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Rates of evaporation accompanying the depressurization of a pool of saturated freon-11

Clegg G.T., Papadakis Georgios

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Summary

A transient technique has been used to study the rate of evaporation of Freon-11 contained in a 0.3 m diameter × 0.7 m high cylindrical glass vessel. Saturation pressures ranging from 7.5 to 10.5 kPa gauge were first established by adjusting the temperature of a water bath in which the tank was submerged. The pressure was then reduced linearly with time, and the resulting evaporation measured by condensation of the vapour issuing from the tank. Rates of depressurization from 1.9 to 6.3 Pa s−1 were employed.It was observed that nucleation was initiated and evaporation rates were increased when the liquid superheat exceeded 1.5 K. In the non-nucleate, or quiescent regime, which is believed to be that which exists in large scale liquefied gas storage tanks, the rate of evaporation (w) was correlated by w = 2.37 × 10−8 (ΔP)1.33 kg s−1 m−2. The exponent of the supersaturation pressure is almost identical to that found in previous studies of water evaporation. In non-dimensional form, the data are represented by Full-size image (<1 K) This equation is shown to give a good prediction of published data on the rate of evaporation from tanks of LNG, which exhibits a similar Rayleigh property to Freon-11. The nature of the liquid phase convective process in the surface layer which appears to control the rate of evaporation is also discussed.

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