Calculate a the indicated thermal efficiency by 60Lr1YGG

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Sr. No. 9

EXAMINATION OF MARINE ENGINEER OFFICER
Function: Marine Engineering at Operational Level
HEAT ENGINES

M.E.O. Class IV
(Time allowed - 3hours)
India (2003)                                      Afternoon Paper                       Total Marks 100

NB : (1) All Questions are Compulsary
(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.   A volume of 0.8 m3of steam at 17 bar 0.95 dry is passed through a reducing valve and throttled to
6 bar. Calculate the dryness fraction and the volume after throttling.

2.   0.9 kg of ice was put into 10 kg of water at 22°C contained in a calorimeter of water equivalent
0.2 kg, and the resultant temperature of the mixture was 13°C. Calculate the initial temperature of
the ice, taking its specific heat as 2.04 kJ/khK and the latent heat of fusion 335 kj/kg.

3.   A length of steel wire 2.5 mm diameter is heated from 16°C to 113°C and its ends are securely
fastened while the wire is hot. Find the stress in the wire when it cools down to its original
temperature assuming the elastic limit of the wire is not exceeded.

4.   The burning period of the fuel in a diesel engine cylinder takes place at constant pressure while the
piston moves a fraction of its power stroke, calculate the external work done during the burning
period if (a) the pressure is constant at 34.5 bar and the volume of the air increases from
0.0425 m3 to 0.0935 m3, (b) the cylinder contains 0.63 kg of air and the temperature increases from
538C to 1511C. Take R for air – 0.287 kJ/kgK.

5.   When developing a certain power, the specific fuel consumption of an internal combustion engine is
0.255 kg/kWh (brake) and the mechanical efficiency is 86%. Calculate (a) the indicated thermal
efficiency, and (b) the brake thermal efficiency, taking the calorific value of the fuel as 43.5 MJ/kg.
If 35 kg of air are supplied per kg of fuel, the air inlet being at 26C and exhaust at 393C, find (c)
the heat energy carried away in the exhaust gases as a percentage of the heat supplied, taking the
specific heat of the gases as 1.005 kJ/kgK.

6.   In a single acting three stage tandem air compressor, the piston diameters are 70, 335 and 375 mm
respectively, the stroke is 380 mm, and it is driven directly from a motor running at 250 rev/min.
The suction pressure is atmospheric (1.013 bar) and the discharge is 45 bar gauge pressure.
Assuming that the air delivered to the reservoirs is cooled down to the initial suction temperature
and taking the volumetric efficiency as 90%, calculate the volume of compressed air delivered to the
reservoirs.
7.    During a test on a single-cylinder steam engine, the mean effective pressure was 4.05 bar when
running at 3 rev/s. The brake load was 1.9 kN acting at an effective radius of 1.2 m. If the cylinder
diameter is 0.275 m and the stroke 0.4 m, calculate (a) the indicated power, (b) the brake power, (c)
the mechanical efficiency.

8.    Steam at a velocity of 600 m/s from a nozzle is directed on to the blades at 20° to the direction of
blade movement. Calculate the inlet angle of the blades so that the steam will enter without shock
when the linear velocity of the blades is 240 m/s. If the exit angle of the blades is same as the inlet
angle, find, neglecting blade friction, the magnitude and direction of the steam leaving blades.

9.    In an experiment to determine the calorific value of an oil fuel by means of a bomb calorimeter, the
mass of the sample of fuel was 0.75 gramme, mass of water surrounding the bomb 1.8 kg, water
equivalent of bomb and fittings 470 grammes, and the rise in temperature was 3.3C. Calculate the
calorific value of this oil in MJ/kg. Take specific heat of water = 4.2 kJ/kgK.

10.   In a CO2 refrigerating plant, the specific enthalpy of the refrigerant as it leaves the condenser is 135
kJ/kg, and as it leaves the evaporator it is 320 kJ/kg. If the mass flow of the refrigerant is 5 kg/min
calculate the refrigerating effect per hour.

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