TITLE.PM5

336 ENGINEERING THERMODYNAMICS

DHARM
M-therm\Th6-2.PM5

1

2 ′

2

s

s= s 12

T

Fig. 6.14

(i)Isentropic efficiency :

ηisen. = Actual work output

Isentropic work

= hh

hh

1

1

−′

−

2

2

= 3247 6 2964 2

3247 6 2840 8

−

−

= 283 4

406 8

= 0.6966 or 69.66%. (Ans.)

(ii)Loss of availability :

Loss of availability = b 1 – b 2

= h 1 – h 2 ′ + T 0 (s 2 ′ – s 1 ′)

= 3247.6 – 2964.2 + 293 (7.379 – 7.127)

= 283.4 + 73.83 = 357.23 kJ/kg. (Ans.)

(iii)Effectiveness :

Effectiveness, ∈ =

W

bb 12 −′

=

hh

bb

12

12

−′

−′

= 3247 6 2964 2

357 9

− = 0.7918 or 79.18%. (Ans.)

Highlights

1. ‘Available energy’ is the maximum portion of the energy which could be converted into useful work by ideal
   processes which reduce the system to a dead state.


2. The theoretical maximum amount of work which can be obtained from a system at any state p 1 and T 1
   when operating with a reservoir at the constant pressure and temperature p 0 and T 0 is called ‘availability’.