Summary of Evaporation Processes

In a reasonably well-insulated cryogenic liquid storage vessel, all the heat inflow through the insulation from the roof, walls and base of the vessel is carried to the free liquid surface by convection processes. 

The evaporation mass flux, in terms of mass evaporated per unit area of liquid free surface, varies with bulk liquid superheat AT as AT for LNG and LCH4. Conversely, the liquid must be superheated for surface evaporation to take place. 

Surface evaporation is the only liquid/vapour phase transition taking place, whereby all the heat inflow is absorbed by the latent heat of vaporisation. The enthalpy of the vapour carried out of the vessel balances this heat inflow under equilibrium conditions of storage. 

Evaporation is controlled by molecular evaporation, mixed thermal conduction/ convection, and Rayleigh-Benard type cellular convection in respectively successive deeper, identifiable, horizontal thin liquid layers, all within a surface sub-layer of about 5 mm below the vapour/liquid interface. The cellular convection is probably driven by surface tension variations in the free surface of the 

LPG and Other Cryogenic Liquid Mixtures, SpringerBriefs in Energy, DOI 10.1007/978-3-319-20696-7 4 

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