Illustration 19.2: Heat Transfer, Conduction

x10-1 W/(m K)



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Heat transfers via three mechanisms: convection, radiation, and conduction. This Illustration briefly describes these mechanisms, but the animation focuses on conduction (temperature is given in degrees Celsius). Restart.

Convection is the transfer of heat energy through the motion of a gas (or liquid): Heated air expands and rises, displacing cooler air, which moves downward and is then heated and rises again, setting up "convection currents."

Radiative heat transfer occurs when an object absorbs/emits electromagnetic radiation and gains/loses energy (see Illustration 19.3).

Conduction, as shown in the animation, is the transfer of heat within a material due to a temperature difference across the object (think of a spoon in hot coffee). We describe materials that transfer heat easily (more heat/time) as having a high conductivity (e.g., metal spoon) and those that do not (e.g., cloth) as having low conductivity. The reason for having insulation in a house, for example, is to reduce the conductivity of the walls so that it requires less power to keep the inside of a house at a given temperature, even though the outside is much colder or warmer. Use the animation to change the conductivity, the temperature on the outside of the "wall," and/or the thickness of the "wall" to see the power loss. The power loss is the power required to heat or cool the inside of the house.

Illustration authored by Anne J. Cox.

Physlets were developed at Davidson College and converted from Java to JavaScript using the SwingJS system developed at St. Olaf College.

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