Thermal conductivity

Thermal conductivity or thermal conductance is the quantity of heat that passes in unit time through unit area of a plate of unit thickness, when its opposite faces differ in temperature by one degree.

In the SI system of units, thermal conductivity is measured in watts per meter-kelvin, (Wm^-1K^-1) where a

• watt is the unit of power
• meter is the unit of distance
• kelvin is the unit of temperature

In general thermal conductance tracks electrical conductance, metals being good thermal conductors. There are exceptions, the most outstanding is that of diamond which has a high thermal conductance, between 1000 and 2600 Wm^-1K^-1, while the electrical conductance is low.

Thermal conductance of other common materials:

• Silver 430
• Copper 390
• Gold 320
• Platinum 70
• Quartz 8
• Glass 1

Since diamond has such a high thermal conductance, natural blue diamond much higher still, one may test gems to determine if they are genuine diamonds using a thermal conductance tester, one of the instruments of gemmology. Diamonds of any size are notably cool to the touch because of their high thermal conductivity, perhaps the origin of the term "ice."

See conduction.