Useful Terminology in Heat Transfer
Heat transfer is the passage of thermal energy from a hot to a cold body. When a physical body, example an object or fluid, is at a different temperature than its surroundings or another body, transfer of thermal energy, also known as heat transfer, occurs in such a way that the body and the surroundings reach thermal equilibrium. Heat transfer always occurs from a hot body to a cold one. Energy occurs mainly through conduction, convection or radiation. Heat transfer can never be stopped; it can only be slowed down.
Heat – a transfer of thermal energy, (that is of energy and entropy) from hotter material to cooler material. Heat transfer may change the internal energy of materials.
Internal Energy — the internal vibrational energy that the molecules or electrons composing all materials contain.
Conduction — transfer of heat by electron diffusion or phonon vibrations.
Convection — transfer of heat by conduction in a moving medium, such as a fluid.
Radiation — transfer of heat by electromagnetic radiation or, equivalently, by photons.
Approach Temperature – is defined as the hot fluid outlet temperature minus the cold fluid inlet temperature