B.E. DEGREE EXAMINATION.
ME 237 — THERMAL ENGINEERING
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ´ 2 = 20 marks)
- What are boiler mountings and accessories? Give some examples.
- What is the function of feed check valve?
- What is compounding of a turbine?
- Define stage efficiency of a multistage turbine.
- What are the importance of valve timing diagram?
- What are the antifreeze solutions used in the water cooling system of an
- Define ‘delay period’ and ‘delay period angle’ in CI Engine.
- What are the major losses in an IC Engine?
- Define Relative humidity and dew point temperature.
- What is psychrometer?
PART B — (5 ´ 16 = 80 marks)
- From the data given below, draw a heat balance sheet for a two stroke diesel engine run for 20 minutes at full load.
r.p.m = 350
m.e.p = 300 kN/sq.m
Net brake load = 650 N
Fuel consumption = 1.5 kg
Cooling water = 160 kg
Water inlet temperature = 35°C
Water outlet temperature = 60°C
Air used/kg of fuel = 30 kg
Room temperature = 20°C
Exhaust temperature = 300°C
Cylinder bore = 20 cm
Cylinder stroke = 28 cm
Brake diameter = 1 m
Calorific value of fuel = 44000 kJ/kg
Steam formed per kg
of fuel in exhaust = 1.35 kg
Pressure of steam = 50 kN/sq.m
Specific heat of steam
in exhaust = 2.1 kJ/kg K
Specific heat of dry gases = 1 kJ/kg K.
- (a) (i) Explain how steam boilers are classified. (6)
(ii) Explain with a neat diagram, the construction and working of a
Babock and Wilcox Water tube boiler. (10)
(b) (i) Explain the functions of blow off cock and flusible plug. (8)
(ii) What are the various criteria for selection of a boiler? (8)
- (a) The blade speed of a single ring of an impulse turbine is 300 m/s
and the nozzle angle is 20°. The isentropic heat drop is 473 kJ/kg and the nozzle efficiency is 0.85. Given that the blade velocity coefficient is 0.7 and the blades are symmetrical, draw the velocity diagrams and calculate for a mass flow of 1 kg/s :
(i) Axial thrust on the blading
(ii) Steam consumption per B.P. hour if the mechanical efficiency is 90 per cent
(iii) Blade efficiency, stage efficiency and maximum blade efficiency.
(b) At a particular stage of a reaction turbine, the mean blade speed is
60 m/s and the steam pressure is 3.5 bar with a temperature of 175°C. The identical fixed and moving blades have inlet angles of 30° and outlet angles of 20°. Determine
(i) the blade height if it is 1/10 of the blade ring diameter, for a flow rate of 13.5 kg/s
(ii) the power developed by a pair and
(iii) the specific enthalpy drop if the stage efficiency is 85%.
- (a) (i) What are the important requirement of the spark ignition system? Name two ignition systems which are in common use and what is the basic difference between them. (8)
(ii) What are the advantages and disadvantages of water cooling system in I.C. Engine? (8)
(b) (i) Explain with neat diagram the pressure lubrication used in I.C. Engine. (8)
(ii) What are the various factors affecting the Ignition Lag. (8)
- (a) 20 m3 of air per minute at 30°C and 60% R.H. is cooled to 22° C DBT maintaining specific humidity constant. Find the following :
(i) Heat removed from air
(ii) R.H. of cooled air
(iii) WBT of the cooled air.
Take air pressure = 1 bar.
(b) Draw a neat diagram and explain the Summer air conditining system for hot and dry weather.