Jump to content

Heat engine

From Tilcayo Cats, the lean encyclopaedia by Tilcayo Knowledge Systems

A heat engine is a device that takes heat from a source and turns some of it into mechanical work, which can be used for many purposes.[1] For example, the steam engine on an old-fashioned train produces the work needed to drive the train.[2] Petrol and diesel engines, jet engines and steam turbines are all heat engines. They do work by using part of the heat that flows from a hot source.[3]

How it works

A heat engine works between something hot, called the hot reservoir, and something colder, called the cold reservoir.[4] It takes in heat from the hot reservoir, uses some of that energy to do useful work, and gives off the rest as heat to the cold reservoir.[5] Energy therefore flows from the hot reservoir to the cold reservoir while the engine does work.[6] Power stations and internal combustion engines are examples of heat engines.[7] A power station uses very hot steam to drive electric generators, and gives off heat to the air or to a nearby body of water. In an internal combustion engine, such as a car engine, a hot mixture of gas and air pushes a piston, and heat is given off to the air around it.[8] Most heat engines, such as piston engines and turbines, run in cycles that bring the engine back to where it started at the end of each cycle.[9]

Limits

How much of the heat can be turned into work is a question that can only be answered by the second law of thermodynamics.[10] One form of this law says that, in a cycle that returns a system to its starting state, it is impossible for heat taken from a reservoir to be turned completely into work.[11] So no such engine can turn all of its heat into work.[12] In 1824 the young French engineer Sadi Carnot worked out, in theory, how efficient a heat engine can be.[13] He described a theoretical cycle, now called the Carnot cycle, which is the most efficient cyclical process possible.[14]

References

  1. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. A heat engine is a device used to extract heat from a source and then convert it into mechanical work that is used for all sorts of applications.
  2. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. For example, a steam engine on an old-style train can produce the work needed for driving the train.
  3. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency". College Physics 2e. OpenStax. Retrieved 18 October 2026. Gasoline and diesel engines, jet engines, and steam turbines are all heat engines that do work by using part of the heat transfer from some source.
  4. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. we assume that a heat engine is constructed between a heat source (high-temperature reservoir or hot reservoir) and a heat sink (low-temperature reservoir or cold reservoir)
  5. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. uses some of that energy to produce useful work W , and then discards the remaining energy as heat Q c Q c into a heat sink ( cold reservoir )
  6. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. Energy flows from the hot reservoir to the cold reservoir while doing work.
  7. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. Power plants and internal combustion engines are examples of heat engines.
  8. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. Power plants use steam produced at high temperature to drive electric generators, while exhausting heat to the atmosphere or a nearby body of water in the role of the heat sink. In an internal combustion engine , a hot gas-air mixture is used to push a piston, and heat is exhausted to the nearby atmosphere in a similar manner.
  9. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency". College Physics 2e. OpenStax. Retrieved 18 October 2026. A cyclical process brings a system, such as the gas in a cylinder, back to its original state at the end of every cycle. Most heat engines, such as reciprocating piston engines and rotating turbines, use cyclical processes.
  10. ↑ Ling, Samuel J.; Moebs, William; Sanny, Jeff (2016). "4.2 Heat Engines". University Physics Volume 2. OpenStax. Retrieved 18 October 2026. This turns out to be a question that can only be answered through the second law of thermodynamics.
  11. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency". College Physics 2e. OpenStax. Retrieved 18 October 2026. It is impossible in any system for heat transfer from a reservoir to completely convert to work in a cyclical process in which the system returns to its initial state.
  12. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency". College Physics 2e. OpenStax. Retrieved 18 October 2026. The second law, just stated in its second form, clearly states that such engines cannot have perfect conversion of heat transfer into work done.
  13. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.4 Carnot's Perfect Heat Engine: The Second Law of Thermodynamics Restated". College Physics 2e. OpenStax. Retrieved 18 October 2026. How efficient, then, can a heat engine be? This question was answered at a theoretical level in 1824 by a young French engineer, Sadi Carnot (1796–1832), in his study of the then-emerging heat engine technology crucial to the Industrial Revolution.
  14. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "15.4 Carnot's Perfect Heat Engine: The Second Law of Thermodynamics Restated". College Physics 2e. OpenStax. Retrieved 18 October 2026. He devised a theoretical cycle, now called the Carnot cycle , which is the most efficient cyclical process possible.
Retrieved from "https://tilcayo.cat/w/index.php?title=Heat_engine&oldid=162712"