Classification of heat exchangers according to transfer process

According to transfer process heat exchangers can be divided into 2 major categories:
1) Indirect contact type;
2) Direct contact type.

Indirect Contact Type Heat Exchangers

In this type of heat exchangers, the fluid streams remain separate, and the heat transfer takes place continuously through a separating wall. There is no direct mixing of the fluids because each fluid flows in separate fluid passages.

Direct Contact Type Heat Exchangers

In this type of heat exchangers, the two fluids are not separated by a wall. Here, closer temperature approaches are attained and the heat transfer process is also accompanied by a mass transfer.