What is "heat engine"

Heat \Heat\ (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See Hot.]

1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion and evaporation, and which, as manifested in fire, the sun's rays, mechanical action, chemical combination, etc., becomes directly known to us through the sense of feeling. In its nature heat is a mode of motion, being in general a form of molecular disturbance or vibration. It was formerly supposed to be a subtile, imponderable fluid, to which was given the name caloric.

   Note: As affecting the human body, heat produces different sensations, which are called by different names, as heat or sensible heat, warmth, cold, etc., according to its degree or amount relatively to the normal temperature of the body.

2. The sensation caused by the force or influence of heat when excessive, or above that which is normal to the human body; the bodily feeling experienced on exposure to fire, the sun's rays, etc.; the reverse of cold.

3. High temperature, as distinguished from low temperature, or cold; as, the heat of summer and the cold of winter; heat of the skin or body in fever, etc.

   Else how had the world . . . Avoided pinching cold and scorching heat!
   --Milton.

4. Indication of high temperature; appearance, condition, or color of a body, as indicating its temperature; redness; high color; flush; degree of temperature to which something is heated, as indicated by appearance, condition, or otherwise.

   It has raised . . . heats in their faces.
   --Addison.

   The heats smiths take of their iron are a blood-red heat, a white-flame heat, and a sparkling or welding heat.
   --Moxon.

5. A single complete operation of heating, as at a forge or in a furnace; as, to make a horseshoe in a certain number of heats.

6. A violent action unintermitted; a single effort; a single course in a race that consists of two or more courses; as, he won two heats out of three.

   Many causes . . . for refreshment betwixt the heats.
   --Dryden.

   [He] struck off at one heat the matchless tale of ``Tam o' Shanter.''
   --J. C. Shairp.

7. Utmost violence; rage; vehemence; as, the heat of battle or party. ``The heat of their division.''
   --Shak.

8. Agitation of mind; inflammation or excitement; exasperation. ``The heat and hurry of his rage.''
   --South.

9. Animation, as in discourse; ardor; fervency; as, in the heat of argument.

   With all the strength and heat of eloquence.
   --Addison.

10. (Zo["o]l.) Sexual excitement in animals; readiness for sexual activity; estrus or rut.

11. Fermentation.

12. Strong psychological pressure, as in a police investigation; as, when they turned up the heat, he took it on the lam. [slang]

    Animal heat, Blood heat, Capacity for heat, etc. See under Animal, Blood, etc.

    Atomic heat (Chem.), the product obtained by multiplying the atomic weight of any element by its specific heat. The atomic heat of all solid elements is nearly a constant, the mean value being 6.4.

    Dynamical theory of heat, that theory of heat which assumes it to be, not a peculiar kind of matter, but a peculiar motion of the ultimate particles of matter.

    Heat engine, any apparatus by which a heated substance, as a heated fluid, is made to perform work by giving motion to mechanism, as a hot-air engine, or a steam engine.

    Heat producers. (Physiol.) See under Food.

    Heat rays, a term formerly applied to the rays near the red end of the spectrum, whether within or beyond the visible spectrum.

    Heat weight (Mech.), the product of any quantity of heat by the mechanical equivalent of heat divided by the absolute temperature; -- called also thermodynamic function, and entropy.

    Mechanical equivalent of heat. See under Equivalent.

    Specific heat of a substance (at any temperature), the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.

    Unit of heat, the quantity of heat required to raise, by one degree, the temperature of a unit mass of water, initially at a certain standard temperature. The temperature usually employed is that of 0[deg] Centigrade, or 32[deg] Fahrenheit.

n. (context thermodynamics English) Any device which converts heat energy into mechanical work, by moving heat from a source to a sink.

n. any engine that makes use of heat to do work

In thermodynamics, 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. 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, i.e. it cannot be used.

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. 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. Reversed heat engine

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.