Thermal Stress: Evaporation and Boiling cont'd

DOE-HDBK-3010-94

3.0 Liquids; Aqueous Solutions

where:

liquid surface tension

superficial gas velocity

acceleration due to gravity

surface tension of gas

gas density

height above pool surface

viscosity of gas

density difference between gas and liquid

diameter of vessel.

All correlations agreed well with the published data and could be applied to estimate ARF for

specific scenarios. The correlations are relatively straightforward although the values depend

upon parameters that are not readily quantifiable for many practical situations and vary with

temperature. Methods to determine the temperature or the values for the parameters as a

function of temperature were not presented. Use of the correlations for this study would

require the definition of a range of accident scenarios (not done as of this time) to determine a

bounding ARF and RF. The results indicate that large variations may be observed in

measured data dependent upon the location and configuration of the sampling system.

Four important observations arise from review of literature on entrainment of liquid droplets

from bubbling or boiling pools performed by Borkowski, Bunz and Schoeck (May 1986):

the influence of surface effects on the amount and composition of the

generated aerosols;

the possibility of chemical enrichment and depletion of substances in aerosols;

the existence of two groups of droplets with different mean sizes and amounts

of airborne mass;

the limited range of ejected jet droplets due to initial velocity;

Droplet formation during boiling is dependent upon conditions of boiling and bubble

characteristics. There appear to be at least two and possibly three boiling regimes that affect

bubble and droplet formation. The first regime occurs at lower rates where the volume

fraction of the bubbles is less than 30%, when discrete bubbles rise through the liquid and

grow due to decreasing hydrostatic head. Bubbles may coalesce or divide during ascent.

Droplets are formed from three mechanisms (bubble film disintegration, jet drops from crater

collapse, and secondary droplets from jet drop reentry into bulk liquid). This regime is the

predominant concern for nonreactor facility accident scenarios. A second regime occurs at

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