Heat Flux Density Converter

Convert heat flux density between W/m², kW/m², W/cm², Btu/ft², and other units with scientific precision.

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Heat Flux Density Units Explained

Watt/Square Meter (W/m²)

The SI unit of heat flux density. It represents the heat transfer rate per unit area in watts per square meter. q = Q / A.

Common uses: Solar radiation, heat transfer calculations, thermal imaging, engineering design, international standards.

Kilowatt/Square Meter (kW/m²)

Heat flux density in kilowatts per square meter. 1 kW/m² = 1000 W/m². Used for high heat flux applications.

Common uses: Industrial heating, concentrated solar power, furnaces, high-power laser applications.

Watt/Square Centimeter (W/cm²)

Heat flux density using centimeter units. 1 W/cm² = 10,000 W/m². Often used for localized heating.

Common uses: Spot heating, laser systems, microelectronics, research applications.

BTU/Hour/Square Foot (Btu/h/ft²)

Heat flux density in British Thermal Units per hour per square foot. Widely used in US engineering. 1 Btu/(h·ft²) ≈ 3.154 W/m².

Common uses: HVAC design, building thermal analysis, US engineering standards.

Kilocalorie/Hour/Square Meter (kcal/h/m²)

Heat flux density using kilocalories. 1 kcal/(h·m²) ≈ 1.163 W/m². Used in some regions and older standards.

Conversion: International unit still found in regional standards.

Heat Flux Calculation

Heat flux density is calculated as the heat transfer rate divided by area: q = Q / A

  • q: Heat flux density (W/m²)
  • Q: Heat transfer rate (Watts)
  • A: Surface area (m²)

Typical Heat Flux Density Values

  • Solar constant (at Earth orbit): ~1361 W/m²
  • Solar radiation (Earth surface, noon): ~1000 W/m² (clear sky)
  • Human skin (comfort): ~80-100 W/m²
  • Room heating: 50-200 W/m²
  • Industrial furnace wall: 10,000-50,000 W/m²
  • Laser cutting (CO₂ laser): 10⁶-10⁷ W/m²
  • Human body total heat generation: ~100 W / ~1.8 m² ≈ 55 W/m²

Heat Transfer Modes

Heat flux density occurs through three primary mechanisms:

  • Conduction: Heat transfer through material in contact (q = k × ∇T)
  • Convection: Heat transfer by fluid motion (q = h × ΔT)
  • Radiation: Heat transfer by electromagnetic waves (q = ε × σ × T⁴)

Common Applications

Heat flux density is essential in numerous engineering and scientific applications:

  • HVAC Systems: Calculating heat exchanger performance
  • Building Design: Thermal comfort and energy efficiency
  • Thermal Protection: Spacecraft and high-temperature applications
  • Solar Energy: Photovoltaic and thermal solar systems
  • Electronics Cooling: CPU and component thermal management
  • Industrial Processes: Furnaces, boilers, and heat exchangers