Additional Evaporation and Bubbling Release Studies

DOE-HDBK-3010-94

3.0 Liquids; Aqueous Solutions

3.2.1.3

A d d ition al E vap oration an d B ub b lin g R elease S tu d ies

Borkowski, Bunz, and Schoeck (May 1986) reviewed 12 experimental studies that examined

the airborne release of dissolved matter from bubble-burst at the surface of aqueous

solutions. The slope of the rate change for fraction entrained as a function of gas velocity

changes at a gas velocity of 15 cm/s. The experimental data reported in this region are

reproduced in Figure 3-2. Data generated by the venting of pressurized liquids is also

presented as Figure 3-3 to assist in overall phenomena assessment.

The data by Mishima, Schwendiman, and Radasch (November 1968) covered in subsection

3.2.1.2 are plotted along with data from six other studies under reasonably comparable

conditions. Manowitz et al. (1955) measured the DF (decontamination factor, the ratio

between the radioactivity retained in the liquid in the vessel to that boiled off) during

evaporation of waste solution using a de-entrainment device (not specified). The DFs ranged

from 1E-4 to 1E-5 depending upon the boiling rate and contents suspended in solution.

Garner et al. (1959) performed experiments at reduced pressures and equilibrium conditions

to identify the main parameters for liquid entrainment during evaporation. Entrainment

increased with evaporation rate and decreasing solute concentration. Entrainment rates

ranged from 1E-5 to 1E-4. Garner et al. (1954) measured the drop size distribution and total

entrainment during evaporation in vessels of various diameters (4-in. and 12-in. diameter

tubes). Entrainment rates were in the 1E-5 range. Although ~95% of the drops were in the

< 20-m diameter range, the total mass entrained was primarily due to the drops > 100-m

in diameter. Shor et al. (1957) measured the radioactivity carried over in boilers by

continuous monitoring of trace 137CsCl driven airborne at elevated pressures (0.93 to

1.0 Mpa). Entrainment (1E-6 to 1E-4) correlated with boiling rate and had an initial high

burst of activity released. Heger et al. (1982, 1983) conducted bubbling experiments to

simulate reprocessing plant components. Stirring air flow velocity was ~10 m/h (2.8 cm/s).

Entrainment values ranged from 1E-7 to 1E-4. The presence of tributyl phosphate (TBP)

reduced the surface tension and increased entrainment by a factor of 5 to 10. The drops

airborne were bimodally distributed with maxima at 0.3 and 0.8-m diameter. Addition of

the TBP increased the generation of larger diameter drops.

It is evident that the ARF of 2E-3 measured by Mishima, Schwendiman and Radasch

(November 1968) bounds the value measured by the other reported studies by approximately

an order of magnitude. Data generated by the venting of pressurized liquids shown in

Figure 3-3 indicate that short of flashing spray conditions (superheating of the liquid by

pressurization), a release value in the range of 1E-3 will bound the airborne release of liquids

during boiling at normal atmospheric pressures. Thus, a bounding ARF of 2E-3 with an RF

of 1.0 is considered a very conservative bound for the airborne release of respirable size

drops during accident condition resulting in the boiling of aqueous solutions.

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