Heat Flux Density Converter

What Is Heat Flux Density

Heat flux density measures heat energy transfer rate per unit area. You express this property in watts per square meter (W/m²) in SI units. Engineers use heat flux to size heat exchangers and evaluate insulation performance.

Solar irradiance represents heat flux from the sun. Peak solar flux reaches 1000 W/m² at Earth surface. Building designers use heat flux calculations to determine cooling loads and insulation requirements.

Heat Flux Formula

Calculate heat flux from heat transfer rate and area:

Where q equals heat flux density in W/m², Q equals heat transfer rate in watts, and A equals area in square meters.

For conduction through a plane wall, use Fourier law:

Where k equals thermal conductivity, ΔT equals temperature difference, and d equals wall thickness.

Example: A wall with k = 0.5 W/(m·K), thickness 0.2 m, and ΔT = 20°C has heat flux:

Common Heat Flux Values

Heat Transfer Modes

Heat flux occurs through three mechanisms. Conduction transfers heat through solid materials. Fourier law governs conductive flux.

Convection transfers heat between surfaces and fluids. Newton law of cooling describes convective flux:

Where h equals convective heat transfer coefficient, Ts equals surface temperature, and T∞ equals fluid temperature.

Radiation transfers heat through electromagnetic waves. Stefan-Boltzmann law gives radiative flux:

Where ε equals emissivity and σ equals Stefan-Boltzmann constant (5.67×10⁻⁸ W/(m²·K⁴)).

Unit Conversion Factors

Frequently Asked Questions