ABSTRACT
An essential insight of contemporary science and engineering is the conservation of energy and the occurrence of energy in various different forms, like heat, electricity, magnetism, elasticity, gravitation, kinetic energy etc., up to Einstein’s famous relativistic energy-mass equivalence. Energy as a property refers to the ability to deliver work. Energy as a quantity can neither be created nor destroyed. It can be either converted between different forms, stored in specific forms, or transported. Energy consumption is thus nothing else than a conversion or transformation of one form of energy into another one, be it work or heat. You might say, it is a good thing that energy cannot be destroyed. However, in many cases the final energy form after a conversion process has less value for usage than the initial form, namely, when heat, or entropy, is generated, as will be discussed later. So the bad message is that energy available for work (sometimes called exergy) can be destroyed. The obviously important ratio of energy which remains for use to the total energy is related to the efficiency.
