95THT-2
Sr. No. 7
EXAMINATION OF MARINE ENGINEER OFFICER
Function: Marine Engineering at Management Level
THERMODYNAMICS AND HEAT TRANSMISSION
India (2003)
NB :
M.E.O. Class II
(Time allowed - 3hours)
Afternoon Paper
Total Marks 100
(1) Answer SIX Questions only.
(2) All Questions carry equal marks
(3) Neatness in handwriting and clarity in expression carries weightage
(4) Illustration of an Answer with clear sketches / diagrams carries weightage.
1. In an engine working on the ideal diesel cycle, the compression ratio is 13.5 and fuel is admitted for
0.1 of the stroke. The temperature of the air at beginning of compression is 38°C. Taking the index of
compression and expansion = 1.4, cp = 1.005 kJ/kgK, cv = 0.718 kJ/kgK, calculate the temperatures
(i) at the end of compression, (ii) at the end of combustion, (iii) at the end of expansion, and calculate
also (iv) the ideal thermal efficiency.
2. A single-acting air compressor takes in air at 1 bar and delivers it at 4 bar, the cylinder is 300 mm
diameter, stroke 450 mm and it runs at 5 rev/s. Initially the index of compression was 1.15 and after
running for some time the index of compression was found to be 1.35. Neglecting clearance,
calculate the power absorbed in each case and the percentage increase in power. Area under pV n
curve is :
p1V1  p2V2
n 1
3. Steam at 15 bar is supplied to the high pressure cylinder of a steam engine and cut off at 0.45 stroke.
The back pressure is 6.5 bar, clearance equal to 10% of the stroke volume, and compression begins at
0.88 of the exhaust stroke. Assume expansion and compression to follow the law Pv - a constant and
to continue to the ends of their respective strokes. Sketch the indicator diagram representing the
above data and calculate the mean effective pressure.
4. Dry saturated steam at 14 bar is expanded in a turbine nozzle to 10 bar, expansion following the law
pVn = constant, where the value of n is 1.135, calculate:
(i) the dryness fraction of the steam at exit,
(ii) the enthalpy drop through the nozzle per kg of steam,
(iii) the velocity of discharge,
(iv) the area of nozzle exit in mm2 per kg of steam discharged per second.
5. A Freon-12 refrigerating machine operates on the ideal vapour compression cycle between the limits 15C and 25C. The vapour is dry saturated at the end of isentropic compression and there is no
undercooling of the condensate in the condenser. Calculate (a) the dryness fraction at the suction of
the compressor, (b) the refrigerating effect per kg of refrigerant, (c) the coefficient of performance,
(d) the cannot coefficient of performance.
6. Show that the slope of the constant pressure line through a point on the temperature entropy diagram
for a perfect gas is proportional to the absolute temperature at that point. What is the slope of a
constant-volume line through the same point ? 0.34 m3 of a perfect gas at constant pressure of 2.8
kgf/cm2 is heated from 100C to 300C and is then cooled at constant volume to its initial
temperature. Calculate the overall change of entropy. Given Cp = 0.25 and Cv = 0.18.
7. Define enthalpy, external work of evaporation and internal energy of steam. Find enthalpy and
internal energy of 1 kg of steam at a pressure of 10 kgf/cm2 (a) when the dryness fraction of steam is
0.75, (b) when steam is dry and saturated, and (c) when steam is superheated to 230C. Neglect the
volume of water.
8. 0.1 kg of fluid have a pressure of 1 bar, a volume of 0.86 m3 and a specific internal energy of 200
kJ/kg. After polytropic compression the pressure and volume of the fluid are 10 bar and 0.0146 m 3
respectively, and the specific internal energy is 360 kJ/kg. Determine (a) the index of compression (b)
the work required for compression and (c) the quantity of heat flow and its direction.
9. In a full load test on an oil engine the following results were obtained: ip 30; bp 24; fuel consumption
7.7 kg/h; cylinder circulating water, 5.9 kg/min with inlet and outlet water temperatures of 15C and
65C respectively; exhaust gas calorimeter circulating water 9.9 kg/min with inlet and outlet
temperatures of 15C and 66C respectively; temperature of exhaust gas leaving calorimeter, 88C;
mean specific heat of exhaust gas, 1.05 kJ/kg K; engine room temperature 18C; air to fuel ratio, 20;
calorific value of fuel, 45200 kJ/kg. Determine the mechanical and indicated thermal efficiencies and
draw up an energy balance for the test on a basis of kW and in Percentages.
-----------------------X--------------------------