What is the Nu (Nusselt Number)?
The Nusselt number is the ratio of convective to conductive heat transfer across a boundary. Nu≈1 means conduction only; large Nu means convection is carrying most of the heat.
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Nusselt Number Calculator
Compute the Nusselt number from convective coefficient, characteristic length and fluid thermal conductivity — the convective-to-conductive heat transfer ratio.
Nu = h·L ÷ k
Frequently asked questions
Can you show a worked example?
h=100, L=0.5, k=0.6 → Nu = (100·0.5)/0.6 ≈ 83.3 → convection dominates conduction.
How do I read the graph?
The visualisation places your computed Nu against colour-coded regime zones, with a live marker so you can see at a glance which flow or transfer regime your inputs fall into and how close you are to the next threshold.
Where is this used in real life?
Sizing heat exchangers, electronics cooling and any forced/natural convection problem.
What are the limits or edge cases?
All inputs must be physically valid; a zero in the denominator (e.g. zero viscosity, velocity or conductivity) is rejected rather than producing infinity. Regime thresholds are standard textbook values and can shift with geometry and conditions.