Question

Viscous and heat sensitive liquids are concentrated in which type of evaporators?

• A. Open pan
• B. Long tube
• C. Agitated film
• D. Short tube

Hint:

Agitated film evaporators are preferred for viscous and heat sensitive liquids because they provide thin film, good heat transfer, and short residence time.

Answer 1

The Correct Option is C

Viscous liquids have high resistance to flow. So, they do not circulate easily in ordinary evaporators. Heat sensitive liquids may decompose or degrade if they are exposed to high temperature for a long time. Therefore, for such liquids, we need an evaporator which gives: \[ \text{short residence time} \] and \[ \text{good heat transfer} \] An agitated film evaporator is suitable for this purpose. In this evaporator, the liquid forms a thin film on the heated surface. Mechanical agitation spreads the liquid and continuously renews the film. Because the film is thin, heat transfer is improved. Also, the liquid remains in contact with heat for a short time. Hence, agitated film evaporators are used for viscous and heat sensitive liquids. Therefore, the correct answer is: \[ \text{Agitated film} \]