Chapter 4 Exergy 4.1 INTRODUCTION Energy can exist in many forms -But, even under ideal conditions, there are some forms of energy, which cannot be completely converted into work. This indicates that the energy and its sources have some sub divisions. i.e., Sources of Energy Low Grade High Grade Energy Energy Available Energy Unavailable| Energy 4.1.1 High grade energy A form of energy which can be completely converted into other forms is called as high grade energy eg: Mechanical work, electrical energy, water power, wind power 4.1.2 Low grade energy A fom of energy which cannot be completely converted into other 1oms ie., a portion of the energy gets dissipated is called as low grade energy. eg: Heat (or) thermal energy, solar energy, heat derived from nuclear Tusion (or) fission, heat derived from combustion of fossil fuels. 4.1.3 Available energy The maximum part (or portion) of a energy which could be converted into useful work is known as available energy.
4.2 Thermodynamics 4.1.4 Unavailable energy The minimum part of energy which is rejected to the environment (orn gets dissipated during the process is known as unavailable energy NOTE: Complete comversion of high grade energy (electrical energy) into low grade energy (heat) is possible. But, the complete conversion of low grade energy (heat) into high grade energy (electrical energy) is impossible ie, a part of the energy gets dissipated.