1) Steam flows through a turbine stage at the rate of 4500kJ/h. The steam velocity at inlet and outlet are 15m/s and 180m/s respectively. The rate of heat energy flow from the turbine casing to the surroundings is 23kJ/kg of steam flowing. If the specific enthalpy of the steam decrease by 420kJ/kg in passing through the turbine stage. Calculate the power developed.
ḿ = 4500 kg/h
c1 = 15 m/s
c2 =180 m/s
Q = 23 kJ/s
⃤h= -420 kJ/kg
SOLUTION:
Q-W = [(h2 - h1) + (C2² - C1² )] ḿ2
(23 x 10³) - w [(-420 x 10³) + (180² - 15²)] (1.25)
2
-w = -(420000) + (16087.5)(1.25) - 23 x 10³
-w = -527.89kw
w = 527.89kw
2) A rotary pump draws 600kg/hour of atmospheric air and dalivers it at a higer pressure. The specific enthalpy of air at the pump inlet is 300kJ/kg and that at the exit is 509kJ/kg. The heat lost from the pump casing is 5000w. Neglecting the changes in kinectic and potential energy determine the power required to drive the pump.
ḿ = 600 kg/h
h1 = 300 kJ/kg
h2 = 509 kJ/kg
Q = 5000 w
w = ?
SOLUTION:
Q-W = [(h2-h1)] ḿ
5000 - w = [(509 x 10³ - 300 x 10³)] (0.166)
w = 34694 - 5000
w = -29.694w
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