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Refrigeration And Air Conditioning Question Paper - Dec 18 - Mechanical Engineering (Semester 8) - Mumbai University (MU)
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Refrigeration And Air Conditioning - Dec 18

Mechanical Engineering (Semester 8)

Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining five questions.
(3) Assumptions made if any should be justified.
(4) Use of Refrigerant Charts, Psychometric chart, Friction chart, and Steam Tables are allowed

1. Answer any four of the following:

1.a. Explain with neat schematic diagram use of Liquid Suction heat exchanger in a Vapour Compression system.
(5 marks) 10336

1.b. What are eco-friendly refrigerants? Discuss with examples.
(5 marks) 10337

1.c. List down types of aircraft refrigeration systems. How are these systems compared on the basis of DART?
(5 marks) 10300

1.d. A reversed Carnot cycle air conditioner of 1 TR capacity operates with evaporator coil temperature $t_0=7^\circ C$. The surrounding air at 43$^\circ$C is used as cooling medium rising to a temperature of 53$^\circ$C. The temperature of heat rejection is $t_k=55^\circ$. Determine COP, power consumption of the air conditioner and the mass flow rate of surrounding air entering the condenser. Take $C_P$ for air as 1.005kJ/Kg K.
(5 marks) 10391

1.e. Define RSHF, GSHF and ERSHF.
(5 marks) 12727

1.f. Discuss advantages of vapour absorption refrigeration system over power vapour compression refrigeration system.
(5 marks) 10348

2.a In a laboratory test, a psychrometer recorded dry bulb temperature at 34$^\circ$C and wet bulb temperature of 26$^\circ$C. Without using Psychrometric chart, calculate:

(i) Vapour pressure (ii) Relative humidity (iii) Specific humidity (iv) Degree of saturation (v) Dew point temperature (v) Enthalpy of mixture.

Barometric pressure = 740 mm of Hg.

(8 marks) 10357

2.b What are different types of Cooling Towers? Explain with a neat sketch and induced draft type Cooling Tower.
(6 marks) 10320

2.c. What are the sources of cooling load? Explain how will you estimate cooling load of your College Library.
(6 marks) 12728

3.a. A regenerative air refrigeration system for an aeroplane is designed to take a load of 25 TR. The temperature and pressure conditions of the atmosphere are 5$^\circ$C and 0.85 bar. The pressure of the air is increased from 0.85 bar to 1.2 bar due to ramming action. The pressure of air leaving the main compressor is 4.8 bar. 60% of the total heat of the air leaving the main compressor is removed in the heat exchanger and then it is passed through the cooling turbine. The temperature of the rammed air which is used for cooling purposes in the heat exchanger is reduced to 50$^\circ$C by mixing the air coming out from the cooling turbine. The isentropic efficiency of the compressor and turbine and 90% and 80% respectively. The pressure and the temperature required in the cabin are 1 bar and 25$^\circ$C respectively. Assuming isentropic ramming and mass of the cooled air passing through the heat exchanger equal to the mass of cooling air, find: (i) the ratio of by-passed air to the ram air used for cooling purposes; and (ii) the power required for maintaining the cabin at the required condition.
(12 marks) 10304

3.b. Discuss with block diagram triple fluid Vapour Absorption refrigeration system.
(4 marks) 10349

3.c. Explain with the help of neat sketch, the working of refrigerating system having three evaporators at different temperatures with individual compressors and multiple expansion valves.
(4 marks) 10339

4.a. A vapour compression system using $NH_3$ works between -15$^\circ$C and 40$^\circ$C as the evaporator and condenser temperature respectively. The vapour is superheated by 5$^\circ$C before entering compressor and liquid is subcooled by 5$^\circ$C. Using P-h chart determine:

(i) COP

(ii) Mass flow of refrigerant per TR

(iii) Piston displacement per TR using volumetric efficiency = 80%

(iv) Heat rejected in the condenser per TR, and

(v) Ideal COP

(10 marks) 10334

4.b. Draw front and side view of the Window Air Conditioner and explain the various components inside the Unit.
(6 marks) 10367

4.c. What are the methods of duct design? Explain any one method in detail.
(4 marks) 10378

5.a. The following data refer to an air conditioner space:

Outdoor condition - $38^\circ C, 50\% RH$

Room condition - $24^\circ C, 50\% RH$

Sensible heat load - 26kW

Latent heat load - 8kW

By-pass factor of the cooling coil - 0.16

If the ventilation requirement is such that on a mass flow rate basis, 20% of the fresh air is introduced and 80% of supply is recirculated, determine:

(i) Supply air flow rate

(ii) Outside air sensible heat

(iii) Outside air latent heat

(iv) Grand total heat

(v) Effective room sensible heat factor.

(14 marks) 12714

5.b. Discuss in details various controls used in Central Plant Air Conditioning system.
(6 marks) 10370

6. Write short notes on any four of the following

6.a. Types of Condenser and Evaporators
(5 marks) 12730

6.b. Thermoelectric refrigeration
(5 marks) 12712

6.c. Year Round Air Conditioning System
(5 marks) 10364

6.d. Pressure and Temperature Controls
(5 marks) 10371

6.e. BEE Star Rating System
(5 marks) 10305

6.f. Bootstrap Cooling System
(5 marks) 10306

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