Boiling, liquid pools, model

SO3 or oleums are usually stored and transported in their liquid form. Therefore, almost all of the accidents that have occurred involved the generation of a liquid pool (with the exception of the Richmond accident [Basket et al., 1994]). Although there are numerous pool evolution models in the literature, most of them deal with nonreactive liquids, with boiling points either much lower or much higher than typical ambient temperatures. The regime of behavior is then clearly either that of a boiling pool or the evaporation of a liquid of low volatility. 

Unfortunately, the available data were not sufficiently accurate for the application of mathematical models governing liquid pool evaporation and spreading. An evaporating liquid pool of ammonia does not produce a heavier-than-air gas cloud, as ammonia vapor at its boiling point is lighter than air at commonly occurring ambient temperatures (0 to 20°C). Therefore, a heavy gas cloud could only be formed if there was significant aerosol formation, which is unlikely in the reported conditions. 

Hancox, W. T., and W. B. Nicoll, 1971, A General Technique for the Prediction of Void Distributions in Non-Steady Two-Phase Forced Convection, Int. J. Heat Mass Transfer 14 1377 1394. (3) Haramura, Y., and Y. Katto, 1983, A New Hydrodynamic Model of CHF Applicable Widely to Both Pool and Forced Convection Boiling on Submerged Bodies in Saturated Liquids, Int. J. Heat Mass Transfer 26(3) 387 399. (2)... 

The decrease of the liquid level above the tube by a quarter of diameter promotes the increase of the average heat transfer coefficient at low and moderate heat fluxes. The measuring of the temperature heads showed that it goes on due to surface superheat decrease in the unflooded part of a tube. It ean be explained with help of following point model. There is not boiling but evaporative meehanism of heat transfer in a sintered powder porous media with the capillary transfer of the liquid from the pool to the zone of heat release. 

Y. Haramura and Y. Katto, A New Hydrodynamic Model of Critical Heat Flux, Applicable Widely to Both Pool and Forced Convection Boiling on Submerged Bodies in Saturated Liquids, Int. J. Heat Mass Transfer (26) 389-399,1983. 

The behavior of pools of liquids with boiling points close to ambient temperatures presents a more complicated modeling problem, especially if the liquid properties are critical, as is the case here, where the temperature range between boiling and freezing points is quite narrow. The chemical reactions that are involved add further to this complexity. 

Both empirical and pscudomechanistic models based on heat and mass transfer concepts are available and are based on the thermodynamic properties of the liquid and, for the boiling pool, on the thermal properties of the substrate (c.g., groimd). Vaporization rates may vary greatly with time. The dimensions of the vapor cloud formed over the pool are often required as input to some dense gas dispersion models (Section 2.3.2) this is empirical and is not provided by most models. 

A more complex model for pool spread has been developed by Webber (1991). This model is presented as a set of two coupled diiSerential equations which models liquid spread on a flat horizontal and solid surface. The model includes gravity spread terms and flow resistance terms for both laminar and turbulent flow. Solution of this model shows that the pool diameter radius is proportional to t in the limit where gravity balances inertia, and as in the limit where gravity and laminar resistance balance. This model assumes isothermal behavior and docs not include evaporation or boiling effects. 

Release Geometry. An ideal release for Gaussian dispersion models would be from a fixed point source. Real releases are more likely to occur as a line source (from an escaping jet of material), or as an area source (from a boiling pool of liquid). 

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