Conduction:
R_th = L / (k × A)
Convection:
R_th = 1 / (h × A)
L = Material thickness (m)
k = Thermal conductivity (W/m·K)
h = Heat transfer coefficient (W/m²·K)
A = Cross-sectional area (m²)
Thermal resistance is a measure of a material's or system's ability to resist the flow of heat. It is the temperature difference across a material or component divided by the heat transfer rate through it. Higher thermal resistance means better insulation and less heat flow, while lower thermal resistance indicates a material that conducts heat more readily.
The concept is analogous to electrical resistance in circuits, where thermal resistance opposes heat flow just as electrical resistance opposes current flow. This analogy allows engineers to analyze complex thermal systems using circuit analysis techniques, making it invaluable in electronics cooling, building insulation design, and thermal management applications.
When heat flows through multiple layers in series (one after another), the total thermal resistance is the sum of individual resistances: R_total = R₁ + R₂ + R₃ + ...This is similar to resistors in series in an electrical circuit.
For parallel heat flow paths (side by side), the equivalent resistance is calculated as: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... This configuration allows heat to flow through multiple paths simultaneously, reducing the overall thermal resistance of the system.
Disclaimer: Thermal resistance calculations are estimates based on ideal conditions. Actual heat transfer may vary due to material imperfections, contact resistance, and environmental factors. Consult engineering references for precise analysis.