Chemical Engineering - Heat Transfer - Discussion

Thanks for explanation @SAA.

Thanks for your detailed explanation @Saa.

Thanks @Saa.

Boiling Point Elevation.

Since evaporators dealing with boiling solutions, and in particular with solutions with non-volatile solutes, any calculations must account for the effect of boiling point elevation.

The vapor pressure of an aqueous solution is less than that of pure water at the same temperature; so the boiling point of the solution will be higher than that of the water. This is called Boiling Point Elevation (BPE) or vapor pressure lowering.

The boiling point of a solution is a colligative property -- it depends on the concentration of solute in the solution, but not on what the solute and solvent are.

When working problems involving heat transfer to or from boiling solutions, it is necessary to adjust the temperature difference driving force for the boiling point elevation.

Note that the equilibrium vapor rising from a solution exhibiting boiling point elevation will exist at a temperature and pressure such that it is superheated with respect to pure vapor. The vapor rises at the solution boiling point, elevated with respect to the pure component boiling point. The vapor, however, is solute free, so it won't condense until the extra heat corresponding to the elevation is removed, thus it is superheated.