Heat Transfer
Film boiling is usually not desired in commercial equipments, because

it is difficult to maintain
none of the listed here
it is not economic
the heat transfer rate is low in view of the large temperature drop. @

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Heat Transfer
In sub-cooled boiling,

Temperature of the heating surface is more than the boiling point of the liquid
Very large vapour space is necessary
Temperature of the heating surface is less than the boiling point of the liquid
Bubbles from heating surface are absorbed by the mass of the liquid

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