Punjab Technical University 2011-1st Sem B.Tech Elements of Mechanical Engineering, B Tech ester, Reappear , , - Question Paper

Time: three Hours
Maximum Marks: 60

Instruction to Candidates:
1) Section- A is Compulsory.
2) Attempt any 5 ques. from Section- B & C
3) choose at lowest 2 ques. from part - B & C

part – A [Marks 2*10=20]

Q1) a) On a hot summer day, a learner turns his fan on when he leaves his room in the
morning. When he returns in the evening, will the room be warmer or cooler
than the neighboring rooms? Why? presume all the door and windows are kept
closed?

b) Can a steady state device have boundary work? Discuss?

c) If the efficiency of a power plant goes up as the low temperature drops why not let the heat rejection go to a refrigerator at say –10ºC instead of ambient 20ºC?

d) How internal combustion engines can be classified on the basis of cylinder arrangement?

e) For the identical maximum pressure and work output, compare Otto cycle and Diesel cycle on P-V and T-S diagrams.

f) What is the difference ranging from a nozzle flow and a throttle process?

g) How does a lifting machine can lift more load than the applied load?

h) State the purpose of cam shaft and piston rings in an I.C. engine?

i) Draw neat sketches of any 2 inversions of 4 bar kinematic chain?

j) Differentiate ranging from creep and fatigue?

part - B [8 Marks each]

Q2) a) An insulated vessel containing five kg of liquid water at 38ºC, one kg of ice at OºC is placed. compute the temperature of the water when the ice is completely melted. Take the latent heat of fusion of ice as 335 kJ/kg and specific heat of water as 4.19 kJ/kg – ºC.

b) A gas having mass 4.5 kg undergoes a process from 50ºC to 100ºC. If the
specific heat of the gas is a function of temperature alone, compute the heat
transfer during the process for the relation1 0.256 KJ/Kg – K.

Q3) a) A reversible heat engine operates ranging from 2 reservoirs at temperatures of 600ºC and 40ºC. The engine drives a reversible refrigerator, which operates ranging from 40ºC and - 20ºC. The heat transfer to the engine is 2000 kJ and the network output from the combined engine and the refrigerator system is 360 kJ. compute heat transfer to the refrigerator and net heat transfer to the reservoir at 40ºC.

b) List down the factors that render a process to be irreversible.

Q4) a) The mass rate of flow into a steam turbine is 1.5 kg/s, and the heat transfer from the turbine is 8.5 kW. The subsequent data are known for the steam entering and leaving the turbine.
Inlet Outlet Enthalpy 3137.0 kJ/kg 2675.5 kJ/kg, Velocity 50 m/s 200 m/s, Elevation above six m three preference plane. obtain the power output of the turbine.

b) Why specific heat of air at constant pressure is greater than specific heat at constant volume?

Q5) a) two kg of water at 367 K is mixed with three kg of water at 283 K in an isolated system. compute the change in entropy due to mixing process.

b) Show that the change of entropy during a polytropic process for a perfect gas per unit mass is.

part - C [8 Marks each]

Q6) a) Prove that the optimum pressure ratio rp for maximum net work done ranging from the temperatures T1 and T3 for a Brayton cycle is provided by?

b) A diesel engine operating on diesel cycle has 20 cm bore and 30 cm stroke. The clearance quantity is 420cm3. The fuel is injected at constant pressure for 5% of the stroke. compute the air standard efficiency. If the cutoff is delayed from 5% to 8%, what will be the percentage loss in efficiency. presume identical compression ratio in both cases?

Q7) a) Establish a relation ranging from Youngs modulus, modulus of rigidity and bulk modulus?
b) A specimen of steel 20 mm diameter with a gauge length of 200 mm is tested to destruction. It has an extension of 0.25 mm under a load of 80 kN and the load at elastic limit is l02 kN. The maximum load is 130 kN. The total extension at fracture is 56 mm and diameter at neck is 15 mm. obtain

i) The stress at elastic limit
ii) Youngs modulus
iii) Percentage elongation
iv) Percentage reduction in area
v) Ultimate tensile stress

Q8) a) In a lifting machine whose velocity ratio is 50, it was obtained that an effort of 100 N was necessary to lift a load of 4000 N. Is the machine reversible? If so, what effort could be removed so that the machine is at the point of reversing?

b) discuss the working of a pantograph with neat sketches.

Q9) a) discuss the working of 2 stroke C.I. engine with the help of neat sketches.

b) A steel rod one cm in diameter is subjected to an axial load of 200 N. If the diameter of the bar is increased by 10%, obtain the change in strain energy per unit length of the rod.

Earning:   Approval pending.