REFRIGERATION & AIR CONDITIONING PAPER 2

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REFRIGERATION AND AIR CONDITIONING ME 304 6th Sem May 2K5

Note: Section A is compulsory. Attempt any four questions each carrying 5 marks from section B and any two each carrying 10 marks from section C.

Section A (10 x 2 = 20)

I (a) Define one ton of refrigeration
(b) Write four important applications of refrigeration.
(c) Write four important applications of air-conditioning
(d) Define COP of a heat pump. Also mention where heat pump is used.
(e) Define compressor capacity.
(f) Explain an Azeotrope. Give one practical azeotrope being used in refrigeration.
(g) Explain sensible heat. Where does it exist in refrigeration?
(h) Explain with a neat sketch Dry and Wet compressions.
(i) Explain the difference between Linde’s and Claude methods of air liquefaction.
(j) Name at least two non-conventional methods of refrigeration with their salient features.

Section B (4 x 5 = 20)

II Explain Primary, Secondary and Tertiary refrigerants. Indicate at least one practical application of each type of refrigerant.

III Compare vapor compression and vapor absorption refrigeration systems. Indicate which one is more preferable and why?

IV A simple saturation cycle using F-12 is designed for taking a refrigeration load of 10 tons. The refrigerator and ambient temperatures are 0 oC and 30 oC respectively. A minimum temperature difference of 5 oC is required in the Evaporator and condenser for heat transfer. Find (i) Mass flow rate through the system, (ii) Power required in kW (iii) Cylinder dimensions assuming L/D ratio as 1.2 for a single cylinder, single acting compressor if it runs at 300 rpm with volumetric efficiency of 0.9

V A cascade refrigeration system is desired to supply 20 tons of refrigeration at evaporator temperature of - 50 oC. The load at - 50 oC is absorbed by a unit using F -22 as the refrigerant and is rejected to the cascade condenser at -10 oC. A unit using F-12 as the refrigerant cools the cascade condenser. The heat transfer in the cascade condenser takes place with 15 oC temperature difference. The F-12 is condensed at 40 oC by using atmospheric water at 25 oC also sub-cooled by 5 oC in that condenser.
Assuming refrigerants leave both evaporators dry and saturated and compressions are isentropic, determine COP of the system.

VI Differentiate between comfort and industrial air-conditioning. Give at least two practical applications of each.

Section C (2 x 10 = 20)

VII Explain with a neat labeled sketch the Electolux refrigeration system. Also write in brief the Global Warming and Ozone Depletion Potentials.

VIII A dense air refrigeration machine operating on Bell-Coleman Cycle operates between 3.4 bars and 17 bars. The temperature of the air after the cooler is 15 oC and after the refrigerator is 6 oC. For a refrigeration capacity of 6 tons, find

1. Temperatures after the compression and expansion
2. Air circulation required in the cycle per minute.
3. COP
4. Rate of water circulation required in the cooler in kg/min if the rise in temperature is limited to 30 oC.

IX An ammonia vapor compression system uses one compressor with individual expansion valves and back pressure valves. The condenser temperature is 35 oC. There are two evaporators having loads of 5 tons at - 25 oC and 3 tons at - 5 oC. There is no under cooling of the liquid and vapor leaving each evaporator is saturated condition. Draw neat labeled sketch of the required components and find the COP of the system