Heating of Shallow Pools

DOE-HDBK-3010-94

3.0 Liquids; Aqueous Solutions

higher boiling rates; the liquid is turbulently mixed and progressively disintegrates at the

surface forming drops from both mechanisms. A possible third regime occurs at very high

boiling rates when splashing and foaming dominate the surface (Borkowski, Bunz and

Schoeck, May 1986).

Gas flow conditions and material characteristics are important parameters in bubble-induced

droplet formation. Bubble size determines the number and size of the droplets formed.

Bubble size is determined by the volume of vapor, surface characteristics such as surface

tension, and bubble contact angle. Contact angle changes due to local turbulence during

bubble formation resulting in a distribution of bubble sizes. Many bubbles are unstable and

coalesce and break up during ascent. Steam bubbles are in the range of 0.5 to 5 cm diameter

at low pressure and nucleate boiling (presence of rough surface, suspended particles). The

formation and detachment of macro-bubbles is a function of contact angle of the liquid and

the degree of superheat.

Bubble shape at the surface may range from spherical to hemispherical depending on size.

The liquid in the dome of the bubble runs down the sides and thins the film. The bubble

bursts when the internal pressure exceeds the external pressure and surface tension of the

film. Droplets are formed by the film breakup. The crater remaining from the bubble

rupture itself collapses forming an ascending liquid jet that decays into droplets after some

critical length. Jets ascend up to 20 cm from the surface of the bulk liquid. Jet drops are

only formed from bubbles <5 to 6 mm in diameter. Droplets from film breakup are only

formed for bubbles >0.2 mm in diameter. Therefore, by inference, only jet drops are

formed from bubbles <0.2 mm in diameter and only film breakup droplets are formed from

bubbles >6 mm in diameter. The number and size distribution of droplets formed from film

breakup correlates with the size of the bubble and may number into the hundreds for the

upper limit of bubble diameter. Figure 3-1, reproduced from the reference document, shows

a number distribution from the burst of two bubbles of 0.1% NaCl in water. Only one jet

drop ejected from collapse of a bubble ~2-mm in diameter with up to 6 ejected from very

small diameter bubbles (high internal pressure). The diameter of the drop is ~20% of the

bubble diameter (100- to 1000-m for the conditions covered here) (Borkowski, Bunz and Schoeck,

May 1986).

3.2.1.1

H eatin g of S h allow P ools

The airborne release during heating of aqueous solution was measured and reported by

Mishima, Schwendiman and Radasch (November 1968). This study involved the collection

and measurement of airborne Pu during drying of shallow pools of concentrated acidic

plutonium nitrate solution at three air velocities and the evaporation of 90% of the volume of

a dilute acidic plutonium nitrate solution. Table 3-1 displays measurements extracted from

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