Heat

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The amount of heat Q is a form of energy transfer between systems that are not in thermal equilibrium. It is expressed in joules.

Between two systems with different temperatures, heat always flows from the higher to the lower temperature. The heat transport can be achieved by

• Conduction
Transfer within a solid.

• Convection
Transfer by the flow of a liquid or gas.

• Radiation
Transfer between two bodies that are not in contact with each other.

• Phase change
No transfer, only a shift in the relation between two phases.

The process function Q was introduced in 1850 by the Prussian physicist Rudolf Clausius.