The maximum efficiency of a heat engine depends only on the temperatures of source and sink and for given source and sink temperatures no heat engine can be more efficient than a reversible engine.
The Carnot cycle can be represented on a graph of pressure against volume (a P-V diagram) as shown here.
D to A isothermal expansion at ; work done by the gas
A to B adiabatic expansion; work done by the gas
B to C isothermal compression at ; work done on the gas
C to D adiabatic compression; work done on the gas
The product of pressure and volume represents a quantity of work. This is represented by the area below a P-V curve.
The area enclosed by the four curves represents the net work done by engine during one cycle.
(i) =
Where K = coefficient of thermal conductivity
A = area of the hotter face
= temperature gradient =
(ii) Units of K are = .
(iii) Dimensions of K are .
(iv) K denotes thermal conductivity, denotes dimensions of kelvin temperature.
(i) Q =
(ii) Cosider two slabs when = = x
Q = =
Q =
Equivalent thermal capacity = K =
= = .
K is harmonic mean between and .
(iii) For two slabs, in general, K =
(i) Q =
Q =
(ii) Equivalent thermal capacity = K.
et = = A
K = for two slabs. K is arithmetic mean between and .
(iii) Generally, for two slabs, K = .
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