Heat Exchanger Effectiveness NTU Calculator
Rate an existing heat exchanger with the effectiveness NTU method: from U, area, flows and inlet temperatures find the duty and both outlet temperatures, without iteration.
- Chot = 8.38 kW/K, Ccold = 12.54 kW/K
- NTU = UA ÷ Cmin = 0.9547
- ε (counterflow) = 0.5290
- Q = ε × Cmin × (Th,in − Tc,in) = 310.3 kW
Effectiveness NTU Equations
Counterflow: ε = [1 − e−NTU(1−Cr)] ÷ [1 − Cr × e−NTU(1−Cr)]
Parallel flow: ε = [1 − e−NTU(1+Cr)] ÷ (1 + Cr)
Q = ε × Cmin × (Th,in − Tc,in)
C = mass flow × specific heat for each side, U the overall heat transfer coefficient and A the area. Use this method to rate a known exchanger; use the LMTD calculator to size one for known temperatures.
Worked example
A 10 m² counterflow exchanger with U = 800 W/m²·K, 2 kg/s of water at 90 °C and 3 kg/s at 20 °C: NTU ≈ 0.95, ε ≈ 0.53, duty ≈ 310 kW, hot outlet ≈ 53.0 °C and cold outlet ≈ 44.7 °C.
Frequently Asked Questions
When should I use NTU instead of LMTD?
Use NTU when the outlet temperatures are unknown (rating an existing exchanger). Use LMTD when temperatures are known and you need the area.
What is effectiveness?
The actual heat transferred divided by the maximum possible, which would cool the smaller capacity stream to the cold inlet temperature.
Why is counterflow better?
It keeps a temperature difference along the whole length, so it reaches a higher effectiveness for the same NTU.
Learn more on the blog
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