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How does heat flow between objects at different temperatures?

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In a thermoelectric generating system a heat source—usually fueled by coal, oil, or gas—is used within a boiler to convert water to high-pressure steam. The steam expands and turns the blades of a turbine, which turns the armature of a generator, producing electric power. A condenser converts any remaining steam to water, and a pump returns the water to the boiler.
heating In a thermoelectric generating system a heat source—usually fueled by coal, oil, or gas—is used within a boiler to convert water to high-pressure steam. The steam expands and turns the blades of a turbine, which turns the armature of a generator, producing electric power. A condenser converts any remaining steam to water, and a pump returns the water to the boiler.

Heat flows between objects at different temperatures as a result of the temperature difference itself, with energy moving from the hotter body to the colder one. This process of energy in transition is known as heat transfer, which occurs through three primary mechanisms:1

  • Conduction: The transfer of energy through direct contact or molecular agitation within a material, typically occurring in solids or fluids at rest.23
  • Convection: The transfer of heat through the physical movement of a heated fluid, such as air or water. This can occur naturally due to density variations or be forced by external means like fans or pumps.4
  • Thermal radiation: The transmission of energy as electromagnetic radiation, which does not require an intervening medium to travel between surfaces.25

According to the second law of thermodynamics, it is physically impossible for heat to spontaneously flow from a colder body to a hotter one without external work being performed. This transfer continues until the objects reach thermal equilibrium, where their temperatures are equal.63