Refrigeration and Air Conditioning - May 2014
Mechanical Engineering (Semester 7)
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.
Attempt any four.
1 (a) Define WBT, DBT, DPT, RH and ADP(5 marks)
1 (b) Explain working of simple air refrigeration cycle and represent the same on T-s chart(5 marks)
1 (c) How are refrigeration classified?(5 marks)
1 (d) To what do you attribute the rapid growth of refrigeration technology over the last century?(5 marks)
1 (e) What is effective temperature? Which are the factors governing effective temperature?(5 marks)
2 (a) Explain the working of thermostatic expansion valve(8 marks)
2 (b) Explain the working of simple vapour compression cycle with schematic and P-h diagram.(6 marks)
2 (c) Explain split air conditioning system and enlist its advantages and disadvantages.(6 marks)
3 (a) A bootstrap cooling system of 35 T is required for an aircraft. Temperature and pressure of the atmosphere is 18 C and 0.75 bar. Pressure of air is increased 0.75 bar to 0.92 bar due to ramming. Pressure of air leaving the main compressor and auxiliary are 3.2 and 5.4 bar respectively. Isentropic efficiency of both compressors is 84% and of turbine is 81%. Heat removed from air leaving the compressors is 60% in the first heat exchanger and 34% in the second heat exchanger which is after auxiliary compressor. Assuming ramming to be isentropic and cabin pressure 1.03 bar, find Power required to take cabin load and COP of the system. Temperature of the air leaving the cabin is 28 C(15 marks)
3 (b) Explain in detail working of commercial Ice Plant.(5 marks)
4 (a) A vapour compression system using R134A works between -10 C and 36 C as evaporator and condenser temperature respectively. Using P-H chart determine
ii) Mass flow of refrigerant per TR
iii) Piston displacement per TR using volumetric efficiency=83%
iv) Heat rejected in the condenser per TR
v) Ideal COP(12 marks) 4 (b) Draw a neat diagram of Aqua-Ammonia absorption system and explain its working. List the major field applications of this system.(8 marks) 5 An air conditioning system is to be designed for a restaurant with the following data
|i||Outside design conditions||39 C DBT, 28 C WBT,|
|ii||Inside design conditions||25 C DBT, 50% RH,|
|iii||Solar heat gain through glass||5.52 kW|
|iv||Solar heat gain through walls, roof and floor||5.87 kW|
|vi||Sensible heat gain per person||57 W|
|vii||Latent heat gain per person||57 W|
|viii||Internal lighting load||10 lamps of 100 W|
|7 lamps of 60W|
|9 fluorescent tubes of 40 W|
|ix||Infiltrated air||15 CMM|
if 25 % fresh air and 75 % re-circulated air is mixed and passed through the conditioner coll, find
i) The amount of total air required in m3/hr
ii) The DDT of the coil
iii) The condition of supply air to the room
iv) The capacity of conditioning plant. Assume BPF = 0.2.(20 marks) 6 (a) What do you mean by comfort charts and how they are used ?(6 marks) 6 (b) What do you mean by load on refrigeration and air conditioning system and how its calculations are made?(6 marks) 6 (c) State the effect and causes of moisture. In refrigerant of refrigeration system. How can it be removed from the system?(8 marks)
Write short notes (any four)
7 (a) Dry Ice and its applications(5 marks) 7 (b) Multistage VCRS(5 marks) 7 (c) Noise and its control in A/C system(5 marks) 7 (d) Duct designing(5 marks) 7 (e) Human comfort and Air-conditioning(5 marks)