Pune University BE Advanced Air Conditioning and Refrigeration Question Papers

Pune University BE Advanced Air Conditioning and Refrigeration

Question Papers

B.E. (Mechanical)

ADVANCED AIR CONDITIONING AND REFRIGERATION (2008 Pattern) (Elective – III) (Sem. – II)

Time :3 Hours]                                                                                              [Max. Marks : 100

Instructions to the candidates:

1)            Answer three questions from each section.

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

3)             Neat diagrams must be drawn whenever necessary.

4)             Figures to the right indicate full marks.

5)             Use of logarithmic tables, Mollier chart, electronic pocket calculator, p – h charts is allowed.

6)            Assume suitable data if necessary.

SECTION – I

Q1) a) Explain Vortex tube expansion cycle.                                                                   [6]

b)        A R-134 a condensing units is specified to give 20 TR capacity for air – conditioning under standard operating conditions of 40°C condensing and 10°C evaporating temperature. What would be its capacity in TR for food freezing for which the evaporator temperature is -30°C? Also obtain the capacity of air – conditioner for condensing temperature of 40°C. [12]

Ts(°C)

h/kJ/kg)

hg(kJ/kg)

S/kJ/kg)

Sg(kJ/kg)

v (m3/kg)

-30

162.33

387.08

1.7766

0.2240

10

213.39

410.85

1.7460

0.0525

40

256.43

426.17

1.1930

1.7350

0.0199

60

288.34

433.91

1.2893

1.7263

0.0114

OR

 

Q2) a) Write a short note on :

i)              Vapour defrosting.

ii)                          Reverse cycle defrosting.                                                                      [10]

b)            Explain rating cycle for domestic refrigerators. [8]

 

Q3) a) Discuss the various methods of capacity controls of centrifugal compressor.        [6]

b)        An open – type compressor employing R-22 has a cooling capacity of 6.25 TR operating at an evaporating temperature of 5°C and a condensing temperature of 50°C. If the ambient DBT is 35°C and the altitude is 1.525 km, what is the capacity of an air-cooled condenser? Take HRF = 1.2; correction factor for TD = 1.2; Altitude correction factor = 0.893. What is its capacity at the ground level. What is the capacity of water – cooled condenser?                                                                                 [6]

c)         State design aspects of evaporator design.                                                     [4]

OR

Q4) a) Discuss various types of cooling tower. [8] b) Discuss the procedure for estimating length of capillary tube & derive

the expression of the same.                                                                                [8]

Q5) a) Explain the construction working of externally compensated regulating valve.                                                                                                                      [6]

b)        Describe the methods of controlling IAQ.                                              [6]

c)        Explain the followings;                                                                             [4]

i)              Thermal overload protection for hermetic motors.

ii)           Adjustable speed drives.

OR

Q6) a) Explain the methods of purging noncondensables.                                  [6]

b)        List the pollutants & contaminants present in the air with source.     [6]

c)        Discuss the types of safety valves.                                                          [4]

SECTION – II

Q7) a) Explain the purpose and scope of ECBC.                                                  [6]

b)        A 25 cm thick wall is exposed to the periodic temperature and incident radiant variation on an hourly basis between 7 am and 6 pm is given in the table. Determine heat gain of the room per unit area of the wall. The outdoor maximum and minimum temperatures are 40°C and 22°C respectively. The outside and inside design temperatures are 40 and 25°C respectively. What is the time of maximum heat gain from the wall?   [12]

Density of material, p = 2400 kg/m3 Thermal conductivity, k = 1.5 W/mK Outside wall coefficient, h0 = 23 W/m2K

Inside wall coefficient, h. = 7 W/m2K.

5 i

Time

7

am

8

am

9

am

10

am

11

am

12

noon

1

pm

2

pm

3

pm

4

pm

5

pm

6

pm

Wall Mass (kg/m2)

Equivalent Temperature Difference (A TE)°C

500

3.9

3.3

3.3

3.3

3.3

3.3

3.9

4.4

5.5

6.7

9.4

11.1

600

6.1

5.5

5.0

4.4

4.4

4.4

5.0

5.5

5.5

5.5

6.1

6.7

 

OR

Q8) a) Draw and discuss modified comfort chart.                                                          [8]

b)        Write a short note on “Choice of Supply Design Conditions”.                   [6]

c)        Write a short note on Sol – air temperature.                                                  [4]

Q9) a) Write a short note on “Air – conditioning of Multiplexes”.                              [8]

b) Draw and explain air – to – liquid heat pump circuit.                                                                                    [8]

OR

Q10) a) Write a short note on “Clean Room”.                                                                 [6]

b)        Discuss the HVAC design criteria for IT centers.                                         [6]

c)         State applications of heat pump.                                                                     [4]

Q11) a) Draw circuit of Liquefaction process of hydrogen.                                         [4]

b)        Discuss various applications of cryogenics.                                                   [8]

c)        Explain the term FOM and liquid yield.                                                        [4]

OR

Q12) a) 2 kg of dry air at 30°C and 1 bar compressed isothermally to 20 MPa in a compressor in a Linde cycle. Make – up air is added to suction at 30°C and 1 bar. Determine the yield of liquid and temperature of air before throttling. Draw the schematic diagram with T-s and p-h diagram. Use p-h chart of air.                                                                    [8]

b) Discuss various properties of cryogenic fluids.

Pune University BE Advanced Air Conditioning and Refrigeration Question Papers                                                                           [8]

 

P 9PP~[P91P] PRESSURE (MPa) o

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