Estimate convection performance with trusted heat transfer equations. Switch methods for pipes, channels, and surfaces. Export results fast with tables, graphs, and practical guidance.
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Nu = hL / k
Use this when the convection coefficient is already known from experiment, simulation, or reliable design data.
h = q / [A(Ts - T∞)]
Nu = hL / k
Useful when total heat transfer, area, and temperatures are known instead of the convection coefficient.
Nu = 0.023 Re0.8 Prn
Choose n = 0.4 for heating the fluid and n = 0.3 for cooling the fluid.
Nu = [(f/8)(Re - 1000)Pr] / [1 + 12.7(f/8)1/2(Pr2/3 - 1)]
f = [0.79 ln(Re) - 1.64]-2
This often improves turbulent internal-flow estimates across a wider range than the simpler power-law form.
Nu = 3.66 for constant wall temperature.
Nu = 4.36 for constant heat flux.
These are standard internal-flow reference values for fully developed laminar conditions.
| Case | Method | Inputs | Approx. Nu | Comment |
|---|---|---|---|---|
| Example 1 | Direct | h = 250, L = 0.12 m, k = 0.62 | 48.39 | Moderate convection enhancement. |
| Example 2 | Heat Flux | q = 300 W, A = 0.25 m², Ts = 80, T∞ = 35, L = 0.10 m, k = 0.60 | 4.44 | Low enhancement over pure conduction. |
| Example 3 | Dittus-Boelter | Re = 25000, Pr = 4.5, heating, L = 0.05 m, k = 0.63 | 138.50 | Turbulent internal convection estimate. |
| Example 4 | Gnielinski | Re = 50000, Pr = 6.0, L = 0.05 m, k = 0.63 | 308.00 | Stronger turbulent convection prediction. |
The Nusselt number compares convective heat transfer to pure conduction across a fluid layer. Larger values usually indicate stronger convection and better thermal transport at the surface.
They are linked by Nu = hL/k. If you know any three of these terms, you can solve the fourth. This calculator uses that link in several methods.
Use the length that matches your geometry and chosen correlation. Common choices are hydraulic diameter for internal flow, plate length for external flow, or tube diameter for crossflow cases.
Use it for turbulent internal flow when your Reynolds and Prandtl numbers fall near the usual recommended range. It is simple, fast, and widely used for screening calculations.
Gnielinski often gives a better turbulent internal-flow estimate because it includes friction factor effects. It is especially useful when you want more detail than a simple power-law correlation.
For fully developed laminar internal flow with ideal boundary conditions, the dimensionless temperature profile reaches a stable form. That makes the reference Nusselt number constant for the selected condition.
Higher Nu means stronger convection relative to conduction, but total cooling also depends on area, fluid properties, flow rate, and allowable temperature rise. It is helpful, but not the only design metric.
Yes. Use consistent units throughout the calculation. SI units are easiest here: meters, watts, square meters, kelvin or degrees Celsius for differences, and W/m·K for conductivity.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.