Convective Heat Transfer

Overview

Engineering reference data for Convective Heat Transfer in heat transfer.

Key Formulas

Fourier's Law

$q = -k \nabla T$

Heat flux proportional to temperature gradient.

Convective Heat Transfer

$Q = hA(T_s - T_\infty)$

Heat transfer between surface and fluid.

Stefan-Boltzmann Law

$q = \varepsilon \sigma T^4$

Radiative heat flux from a surface.

Thermal Resistance

$R_{th} = \frac{L}{kA}$

Resistance to heat conduction.

Variables

Types of Convection

Convective heat transfer occurs in two primary modes:

• Forced Convection: Fluid flow is induced by an external force such as a pump, fan, or mixer.
• Natural (Free) Convection: Flow is driven by buoyancy forces. Density differences caused by temperature variations in the fluid create circulation (e.g., heated fluid rises, cooler fluid descends).

Empirical Formula for Air

A common empirical formula for estimating the convective heat transfer coefficient for air flow over a surface is:

$$h_c = 10.45 - v + 10 v^{1/2}$$

where:

• $h_c$ is the convective heat transfer coefficient (kcal/m² h °C)
• $v$ is the relative air velocity (m/s)

To convert to W/m² K, use:

$$h_{c,W} = 1.16 \times (10.45 - v + 10 v^{1/2})$$

Note: This formula is valid for air velocities between 2 and 20 m/s.

Heat Transfer Coefficient Ranges

The following table provides typical ranges for convective heat transfer coefficients under various conditions.

References

• Original Source