Enrollment No.
GUJARAT TECHNOLOGICAL UNIVERSITY
Dr. JIVRAJ MEHTA INSTITUTE OF TECHNOLOGY
MOJAR, ANAND.
B.E. 5th Semester Mechanical Engineering
MID SEMESTER EXAMINATION
Date/Day : 05/09/2012, Wednesday
Sub Code : 151904
Time
: 10:30am to 12:00noon
Instructions:
1) All questions are compulsory.
Branch
: Mechanical Engineering
Subject Name : POWER PLANT ENGINEERING
Max. Marks
: 30
2) Figures to the right indicate full marks.
3) Use of steam table is permissible.
4) Indicate clearly, the options you attempt along with its respective question number.
Q.1
(A)
(B)
Q.2
(A)
(B)
Q.3
(A)
(B)
Draw neat line diagram of a high pressure boiler in which stem is generated by mixing the superheated
steam with feed water. Discuss relative merits & demerits.
Convection & radiant superheaters have opposite characteristics of temperature v/s load – Explain.
05
Draw a neat named general layout of modern thermal power plant. Explain four main circuits. Name
factors to be considered for selection of site for thermal power station.
A boiler uses 1000 kg of coal/ h. The temperature of hot gases inside the chimney is 650 K and the
outside air temperature is 300 K. The draught produced by the chimney of 25 m height is 15 mm of
water. Determine the air supplied per kg of fuel burnt , draught in terms of hot gases, mass flow rate of
hot gases and area of the chimney required if the co-efficient of velocity is 0.4
OR
A 40 m high chimney is discharging flue gases at 350 °C, when the ambient temperature is 30 °C. The
quantity of air supplied is 18Kg/Kg of fuel burnt. Determine: (i) Draught produced in mm of water (ii)
Equivalent draught in m of hot-gas column (iii) Efficiency of chimney if minimum temperature of
artifical draught is 150 °C mean
specific heat of flue gases is 1.005K J/Kg K, (iv) Percentage of heat
spent in natural draught system if Calorific value of fuel supplied is 30600K J/Kg (v) Temperature of
chimney gases for maximum discharge in given time and what will be corresponding draught in mm of
water produced.
05
1) Why is draught necessary in a boiler? Compare the natural draught and artificial draught.
2) Derive an expression for chimney height in order to obtain a draught of ‘h’ mm of water column if
the boiler used ‘m’ kg of air / kg of fuel. Assume, surrounding air temperature as ‘T1’ and flue gas
temperature as ‘T2’ in degree absolute.
A steam turbine of 20 MW capacity requires 5 kg of steam per hour per kW. The quantity of air
leakage into the condenser is 1 kg per 1000 kg of steam used by turbine. The vacuum in the condenser
is 70 cm of Hg when the barometer reads 76 cm of Hg. The temperature at the suction of the air pump
is 300C. The surface condenser used is fitted with a separate condensate pump and air pump. Find: (a)
The capacity of the air pump requires per minute. (b) Vacuum efficiency (c) Condenser efficiency (d)
The mass of water vapor carried by air in kg/hr. (e) The quantity of cooling water required per minute
in tons if the rise in temperature of water is limited to 80C. The quantity of steam entering the
condenser is 0.9 dry and there is no under cooling in the condenser. Assume inlet temperature of water
as 20°C. Properties of steam at 300C : Absolute Pressure = 0.04325 bar, Enthalpy of liquid hf = 125.8
kJ/kg, Enthalpy of evaporation hfg = 2438.1 kJ/kg, Specific volume = 32.8 m3/kg
05
05
05
05
OR
Q.3
(A)
(B)
1) Why cooling towers used in a thermal power plant? Discuss the working of a natural cooling tower.
2) Explain following terms pertaining to cooling tower: Drift, Fill, Approach and Range of cooling
tower
The air leakage into a surface condenser operating with a steam turbine is estimated 84kg/hr. the
vacuum near the inlet of air pump is 70mm of Hg when barometer reads 76mm of Hg. The temperature
at the inlet of vacuum pump is 20 °C Calculate: (i) Minimum capacity of pump in cu-meters per hour
(ii) Dimensions of reciprocating air pump to remove air if it runs at 200rpm (iii) L:D=3:2 and
volumetric efficiency=80% (iv) Mass of vapour extracted per minute with air
05
05
GUJARAT TECHNOLOGICAL UNIVERSITY
Dr. JIVRAJ MEHTA INSTITUTE OF TECHNOLOGY
MOJAR, ANAND.
B.E. 5th Semester Mechanical Engineering
RESPONSE OF MID SEMESTER EXAMINATION
Date/Day : 05/09/2012, Wednesday
Sub Code : 151904
Time
: 10:30am to 12:00noon
Q.1
(A)
(B)
Q.2
(A)
(B)
Branch
: Mechanical Engineering
Subject Name : POWER PLANT ENGINEERING
Max. Marks
: 30
Draw neat line diagram of a high pressure boiler in which stem is generated by mixing the superheated
steam with feed water. Discuss relative merits & demerits.
Convection & radiant superheaters have opposite characteristics of temperature v/s load – Explain.
05
Draw a neat named general layout of modern thermal power plant. Explain four main circuits. Name
factors to be considered for selection of site for thermal power station.
A boiler uses 1000 kg of coal/ h. The temperature of hot gases inside the chimney is 650 K and the
outside air temperature is 300 K. The draught produced by the chimney of 25 m height is 15 mm of
water. Determine the air supplied per kg of fuel burnt , draught in terms of hot gases, mass flow rate of
hot gases and area of the chimney required if the co-efficient of velocity is 0.4
05
05
05
OR
A 40 m high chimney is discharging flue gases at 350 °C, when the ambient temperature is 30 °C. The
quantity of air supplied is 18Kg/Kg of fuel burnt. Determine: (i) Draught produced in mm of water (ii)
Equivalent draught in m of hot-gas column (iii) Efficiency of chimney if minimum temperature of
artifical draught is 150 °C mean
specific heat of flue gases is 1.005K J/Kg K, (iv) Percentage of heat
spent in natural draught system if Calorific value of fuel supplied is 30600K J/Kg (v) Temperature of
chimney gases for maximum discharge in given time and what will be corresponding draught in mm of
water produced.
hw = 23.30 mm of water
Q.3
(A)
(B)
3) Why is draught necessary in a boiler? Compare the natural draught and artificial draught.
4) Derive an expression for chimney height in order to obtain a draught of ‘h’ mm of water column if
the boiler used ‘m’ kg of air / kg of fuel. Assume, surrounding air temperature as ‘T1’ and flue gas
temperature as ‘T2’ in degree absolute.
A steam turbine of 20 MW capacity requires 5 kg of steam per hour per kW. The quantity of air
leakage into the condenser is 1 kg per 1000 kg of steam used by turbine. The vacuum in the condenser
is 70 cm of Hg when the barometer reads 76 cm of Hg. The temperature at the suction of the air pump
is 300C. The surface condenser used is fitted with a separate condensate pump and air pump. Find: (a)
The capacity of the air pump requires per minute. (b) Vacuum efficiency (c) Condenser efficiency (d)
The mass of water vapor carried by air in kg/hr. (e) The quantity of cooling water required per minute
in tons if the rise in temperature of water is limited to 80C. The quantity of steam entering the
condenser is 0.9 dry and there is no under cooling in the condenser. Assume inlet temperature of water
as 20°C. Properties of steam at 300C : Absolute Pressure = 0.04325 bar, Enthalpy of liquid hf = 125.8
kJ/kg, Enthalpy of evaporation hfg = 2438.1 kJ/kg, Specific volume = 32.8 m3/kg
05
05
OR
Q.3
(A)
(B)
3) Why cooling towers used in a thermal power plant? Discuss the working of a natural cooling tower.
4) Explain following terms pertaining to cooling tower: Drift, Fill, Approach and Range of cooling
tower
The air leakage into a surface condenser operating with a steam turbine is estimated 84kg/hr. the
vacuum near the inlet of air pump is 70mm of Hg when barometer reads 76mm of Hg. The temperature
at the inlet of vacuum pump is 20 °C Calculate: (i) Minimum capacity of pump in cu-meters per hour
(ii) Dimensions of reciprocating air pump to remove air if it runs at 200rpm (iii) L:D=3:2 and
volumetric efficiency=80% (iv) Mass of vapour extracted per minute with air
05
05
mw = 21.59 kg/hr
= 0.359 kg/min