What is heat engine!? Explain principle and efficiency?
Answers
In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work.[1][2] It does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a low temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, a lot of heat is lost to the surroundings and so cannot be converted to work.
In general an engine converts energy to mechanical work. Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem.[3] Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can be easily converted to heat by processes like exothermic reactions (such as combustion), absorption of light or energetic particles, friction, dissipation and resistance. Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines are very versatile and have a wide range of applicability.
Heat engines are often confused with the cycles they attempt to implement. Typically, the term "engine" is used for a physical device and "cycle" for the model.
The efficiency of a heat engine relates how much useful work is output for a given amount of heat energy input.
From the laws of thermodynamics, after a completed cycle:
{\displaystyle W\ =\ Q_{c}\ -\ (-Q_{h})} {\displaystyle W\ =\ Q_{c}\ -\ (-Q_{h})}
where
{\displaystyle W=-\oint PdV} {\displaystyle W=-\oint PdV} is the work extracted from the engine. (It is negative since work is done by the engine.)
{\displaystyle Q_{h}=T_{h}\Delta S_{h}} {\displaystyle Q_{h}=T_{h}\Delta S_{h}} is the heat energy taken from the high temperature system. (It is negative since heat is extracted from the source, hence {\displaystyle (-Q_{h})} {\displaystyle (-Q_{h})} is positive.)
{\displaystyle Q_{c}=T_{c}\Delta S_{c}} {\displaystyle Q_{c}=T_{c}\Delta S_{c}} is the heat energy delivered to the cold temperature system. (It is positive since heat is added to the sink.)
In other words, a heat engine absorbs heat energy from the high temperature heat source, converting part of it to useful work and delivering the rest to the cold temperature heat sink.
{\displaystyle \eta ={\frac {-W}{-Q_{h}}}={\frac {-Q_{h}-Q_{c}}{-Q_{h}}}=1-{\frac {Q_{c}}{-Q_{h}}}} {\displaystyle \eta ={\frac {-W}{-Q_{h}}}={\frac {-Q_{h}-Q_{c}}{-Q_{h}}}=1-{\frac {Q_{c}}{-Q_{h}}}}
The theoretical maximum efficiency of any heat engine depends only on the temperatures it operates between. This efficiency is usually derived using an ideal imaginary heat engine such as the Carnot heat engine, although other engines using different cycles can also attain maximum efficiency. Mathematically, this is because in reversible processes, the change in entropy of the cold reservoir is the negative of that of the hot reservoir (i.e., {\displaystyle \Delta S_{c}=-\Delta S_{h}} {\displaystyle \Delta S_{c}=-\Delta S_{h}}), keeping the overall change of entropy zero.
_________________________________________
Hope this answer helps u.. Plss mark it as brainliest ✌️
