TYPES OF HEAT EXCHANGERS
D T2 D T1
Heat transfer in a heat exchanger is by conduction and convection. The rate of heat
transfer, "Q", in a heat exchanger is calculated using the following equation.
Heat transfer rate (BTU/hr)
Uo = Overall heat transfer coefficient (BTU/hr-ft2-F)
Ao = Cross sectional heat transfer area (ft2)
Log mean temperature difference (F)
Consider the following example of a heat exchanger operated under identical conditions as a
counter flow and then a parallel flow heat exchanger.
represents the hot fluid temperature
Uo = 70 BTU/hr-ft2-F
Ao = 75ft2
represents the cold fluid temperature
Counter flow DTlm =
(200 120oF) (145 80oF)