Chapter 4

Heat transfer and diffusion of particles

To test the understanding of the lesson

Question

Why is a metal a good heat conductor ?

Hint

Solution

Thermal conductivity goes hand in hand with electric conductivity.

Thus, metals, good electric conductors, are good thermal conductors thanks to their electrons that take part in the heat conduction phenomenon.

Question

  • Outline Fick's and Fourier's laws.

  • Give the dimensions of the thermal conductivity and , the coefficient of particle scattering.

Hint

Solution

  • Fourier's law :

  • Fick's law :

  • is in and in m^2.s{-1}.

Question

Give the volumetric power dissipated in an ohmic conductor (with its conductivity) carrying a volumetric current .

Hint

Solution

The volumetric power is :

Question

  • Give the equation of heat diffusion, with and without source.

  • Give the equation of particle scattering, with and without source.

Hint

Solution

  • Equation of heat diffusion, with and without source :

  • Equation of particle scattering, with and without source :

Question

What is it worth for a laterally isolated rod, with its conductivity?

Hint

The thermal resistance is defined by :

Where is the thermal flow  :

For an isolated rod :

Where is the length of the rod and its surface.

Solution

Question

Outline Newton's law. is the coefficient of convective exchange.

Hint

Solution

The thermal transfers between a nody and the external medium follow Newton's law is the density of the thermal flow (algebraically exiting through the surface of the material) is proportional to the temperature difference between the external medium and the surface of the material.

is called film coefficient of heat transfer.

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