Punjab Technical University 2011-2nd Sem B.Tech Elements of Mechanical Engineering, B Tech ester, Regular , , - 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) Minimum number of processes needed to complete a workable ideal. Heat Engine cycle are 1, 2, 3, 4, 5, six (Select the accurate answer)

b) Why a constant quantity process line is more steeper than the constant pressure process line on the T - S coordinates. discuss the cause just in two/three lines with the aid of TS chads, or otherwise.

c) COP which factor implies the efficiency of a Heat pump is always greater than unity. But on the contrary, the efficiency of any system(including Heat Pump) can not be more than I00%o, otherwise the basic laws of thermodynamic (eg legal regulations and second legal regulations etc.) would fail. Justify in 2 to 3 lines, that actual efficiency even in case of a Heat Pump can not be more than 100%.

d) Substantiate by giving a few live example with numerical values or otherwise, that dS irreversible heat exchange for an irreversible heat exchange process, say, for the case of irreversible heat rejection dQ, from a Heat Engine to the Sink (atmosphere).

e) Starting from the identical initial state plot a reversible and an irreversible adiabatic compression processes on T - S Coordinates with arrow heads indicating the direction of the 2 processes. Show the area which is representative of the fraction of energy which became unavailable during this irreversible process.

f) Prove that 2 adiabatic processes can not cut every other i.e. they cannot have a common state.

g) Can free expansion process be plotted on PV coordinates? provide ans in YES or NO and provide reasons for the identical.

h) Fuel used in an engine operating on otto cycle (i.e., constant quantity heat addition cycle) is Petrol because (Fill the blanks to complete the statement).

i) Temperature decreases/increases/remains constant during throtting Process (Select the accurate Answer)

j) Sketch stress - strain curves for ductile and brittle materials and show the salient points on it.

part - B [Marks eight Each]

Q2) (a) What is the difference ranging from total energy and enthalpy? Express both terms in detail.

(b)One of the requirements for a process to become most efficient or reversible process is that it should be carried out in system under complete thermodynamic equilibrium condition. Justify and substantiate the above statement by thermodynamic or any other logics.

Q3) {a) dQ= dE + PdV. Is this formula valid for a process occurring in an open system, or

(ii) In a Closed System, or

(iii) In both?

What is PdV?

(b) A mass of 10 kg at room temperature is dropped from a height of 100 m into a pond containing 1000kg of water at room temperature. compute the change in internal, potential and kinetic energies, heat and work transfer for the subsequent 3 cases:

(i) Stone is just about to strike the water.

(ii) Stone just after striking the water, stopped immediately at the bottom
of pond.

(iii) Stone achieves the ambient temperature after reasonable amount of time.

Q4)(a)Select suitable coordinates for plotting throttling process, and plot it on these coordinates along with an arrow - heat indicating the direction of the process.

(b) 0.2 pi of ideal gas at a pressure of 20 bar and 600K is expanded is expanded isothermally to 1m3. It is then collected to 300K at constant quantity and then compressed back polytropically to its initial state. obtain not work done and the net heat transfer during the cycle.

Q5) (a) A Carnot Engine operating ranging from a heat reservoir at T, and cold reservoir at T, is to drive a Carnot Refrigerator removing heat Q from a reservoir at a temperature T and rejecting the heat. What is the minimum amount of heat Q, that is to be taken out from the hot body at T, to remove Q from coolest reservoir?

(b) Determine the minimum value of e, if Q is 100 KW and heat is rejected by the heat pump at temperature T.

part - C [Marks eight Each]

Q6) (a) discuss and justify how isentropic expansion process contributes in rising the output and hence efficiency of the Carnot Cycle.

(b) Why a diesel engine is less efficient as compared to the Carnot cycle, when both are operating ranging from the identical temperature limits? discuss it with the aid of T - S diagrams of the cycles.

Q7) In an air standard diesel cycle, the compression ratio is 15 and the pressure and temperature of air at the beginning of the compression are one bar and 288 K. The peak temperature in the cycle is 2700K. Determine

(a) heat supplied.

(b) Cycle Efficiency

(c) Cut off ratio.

(d) Work done.

(e) Peak Pressure of the Cycle

(f) M.E.P.

Q8) explain different inversions of double slider crank chain mechanism.

Q9) discuss longitudinal and lateral strain, poissions Ratio, yield point and Bulk Modulus.

Earning:   Approval pending.