write the expression for thermal conductivity and explain the terms
Answers
Thermal conductivity refers to the ability of a given material to conduct/transfer heat. It is generally denoted by the symbol ‘k’ but can also be denoted by ‘λ’ and ‘κ’. The reciprocal of this quantity is known as thermal resistivity. Materials with high thermal conductivity are used in heat sinks whereas materials with low values of λ are used as thermal insulators.
Fourier’s law of thermal conduction (also known as the law of heat conduction) states that the rate at which heat is transferred through a material is proportional to the negative of the temperature gradient and is also proportional to the area through which the heat flows. The differential form of this law can be expressed through the following equation:
q = -k.∇T
Where ∇T refers to the temperature gradient, q denotes the thermal flux or heat flux, and k refers to the thermal conductivity of the material in question.
Thermal Conductivity
An illustration describing the thermal conductivity of a material in terms of the flow of heat through it is provided above. In this example, Temperature1 is greater than Temperature2. Therefore, the thermal conductivity can be obtained via the following equation:
Heat Flux = -k * (Temperature2 – Temperature1)/Thickness
Formula
Every substance has its own capacity to conduct heat. The thermal conductivity of a material is described by the following formula:
K = (QL)/(AΔT)
Where,
K is the thermal conductivity in W/m.K
Q is the amount of heat transferred through the material in Joules/second or Watts
L is the distance between the two isothermal planes
A is the area of the surface in square meters
ΔT is the difference in temperature in Kelvin