Why use log mean instead of arithmetic mean temperature difference?

Temperature driving force varies along the exchanger length. LMTD correctly averages this varying ΔT. Arithmetic mean overestimates for large temperature ratios (ΔT₁/ΔT₂ > 2).

What happens to LMTD when temperature differences are equal?

When ΔT₁ = ΔT₂, LMTD = ΔT (the constant temperature difference). This is the mathematical limit of the logarithm as the ratio approaches 1.

How do I calculate LMTD for condensers and evaporators?

For condensers: T_hot,in = T_hot,out (condensing at constant T). ΔT₁ = T_cond - T_cold,in, ΔT₂ = T_cond - T_cold,out. Same formula applies.

Log Mean Temperature Difference Calculator

Calculate LMTD = (ΔT₁ - ΔT₂)/ln(ΔT₁/ΔT₂) for heat exchanger design. Special case: when ΔT₁ = ΔT₂, LMTD = ΔT. Counterflow vs parallel flow LMTD comparison for same terminal temperatures.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Calculate LMTD = (ΔT₁ - ΔT₂)/ln(ΔT₁/ΔT₂) for heat exchanger design. Special case: when ΔT₁ = ΔT₂, LMTD = ΔT. Counterflow vs parallel flow LMTD comparison for same terminal temperatures. Use the log mean temp result to inform your clinical assessment.

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Log Mean Temperature Difference Calculator

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Frequently Asked Questions

Why use log mean instead of arithmetic mean temperature difference?

What happens to LMTD when temperature differences are equal?

How do I calculate LMTD for condensers and evaporators?