78HE-1
Sr. No. 4
EXAMINATION OF MARINE ENGINEER OFFICER
HEAT ENGINES
CLASS – I
(Time allowed - 3 hours)
INDIA (2001) Afternoon Paper Total Marks 100
N.B. - (1) Attempt SIX questions only.
(2) All questions carry equal marks.
(3) Neatness in handwriting and clarity in expression carries weightage
1. A quantity of air at a pressure of 100 kN/m2 and a temperature of 200C is compressed according to the law PV1.36 = constant, from a volume of 0.56 m3 to a volume of 0.15 m3. Find the pressure and temperature of the air after compression and the work done during compression. After compression, the air is cooled at constant pressure until the volume is reduced to 0.1 m3. Calculate the temperature at this volume and the heat transferred during cooling.
CP = 1.006 kJ/kg K. R = 0.287 kJ/kg K
2. A fuel having an analysis by mass of 86% carbon and 14'% hydrogen is burnt with 20% excess air at 20 tonne / 24 hours. The gases issue from the funnel top at 2050C and 1.8 meter/sec. R for gases being 0.24 kJ/kg K. If the cross sectional area of the funnel is elliptical with axis in the ratio of 3:4, calculate the length of these axis.
3. An ammonia refrigerating plant operates between temperature units of -120C and 260C. Vapour leaving the compressor is dry saturated and at entry has a dryness fraction of 0.9. Find the cylinder dimensions of the double acting compressor of volumetric efficiency 80% at 200 rev/min to give a refrigerating effect of 100,000 kJ/h. Stroke = 1.25 bore.
4. Dry saturated steam enters a convergent-divergent nozzle at 9 bar, and the Pressures at the throat and exit are 5 bar and 0.14 bar respectively. The specific enthalpy drop of the steam from entrance to the throat is 107 kJ/kg and from entrance to exit it is 633 kJ/kg. Assuming 8 % of the enthalpy drop is lost to friction in the divergent part of the nozzle, calculate the area in mm2 of the nozzle at the throat and exit to pass, 23 kg of steam per minute.
5. In a simple gas turbine working on the ideal cycle, the pressure ratio of both the compressor and turbine is 4.3:1. The temperature at inlet to the compressor and inlet to the turbine are 160C and 6000C respectively. Calculate-
(a) Net output of the turbine for 1 kg/sec mass flow. (b) The thermal efficiency.
Take g = 1.4 and CP =1.005 kJ/kg K.
6. A steam pipe 140 mm outside diameter and 25m long is lagged with insulating material of thermal conductivity 0.13 W/mK. Steam passes along the pipe at the rate of 1200 kg/h entering at 18 bar dry saturated and leaving at the same pressure. Thickness of the lagging is 31mm and the outside temperature is 350C. Find the condition of the steam leaving the pipe neglecting the thickness of the pipe.
7. A two-stage, single acting, reciprocating compressor takes in air at the rate of 0.2 m3/s. Intake pressure and temperature are 1 bar and 160C. The air is compressed to a final pressure of 7 bar. The intermediate pressure is ideal and intercooling is perfect. The compression index is 1.25 and the compressor runs at 10 rev/s. Neglecting clearance, determine..—
A. the intermediate pressure.
B. the total volume of each cylinder.
C. the cycle power.
8. A two stroke engine develops an indicated power of 2700 kW, the specific fuel consumption is 0.225 kg/k Wh (indicated) and 18 kg of air is supplied per kg of fuel burnt. The exhaust gases pass through an exhaust gas boiler, entering at 3270C and leaving at 2150C. Steam is generated in the boiler at 15 bar, 0.96 dry, from feed water at 500C. If the efficiency of the boiler is 0.8, calculate the mass of steam generated per hour, taking the specific heat of gases as 1.05 kJ/kg K.
9. Steam enters the moving blades of an impulse turbine with a speed of' 915 m/sec at 200 to blades. Mean diameter of the moving blades is 250 mm and r.p.m. 20,000. The blade inlet and outlet angles are equal and the loss in kinetic energy due to friction in the, moving blades is 32 per cent of the kinetic energy corresponding to the relative velocity of inlet to the blades. If the weight of steam flowing per second is 0.225 kg calculate the axial thrust and power developed.
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78HE-1
Sr. No. 4
EXAMINATION OF MARINE ENGINEER OFFICER
HEAT ENGINES
CLASS I
(Time allowed - 3 hours)
INDIA (2001) Afternoon Paper Total Marks 100
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
Pressure = 599.86 kn/m2
Temperature = 1970C
Work done = 94.5kV
Temperature = 410C
Heat transfer = 104.5KJ
Answer for Question No. 2
Major = 2.166m
Answer for Question No. 3
Cylinder dimension = 12.96 cm
Stroke = 16.14 cm
Answer for Question No. 4
Area of nozzle at throat = 298.5mm2
Area of exit to pass = 3150mm2
Answer for Question No. 5
Net out put of turbine = 149 kw
The thermal efficiency = 34%
Answer for Question No. 6
Dynamic fraction = 0.98496
Answer for Question No. 7
(a) The intermediate pressure = 2.64 bar
(b) Total volume of L.P. cylinder = 0.02m3 Total volume of H.P. cylinder = 0.0076m3
(c) The Cycle Power = 42.85 kw
Answer for Question No. 8
Mass of Steam Generated = 433.6 kg/h
Answer for Question No. 9
Axial Thrust = 12.375N
Power = 64.314kw