Aerodynamic Entrainment and Resuspension

DOE-HDBK-3010-94

5.0 Surface Contamination; Solid, Noncombustible Surfaces

ARF assessed for suspension from a pile of powder from a hard, unyielding surface due to

accelerated flow generated by an explosion parallel to the surface is 5E-3 with an RF of 0.3

(see subsection 4.4.2.2.2). The stresses upon the surface contaminant, much of which is

embedded in the surface, appear to be fewer than those described for powders on unyielding

surfaces. The stresses are certainly greater than those assumed for the resuspension of

materials from nominal airflow in facilities or outdoors, 4E-5/hr. An ARF of 1E-3 with a

RF of 1.0 was selected for this phenomenon by Mishima, Schwendiman and Ayer (October

1978) in an analysis of severe natural phenomena effects. The ARF value is 20% of the

value assigned for the suspension of loose powders by explosion generated accelerated flows

parallel to the surface and more than an order of magnitude greater than values assigned for

resuspension. On these bases, an ARF of 1E-3 with a RF of 1.0 is assessed to bound the

suspension of surface contamination from non-brittle solid material for this phenomena.

5.3.4

A erod yn am ic E n train m en t an d R esus pen sion

The parameters governing the suspension of particles from a heterogenous surface (e.g.,

metal, some plastic, concrete, glass) are the same as for suspension from a homogeneous

bed; the parameters are the characteristics of the flow, particles and surface. The effects of

the various factors that contribute to the parameters (e.g., aerodynamic lift forces, drag

forces, adhesive forces) vary greatly. Figure 5-2 reproduced from Brockman (February

1985) shows the effect of particle size on various adhesive forces. Figure 5-3 reproduced

from Fromentin (January 1987) illustrates the effect of surface roughness on the

suspendability of small particles. Adhesion decreases with substrate surface roughness until

the macroroughness becomes the same size as the particles, when it increases rapidly

(Hubbe, 1984). The surface roughness of the particles, the presence of moisture, the

plasticity of the surface (Johnson, Kendall and Roberts, 1971), and other factors all appear to

affect the adhesion of particles to substrates or to each other.

Current consensus assumes that flow must be turbulent before significant suspension occurs

(Fromentin, January 1987). This is not necessarily the case for aerodynamic entrainment in

facility ventilation flow or outdoors at windspeeds less than 5 m/s. The turbulent flow is

divided into three regions: 1) core; 2) transition; and 3) viscous sublayer with regions two

and three comprising the wall region (Alonso, Bolado and Hontanon, July 1991). Present

consensus also agrees that turbulent bursts (intermittent ejections of discrete fluid elements

from wall region towards the core) play some role in suspension (Cleaver and Yates, 1973).

The burst process is composed of three steps: 1) deceleration of axial fluid velocity within

local region near wall, 2) progressive acceleration from approach of fluid with mean velocity,

and 3) before affected region totally accelerated, ejection of fluid from region of

unaccelerated fluid. The process is shown schematically in Figure 5-4.

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