Heat Transfer Calculator
Our thermodynamics & heat calculator computes heat transfer accurately. Enter measurements for results with formulas and error analysis.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
Q = kAΔT/L (conduction) | Q = hAΔT (convection) | Q = εσA(T₁⁴-T₂⁴) (radiation)
Heat conduction rate depends on thermal conductivity, area, temperature difference, and thickness (Fourier's Law). Convection depends on the heat transfer coefficient. Radiation follows the Stefan-Boltzmann law with the fourth power of absolute temperature.
Worked Examples
Example 1: Wall Insulation Heat Loss
Problem:Calculate heat loss through a 150mm fiberglass-insulated wall (k = 0.04 W/m·K), area = 20m², with 20°C inside and -10°C outside.
Solution:k = 0.04 W/(m·K), A = 20 m², ΔT = 30°C, L = 0.15m\nQ = kA(ΔT)/L = 0.04 × 20 × 30 / 0.15 = 160W\nThermal Resistance = L/(kA) = 0.15/(0.04×20) = 0.1875 °C/W\nR-value = L/k = 0.15/0.04 = 3.75 m²·K/W\nHeat Flux = 160/20 = 8 W/m²
Result:Q = 160W | R_th = 0.1875 °C/W | R-value = 3.75
Example 2: Cooling Electronics with Forced Convection
Problem:A 50W processor has a heatsink with 0.02m² surface area. Air is forced over it with h = 150 W/(m²·K). What is the temperature rise?
Solution:Q = hA(ΔT), so ΔT = Q/(hA)\nΔT = 50 / (150 × 0.02) = 16.7°C\nIf ambient = 25°C, heatsink temp = 41.7°C\nThermal Resistance = 1/(hA) = 1/(150×0.02) = 0.333 °C/W
Result:ΔT = 16.7°C | T_surface = 41.7°C | R_th = 0.333 °C/W
Frequently Asked Questions
What are the three modes of heat transfer?
Heat transfers through three fundamental mechanisms: (1) Conduction — heat flows through a solid material or between materials in direct contact, driven by a temperature gradient. Rate depends on thermal conductivity, area, temperature difference, and material thickness. (2) Convection — heat transfer between a surface and a moving fluid (liquid or gas). Can be natural (driven by buoyancy) or forced (driven by fans/pumps). Rate depends on the convection coefficient, area, and temperature difference. (3) Radiation — heat transfer via electromagnetic waves (infrared). Does not require a medium and can occur through vacuum. Rate depends on emissivity, temperature, and area.
What is the convection heat transfer coefficient?
The convection heat transfer coefficient (h) quantifies how effectively heat transfers between a surface and a fluid. It depends on fluid properties, flow velocity, geometry, and whether convection is natural or forced. Typical values: Natural convection in air = 5-25 W/(m²·K). Forced convection in air = 25-250 W/(m²·K). Natural convection in water = 100-900 W/(m²·K). Forced convection in water = 250-12,000 W/(m²·K). Boiling water = 3,000-100,000 W/(m²·K). The coefficient is often determined empirically using dimensionless correlations involving Nusselt, Reynolds, and Prandtl numbers.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy