B.E./B.Tech. Degree
Examinations April/may 2016
Question Paper code : 57556
Fourth Semester
Mechanical Engineering
ME6404-THERMAL ENGINEERING
(Regulation 2013)
Answer All Questions
Part A- (10 x 2 = 20 Marks)
1. State the assumptions made in air
standard cycle analysis?
2. Define Mean effective pressure. Show
that on a p-v diagram.
3. Show the valve overlapping period of a
typical 4-stroke petrol engine on valve timing diagram.
4. Define the phenomenon knocking in SI
engines.
5. Draw the shape of a supersonic nozzle.
6. Distinguish between impulse and
reaction principles.
7. Define volumetric efficiency of an air
compressor.
8. State the conditions which lower the
volumetric efficiency of an air compressor.
9. Show the simple vapour compression
cycle on pressure-enthalpy diagram.
10. List out the basic elements of an air
conditioning system.
Part-B (5 x 16 = 80 Marks)
11.(a) The compression ratio for a
single-cylinder engine operating on a dual cycle is 9. The maximum pressure in
the cylinder is limited to 60 bar. The pressure and temperature of the air at
the beginning of the cycle are 1 bar and 30'C. heat is added during constant
pressure process upto 4 percent of the stroke. Assuming the cylinder diameter
and stroke length as 250 mm and 300 mm respectively. If the number of working
cycle is 3 per second.
(OR)
(b) The swept volume of a diesel
engine working on a dual cycle is 0.0053 m3 and clearnce volume is 0.00035 m3.
the maximum pressure is 65 bar. Fuel injection ends at 5 percent of the stroke.
the temperature and pressure at the start of the compression are 80'C and 0.9
bar. determine air standard efficiency of the cycle.
12.(a) Describe with suitable sketches the
following system of a modern carburetor. (i) Main metering system (ii) Idling
system (iii) Economic system (iv) Acceleration pump system (v) Choke
(OR)
(b) (i) With a neat sketch, explain the principle
of work of a diesel injector.
(ii) A four stroke,
four cylinder gasoline engine has a bore of 60 mm and a stroke of 100 mm. On
test it develops a torque of 66.5 Nm when running at 3000 rpm. If the clearance
volume in each cylinder is 60cc, the relative efficiency with respect to brake
thermal efficiency is 0.5 and the calorific value of the fuel is 42 MJ/Kg,
determine the fuel consumption in kg/h and the brake mean effective pressure.
13.(a) (i)Define
critical pressure ratio of a nozzle and discuss why attainment of sonic
velocity. Determine the maximum discharge through the nozzle.
(ii) Explain the
metastable expansion of steam in a nozzle with help of h-s diagram.
(OR)
(b) A simple
impulse turbine has one ring of moving blades running at 150 m/s. the absolute
velocity of steam at exit from the stage is 85 m/s at an angle of 80’ from the
tangential direstion. Blade velocity co-efficient is 0.82 and the rate of steam
flowing through the stage is 2.5 kg/s. if the blades are equiangular, determine
(i) Blade angles (ii) Nozzle angle (iii) Absolute velocity of steam issuing
from the nozzle (iv) Axial thrust.
14.(a) A two stage
air compressor consists of three cylinder having the same bore and stroke. The delivery
pressure is 7 bar and the free air deliver is 4.3 m3/min. Air is drawn in at
1.013 bar, 150’C and an intercooler cools the air to 38’C. The index of
compression is 1.3 for all three cylinders, Neglecting clearance volume. Calculate
(i) the
intermediate pressure (ii) The power required to drive the compressor (iii)
Isothermal efficiency.
(OR)
(b) With a neat
sketch, describe the construction and working of a single-stage acting reciprocating
air compressor. Also derive the equation for work done with clearance and
without clearance.
15.(a) Describe the
following refrigeration with layout : (i) Ammonia water system (ii) Lithium-Bromide water system
(OR)
(b)(i) Describe the
working principle of a centralized air conditioning system and enumerate the
need for it.
(ii) List the loads
the contribute to the overall cooling load.
