Question Paper: Refrigeration And Airconditioning : Question Paper Dec 2014 - Mechanical Engineering (Semester 8) | Gujarat Technological University (GTU)

Refrigeration And Airconditioning - Dec 2014

Mechanical Engineering (Semester 8)

(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
1 (a) Define Refrigeration. State types of refrigeration systems. Explain Bell-Coleman air refrigeration cycle.(7 marks) 1 (b) An air refrigeration open system operating between 100 KPa and 1 MPa is required to produce a cooling effect of 2000 kJ/min. Temperature of the air leaving the cold chamber is -5°C and at leaving the cooler is 30°C. Neglect losses and clearance in the compressor and expander.
(i) Mass of air circulated per min,
(ii) Compressor work, expander work, cycle work ,
(iii) COP and power in kW required.
(7 marks)

Answer any two question from Q2 (b) or Q2 (c)

2 (a) A 5 tonne R-12 refrigeration plant has saturated suction temperature of -5°C. The condensation takes place at 32°C and there is no undercooling of refrigerant liquid. Assuming isentropic compression, find
(i) COP of the plant,
(ii) Mass flow rate of refrigerant
(iii) Power required to run the compressor in KW. Take the following properties of R-12.

P (bar) Sat. Temp (oC) hf (Kj/Kg) hg (Kj/Kg) Sg (Kj.Kg-K)
7.85 32oC 130.5 264.5 1.542
2.61 -5oC 95.4 249.3 1.557
(7 marks) 2 (b) State limitations of air refrigeration system. Explain construction and working of simple vapour compression refrigeration system with P-V,T-S and P-H diagram.(7 marks) 2 (c) Write brief note on human comfort chart.(7 marks)

Answer any two question from Q3 (a), (b) or Q3 (c), (d)

3 (a) How sub-cooling improves performance of vapour compression refrigeration cycle?(7 marks) 3 (b) What is basic principle of Vapour absorption refrigeration system? Write brief note on Electrolux(NH 3 -H 2 ) refrigerator.(7 marks) 3 (c) Explain multistage refrigeration system with intercooling between stages.(7 marks) 3 (d) Write brief note on Hermetically sealed compressor.(7 marks)

Answer any two question from Q4 (a), (b) or Q4 (c), (d)

4 (a) Explain working of steam jet refrigeration system. Also state applications, advantages and limitations of steam jet refrigeration system.(7 marks) 4 (b) Write brief note on natural refrigerants.(7 marks) 4 (c) Define following terms:
i) Saturated air
ii) Specific humidity
iii) Relative humidity
iv) Absolute humidity
v) Dry bulb temperature
vi) Dew point temperature
vii) Wet bulb depression
(7 marks)
4 (d) The sling- psychrometer reads 35°C DBT and 25°C WBT calculate followings:
(i) Specific humidity (ii) Relative humidity (iii) Absolute humidity in air (iv) Dew point temperature (v) Enthalpy of the mixture per kg of dry air.
Assume atmospheric pressure to be 1.01 bar.
(7 marks)

Answer any two question from Q5 (a), (b) or Q5 (c), (d)

5 (a) Classify air conditioning systems and enlist factors affecting comfort air conditioning.(7 marks) 5 (b) 40 m3 of air at 35°C DBT and 50% R.H. is cooled to 25°C DBT maintaining its specific humidity constant.
(i) Relative humidity (R.H.) of cooled air;
(ii) Heat removed from air.
(7 marks)
5 (c) State important applications of refrigeration system. Explain construction and working of an Ice plant.(7 marks) 5 (d) Describe different methods of duct design.(7 marks)

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