BE (2nd Semester)
Examination May-June, 2007
Basic Mechanical Engineering
1. (a) A, piston of a diesel engine of 50 cm” area moves 8 cm during part of a suction of stroke. Fresh air of 350 cm3 is drawn in from the atmosphere. The pressure of atmosphere is 1.013 X 10s N/m2 and the pressure inside the cylinder during the suction I stroke is 0.8-X 10s N/m2. The difference between the suction and atmospheric pressure is accounted -for flow resistance in the induction pipe and inlet valve. Determine the network done during the process.
(b)Differentiate between the two works p.dv and v.dp. The work supplied to a closed system is 160kJ. The initial volume is v, = 0.80 m’ and pressure of the system changes asp = 7-3v’where p is in bar and v is in m3. Determine the final volume and-pressure of the system.
(c)In an air compressor, air flows steadily at the rate of 15 kg per minute. The air enters the compressor at 5 m/s with a pressure of 1 bar and a specific volume of 0.5 m’/kg. It leaves the compressor at 7.5 m/s with a pressure of 7 bar and a specific volume of 0. 15 m’/kg. The internal energy of the air entering. The cooling water in the compressor jackets absorbs heat from the air at the rate 125 kJ/s. Find:
(i)power required to drive compressor
(ii)ratio of the inlet pipe diameter to the outlet diameter.
2. (a)What is principle of increase of entropy. Explain and ex- amples. Give causes for increase in entropy.
(b)A reversible heat engine operates between two reservoirs of 600°C and 40°C. The engine drives a reversible refrigerator which operates between reservoirs at temperature of 40°C and- 20°C. The heat transfer the heat engine is 2000 kJ and the work output, of the con- engine refrigerator plant is 360kJ.
(i)Show the above arrangement is figure.
(ii)Evaluate the heat transfer to the refrigerant.
(iii) When the efficiency of the heat engine and C.O.P. refrigerator are each 40% of their maximum possible, evaluate heat transfer to the refrigerant and net heat transfer reservoir at 40°C -4
(c)An oil engine with 20 cm cylinder diameter and 30 cm words on theoretical diesel cycle. The initial pressure temperature of the air used are 1 bar and 30°C. The cut o1 of the stroke. Find the following :
(i)Draw the cycle in p-v, h-s and T-s diagrams.
(ii)Air standard efficiency
3. (a) Differentiate between isothermal and hyperbolic process of with examples. Steam at a pressure of 10 bar and 0 expands to atmospheric pressure hyperbolically. Find :
(i) work done (ii) change in enthalpy
(iii) change in internal energy (iv) heat absorbed
(v)change of entropy
Given that Cp of steam at constant pressure = 2 kJ/kg-K.
(b)Define equivalent evaporation and boiler efficiency. A Lancashire boiler generates 2400 kg of dry steam per calorific value of coal is 33180 and temperature of feed water is 17.5°C.
(i) actual evaporation per kg of coal .
(ii) equivalent evaporation from and at 100°C and
(iii) efficiency of boiler.
(c)Steam from an initial pressure of 7 bar and 200°C is exp isentropically to a pressure of 1 bar. Calculate:
(i) final condition of steam
(ii)change in internal energy
(iii)Work done during the process
(iv)The value of index n if the expansion follows the law pvn = constart. Draw p-v, T-s and h-s diagram for problem.
Solve the problem without using Mollier chart.
4. (a) (i)What are different types of ‘Electric Arc Welding’ compare D.C. an A.C. arc weldings.
(ii) What are different types of flames in gas welding? Compare the advantages and disadvantages of the different types of gas welding.
(b)Explain the different operations on lathe by drawing figures showin position of job and tool. Define cutting speed, feed and depth of cut:1 What calculations are to be done for taper turning and thread cutting?
(c)What do you understand by Machine Tools? Differentiate between shaper and planer. What are the specifications and operations of shaper machine.
5. (a) Describe a machine which determines experimentally all the three types of main stresses and gives yield point.
(b)The following data relate to a bar subject to a tensile test:
Diameter of bar, d = 30 mm (0.03) tensile load P =54 kN. Gauge length 1= 0.3 m, extension of bar 1
ᵹ1= 0.112 mm, change in diameter <?d = 0.00366 mm.
(ii) valeus of three moduli.
(c)A steel wire I” mm in diameter is stretched horizontally between two fixed points 2 m apart vertical load applied at the mid span of the wire causes a vertical displacement of 45 mm at the point of application of the load. What will be the stress induced in the wire and the load applied. Neglect the weight of the wire. Take E for the wire material as 200 GN/m2.