow. This fact limits the possibility of calculating K ep by reference to the criteria Cj and C2 in practice. However, the calculation of the deposition coefficient as a function of the properties of the flow, surface, and dust, and also the number of particles in the flow, deserves attention and further development. 

Both the deposition coefficient and wind speed ratio depend upon the degree of atmospheric stablllty( ) as shovn In Table F-4. The Integrals have been evaluated numerically and the wind speed ratio has been evaluated assuming the hel t of the elevated release to be 200 feet. 

Equation (Ua) has been eonpared with numerically Integrated areas enclosed by Equation (9). These comparisons were made for several values of exposure and for five different values for atmospheric stability three different release helc tSi three wind speeds, and three values of deposition coefficients. As a result. It was found that Equation (Ua) overestimates the enclosed area consistently by... 

As an example, curves of Equation (11) for a moderately stable atmosphere are plotted In Figures F-1 through F-6 for 1, 5, axad 10 m/s, respectively. Each figure shows areas for three different deposition coefficients. 

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