When should NTU method be used vs LMTD?

NTU-effectiveness is preferred when both inlet temperatures are known but outlet temperatures are unknown (common in design). LMTD is preferred when all four temperatures are known (rating existing exchangers). Results are identical.

What does NTU represent physically?

NTU = UA/(Cmin) where U is overall heat transfer coefficient, A is area, and Cmin = (ṁcp)min. NTU represents the number of heat transfer units — higher NTU means more thermal driving force is utilised. At NTU = 1, ε ≈ 63% for C* = 0.

Heat Exchanger NTU-Effectiveness Calculator

Calculate heat exchanger effectiveness ε using NTU method: ε = (1−exp(−NTU(1−C*))) / (1−C*×exp(−NTU(1−C*))) for counterflow; determine required NTU for given duty.

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 It Works

Calculate heat exchanger effectiveness ε using NTU method: ε = (1−exp(−NTU(1−C*))) / (1−C*×exp(−NTU(1−C*))) for counterflow; determine required NTU for given duty

Each component has a specific meaning:

NTU method: ε = )) / )) — The ntu method: ε = )) / )) recorded for the scenario being assessed.

Note: Interpret the ntu-effectiveness result against the thresholds and context described above.

How to Use

Enter the NTU method: ε = )) / )) for the scenario you are assessing. Calculate heat exchanger effectiveness ε using NTU method: ε = (1−exp(−NTU(1−C*))) / (1−C*×exp(−NTU(1−C*))) for counterflow; determine required NTU for given duty. Use the ntu-effectiveness result to inform your calculation.

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