BE (2nd Semester)
Examination Dec-Jan, 2008-2009
Basic Mechanical Engineering
1. (a) What is a Quasi-Static Process?
(b)A mass of gas is compressed in a quasi-static process from 80kPa,m3 to 0.4 MPa, 0.03 m3. Assuming that the pressure and volume q, related by pVn= constant. Find the work done by the gas system.
(c)A gas undergoes a thermodynamic cycle consisting of three process beginning at an initial state where P1=1 bar, V1= 1.5 m3 and U1 = 5kj. The processes are as follows:
(i)Process 1-2: Compression with PV = constant to P2= 2 bar, u2=690kJ
(ii)Process 2-3 W23 = 0, Q23= -150 kj
(iii)Process 3-1 W31 = + 50 kJ
Neglecting KE and PE change, determine the heat interactions Q12 and Q31
(d) Two stream of air, one at I bar, 27°C and velocity of 30 m/sec and of at 5 bar, 227°C and velocity of 50 m/sec, mix in equal proportion it chamber from which heat at the rate of 100 kJ/kg is removed. The mi tore is then passed through an adiabatic nozzle. Find the velocity of t stream issuing out of the nozzle. The temperature of air leaving t nozzle is 27°C and it’s CP = 1.005 kJ/kgK.
2. (a)What is a heat pump? How does it differ from a refrigerates?
(b)Two reversible heat engines A and B are arranged in series. A rejective lit directly to B. Engine A receives 200 kJ at a temperature of 421 “from a hot soruce while engine B is in communication with a cold at a temperature of 4.4°C: If the work output of Ais twice that of B, find
(i) Intermediate temperature between A and B.
(ii)The heat rejected to cold sink.
(c) Two kg of water at 80° are mixed adiabatically with three kg of water at 30°C in a constant pressure process of 1 atmosphere. Find the increase in entropy of the total mass of water due to mixing process. (CP of water = 4.187 kJ/kgK).
(d) in an air standard diesel cycle, the compression ratio is 15. Compression beings at 0.1 Mpa 40°C . The heat added is 1.675 MJ/kg find:
(i)Maximum temperature of cycle
(ii)The efficiency of cycle
(iii)The work done per kg of air
(iv)The cut off ratio
(v)The temperature at the end of expansion
(vi)The maximum pressure
3. (a)Explain the principle of fire tube and water tube boilers.
(b)What do you understand by “Draught”? What are the different methods of producing draught? Describe
(c)In a steam engine cylinder dry and saturated steam expands from 22 bar to 2 bar isothermally. Calculate:
(i)change in enthalpy
(ii)change in entropy
(iii)change in internal energy
(d) Steam initially 1.5 MPa, 300% expands reversibly adiabatically in a nozzle to 40° C. Determine the velocity steam leaving the nozzle. Neglect velocity of steam at entrance of nozzle.
4. (a)Define ‘Machine Tool’.
(b)Describe in brief the equipment used for high pressure and low pressure gas welding.
(c)Discuss with the help of a neat sketch, the principle of ric arc welding. What is straight and reversed polarity?
(d)What is Shaper? Describe the working principle of a shaper. How is it specified?
5. (a)Define the term, ‘Modulus of Elasticity4 and modulus of rigidity.
(b)Define the term volumertic strain and Bulk-Modulus and find the re tion between Bulk modulus and modulus of elasticity.
(c)State principle of superposition. A steel bar 25mmdiameer is loaded shown in figure. Determine the stresses in each part and total elongat.
E = 210 GPa.
(d) A tensile test was conducted on a mild steel bar following data were tained. Diameter of steel bar =3cm; Gauge length bar=200mm Load at elastic limit = 250 kN. Extension at Load 150 kN=0.21mm Maximum load 380 kN, Total extension 60 mm, Diameter of rod at failure 2.25 cm. Determine
(i)The Young’s modulus
(ii)The stress at elastic limit
(iii)The percentage elongation
(iv)The percentage reduction in area