Heat flow is the transfer of heat energy or enthalpy. Heat energy is transferred through conduction(physical contact of surfaces), convection(movement of fluids), and radiation(emitted electromagnetic energy). As heat energy is transferred from one source to another, the kinetic energy of the receiving source increases. An increase in kinetic energy results in an increase in sensible heat or temperature. Sensible heat will continue to increase until the source has reached a phase change temperature. At this point, the source begins to change from a solid to a liquid or a liquid to a gas. At this point, the source begins storing latent heat until it completely changes phase and cycles back to storing sensible heat.