Is there film boiling inside the rising film evaporator?
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Is there film boiling inside the rising film evaporator? Still nucleate boiling? Please explain!
The mechanism of falling-film evaporators and rising-film evaporators is more based on evaporation rather than boiling. It is the material that forms a film on the wall of the heat exchange tube and then is heated to evaporate. If the temperature difference is too large, boiling will also occur; however, boiling can cause the membrane to break and lead to dry walls, thereby worsening heat transfer. Film boiling refers to the phenomenon in which, when the heat flux exceeds a critical value, the gas generated by boiling forms a film on the tube wall. It is different from the mechanism of falling-film evaporators.
In falling-film and rising-film evaporators, or in heat-siphon reboilers, boiling is definitely necessary for evaporation. Does the evaporation you’re referring to also involve bubbles? Is that boiling at the bubble point? But since it is called rising film and falling film, bubbles must have formed a gas film; and if it is a gas film, why isn’t it film boiling? Or is it at a boiling point where film boiling occurs, at that critical point in the spiritual realm?