# Pune University Exam Paper

## RELIABILITY(Elective-IV)(Sem.- II)

Instructions to the candidates :-

1)                                             All questions are compulsory.

2)                    Answer 3 questions from Section -1 and 3 questions from Section – II.

3)                    Answers to the two sections should be written in separate books.

4)                                             Neat diagrams must be drawn wherever necessary.

5)                    Use of slide, electronic pocket calculator is allowed.

6)                                             Assume suitable data, if necessary.

SECTION – I

QI) a)        Explain Bath Tub curve.                                                                                        

b)                   In life testing of 110 machine components the number of failures during

each time of interval of 20 hours is as below.                                                     

Time interval (hours)                     No.  of   failures

 T< 1000 0 1000 < T < 1020 20 1040 60 1060 10 1080 10 1100 5 Estimate MTTF.

c)     Write down the causes of failures and unreliability.                                            

OR

Q2) a)       Explain the term MTTF and MTBF.                                                                     

b)                   Explain the term failure density fd.                                                                      

c)                    Explain Maintainability and availability.                                                             

The time to wear out of a cutting tool Edge is distributed normally with ju = 2.8hr and O = 0.6hr

 Q3) a)

i)                            What is the probability that the tool will wear out in less than 1.5 hour?

ii)                      How often the cutting edges be replaced to keep the failure rate less than 10% of the tool.

Consider 0 (-2.1667) = 0.0151 and z = -1.28.                                          

 b) c) Q4) a)

Explain system reliability model in series configuration.                                  

Explain Delta star method to determine reliability of bridge network. 

OR

Fatigue life data for industrial rocker arm is fit to longnormal distribution. The following parameters are obtained.                                                                                                                

y0 = 2 x 10U cycles, w = 2.3

i)                            To what value should the design life be set if probability of failures is not to exceed 1%.

ii)                       If the design life is set to 1.0 x 106 cycles what will be the failure probability.

 b) c) QS —) b) c)

Take ^ (—2.32) = 0.01 and ^ (—1.302) = 0.096 Explain system reliability model in parallel configuration.                                                                                                                               

Discribe Redundance Allocation.                                                                        

Discribe ARINC apportionment technique.                                                        

Write note about cold, Hot and standby redundancy.                                          

A system requires a reliability of 0.9 for 10 hours of operation. There are four units connected in series with failure rates \ = 0.003,                                                                                 =  0.006,

^•3 = 0.008, ^4 = 0.010 allocate reliabilities to four units.                             

OR

 Q6) a) b) c)

Discribe AGREE apportionment technique.                                                       

Explain minimum Effort method to determine reliability.                                

Write objectives of Apportion Method.                                                              

SECTION – II

 07) a) b)

Explain Maintainability with derivation and diagram Enlist the factors affecting maintainability.         

A sulphur dioxide scrubber is Known to have a MTBF of 137 days. Testing a scrubber requires half a day and mean time to repair is 4 days.                                                                              

i)                                     Chose the test period to maximise availability.

ii)                                What is maximum availability.

 7 0V —) b) c) Q9) a) b) c)

Discribe Reliability centered maintenance.                                                         

OR

Explain availabilty and its types.                                                                         

If an inherent availability 0.9 is mean and MTBF is 200 hours. What is maximum possible MTTR?      

Write note on TQM.                                                                                             

                        

Discribe FMECA.

Write note about Monte carlo Evaluation.

For the logic diagram shown construct the fault tree.

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OR

 010)—) b) c)

Explain fault Tree Analysis.                                                                                 

Explain Minimal cut set Method.                                                                        

Draw Fault Tree for the motor circuit shown in figure the top event for the fault tree analysis is simply failure of the motor to operate.                                                                                             

Qll)a)             Discribe Reliability Testing.                                                                            

b)                    Load and capacity on a device are known within a factor of two with

90% confidence. What value of safety factor co/lo, must be used if failure probability is to be no more than 1%. Take 0 (p) = 0.99, P = 2.3                                                     

c)                     Derive Reliability function using markov model.                                                

OR

Ql2)a)       Explain Accelerated life Testing and HALT.                                                       

b)     In short sample accelerated life testing of a system based weibull

distribution, the following data is recorded.                                                

 Failure Number 1 2 3 4 5 6 7 8 9 MTTF (hour) 24 22 12 28 35 38 30 19 25

Plot the variation of Reliability against time using.

i)          Mean ranking method and

ii)     Median ranking Method.

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Total No. of Questions : 12]                                                             SEAT No

P1«5Q                                                                                                           [Total No.  of   Pages : 4

 – 453 B.E. (Mechanical S/W)

REFRIGERATION AND AIR CONDITIONING (2008 Pattern) (Elective-II) (Sem. – I)

Time :3 Hours]                                                                                              [Max. Marks :100

Instructions to the candidates :

1)                    Answer 3 questions from Section -1 and 3 questions from           Section – II.

2)                    Answers to the two sections should be written in separate            books.

3)                    Neat diagrams must be drawn wherever necessary.

4)                    Pigures to the right indicate full marks.

5)                         Use of logarithmic tables slide rule, Mollier charts, electronic pocket calculator and steam tables P-h chort is allowed.

6)                    Assume suitable data, if necessary.

SECTION – I Unit-I

Ql) a)        Write a note on‘magnetic refrigeration.                                                               

b)                   What is the necessity of air-craft refrigeration.                                                   

c)                    Explain boot strap system with the help of T-S diagram. Derive expression

for COP.                                                                                                                

OR

Q2) a)       An open air refrigeration system operating between pressures of 10.5

bar and 1.05 bar, is required to produce 10 tonnes of refrigeration. Temperature of air leaving the cooler is 150C and leaving the refrigerator room is -70C. Neglecting all losses and clearance,                                                                                               calculate.              

i)                       Temperatures at salient points.

ii)                  Weight of air circulated in kg/min.

iii)                                               Piston displacement of compressor and expander in mQ/min.

iv)                                                 Net work of the cycle.

v)      C.O.P.

vi)                                                 Power required to drive the compressor.

b)     Write a note on solar refrigeration system.