Transfer of heat is the exchange of thermal energy between physical objects depending on pressure and temperature. Transfer of heat is based on the principle of the first law of thermodynamics, which states that the total energy of a system is constant and energy can only be altered from one form to another but cannot be created or destroyed. Heat transfer continues until the objects involved in the process reach a phase of thermal equilibrium, i.e., equivalent temperature. Heat transfer fluids are used to avoid overheating or cooling of substances. In a heat transfer process, the fluid is spread through the mechanical parts of the equipment, and by this process, heat is transferred from the higher temperature object to the lower temperature object.