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Past incidents in liquefied gas storage tanks indicate that the liquid may develop rollover, usually linked to liquefied natural gas (LNG), accompanied by an unpredictably enhanced boil-off rate. Rollover prediction models are not fully reliable and initiating events such as liquid stratification and thermal overfill are frequently undetectable since liquid superheats are very low. The usual way to derive boil-off in practice cannot account for discrepancies introduced by unsteady state, the uneven dependence of boil-off on heat influx, and the surface layer phenomenon. The largest relief requirement in this kind of storage remains uncertain. Earlier experimental study indicated that evaporation is mainly controlled by a non-nucleate liquid density-driven convective process. A correlation derived by experimental evaporation data of Freon-11 predicts LNG boil-off rates in steady and unsteady state. Heat transfer at free boundaries is expressed according to the data by the formula: Nu = 0.11 Ra(0.33). The expression is examined against previous studies on natural convection and good agreement is obtained.

Additional information

Authors: PAPADAKIS G A, JRC Ispra (IT)
Bibliographic Reference: Paper presented: 8th International Symposium on Loss Prevention and Safety Promotion in the Process Industries, Antwerp (BE), June 6-9, 1995
Availability: Available from (1) as Paper EN 38828 ORA
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