Physics

LMTD Calculator (Log Mean Temperature Difference)

Find the log mean temperature difference of a heat exchanger.

Calculated Output

LMTD (K) 32.741

Formula: LMTD = (ΔT₁ − ΔT₂) ÷ ln(ΔT₁ ÷ ΔT₂)

Step-by-Step Breakdown

1. Values used:

2. ΔT at end 1 = 50 K

3. ΔT at end 2 = 20 K

5. LMTD = 32.741K

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The math behind it

LMTD = (ΔT₁ − ΔT₂) ÷ ln(ΔT₁/ΔT₂). It's used in Q = U·A·LMTD to size exchangers.

ΔT 50 K and 20 K → LMTD ≈ 32.7 K.

Why log mean, not average?

The temperature difference varies exponentially along the exchanger.