🔥 Heat Transfer Rate Calculator
Select heat transfer mode. Input parameters to compute heat transfer rate (W or BTU/h).
📐 Heat Transfer Formulas – Fourier, Newton, Stefan‑Boltzmann
Where Q = heat transfer rate (W), k = thermal conductivity (W/m·K), A = area (m²), ΔT = temperature difference (K or °C), d = thickness (m), h = convective coefficient (W/m²·K), ε = emissivity, σ = 5.67×10⁻⁸ W/m²·K⁴.
🧱 Fourier’s Law of Heat Conduction
Conduction is the transfer of heat through a solid material from a region of high temperature to low temperature. The rate depends on the material's thermal conductivity (k), the cross‑sectional area, and the temperature gradient. Insulation materials have low k values, reducing heat flow.
Example: Wall Heat Loss
A brick wall (k=0.72 W/m·K) of area 10 m², thickness 0.2 m, with ΔT=20°C loses Q = 0.72×10×20/0.2 = 720 W. Adding 50 mm PIR insulation (k=0.022) reduces it drastically.
💨 Convection Heat Transfer – Fluid & Airflow
Convection involves heat transfer between a solid surface and a moving fluid (air, water, etc.). The convective heat transfer coefficient (h) depends on fluid velocity, properties, and geometry. Natural convection (still air) h ≈ 5–25 W/m²·K; forced convection (fan, wind) h ≈ 25–250 W/m²·K.
In HVAC, convection governs radiator output, cooling coil performance, and duct heat exchange.
🌞 Thermal Radiation Heat Transfer
All bodies emit electromagnetic radiation based on their temperature. The net radiative heat exchange between two surfaces depends on their absolute temperatures (Kelvin) and emissivity (ε). High‑emissivity surfaces (ε≈0.9) like painted metal radiate effectively; low‑ε (polished aluminium) reflect.
📊 Thermal Conductivity of Common Materials
| Material | k (W/m·K) | Application |
|---|---|---|
| Copper | 401 | Heat exchangers |
| Aluminium | 237 | Heat sinks |
| Steel (mild) | 50 | Structural |
| Brick | 0.72 | Walls |
| Concrete | 1.4 | Floors |
| Glass wool | 0.04 | Insulation |
| PIR foam | 0.022 | High‑perf insulation |
| Air (still) | 0.026 | Cavities |
🏢 HVAC & Building Heat Transfer
Heat transfer principles govern building energy performance: conduction through envelope, convection at surfaces, and radiation exchange between interior surfaces. Proper insulation and airtightness minimize heat loss.
📝 Worked Engineering Examples
1. Wall Conduction
10 m² brick wall (k=0.7, d=0.22 m), indoor 21°C, outdoor 2°C. Q = 0.7×10×19/0.22 ≈ 604 W.
2. Convection from Radiator
Surface area 2.5 m², h=10 W/m²·K, ΔT=40°C → Q = 10×2.5×40 = 1000 W.
3. Radiation from Heated Floor
Area 20 m², ε=0.9, T₁=303 K, T₂=293 K. Q ≈ 0.9×5.67e-8×20×(303⁴-293⁴) ≈ 936 W.