Heat Flux Density & Solar Irradiance Converter

Heat Transfer, Solar Physics & Heat Flux Density Metrology

Heat Flux Density is the rate of thermal energy transfer per unit of surface area:

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• Universal Heat Flux Conversion Formulas (ISO Standards)**:

q''_BTU/(h·ft^2) = q''_W/m^23.15459 = q''_W/m^2 × 0.316998

q''_W/m^2 = q''_BTU/(h·ft^2) × 3.15459 = q''_kW/m^2 × 1,000

1 Langley/min = 1 cal/(min·cm^2) = 697.333 W/m^2

1 W/cm^2 = 10,000 W/m^2 = 10 kW/m^2

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• Total Incident Power & Stefan-Boltzmann Radiation Equations**:

Q = q'' × A (Watts or Kilowatts, kW)

T_bb = ( (q'') / (σ) )^0.25 )

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• Standard Thermal Radiation & Flux Benchmarks**:

• Peak Ground Sun (1 Sun): 1,000 W/m^2 317.0 BTU/(h·ft^2) 1.434 Ly/min

• Solar Constant (AM0 Space): 1,361 W/m^2 431.4 BTU/(h·ft^2)

• High-Performance CPU Die: 100 W/cm^2 = 1,000 kW/m^2 316,998 BTU/(h·ft^2)

• Critical Heat Flux (Pool Boiling): 1,200 kW/m^2 380,398 BTU/(h·ft^2)

How to Use This Calculator

Enter your Heat Flux Density (q'' / Irradiance) (e.g. 1000 in q''), From Heat Flux Unit — choose from Watts per Square Meter (W/m² - SI Base Unit), Kilowatts per Square Meter (kW/m²), BTU per Hour-Square Foot (BTU/(h·ft²) - Imperial Standard), To Heat Flux Unit — choose from BTU per Hour-Square Foot (BTU/(h·ft²)), Watts per Square Meter (W/m²), Kilowatts per Square Meter (kW/m²), Receiver Surface Area (A in m²) (e.g. 2.0 in m²), and Thermal Radiation & Solar Benchmark — choose from Custom Heat Flux, Peak Solar Irradiance (1,000 W/m² = 1 Sun) → 317.0 BTU/(h·ft²) | 1.434 Ly/min | Q̇ = 2.0 kW (2m² panel), Solar Constant AM0 (1,361 W/m²) → 431.4 BTU/(h·ft²) | 1.951 Ly/min | Extraterrestrial irradiance. Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Total Incident Heat Rate: Q_dot = q'' * A (in kW)

Stefan-Boltzmann Blackbody Equivalent Temperature: T = (q'' / sigma)^0.25 (sigma = 5.670374e-8 W/(m²·K⁴))

Worked Example

A solar energy engineer installing a 2.0 m² solar thermal collector under peak 1,000 W/m² clear sky sunlight calculates the collector receives exactly 2.00 kW of incident solar radiation.

Understanding Your Result

Unit conversions are exact by definition within a given measurement system (e.g., 1 km = exactly 1,000 m). Cross-system conversions (metric to imperial) use defined exchange factors: 1 inch = exactly 2.54 cm; 1 pound = 0.45359237 kg. Round your converted result to match the precision of your original measurement — expressing more decimal places than your input justifies implies false accuracy. For regulatory, legal, or safety-critical applications, verify which measurement system is required by the applicable standard.