Evaporation - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes



Introduction to evaporation

Basic concept of phase equilibrium

Factors affecting evaporation

Theory of evaporation

Classification of evaporators

Parts of an evaporator

Construction & working of evaporating still

Horizontal and vertical tube evaporator

Multiple effect evaporator

Learning objectives

At the end of this notes student will be able to:

• Outline the industrial applications of evaporation

• Explain the differences between evaporation and distillation

• Describe the basic concepts of phase equilibrium

• Discuss the factors affecting evaporation process

• Explain the theory of evaporation process

• Describe the parts of an evaporator

• Discuss the construction and working process of evaporating still

• Explain the process of horizontal and vertical tube evaporator

• Discuss the construction and working process of multiple effect evaporator

• Recommend suitable evaporator for the evaporation process


• Evaporation is nothing but a thermal separation process.

• Theoretically, evaporation means simply vaporization from the surface of a liquid.

• Vaporization of a liquid below its boiling point is called evaporation.

Thus, no boiling occurs and the rate of vaporization depends on the diffusion of vapour through the boundary layers above the liquid.

Evaporation is a type of phase transition; it is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapour).

Evaporation is a unit operation of vaporizing large quantities of volatile liquid to get a concentrated product

Evaporation v/s Distillation


Vaporization takes place below the boiling point

Takes only from the surface of the liquid

There is no bubble formation in evaporation

Not necessarily a separation or purification technique. Vaporisation occurs rapidly


Vaporization takes place at the boiling point

Takes place from whole of the liquid

There is bubble formation

It is a separation or purifying technique. It is a slow process

Drying v/s Evaporation


It refers to the removal of relatively small amounts of water from solid or nearly solid material

In most cases drying involves the removal of water at temperatures below its boiling point


It refers to the removal of relatively large amounts of water from solutions

Removal of water by boiling a solution- (wherever removing water is necessary)

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