78HE-1
Sr. No. 7
EXAMINATION OF MARINE ENGINEER OFFICER
HEAT ENGINES
CLASS I
(Time allowed - 3 hours)
INDIA (2001)
Afternoon Paper
N.B. -
Total Marks 100
(1) Attempt SIX questions only.
(2) All questions carry equal marks.
(3) Neatness in handwriting and clarity in expression carries weightage
1.
A vacuum gauge on a condenser reads 678 mm of Hg. and the barometer height is 766 mm Hg. Steam
enters the condenser with a dryness fraction of 0.9 and has a temperature of 45.8 0 C. Determine the
partial pressure of the air and steam in the condenser. If the steam is condensed at the rate of 900
Kg/h, determine the 'Mass of air which will be associated with this steam,.
Take R for air 0. 29 KJ/KgK.
2.
A gas turbine has an overall, pressure ratio of 5:1 and maximum cycle temperature of 550 0C. The
turbine drives the compressor and an electric generator, the mechanical efficiency of the drive being
97%. The ambient temperature is 200C and the insentropic efficiencies of the compressor and turbine
are 0.8 and 0.83 respectively. Calculate the power output in kilowatts for an air-flow of 15 Kg/s.
Calculate also the thermal efficiency and the work ratio. Neglect changes in kinetic energy, and the
loss of pressure in the combustion chamber. Neglect also the mass of fuel. Take  =1.4, CP = 1.005
KJ/KgK for compression process; and  =1.333, CP = 1.15 KJ/KgK for all combustion and expansion
processes.
3.
In a refrigerating plant using freon-12, the vaPour which leaves the evaporator in a dry saturated state,
is compressed adiabatically but not reversibly in a centrifugal compressor. The evaporator and
condenser pressures are 1.826 bar and 7.449 bar respectively, and the temperature of the vapour
leaving the compressor is 450C. The liquid leaves the condenser is undercooled and is at 250C. The
liquid leaving the condenser is throttled to the evaporator pressure. Calculate(a) the refrigerating effect,
(b) the work done per Kg of the refrigerant,
(c) the C.O.P.(r) for this machine.
What would be the C.O.P. (r) if the compression could be carried out reversibly and approximately
adiabatically, in a reciprocating compressor. Note that the compression in the 2nd case may be
assumed to have taken place isentropically.
4.
0.03 m3 of air at a pressure of 1.3 bar and temperature 250C is compressed to a volume Of 0.005 m3
according to the law PV1.3= constant. Calculate(a) the final temperature and pressure,
(b) the work done during compression,
Find the reduction in pressure at constant volume required to bring the air back to its original temperature.
5.
The three stage, single acting, reciprocating air compressor takes in 0.5 m3 of air/s at 1 bar and 200 C.
The air is compressed to a delivery pressure of 20 bar. The intermediate pressures are ideal and
intercooling between stages is perfect. The compressor index can be taken as 1.25 in all stages. The
compressor runs at 8.5 rev/s. Neglecting clearance, determine (a) the intermediate pressures;
(b) the total volume of each cylinder;
(c) the air power of the compressor.
6.
A 6 cylinder 4 stroke diesel engine of bore 260 mm and 330 mm stroke, tested at 720 rev/min at halffull load, gave the following results –
Brake, power
515 KW
Indicated
mean
effective 10 bar
pressure
Fuel consumption per hour
115.5 Kg
Gross calorific value of fuel
44801 KJ/kg
Hydrogen content of fuel
14 %
Air consumption
75 Kg/min
Jacket water used
120 Kg/min
Temperature rise of jacket 350C
water
Piston cooling oil specific heat
2.1 KJ/KgK
Temperature rise of piston 230C
cooling oil
Room temperature
200C
Exhaust gas temperature
1900C
Cp. of dry exhaust gas
1.09 KJ/KgK
0
The exhaust gas at 190 C may be considered at 1.0325 bar for evaluating the enthalpy of vapour.
Draw up a heat balance sheet in KW and in' y. of heat input from fuel.
Assuming no change in indicated thermal efficiency, calculate the brake specific fuel consumption at
full load.
Two rows of a velocity compounded impulse turbine have a mean blade speed of 160 m/s, and a
nozzle velocity of 700 m/s. The nozzle angle is 200. The exit angles of the first moving row, fixed and
second row of moving blades are 250, 250 and 300 respectively. There is a10 % loss of velocity due to
friction in all blades. The steam flow is 5Kg/Sec. Determine(a) power output of the turbine (b) the diagram efficiency8. The wall of a cold room consists of an outer and inner layer of wood of thickness 25rnm each, having
thermal conductivity of 0.18 W/mK. A cork lining of thickness 50m is sandwiched between outer
and inner wood lining. The thermal conductivity of cork is 0.05 W/mK, The rate of heat transfer of
inner exposed surface of the cold room is 10 W/m2K while the outer exposed surface is 15 W/m2K.
The cold room temperature is maintained at -200C when the ambient temperature is 250 C. Calculate(a) The heat flow through the wall per m2 of wall.
(b) The inner and outer wall surface temperature.
(c) The temperatures on both sides of cork.
7.
9.
A fuel oil consists of 86% carbon and 14% hydrogen. During a test on an engine using this oil, the
dry exhaust gas analysis by volume was 11.25%,CO2, 1.2%, O2 2.8% CO and the remainder
Nitrogen. Estimate the air fuel ratio- by mass being supplied to the engine.
------------------------------X--------------------------
78HE-1
Sr. No. 7
EXAMINATION OF MARINE ENGINEER OFFICER
HEAT ENGINES
CLASS I
(Time allowed - 3 hours)
INDIA (2001)
Afternoon Paper
N.B. -
(1) Attempt SIX questions only.
(2) All questions carry equal marks.
(3) Neatness in handwriting and clarity in expression carries weightage
Answers
Answer for Question No. 1
1.74 KN/m2
223.6 kg
(i)
(ii)
Answer for Question No. 2
3781.5 kw
12.38%
0.173
Answer for Question No. 3
(a)
(b)
(c)
(d)
121.27 kJ/kg
29.66 kJ /kg
4.09
4.89
Answer for Question No. 4
(a) 13.35 bar 5100K 237.00C
(b) 9.25 kJ 5.55 bar
Answer for Question No. 5
(a)
(b)
(c)
(d)
2.71 bar 7.34 bar
0.0265 m3
0.0217m3
165.5 kw
Answer for Question No. 6
1145.82 kw
0.20 kg / kw – h
Answer for Question No. 7
983.17KW
80.25%
Total Marks 100
Answer for Question No. 8
(a) 31.142 w /m2
(b) - 16.880C & 22.920C
(c) – 12.550C
Answer for Question No. 9
15.694