Advanced Thermodynamics for Engineers, 2nd Edition

where dQ ¼ heat transferred to system and dQ

0

¼ heat rejected from system, as in an engine (E

R

)

undergoing an infinitesimal Carnot cycle.

In reality, dQ

0

is the minimum amount of heat that can be rejected because processes 1 to 2 and 3 to

4 are both isentropic, i.e. adiabatic and reversible.

Hence the amount of energy that must be rejected is

E

unav

¼

Z

dQ

0

¼ T

0

Z

dQ

T









R

¼ T

0

DS (4.14)

Note that the quantity of energy, dQ, can be written as a definite integral becau se the process is an

isentropic (reversible) one. Then E

unav

is the energy that is unavailable and is given by cdefc. The

available energy on this diagram is given by abcda and is given by

E

av

¼ Q 