What is the solar constant?

The solar constant is approximately 1,361 W/m² at Earth's distance from the sun, measured perpendicular to the sun's rays outside Earth's atmosphere. At Earth's surface, peak solar radiation is about 1,000 W/m² due to atmospheric absorption.

How is heat flux related to temperature?

Heat flux is proportional to temperature difference: q = k × (ΔT/Δx) for conduction (Fourier's law), where k is thermal conductivity and Δx is thickness. Greater temperature difference or higher conductivity increases heat flux.

What limits CPU heat flux?

Modern CPUs generate 50,000-100,000 W/m² at the die surface—comparable to a nuclear reactor surface. Cooling is the limiting factor for CPU performance. Heat sinks spread this flux over larger areas, and thermal interface materials ensure good contact.

How do I calculate building heat loss?

Total heat loss = Σ(U × A × ΔT) for each surface, where U is thermal transmittance (1/R-value), A is area, and ΔT is indoor-outdoor temperature difference. Add infiltration losses for a complete calculation. Heat flux through each surface is q = U × ΔT.

Densité de flux thermique Converter

About Heat Flux Density Conversion

Heat flux density (also called heat flux, thermal flux, or heat flow rate density) measures the rate of heat energy transfer per unit area—how intensely heat flows through or from a surface. It's a vector quantity representing the power (energy per unit time) passing through each square meter of a surface, essential for thermal analysis of buildings, electronics cooling, solar energy systems, and industrial process equipment.

The SI unit is watts per square meter (W/m²). Heat flux analysis helps engineers size cooling systems, design appropriate insulation, prevent overheating in electronics, calculate building energy loads, and understand energy flows in systems from microscale computer chips to massive industrial furnaces. The sun delivers approximately 1,000 W/m² at Earth's surface on a clear day—a fundamental reference point in solar engineering.

Our converter handles all standard heat flux density units for thermal engineering, building science, and electronics cooling applications.

Common Heat Flux Density Conversions

From	To	Multiply By
W/m²	BTU/hr·ft²	0.3170
BTU/hr·ft²	W/m²	3.1546
W/m²	kW/m²	0.001
kW/m²	W/m²	1,000
W/m²	kcal/hr·m²	0.8598
kcal/hr·m²	W/m²	1.163
W/m²	W/cm²	0.0001
W/cm²	W/m²	10,000
W/m²	cal/s·cm²	0.0000239

Heat Flux Density Unit Reference

Watt per square meter (W/m²) – The SI unit for heat flux density. Heat power flowing through or from one square meter of surface. Most common in scientific and engineering work worldwide. Solar radiation is about 1,000 W/m² at peak; a human body radiates roughly 100 W/m²; a well-insulated wall loses 10-30 W/m² in winter.

BTU per hour square foot (BTU/hr·ft²) – US customary unit used in HVAC design, building energy analysis, fire safety codes, and industrial thermal applications. 1 BTU/hr·ft² ≈ 3.155 W/m². Building heat load calculations in the US are typically performed in these units. Fire exposure standards often specify critical heat flux in BTU/hr·ft².

Kilowatt per square meter (kW/m²) – Convenient for high heat flux applications like industrial furnaces, concentrated solar power, laser applications, or fire exposure analysis. 1 kW/m² = 1,000 W/m². Concentrated solar power systems can achieve 100+ kW/m² at the focal point.

Watt per square centimeter (W/cm²) – Used in electronics cooling, high-power laser applications, and nuclear engineering. 1 W/cm² = 10,000 W/m². Modern CPU dies can reach 50-100 W/cm², rivaling nuclear reactor surface heat fluxes. Critical for thermal interface material selection.

Kilocalorie per hour square meter (kcal/hr·m²) – Older metric unit found in European industrial references and some food processing applications. 1 kcal/hr·m² ≈ 1.163 W/m². Occasionally used in metabolic heat flux calculations.