Nusselt Number & Heat Transfer Coefficient
Calculate the Nusselt number and convective heat transfer coefficient for internal pipe flow (Dittus-Boelter) and flat plate (laminar/turbulent) correlations.
Results
What is it?
The Nusselt number (Nu) is the dimensionless heat transfer coefficient: Nu = h·L / k, where h is the convective HTC (W/m²·K), L is the characteristic length (m), and k is thermal conductivity (W/m·K). Dittus-Boelter correlation for turbulent pipe flow: Nu = 0.023 × Re⁰·⁸ × Pr^n (n=0.4 heating, 0.3 cooling). Valid for Re > 10,000, 0.6 < Pr < 160.
How to use
Select the flow configuration, enter the Reynolds and Prandtl numbers, the fluid's thermal conductivity, and the characteristic dimension (pipe inner diameter or plate length). The calculator outputs Nu and the actual heat transfer coefficient h.
Example scenario
Water (Pr=7, k=0.607 W/m·K) flowing in a 50 mm pipe at Re=50,000 (turbulent), being heated. Nu = 0.023 × 50000⁰·⁸ × 7⁰·⁴ = 0.023 × 3311 × 2.18 = 165.8. h = 165.8 × 0.607 / 0.05 = 2013 W/m²·K.
Pro tip
Prandtl number for common fluids: water ≈ 7 (at 20°C), engine oil ≈ 100–1000, air ≈ 0.71, liquid metals ≈ 0.001–0.03. The Dittus-Boelter correlation requires turbulent flow (Re > 10,000) and a fully developed hydrodynamic and thermal boundary layer. For entry-length effects or high Pr fluids, use the Gnielinski correlation for better accuracy.