Refrigeration & Air Conditioning - May 2016
Mechanical Engineering (Semester 8)
TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (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.
Answer any four of the following:
1(a) Define Energy Efficiency Ratio, Write a note on star rating of BEE.(5 marks)
1(b) What are the advantages of air refrigeration for cooling of aircraft?(5 marks)
1(c) Write a note on designation of refrigerants.(5 marks)
1(d) Explain in brief an adiabatic saturation process. Represent the same on a Psychometric chart.(5 marks)
1(e) What is the function of a flash inter-color? Why it is not preferred for R-12 refrigerant.(5 marks)
1(f) Discuss the static regain method of duct design.(5 marks)
2(a) Derive an expression for COP of an ideal Bell Coleman cycle in terms of pressure ratio.(4 marks)
2(b) An airplane using 20 TR bootstrap air refrigeration system has ambient conditions of 0.9 bar and 15°C. Ram air pressure after isentropic compression is 1.1 bar. Main compressor exit pressure is 3.5 bar, and exit pressure of secondary compressor is 4.5 bar. The carbine is required to be maintained at 1 bar and 25°C. Isentropic efficiency of each compressor is 85% and that of cooling turbine is 90%. The effectiveness of both heat ex-changers is 60%. Find
(i) Mass flow rate of air passing through the carbine (ii) Power required, (iii) COP of the system. Assume Cp=1.01 kJ/kg K.(12 marks) 2(c) Discuss the effect of evaporator and condenser pressure on the performance of a Vapour Compression Refrigeration System.(4 marks) 3(a) Define bypass factor of a cooling coil. What are the factors affecting it?(4 marks) 3(b) Explain with a block diagram the working of a practical Ammonia Water vapor absorption refrigeration system.(6 marks) 3(c) A refrigeration machine using R-12 as refrigerant operates between the pressures 2.5 bar and 9 bar. The vapor entering the compressor is dry saturated and there is no sub-cooling in the condenser. If the capacity of the plant is 20 TR and the relative COP is 6.5%.
Determine: i) Actual COP, ii) Actual power input to the compressor.
Properties of the refrigerant are given below:
|Sp.Enthalpy, kJ/kg||Sp. Enthalpy, KJ/kg K|
Outside air conditions = 40°C DBT and 50% RH, Inside design conditions = 26°C DBT and 50% RH, Apparatus Dew Point = 10°C; By-pass factor of the cooling coil = 0.2
The return air from the room is mixed with the outside air before entry to the cooling coil in the ratio of 3 : 1 by mass. If 20 m3/min of fresh air is supplied find:
(i) Condition of air leaving the coil
(ii) Capacity of cooling coil in TR
(iii) Room sensible heat factor.(14 marks)
Write short notes on any four of the following
6(a) Types of cooling tower.(5 marks) 6(b) Methods of defrosting.(5 marks) 6(c) Thermoacoustic refrigeration.(5 marks) 6(d) Variable refrigerant flow systems.(5 marks) 6(e) Liquefaction of Natural Gas (LNG).(5 marks) 6(f) Deep sea air conditioning(5 marks)