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Log Mean Temperature Difference

Effective average temperature gap driving heat across an exchanger.

Formula

LMTD=ΔT1−ΔT2ln⁡(ΔT1/ΔT2)LMTD = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1 / \Delta T_2)}

Variables

LMTDMean temp difference
\Delta T_1Gap at one end
\Delta T_2Gap at other end

Example

ΔT₁=40, ΔT₂=20: LMTD = 20/ln2 ≈ 28.9

Did You Know?

LMTD is used because the temperature difference along a heat exchanger changes non-linearly.

hvacheat exchangerlmtd

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