Corolaries of 2nd Law of Thermodynamics

Topics: Heat engine, Temperature, Heat Pages: 2 (648 words) Published: July 25, 2011
Corollary 1: The clausius statement of second law of thermodynamics is the first corollary i.e. ‘It is impossible to construct a device operating in a closed cycle that performs no effect other than the transfer of heat from a cooler body to a hotter body.’ The mathematical statement of which is given by; Q1‐Q2=W Q1 W Q2 Corollary 2: It is impossible to construct an engine operating between only two heat reservoirs, which will have a higher efficiency than a reversible heat engine operating between the same two reservoirs. Hot reservoir Cold reservoir Heat engine

Q1 Q1 WX WR Q1‐WX Q1‐ WR Suppose these conditions are true, LetηX>ηR If the reversible engine also receives heat Q1 from the source, it will do work WR. Let us convert that heat engine to a heat pump, then we have, that R receives Q1‐WR & receives WR from the surroundings & rejects Q1 heat to high temperature reservoir. Coupling it to heat engine the net work done now becomes; (Q1‐WR) – (Q1‐WX) =WX‐WR Thus of corollary 2 is true, then we have we have that following condition is also possible. X R Q1 Q1 WX‐WR Q1‐WX Corollary 3: All reversible heat engines operating between the same two reservoirs have same efficiency. Since the second corollary has been proved true then it is impossible that one has higher efficiency. Thus according to the Carnot theorem both heat engines have same efficiency. i.e. η= (Q1+Q2)/Q1 = (T1‐T2)/T1 Corollary 4: A scale of temperature can be defined which is independent of any particular thermometric substance and which provides an absolute zero of temperature. ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ X R Q W Q0 Let us suppose a heat engine as shown in figure above Thus from corollary 3, the efficiency of that heat engine depends only on the temperature of the reservoirs. η= 1–Q/Q0 Let the temperature of the heat reservoir be T0, Now, if T be the temperature of cold reservoir,

Then sinceηα(1 – Q / Q1)

Alsoη = 1 – T / T0 {Carnot’s efficiency} Hot reservoir Heat engine Cold reservoir...
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