Considering the heat exchanger given in the figure the continuous, steady-state heat duty is given by,

Q=m (Hout-Hin)

where

Q is the heat duty (rate of heat transfer)

m is the flow rate of the stream (mass or molar)

Hin is the enthalpy of the stream entering (per unit mass or mole)

Hout is the enthalpy of the stream leaving (per unit mass or mole)

● Heat is transferred to or from process streams using other process streams or “heat transfer media”. In a heat exchanger design, every effort is made to exchange heat between process streams and thereby minimize the use of heat transfer media (referred to as utilities).

● Heat transfer media are classified as “coolants (heat sinks)” when heat is transferred to them from process streams, and as “heat sources” when heat is transferred from them to process

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