Heat Engines
A heat engine is a device that takes in heat energy, converts some of it to mechanical energy, and discards the remainder as waste heat. The simplest heat engine consists of a frictionless piston in a cylinder with a movable piston rod. If this cylinder is maintained at a higher temperature than that of its environment, some of the heat energy from the cylinder is converted to work by the piston as it moves in its cylinder.
The concept of a heat engine was initially developed as a theoretical model for understanding the workings of engines. Early steam engines, for example, have been used for centuries to convert the energy of heat into mechanical work, but the understanding of why this was so was limited. Heat engine theory helped to explain this by describing the process of heat input, conversion to mechanical energy, and waste heat.
Heat engine operation can be understood in terms of the First Law of Thermodynamics. This states that energy is neither created nor destroyed, and that it is only converted between various forms. In a heat engine, energy is supplied to the engine as heat energy (chemical, electrical, or otherwise), and some of this energy is converted into mechanical energy by the piston moving and creating a force. The remainder of the energy is discarded as waste heat and lost to the environment.
The efficiency of a heat engine depends on the ratio of useful energy output to heat energy input, as well as on the temperature differential between the two sides of the piston. Higher efficiency is achieved when the temperature differential is greater, and when the input and output are well matched for the application. In general, the smaller the temperature difference, the less efficient the engine.
Modern heat engine designs vary greatly in sophistication and complexity, but all have the same basic principles in common. Heat engines are used in countless applications in industry, transportation, commercial and residential settings, and research and development. They are used to generate electricity, power hot and cold liquids, and generate mechanical power for industrial machinery, among other things.
The development and use of heat engines has had a major impact on the development of many technologies and has brought about far reaching impacts on both societies and the environment. Heat engines have made possible the mass production of many products, and their efficient use of energy has significantly reduced our reliance on natural resources. Heat engines have also given us access to many sources of energy that would otherwise impossible to harness and use. As a result of this, we have been better able to meet our need for energy, not only for the production of goods, but also for our very survival.
