Flashing Spray

DOE-HDBK-3010-94

3.0 Liquids; Aqueous Solutions

For liquids that only contain dissolved/trapped gases at normal pressure and have a

surface level greater than the critical freeboard height from the venting point, an

undefined but insignificant fraction may be released depending on the size of the

drops, the velocity of the gas to carry the drops (most of the gas has been vented

prior to the formation of the drops), and the distance to the vent. Greater releases

would be expected if the liquid surface level was less than the critical freeboard

height from the venting point. A possible technique to estimate the fraction of these

liquids released is as follows:

Estimate the pressure based on increase in volume of the combustion

product and air components raise to a temperature based on the heat

generated by the deflagration.

Estimate the volume of the combustion products and air components at

standard and temperature vented.

Estimate fraction of gas in volume vented using Equation 5.11 in

Schrock et al. (August 1987).

Estimate the mass of liquid in the gas estimated above by subtraction.

Unfortunately, the equation for estimating the Critical Freeboard Height requires

estimating the gas density at the moment of pressurized release. There is no simple

or recognized means other than experimentation to estimate gas density at release.

The only gas density known at this point is the initial gas density at saturation, which

is less than the gas density with the liquid droplets. Accordingly, the more

conservative bounding estimates for the release of absorbed/trapped gases are assessed

as most applicable for general use.

3.2.2.3.3 F lashin g S p ray. Liquids heated above the boiling temperature of the

liquid/solvent/diluent "flash" upon release; that is, the excess heat above the boiling point of

the liquid is expended in the bulk vaporization of the liquid and the remaining liquid is

fragmented into fine droplets. The phenomenon has been investigated in experimental studies

and through empirical correlations and models, as summarized below.

A . E xp erim en tal S tu d ies. Brockman (February 1985) reviewed the literature on the

possible flashing of condensed moisture during the depressurization of a LWR post-

accident containment vessel. The event postulated was the vigorous boiling of water

during depressurization with droplets entrained in the vapor generated. A simplified

model was used to calculate the amount of water entrained. Entrainment is defined as

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