Radiation Surface Absorptivity

Overview

Engineering reference data for Radiation Surface Absorptivity 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

Definition

Absorptivity (α) is defined as the ratio of the power absorbed by a surface to the incident radiant power. In the context of thermal radiation and Kirchhoff's law, the absorptivity of a surface for a given wavelength and direction is equal to its emissivity under the same conditions. For a "gray" surface, the total absorptivity is often approximated by its total emissivity.

Surface Absorptivity Data Table

The following table provides typical solar radiation absorptivity values for various common surfaces. These values are crucial for calculating radiative heat transfer and solar heat gain in engineering applications.

References

• Original Source