Heat Exchanger Technology

Generic Heat Transfer equation in heat exhanger,

where

Q = Rate of heat transfer

U = Mean overall heat transfer coefficient

A = Heat transfer surface area

LMTD = Log mean temperature difference

F = Correction factor

LMTD = (DT1-DT2) / Ln (DT1-DT2)

Where

DT1 = Th,i - Tc,o

DT2 = Th,o-Tc,i

For a given heat transfer service with known mass flow rates and inlet and outlet temperatures the determination of Q is straightforward and ΔT can be easily calculated if a flow arrangement is selected (e.g. logarithmic mean temperature difference for pure countercurrent or cocurrent flow). This is different for the overall heat transfer coefficient U. The determination of U is often tedious and needs data not yet available in preliminary stages of the design. Therefore, typical values of U are useful for quickly estimating the required surface area. The literature has many tabulations of such typical coefficients for commercial heat transfer services. Below are tabulation of U value for different applications and heat exchanger types.

Source : DELTA T (CheResources, Built-It-Solar)

Source : Engineering Page

Source : The Engineering Tool Box