A First Law Thought Experiment with a Second Law Result for Heat Engines Based on a Self-Contained Modified Carnot Cycle

Autor/in	Kaufman, Richard
Titel	A First Law Thought Experiment with a Second Law Result for Heat Engines Based on a Self-Contained Modified Carnot Cycle
Quelle	In: European Journal of Physics Education, 10 (2019) 1, S.24-37 (14 Seiten) PDF als Volltext kostenfreie Datei Verfügbarkeit
Sprache	englisch
Dokumenttyp	gedruckt; online; Zeitschriftenaufsatz
ISSN	1309-7202
Schlagwörter	Thermodynamics; Scientific Principles; Heat; Efficiency; Engines + Suchen Sie Ihr Suchwort? Thermodynamik; Hitze; Effectiveness; Effektivität; Wirkungsgrad; Maschine
Abstract	The first law of thermodynamics does not forbid heat engines with 100% thermodynamic efficiency; it is the second law of thermodynamics which states that heat engines cannot obtain 100% efficiency. Can the first law ever show this second law result? Yes. We show that the first law alone can show that some heat engines cannot achieve efficiencies of 100% when self-contained cycles (which we define) are considered for some temperature reservoirs. Self-contained cycles do not rely on the surroundings for anything but heat transfer to the cycle. Self-contained cycles require that any work input required by the cycle must come from previously stored energy from the cycle (such as, by potential energy in a weight previously lifted by the engine when performing work). Also, any regenerative heat output must occur before it is used as regenerative heat input. Using an example of a self-contained modified Carnot cycle that utilizes an ideal gas, the first law shows that efficiencies of 100% are not possible for T[subscript H] < 2 T[subscript C], where TH is at a hotter temperature than T[subscript C], a colder temperature. These cycles, which could operate through a finite temperature difference ??? in some regions of a PV diagram, are not possible in other regions. (As Provided).
Anmerkungen	Erciyes University. Melikgazi, Kayseri, 38039 Turkey. Tel: +90-352-207-6666; Web site: http://www.eu-journal.org/index.php/EJPE
Erfasst von	ERIC (Education Resources Information Center), Washington, DC
Update	2020/1/01