TITLE.PM5

178 ENGINEERING THERMODYNAMICS

dharm

/M-therm/Th4-5.pm5

Water

out

h = 192 kJ/kg 2

h = 240 kJ/kg

Water in

1

2

1

20 m

(Z – Z )

21

Boundary

Q

Fig. 4.53

Q = (h 2 – h 1 ) +

CC 22 12

2

F −

HG

I

KJ

+ (Z 2 – Z 1 ) g + W

Here W = 0 (no pumps)

CC 22 12

2

−

= 0 (given)

∴ Q = (192 – 240) + 20 9 81 1000 ×. = – 47.8 kJ/kg
∴ Heat transfer from water/kg = 47.8 kJ/kg. (Ans.)
Example 4.47. The gas leaving the turbine of a gas turbine jet engine flows steadily into
the engine jet pipe at a temperature of 900°C, a pressure of 2 bar and a velocity of 300 m/s relative
to the pipe. Gas leaves the pipe at a temperature of 820°C and a pressure of 1.1 bar. Heat transfer
from the gas is negligible. Using the following data evaluate the relative velocity of gas leaving
the jet pipe. For the gas at t = 820°C, h = 800 kJ/kg and at 910°C, 915 kJ/kg.
Solution. Pressure at entry to the engine jet pipe, p 1 = 2 bar
Velocity relative to the pipe, C 1 = 300 m/s
Heat transfer from gas, Q = 0
At temperature, t 1 = 910°C, h 1 = 915 kJ/kg
At temperature, t 2 = 820°C, h 2 = 800 kJ/kg
Relative velocity of gas leaving the jet pipe, C 2 :
Steady flow energy equation is given by :

h 1 +

C 12

2 + Z^1 g + Q = h^2 +

C 22

2 + Z^2 g + W

Q = 0

W = 0

Z 1 = Z 2 (assumed)

h 1 + C^1

2

2 = h^2 +

C 22

2