TEMA / Heat Transfer · Engineering tool
Heat exchanger LMTD
Q = U · A · F · LMTD
Shell-and-tube duty or area from the log-mean temperature difference — counterflow LMTD with a correction factor.
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Duty Q
208.6kW
- LMTD
- 69.5°C
- ΔT1
- 80.0°C
- ΔT2
- 60.0°C
- Correction factor F
- 1
- Heat-transfer area
- 10m²
How it works
The log-mean temperature difference (LMTD) is the effective driving temperature for a heat exchanger. For counterflow, LMTD = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2), where ΔT1 and ΔT2 are the hot/cold terminal temperature differences at each end.
The duty is Q = U·A·F·LMTD, where U is the overall heat-transfer coefficient, A the heat-transfer area, and F a correction factor accounting for non-counterflow arrangements (1.0 for true counterflow; read from a correction-factor chart for 1-2, 2-4, etc.).
This tool computes the counterflow LMTD and either the duty (given U, A, F) or the required area (given a target duty). U and F come from the exchanger geometry and stream properties — this tool does not rate a specific unit.
Assumptions & limitations
- Steady-state, no phase change unless the terminal ΔTs reflect it; constant U and cp across the exchanger.
- Counterflow LMTD. For shell-and-tube arrangements apply the correction factor F (≤1); F ≈ 1 for pure counterflow and falls off near a temperature cross.
- Terminal temperatures must be monotonic (no temperature cross); if ΔT1 or ΔT2 ≤ 0 the configuration is infeasible.
- Overall U and F are user inputs; this tool does not compute film coefficients, fouling, or shell/tube geometry rating.
Related reading
Companion articles
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