SPPU Mechanical Engineering (Semester 8)
Refrigeration & Air Conditioning Equipment Design
April 2017
Total marks: --
Total time: --
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Solve any one question from Q.1(a,b) &Q.2(a,b)
1(a) Explain in detail the commercial refrigeration system used for ice plant.
5 M
1(b) A vapour compression refrigeration system works between the pressures of 4.98 bar and 1.86 bar. The vapour is superheated at the end of compression, its temperature being 25°C. The liquid is sub cooled to 9°C before throttling. The vapor is 95% dry before compression. Using the data given below find COP of the refrigerator. The specific heat at constant pressure of superheated vapor is 0.65kJ/kgK and that of liquid is 0.97 kJ/kgK.
Pressure(bar) Termp(°C) hf(kJ/kg) hfg(kJ/kg)
4.98 14.45 49.22 148.3
1.86 -15 21.74 162
5 M

2(a) Explain how practical VCC deviates from simple saturated VCC.
6 M
2(b) What is the necessity of multi-pressure systems? Name the commonly used multipressure systems.
4 M

Solve any one question from Q.3(a,b) & Q.4(a,b)
3(a) Explain the use following components in vapour compression system:
i) Accumulator; ii) Receiver;
iii) Filter/dryer; iv) liquid suction heat exchanger
4 M
3(b) Adense air refrigerating system operating between pressure of 17.5 bar and 3.5 bars is to produce 10 tonnes of refrigeration. Air leaves the refrigerating coils at -7°C and it leaves the air cooler at 15.5°C. Neglecting losses and clearance, calculate the net work done per minute and the COP. For air Cp = 1.005 kJ/kgK and γ=1.4.
6 M

4(a) Discuss ODP, GWP and LCCP or refrigerant.
6 M
4(b) Find out the generator temperature for an absorption system having evaporator and absorber temperature as 250 K and 310 K respectively. Maximum C.O.P is to be 1.30. If the saturated steam is supplied at a temperature 15K above the generator temperature, what is the steam pressure?
4 M

Solve any one question from Q.5(a,b) & Q.6(a,b)
5(a) Moist air at saturated atmospheric pressure is passed over a cooling coil. The inlet state -DBT 30°C. RH 50% and exit state-DBT 15°C,RH=90%. Show the process on psychrometric chart. Determine the amount of heat and moisture removed per kg of dry air.
6 M
5(b) Calculate; 1 Relative humidity 2. Humidity ratio 3. Dew point temperature 4. Density 5. Enthalpy of atmospheric air when the DBT is 35°C, WBT is 23°C and barometer reads 100kPa.
10 M

6(a) Derive an expression for specific humidity and show that it is function of vapour pressure and barrometric pressure of air.
6 M
6(b) A building has the following calculated cooling loads:
RSH gain = 310 kW, RLH gain = 100kW
The space is maintained at the following conditions:
Room DBT = 25°C and 50% RH. And 10% of mass of air supplied to the building is outdoor air. If the air supplied to the space is not to be at a temperature lower than 18°C Find.
i) Minimum amount air supplied to space in m3/s
ii) Volume flow rates of return air, exhaust air and outdoor air
iii) State and volume flow rate of air entering the cooling coil
iv) Capacity ADP, BPF and SHF of cooling coil.
10 M

Solve any one question from Q.7(a,b,c) &Q.8(a,b,c)
7(a) State the factors which should be taken into consideration while selecting a system of air conditioning.
6 M
7(b) Explain the following control devices.
i) Thermostats ii) Automatic humidity control
8 M
7(c) Enumerate the functional elements of control unit.
4 M

8(a) Explain briefly the following types of reciprocating compressors:
i) Semi sealed type ii) Hemetically sealed type
6 M
8(b) Give the main types of codensers with specific application of each type.
6 M
8(c) Explain Flooded type evaporator with neat sketch.
6 M

Solve any one question from Q.9(a,b) Q.10(a,b)
9(a) Define the following as applied 'Air distribution'. Intake, Outlet, Grille, Register, Diffuser, Throw, Drop and Primary air
12 M
9(b) The main supply air duct of an air-conditioning system is 100cm×90cm in cross section and carries 10m3/s of air. It branches off in to two ducts, 80cm×80cm and the 80cm×80cm. If the mean velocity in the larger branch is 9m/s, find the mean velocity in the larger branch is 9m/s, find the mean velocities in the main duct and smaller branch.
6 M

10(a) Explain any two of the following air distribution system:
i) Ejector system
ii) Downward system
iii) Upward system
8 M
10(b) A centrifuagal fan with 90cm X70cm outlet is moving standard air at a rate of 11.5m3/s through a system which consists of straight inlet and outlet ducts. The inlet duct is 90cm in diameter and 15m long. The outlet duct is 100cm in diameter and 60m long. There is a fan diffuser between the fan discharge and the 100cm diameter duct for which thepressure loss is one third the difference in velocity pressures. The pressure drop at the filter, damper and cooling coil (AC apparatus) in the inlet duct is 150 Pa. The loss at the entry to the inlet0.5× velocity pressure. The friction factor for the outlet duct is 0.0035 and that for the inlet duct is 0.004. Determine the fan total pressure. The air is sucked in by the inlet duct and delivered by the outlet at atmospheric pressure.
10 M

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