# Thermal conductivity

Thermal conductivity is defined as the property of any material to conduct heat. Heat transfer takes place at a lower rate in all the materials of low thermal conductivity. Materials having thermal conductivity are greatly used in heat sink applications and materials having low thermal conductivity are used as thermal insulation. A thermal conductivity of  a material depends on the temperature, and its reciprocal is known as thermal resistivity.

Units of Thermal Conductivity

The SI unit of thermal conductivity is watts per meter-Kelvin and its variables are Mass, Length, Time, and temperature. In the Imperial unit, thermal conductivity is measured in BTU. There are other units which are closely related to the thermal conductivity which is in common use in the construction and textile industries. The construction makes use of units such as R-value and U-value. R and U values are dependent on the thickness of the product although thermal conductivity of a material is used in an insulation product.

The textile industry has different units which include the tog and the clo. It defines the thermal resistance of the material in a way analogous to the R- values that are used in the construction industry.

Measurement

There are many ways to measure thermal conductivity where each one is suitable for a limited range of materials. It depends on the thermal properties and the medium temperature. There is a difference between steady-state and transient techniques. Usually, the steady-state techniques are very useful when the temperature of the material does not change with time. It makes the signal analysis straightforward. There is also one disadvantage that a well-engineered experimental setup is usually needed.

#### Practise This Question

6×103mol K2Cr2O7 reacts completely with 9×103 mol of  Xn+ to give XO3 and Cr+3 The valve of n is: