Advanced #65

The thermal conductivity of water is high and reaches a maximum at 130 degrees Celsius

The thermal conductivity of liquid water is high and shows a maximum at elevated temperature.

Scientific Explanation

The thermal conductivity of liquid water at room temperature is about 0.6 watts per meter per kelvin — higher than nearly all other non-metallic liquids. Even more surprising, this value continues to increase with temperature and reaches a maximum of roughly 0.686 W/(m K) at about 130 degrees Celsius (under pressure to prevent boiling). Beyond this point, thermal conductivity decreases.

This behavior is anomalous because in most liquids, thermal conductivity decreases monotonically with temperature: increasing disorder impedes heat transport. In water, hydrogen bonds play an additional role: they enable efficient energy transfer between neighboring molecules, similar to phonons in a solid. As temperature rises, molecules become more mobile and can relay heat faster, while the bonds, though weakened, are restructured more rapidly.

The maximum at 130 degrees marks the point at which the bond network is disrupted enough that solid-like heat conduction noticeably fades and the normal liquid-like decline sets in.

Thermal Conductivity of Water vs Temperature Line chart showing the thermal conductivity of liquid water versus temperature. The conductivity increases from 0 degrees Celsius, reaching a maximum of about 0.686 watts per meter per kelvin at approximately 130 degrees Celsius (under pressure), then decreases. Most liquids show a monotonic decrease. Temperature (°C) λ (W m⁻¹ K⁻¹) 0 50 100 130 200 0.56 0.65 0.69 Max ≈ 130 °C Typical Thermal Conductivity of Liquid Water
Thermal conductivity of liquid water. The maximum at 130 degrees Celsius sets water apart from typical liquids.

Everyday Relevance

High thermal conductivity makes water an excellent coolant. In internal combustion engines, coolant water circulates to transport heat efficiently from the engine block to the radiator. Nuclear power plants and industrial processes also use water as a primary cooling medium. The fact that thermal conductivity actually increases at higher temperatures is a major advantage: the hotter the water gets, the better it conducts heat away.