Page 144 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Compressor:

H3 + Q34 = h4 + W34
The compression is isentropic ( i.e. s3 = s4 ), and adiabatic ( i.e. Q = 0 ).

 W34 = ( h3 – h4 ) = -( h4 – h3 )

i.e. Work input to pump = ( h4 – h3 ) (4.7)

Thermal efficiency of Carnot cycle
The thermal efficiency of a heat engine, defined in chapter 4, was shown to be given by

the equation,

Q
 = 1− 2
Q 1

In the Carnot cycle, with reference to Fig. 11.1, it can be seen that the heat supplied is
given by the area 41BA4,

i.e. Q1 = area 41BA4 = T1(sB- sA)

Similarly the heat rejected, Q2, is given by the area 23AB2,
i.e. Q2 = area 23AB2 = T(sB – sA)

Hence we have

T (s − s )
Thermal efficiency of Carnot cycle,  = 1− 2 B A
carnot
T 1 (s − s A )
B

T
i.e.  = 1− 2 (4.8)
carnot
T 1

Net work output
or  carnot =
Heat supplied in the boiler

(h − h ) − (h − h )
i.e.  Carnot = 1 2 4 3 (4.9)
h −
1 h 4

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