Maharashtra State Board of Technical Education 2007 Diploma Mechanical Engineering Refrigeration & Air Conditioning - Question Paper

Refrigeration & Air Conditioning
Third Year : 2007
2 Hr / 50 Marks

Instructions:

1. All ques. are compulsory.
2. Illustrate your answers with neat sketches wherever necessary.
3. Use of Blockpatterns, Psychrometric Chart, Mathematical and Steam Tables, Non-Programmable Electronic Pocket Calculator and Mollier's Charts is

permissible.
4. Figures to the right indicate full marks.
5. presume suitable additional data, if necessary.


1. a) Solve any 5 of the following: [Marks: 10]

i) describe ton of refrigeration.

ii) What is psychrometric chart?

iii) Show Bell-Coleman Cycle on PV-TS diagrams.

iv) What is the difference ranging from refrigerator and heat pump?

v) What is the wet bulb temperature?

vi) What is evaporative cooling?

vii) What is meant by year-round air conditioning?


b. Solve any 1 of the following: [Marks: 4]

i) discuss vapour compression refrigeration system with the help of PV-TS diagram.

ii) What is hermetic sealed compressor? discuss its importance in the system over open kind compressor.


2. Solve any 3 of the following: [Marks:12]

a) discuss the working of electrolux refrigeration with suitable diagrams.

b) elaborate the desirable properties of ideal refrigerant with respect to thermodynamic and safe working properties?

c) What is frosting and defrosting of evaporators? discuss the importance of defrosting.

d) discuss the working of over load protector. Where it can be located in the circuit?

e) describe the following:

i) Degree of saturation
ii) By-pass factor of the coil


3. a) Solve any 1 of the following: [Marks:4]

i) Show subsequent processes on psychrometric chart:

1. Sensible heating
2. Cooling with dehumidification

ii) Define:

1. Relative humidity
2. Enthalpy of moist air


b) Solve any 1 of the following: [Marks:8]

i) A cold storage room has walls made of 0.23 m of brick on the outside, 0.08 m of plastic foam and finally 15 mm of wood on the inside. The outside and

inside temperatures are 22°C and -2°C respectively. If the inside and outside heat transfer co-efficient are 29 and 12 w/m²°k respectively and thermal

conductivities of brick, foam and wood are 0.98, 0.02 and 0.17 w/m°k respectively. Determine rate of heat removal by refrigeration per unit area of wall.

ii) discuss the working of thermostatic expansion valve.


4. Solve any 3 of the following: [Marks:12]

a) With a neat sketch discuss the working of a flooded evaporator.

b) Differentiate ranging from primary and secondary refrigerant.

c) Sketch and discuss the working of evaporative condenser.

d) elaborate the kinds of insulating material used in regrigeration and air conditioning applications. Mention their desirable properties?

e) Write a note on grills and registers.

Earning:   Approval pending.