M.13Heat Exchanger (LMTD)

Enter the inlet and outlet temperatures of the hot and cold fluids; optionally find the required area from heat duty and U value.

Typical: water–water 800–1500 · steam–water 1000–3500 · gas–gas 10–50 W/m²·K

Results

LMTD
—
Correction factor F
—
Effective temperature difference F·LMTD
—
Required area
—
Terminal differences ΔT₁ / ΔT₂
—

    This tool is for preliminary sizing. Final design must be verified with material tests, the relevant standards and equipment manufacturer data.

    Formulas

    LMTD
    LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂)
    Area
    A = Q / (U · F · LMTD)
    F (1–2 shell)
    R = (T₁ − T₂)/(t₂ − t₁), P = (t₂ − t₁)/(T₁ − t₁) → Bowman relation

    Note

    Counter-flow gives the highest LMTD for given temperatures. In shell-and-tube exchangers the F factor accounts for departure from counter-flow; designs usually target F ≥ 0.75–0.8. U depends on the fluids, velocities and fouling resistance; typical values can be used for initial sizing.

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