Chemical Engineering - Heat Transfer - Discussion

Thanks for explaining @Babu.

U=W/m2k.

So liquid level increase means heat transfer area increases then automatically U decreases.

Thanks @Babushona.

Thanks @Babu.

Increasing liquor level means increase in pressure and decrease in velocity there by less turbulence and hence h decreases.

In this type of evaporator, boiling takes place inside the tubes, due to heating made (usually by steam) outside the same. Submergence is therefore not desired; the creation of water vapor bubbles inside the tube creates an ascensional flow enhancing the heat transfer coefficient.

This type of evaporator is therefore quite efficient, the disadvantage being to be prone to quick scaling of the internal surface of the tubes. This design is then usually applied to clear, non-salting solutions. Tubes are usually quite long, typically 4+ meters (13+ ft).

Sometimes a small recycle is provided. Sizing this type of evaporator is usually a delicate task, since it requires a precise evaluation of the actual level of the process liquor inside the tubes. Recent applications tend to favor the falling-film pattern rather than rising-fi.