LMTD Calculator — Log Mean Temperature Difference | Engineering Calc Pro

🔥 LMTD Calculator

Log Mean Temperature Difference for heat exchangers

Results

LMTD
—
°C (or °F)
ΔT₁
—
°
ΔT₂
—
°
Heat Duty Q
—
W

Formula Reference

LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂)

Counter-flow: ΔT₁ = Th,in − Tc,out  |  ΔT₂ = Th,out − Tc,in

Parallel-flow: ΔT₁ = Th,in − Tc,in  |  ΔT₂ = Th,out − Tc,out

Q = U × A × LMTD

📝 Worked Example

Counter-flow heat exchanger: hot water 150→80°C, cold water 20→60°C.

InputValue
Th,in150 °C
Th,out80 °C
Tc,in20 °C
Tc,out60 °C

ΔT₁ = 150 − 60 = 90 °C  |  ΔT₂ = 80 − 20 = 60 °C

LMTD = (90 − 60) / ln(90/60) = 30 / 0.405 = 74.1 °C

Result: LMTD = 74.1 °C