Table of Contents
What Is Thermal Diffusivity?
Thermal diffusivity measures the rate at which temperature changes propagate through a material. Unlike conductivity (steady-state), diffusivity governs transient behavior. High diffusivity means quick thermal equilibrium. It equals k/(rho*cp). Metals have high diffusivity (copper: 111 mm²/s), water is low (0.14 mm²/s) despite fair conductivity due to high volumetric heat capacity.
This property is critical for thermal processing, cooking science, and manufacturing. The thermal penetration depth after time t is approximately sqrt(4*alpha*t), useful for estimating how deep heat reaches into a material.
Formula
α = k / (ρ × cp)
Penetration depth ≈ √(4αt)
Values for Common Materials
| Material | α (mm²/s) |
|---|---|
| Silver | 174 |
| Copper | 111 |
| Aluminum | 84 |
| Steel | 12 |
| Concrete | 0.75 |
| Water | 0.14 |
FAQ
Why does aluminum heat faster than steel?
Aluminum's diffusivity (84 mm²/s) is 7x steel's (12), so temperature changes propagate much faster through aluminum cookware.