Radiation Heat Emissivity
Reference data and engineering information about radiation heat emissivity for heat transfer applications.
radiationheatemissivity
Overview
Engineering reference data for Radiation Heat Emissivity in heat transfer.
Key Formulas
Fourier's Law
Heat flux proportional to temperature gradient.
Convective Heat Transfer
Heat transfer between surface and fluid.
Stefan-Boltzmann Law
Radiative heat flux from a surface.
Thermal Resistance
Resistance to heat conduction.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Heat flux | W/m² | |
| Thermal conductivity | W/(m·K) | |
| Convection coefficient | W/(m²·K) | |
| Temperature | K | |
| Emissivity | — | |
| Stefan-Boltzmann constant | 5.67×10⁻⁸ W/(m²·K⁴) |
Emissivity Coefficients
The following table lists typical emissivity coefficients for common natural material surfaces.
6 rows
Material | Emissivity Coefficient - ε |
|---|---|
| Water (0 - 100 °C) | 0.95 - 0.963 |
| Ice | 0.96 - 0.99 |
| Snow | 0.96 - 0.98 |
| Sand | 0.9 |
| Granite | 0.96 |
| Green Grass | 0.975 - 0.986 |
Source: engineeringtoolbox.com
Key Concepts
- Emissivity (ε) is a dimensionless material property, ranging from 0 to 1, that describes a surface's effectiveness in emitting thermal radiation.
- A black body is an idealized perfect emitter with an emissivity of exactly *ε = 1. It emits the maximum possible thermal radiation at a given temperature.
- Real-world surfaces (gray bodies) have an emissivity between 0 and 1 (ε < 1). The emissivity coefficient directly scales the radiative heat flux calculated by the Stefan-Boltzmann Law.