University of Mumbai 2009-1st Sem M.E Thermal Engineering Refrigeration System Design -e - Question Paper
(4 Hours) [Total Marks : 100
N.B. : (1) Question No. 1 is compulsory.
(2) Answer any four questions out of remaining six questions.
(3) Answers to all parts of a question should be written together one below the other.
(4) Assume any suitable data wherever required but Justify the same.
(5) Use of refrigeration tables arid charts, are permitted.
1. (a) An air conditioner of 1*5 TFT capacity has a powr input of 1*2 kW. Find EER (1TR = 12,000 Btu/h).
41 m
(b) A compressor operating with an SST of 15aC and a SDT of 40C delivers 100 TR when system is charged with refrigerant R 12. What will be the system capacity if the refrigerant is changed to R 22 ?
(c) A refrigeration plant using ammonia is provide 150 kW of refrigeration at -15C and 50 kW at -30C. Condensation is at + 40C The system uses 2-stage compression with intercooling. The discharge pressure of the low sage compressor and suction pressure of high stage compressor is equal to pressure in -15C evaporator. Draw a neat sktech of the system and determine the power required and COR Assume dry saturated compression and sub cooling of 5C.
10
What is meant by 'superheat horn' in a vapor compression cycle ?
(a)
(b)
2.
For a compressor with fixed displacement and condensing temperature, discuss the variation of mass flow rate and power input with change in evaporating temperature.
What is the need for purging in a refrigerant system ? Give a schematic of the system used for the same.
(c)
10
What is the need for capacity control of a compressor ? Describe any on method in detail.
3. (a) <b)
10
10
With a neat sketch explain the working of a thermostatic expansion valve. List the main advantages and disadvantages.
The power input to a compressor used in a refrigeration system with an air cooled condenser is more than that if the system had water cooled condenser. State if this statement is true or false and justify your answer.
4. (a)
(b)
(c)
Discuss the effect of fouling factor on the performance of a refrigeration system. Discuss the essential components of a cooling tower. What is meant by NTU of the tower ? What is its significance ?
4
10
What are ecofriendly refrigerants ?
5.
(a)
(b)
(c)
(a)
(b)
(c)
What materials are used to insulate cold storages ? Explain what is optimum economic insulation ?
What do you understand by pull down condition and normal condition of a refrigeration plant ?
Compare Li Br-water and aqua ammonia absorption refrigeration systems. Explain the phenomena of crystallization in a Li Br-water system. Which is the location most susceptible to crystallization ?
6.
Discuss the different types of evaporators used in refrigeration practice.
Write notes on the following
7.
20
(a) Balancing of a refrigeration system
(b) Comparison of scroll and reciprocating compressors
(c) Safety controls incorporated into a refrigeration system
(d) Refrigeration applications in a milk processing plant.
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