What is Fourier’s Law?

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What is Fourier’s Law? Blog Image

Overview:

Scientists have discovered an exception to a 200-year-old Fourier’s Law that governs how heat diffuses through solid materials.

About Fourier’s Law

  • Fourier’s law, or Law of Heat Conduction, describes how heat is transferred, or conducted, through solid materials.
  • As molecules vibrate and electrons shuttle about, the heat diffuses from the hotter end of an object to the colder end.
  • It states that the rate of heat conduction through a plane layer is proportional to the temperature gradient across the layer and the heat transfer area of the layer.
  • Basically, it is an empirical relation between the rate of heat conduction, heat transfer, and temperature gradient in the direction of heat flow.
  • Formula: q = - k▽T, where,
    • q is the heat flux, which is expressed as energy per unit area per unit time.
    • k is the heat conductivity coefficient (thermal conductivity). The dimension is area per unit time, so typical units for expressing it would be m2/s.
    • ∇T is the temperature gradient (K/m).
  • The thermal conductivity of the material (k) is also known as the proportionality constant that is obtained in the formula. A high value of k denotes that the material is a good thermal conductor, and easily transfers energy through it.

What is Conduction?

  • Conduction is one of the three main ways that heat energy moves from place to place. The other two ways heat moves around are radiation and convection.
  • Conduction is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules.
  • Conduction occurs more readily in solids and liquids, where the particles are closer together, than in gases, where particles are further apart.
  • Anything that involves direct physical contact to transfer heat is an example of conduction.

Q1) What is convection?

Convection is a mode of heat transfer that occurs when heat is carried through a fluid (liquid or gas) due to its movement.In free convection, air or water moves away from the heated body as the warm air or water rises and is replaced by a cooler parcel of air or water. In forced convection, air or water is forcibly moved across the body surface (such as in wind or wind-generated water currents) and efficiently removes heat from the body.

Source: Startling Exception Discovered to 200-Year-Old Law of Physics