Outline of Evaporators

This quiz contains multiple-choice problems on evaporators types, liquid characteristics, single effect operations, short- and long-tube vertical evaporators, climbing and falling film evaporators, forced circulation and agitated film evaporators, evaporator capacity, Dühring's rule, enthalpy concentration diagram, feeding types, multiple effect evaporators, liquid head effect, multiple effect evaporators economy, capacity and calculations.

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How are the tube surfaces in falling film evaporators heated to enhance evaporation?

Heaters at about 200℃ Heaters at above 200℃ Heaters at just above 100℃ Steam condensing at the outer wall

Which of the following is not a type of evaporator?

Forced circulation

Natural circulation

Nucleate boiling

Gasketed evaporators

Refrigerators use liquid coolants which evaporate in an evaporator installed in a closed chamber. True or false?

True

False

Why do we not use natural convection for evaporating waste streams, crystallizers, and viscous fluids?

Slow process

Sedimentation problem

Prevents fouling at the heating surface

Causes overheating

Falling film evaporators are those in which evaporation occurs from the film interface with nucleate boiling at the wall. True or false?

True

False

Which of the following is not a suitable application of evaporators?

Refrigeration

Cooling

Heating

Crystallisation

How are evaporators different from dryers?

Final product is not a solid in evaporator

Evaporator is less efficient

Dryers use boiling to remove liquid

Dryers use very high temperatures to remove liquid

Where does the heat supplied to an evaporator go?

100% to evaporating liquid

99% evaporating the liquid

95% evaporating it and rest in overcoming surface tension

99% in overcoming surface tension

Which of the following evaporators allow for boiling and evaporation to occur inside the tubes, in that order?

Falling film evaporator

Rising film evaporator

Non-nucleate boiling evaporator

Forced circulation evaporator

Which are the two phases that cover the basic design of the climbing/falling film plate evaporator?

First climbing phase, then falling phase

First falling phase, then climbing phase

Liquid to vapour phase whilst climbing

Liquid to vapour phase whilst falling

Which of the following is not a subset of nucleate boiling evaporators?

Climbing film evaporator

Rising film evaporator

Short-tube vertical evaporator

Falling film evaporator

Crystallizers are one of the most important setups in industries nowadays. It is solely used to dry a solution to an extent to obtain the crystals of the solute. Which one of the following is the most suitable operation to carry out this process?

Forced circulation

Natural circulation

Nucleate boiling

Non-nucleate boiling

What is the driving force that sets off evaporation?

Difference in partial pressure

Difference in pressure

Difference in concentration

Difference in temperature

What is the advantage of basket type evaporators over short tube evaporators?

More evaporation per unit time

More heat transfer coefficient