• People have always understood that something flows from hot objects to cold ones. We call that flow “heat”.
  • The flow of the heat is all-pervasive. It is active to some degree or another in everything. Heat flows constantly from our bloodstream to the air around us. Such processes go on in all plant, animal life and in the air around us. They occur throughout the earth, which is hot at its core and cooled around its surface.
  • Heat transferdescribes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat.
  • The exchange of kinetic energy of particles through the boundary between two systems which are at different temperatures from each other or from their surroundings. Heat transfer always occurs from a region of high temperature to another region of lower temperature.
  • Heat transfer changes the internal energy of both systems involved according to the First Law of Thermodynamics. The Second Law of Thermodynamics defines the concept of thermodynamic entropy, by measurable heat transfer.
  • Thermal equilibrium is reached when all involved bodies and the surroundings reach the same temperature. Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.
  • The fundamental modes of heat transfer are conduction or diffusion, convection and radiation.