Engineering tools · Free to use

Dittus–Boelter Turbulent Tube Convection

Estimate Nu for fully developed single-phase turbulent flow in a smooth circular tube. Add fluid conductivity and inside diameter to estimate h.

Inputs

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Reynolds number Re based on inside diameter (above 10000) Prandtl number Pr (0.7–160) Straight-tube length / inside diameter L/D (at least 10) Heat direction relative to the fluid Fluid thermal conductivity k (required for h)W/(m·K) Inside diameter D (required for h)

For Nu only, clear both k and D. To calculate h, enter both.

I confirm single-phase flow in a smooth straight circular tube, fully developed velocity and temperature fields, and modest property variation between wall and bulk fluid.

L/D ≥ 10 alone does not prove that flow and thermal fields are fully developed.

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Result

Nusselt number Nu: —

Tube-side convection coefficient h: — W/(m²·K)

h is the fluid-side convection coefficient only; it excludes wall, fouling and other-side resistance.

Equation

Nu = 0.023 Re^0.8 Prⁿ; h = Nu · k / D

n=0.4 when the fluid is heated; n=0.3 when the fluid is cooled. This is the commonly used revised form with coefficient 0.023.

Properties and applicability

Evaluate ρ, μ, cp and k at the mean bulk fluid temperature and relevant pressure; use consistent conditions for Re, Pr and k. The correlation requires a smooth straight circular tube, single-phase forced convection, fully developed velocity and temperature fields, and modest property variation between wall and bulk fluid.

This tool uses the conservative limits Re > 10000, 0.7 ≤ Pr ≤ 160 and L/D ≥ 10; verify that both fields are fully developed. Entrance regions, significantly rough or noncircular tubes, phase change, strong property variation and near-critical states are outside the model. This is an empirical estimate whose error depends on the application.

Sources

NPTEL: turbulent forced convection in tubes: heating/cooling exponents, bulk-fluid properties and fully developed conditions.

BMS College of Engineering: Heat and Mass Transfer Laboratory Manual: common equation and Re, Pr and L/D conditions.

Worked example

Assume single-phase flow in a smooth straight round tube with fully developed flow and temperature fields and modest wall-to-bulk property variation. For Re = 100000, Pr = 1.2, L/D = 60, fluid heating, k = 0.6 W/(m·K) and D = 0.025 m, Nu ≈ 247.400 and the tube-side h ≈ 5937.6 W/(m²·K). L/D alone does not establish fully developed conditions.

For engineering estimates; verify operating conditions and applicable standards for design.