Thermal diffusivity comparison: “The thermal diffusivity of solids is generally less than that of liquids and gases.” Is this statement correct?

Introduction / Context:
Thermal diffusivity (often written as alpha_th) indicates how quickly a material responds to temperature changes. It combines thermal conductivity, density, and specific heat and is central to transient heat transfer problems.

Given Data / Assumptions:

• Thermal diffusivity definition: alpha_th = k / (rho * c).
• Typical orders of magnitude: metals have high k and often high alpha_th; liquids like water have lower k and thus lower alpha_th; gases can have comparable or higher alpha_th than some liquids, depending on conditions.
• We compare broad classes: solids, liquids, gases.

Concept / Approach:
Since alpha_th rises with conductivity and falls with heat capacity and density, metals (solids) frequently exhibit large thermal diffusivities (fast temperature equalization). Water and many liquids have much lower alpha_th. Gases can have alpha_th on the order of 10^-5 m^2/s, while water is ~10^-7 m^2/s; many metals exceed 10^-5 m^2/s.

Step-by-Step Solution:

Verification / Alternative check:
Compare typical values: aluminum ~ 8.4e-5 m^2/s, copper ~ 1.1e-4 m^2/s; water ~ 1.4e-7 m^2/s; air ~ 2e-5 m^2/s. Solids (metals) are not “generally less.”

Why Other Options Are Wrong:

“True” and conditional versions contradict well-known property tables; temperature dependences do not reverse the general trend for common ranges.

Common Pitfalls:
Confusing conductivity with diffusivity or assuming all solids behave like insulators. Materials vary widely; always use alpha_th = k/(rho*c).

Final Answer:

False