Mechanical Engineering III Yr B.Tech -II Sem

Refrigeration and Air Conditioning Question Paper for JNTUH

Unit I Air Refrigeration

1. What are the Advantages and Disadvantages of Air Refrigeration System?An air refrigerator works between pressure limits of 1 and 4 bar. The temperature of the air entering the compressor is 15oC and entering the expansion cylinder is 300C.The expansion follows the law PV 1.25 = constant.Take for air CP = 1 kJ/kg K and CV = 0.7 kJ/kg K. Find the following:(a) COP of the refrigerating cycle.(b) If the air in circulation through the system is 25 kg/ min, find the refrigeration capacity of the system.

2. 20 m3 of air per minute at 30oC and 60% RH is cooled to 22oC DBT maintaining specific humidity constant. Find the following:(a) Heat removed from air(b) R.H. of cooled air(c) WBT of the cooled air.Take air pressure = 1 bar.

Unit II Vapour Compression Refrigeration

3. What is sub cooling and super heating? Explain with the help of a diagram. Why is super heating considered to be good in certain cases?(b) A refrigerating unit is working between 40oC and –10oC. The load on the unit is 5 tons. Find:(i) COP of the system(ii) Power required to run system.Assume that the refrigerant is dry and saturated vapour leaving the evaporator and compression is isentropic. The refrigerant used is MHzIf the temperature of the refrigerant required in the evaporator is –20oC, then, find the change in COP of the system and the power required.

Unit III Principle of Evaporators & Refrigerants

4. What is Refrigerant? Briefly Discuss the desirable properties of a refrigerant. Explain. What are Primary and Secondary Refrigerants?

Unit IV Vapour Absorption System

5. Draw a neat diagram of lithium bromide water absorption system and explain its working. List the major field application of this system.

Unit V Steam Jet Refrigeration System

6. Write Short Notes on

a) Vertex Tube Refrigeration

b) Industrial Refrigeration-classical Industry

c) Inter Cooling

Unit VI Air Conditioning

7. The following are the design data for an air conditioning system prepared for a restaurant:Outdoor condition = 34o DBT and 28oDBTIndoor condition = 24o DBT and 50 RHSolar heat gain through walls roof and floor = 4.4 kWOccupants = 25Sensible heat gain per person = 85 WLatent heat gain per person =105 WInternal lighting load = 15 lamps of 100 watts capacity eachplus 10 fluorescent fixtures of 80 W each.Sensible heat gain from other sources = 11.6 kWInfiltration air = 14 m3 /minCoil by pass factor = 0.15If the return and outdoor are adiabatically mixed in the ratio 3:2 (by bass) and then passed through the conditioner: determine:(a) dry bulb temperature and wet bulb temperature of supply air(b) apparatus, dew point(c) capacity of the air –conditioning plant.

Unit VII Requirements of Human Comfort

8. What are Human Comfort Conditions? Discuss thermodynamics of Human Body in detail. Explain briefly the term Body Defence.