PT317_DAY14_072_EVAPORATION

A forced circulation long tube vertical evaporator as compared to the natural circulation evaporator

• Is economical in operation

• Employs high velocity, high heat transfer rate and less heating surface requirement

• Employs a centrifugal pump placed between external downtake from vapor drum and inlet to tube bundle

• Both B & C

liquor is best handled in a long tube vertical evaporator.

• Foamy

• Scaling

• Viscous

• Salting

Long tube evaporators can be classied as rising or climbing film.

• True

• False

Long tube evaporators are usually ______ evaporators

• Natural convection

• Forced convection

• Nucleate boiling

• Radiation heated

What is the average tube length of long tube evaporators?

• 4-10ft

• 4-10m

• 1-2ft

• More than 10m

The heating medium in the Long tube evaporator is usually

• Gas at temperature just above 130℃

• Steam

• Gas at temperature just below 100℃

• Gas at very high temperatures

While using Long tube evaporators, the desired concentration is usually not achieved in single flow

• True

• False

Which one of the following is not an advantage of Long tube evaporators?

• Good heat transfer coecients at low temperature gradients

• Low head space required

• Thin fluids have very large product economy

• Relatively inexpensive to manufacture

The following are few demerits of using short tube vertical evaporators, select the incorrect one.

• Long tubes efficiently evaporate and hence recirculation is hardly required

• Corrosive fluids cannot be used as it increases cleaning cost

• Large head room requirement

• Very low heat transfer coecients with thick uids

What is the direction of flow in the centre tubes and wall side tubes of a long tube falling film evaporator?

• Both upwards

• Both downwards

• Downward and upward respectively