a) What are the advantages and disadvantages of steam jet refrigeration system over other types of refrigeration system [6] b) A steam jet refrigeration system is to supply 1200 kg

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IV B.Tech I Semester Supplementary Examinations, Feb/Mar - 2015

REFRIGERATION & AIR CONDITIONING

(Mechanical Engineering)

Time: 3 hours Max. Marks: 75

Answer any FIVE Questions

All Questions carry equal marks

*****

1 a) Explain the following terms

i) Refrigeration effect ii) Ton of refrigeration iii) C.O.P [6]

b) With a neat sketch explain the working of Bell Colemann cycle and derive the

expression for COP [9]

2 a) Distinguish between Dry and Wet compression in vapour compression

refrigeration system. [6]

b) A vapour compression refrigerator works betweenthe pressure limits of 60 bar

and 25 bar. The working fluid is just dry at the end of the compression and

there is no under cooling of the liquid before the expansion valve. Determine:

i) C O P of the cycle and

ii) Capacity of the refrigerator if the fluid flow is at the rate of 5 kg/min.

Data:

Pressure

(Bar)

Saturation

Temp. (K)

Enthalpy (kJ/kg) Entropy (kJ/kg – K)

Liquid vapour Liquid vapour

60 295 151.96 293.29 0.554 1.0332

25 261 56.32 322.58 0.226 1.2464 [9]

3 a) Explain the role of refrigerants in the depletion if ozone layer [7]

b) With a neat sketch explain the working of thermostatic expansion valve [8]

4 a) With a neat sketch explain the working of a simple absorption refrigeration

system [7]

b) In absorption refrigeration system, heating, cooling, and refrigeration take place

at the temperatures of 1500C, 30

0C, and -20

0C. Find the theoretical COP of the

system. If the heating temperature is increased to 2000C and refrigeration

temperature is decreased to -400C, find the percentage change in the theoretical

COP. [8]

Code No: R41031 Set No. 1 R10

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5 a) What are the advantages and disadvantages of steam jet refrigeration system

over other types of refrigeration system

[6]

b) A steam jet refrigeration system is to supply 1200 kg per minute of chilled

water at 6.50C. The make up water from the mains is at 27

0C. If the steam

supply is available at 9.5 bar and 2000C and nozzle, entrainment and diffuser

efficiency can be assumed as 89%, 63% and 72% respectively, the quality of

vapour entering the ejector may be assumed 0.98, and condensate leaves the

condenser at 330C. Determine:

i) Steam consumption in kg/hour and kg/hr per ton of refrigeration

ii) Heat rejected in the condenser in kJ/hr and kJ/hr per ton of refrigeration

[9]


i) Wet bulb temperature ii) Dry bulb temperature

iii) Degree of saturation iv) Relative humidity

[8]

b) 400 m3/min of air at 20

0C DBT and 10

0C DPT coming out from air conditioned

hall is mixed with 150 m3/min of fresh air at 35

0C DBT and 45% relative

humidity. Find a) enthalpy b) specific humidity c) specific volume d) DPT of

the mixture

[7]

7 a) Explain the requirements of comfort air conditioning [6]

b) Air flowing at the rate of 100 m3/min at 40

0C DBT and 50% RH is mixed with

another stream flowing at the rate 20 m3/min at 26

0C DBT and 50%RH. The

mixture flows over a cooling coil whose ADP temperature is 100C and by-pass

factor is 0.2. Find DBT and RH of air leaving the coil. If this air

supplied to an air-conditioned where DBT of 260C and RH of 50% are

maintained, estimate (i) Room sensible heat factor and (ii) Cooling load

capacity of the coil in tones of refrigeration.

[9]

8 a) With a neat sketch explain the working of a bag type filter [7]

b) With a neat sketch explain the working of a impact type humidifier [8]


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i) Heat Pump ii) C.O.P

[6]

b) In simple air refrigeration system the regenerative cooling reduces the

temperature of air from the heat exchanger by 200 C before it expands through

the cooling turbine. The air leaves the cabin at 270 C and the ram air

temperature is 150 C. Obtain the amount of air bled from the refrigeration and

COP. If 0.5 Kg/s of air from the main compressor is used for the air

conditioning. Calculate the power requirement and tonnage of the system. Take

Pamb= 0.8 bar, Pram= 1 bar, efficiency of compressor = 0.8, efficiency of turbine

= 0.8, heat exchanger effectiveness is 0.75. The cool air leaves the regenerative

heat exchanger at 270 C

[9]

2 a) Explain the effects of sub cooling and super heating on the performance of a

vapour compression refrigeration system

[7]

b) An ammonia ice plant operates between a condenser temperature of 300C and

an evaporator temperature of -200C. It produces 10 tons of ice per day from

water at 250C to ice at -10

0C. Assuming simple saturation cycle, determine i)

the capacity of refrigerating plant ii) mass flow rate of refrigerant and iii) COP

of the cycle.

[8]

3 a) Explain the desirable properties of ideal refrigerants. Write the properties of

carbon dioxide refrigerant

[8]

b) Write the advantages and disadvantages of centrifugal compressor over

reciprocating compressor

[7]

4 a) With a neat sketch explain the working of Li-Br absorption refrigeration

system

[8]

b) In a vapour absorption refrigeration system, the refrigeration temperature is -

150C. The generator is operated by solar heat where the temperature reached is

1000C. The temperature of the heat sink is 55

0C. What is the maximum

possible COP of the system?

[7]

Code No:R41031 Set No. 2 R10

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5 a) With a neat sketch explain the working of steam jet refrigeration system [8]

b) With the help of graphs explain how the performance of steam jet refrigeration

system is affected varying the evaporating and condensing temperatures.

[7]

6 a) Explain the following i) comfort chart.

ii) Zone of comfort for year round air conditioning. iii) Bypass factor

[7]

b) Air at 370C, 44 percent relative humidity, is cooled to 23

0C by spraying water

at 130C into it. The mixture pressure remains constant at 101.3 kPa. Assuming

that all of the water evaporates and that the mixing occurs in an insulated duct,

calculate the mass of water added per kilogram of air.

[8]

7 a) Explain the factors governing optimum effective temperature [6]

b) An air-conditioned building has a space volume of 1000 m3 and a room

sensible heat gain of 20 kW. The room is maintained at 250C DBT and 50%

RH. The outside design conditions are 430C DBT and 26.5

0C WBT. The

ventilation air is 20% of the supply air.The apparatus dew point of the coil is

110C and its bypass factor is 0.1. Determine:

i) The state and mass flow rate of the supply air

ii) The latent heat gain of the room

iii) The cooling load of the refrigeration plant

[9]

8 a) Differentiate between central, district and Unitary air-conditioning systems [7]

b) With a neat sketch explain the working of a forced evaporation humidifier [8]


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1 a) What are the advantages of dense air refrigeration system over an open

air refrigerating system

[6]

b) A simple air cooled system is used for an aero plane to take a load of 10 tons.

Atmospheric temperature and pressure is 25°C and 0.9 atm respectively. Due

to ramming the pressure of air is increased from 0.9 atm, to 1 atm. The pressure

of air leaving the main compressor is 3.5 atm and its 50% heat is removed in

the air-cooled heat exchanger and then it is passed through a evaporator for

future cooling. The temperature of air is reduced by 10°C in the evaporator.

Lastly the air is passed through cooling turbine and is supplied to the cooling

cabin where the pressure is 1.03 atm. Assuming isentropic efficiency of the

compressor and turbine are 75% and 70%,

find i) Power required to take the load in the cooling cabin

ii) COP of the system.

The temperature of air leaving the cabin should not exceed 25°C

[9]

2 a) Explain in detail all the four methods to improve the COP of a vapour

compression refrigeration system

[8]

b) Under what circumstances the superheating of vapour before coming to

compressor is more objectionable? Mention the ways to prevent it.

[7]

3 a) Explain the role of refrigerants in global warming [7]

b) Explain the role of a condenser in a refrigeration system. With a neat sketch

explain the working of evaporative condenser

[8]


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4 a) With a neat sketch explain the working of triple fluid absorption refrigeration

system. Write its salient features

[7]

b) In an absorption type refrigeration system, the heat supplied to NH3 generator

by condensing steam at 2 bar and 0.9 dry. The temperature to be maintained in

the refrigerator is -50C. The temperature of the atmosphere is 30

0C. Find the

maximum COP possible for the system. If the refrigeration load is 20 tons and

actual COP is 70% of max COP, Find the mass of steam required per hour.

[8]

5 a) Derive the expression for finding the quantity of steam required per ton of

refrigeration in a steam refrigeration system

[8]

b) With a neat sketch explain the working of Vortex tube refrigerator.

[7]

6 a) Define the term effective temperature and explain its importance in air

conditioning system. Describe the factors which affect effective temperature.

[7]

b) 180 m3 of air at 40

0C DBT and 15% relative humidity is passed through an

adiabatic cooling pad and it comes out at 250C DB and 20

0C WBT. Find

i) DPT of the air coming out

ii) amount of water vapour added into the air per minute.

[8]

7 a) Discuss the requirements of industrial air-conditioning [6]

b) A big hall with 1200 seating capacity is to be air conditioned when outdoor

condition is 390C DBT and 20

0C WBT. The required inside condition is 20

0C

DBT and 60% Relative humidity. The outdoor air supplied is 0.3

m3/min/person. The required condition is achieved first by adiabatic

humidification and then by cooling. Determine

i) capacity of cooling ii) capacity of humidifier

[9]

8 a) What are the different Heat pump circuits? Explain any one of them with the

help of neat sketch

[7]

b) With a neat sketch explain the working of a mechanical separator humidifier [8]


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1 a) The COP of air refrigeration system is very low, even then why air

refrigeration system is most common in the aircraft. Explain?

[6]

b) An air refrigerator working on the principle of Bell-Coleman cycle. The air

enters into the compressor 1 atm at -10ºC. It is compressed to 10 atm and

cooled to 40ºC atthe same pressure. It is then expanded to 1 atm and discharged

to take cooling load.The air circulation is 1 kg/s.

The isentropic efficiency of the compressor = 80%

The isentropic efficiency of the expander = 90%

Find the following:

i) Refrigeration capacity of the system

ii) C.O.P of the system

Take γ = 1.4, Cp = 1.00 kJ/kg ºC

[9]

2 a) List out the advantages of vapour compression refrigeration system over air

refrigeration system.

[6]

b) With a neat sketch explain the working of a simple vapour compression

refrigeration system and derive the expression for COP.Also indicate the

processes on a T-S diagram

[9]

3 a) How are refrigerants classified? Explain the properties of ammonia refrigerant. [7]

b) Explain the role of an evaporator in a refrigeration system? With a neat sketch

explain the working of a flooded type evaporator

[8]

4 a) Write the advantages of absorption refrigeration system over compression

refrigeration system.

[6]

b) In absorption refrigeration system, the heating in generator is carried out by

using steam at 3 bar and 85% dry. The refrigeration temperature is – 100C. the

condensation of the refrigeration is carried out at 300C using cooling water.

Determine i) maximum possible COP of the system ii) if the steam leaves the

generator as saturated water at same pressure, determine the quality of steam

required to run a plant of 20 tons. Assume relative COP as 0.4.

[9]


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5 a) With a neat sketch explain the working of steam jet refrigeration system with

barometric condenser.

[7]

b) The following data is collected for steam jet refrigeration system

Steam condition supplied to nozzle = 7 bar and 0.95 dry

Flash chamber (evaporator) water temperature = 40C

Temperature of makeup water to flash chamber = 170C

Pressure in condenser = 0.6 bar

Nozzle, entrainment and compressor efficiency can be assumed as90%, 60%

and 70% respectively

Determine the following

i) Mass flow of steam / Kg of flash vapour

ii) Refrigeration capacity in TOR/Kg of flash vapour

iii) mass of steam/TOR

iv) Volume flow rate of vapour leaving flash chamber/TOR

[8]

6 a) Explain how psychometric chart is prepared [6]

b) The air-handling unit of an air-conditioning plant supplies a total of 4000

m3/min of dry air which comprises by weight 25% fresh air at 40

0C DBT and

250C WBT, and 75% recirculated air at 23

0C DBT and 50% relative humidity.

The air leaves the cooling coil at 120C saturated state. Calculate the total

cooling load and room heat gain

[9]

7 a) Define the term comfort factor as used for cooling coils and explain under what

conditions it remain constant

[7]

b) What are the different loads to be considered to estimate the total cooling load

in the design of air-conditioning systems? Discuss in detail each of these loads

and give the design procedure considering various parameters

[8]

8 a) What are the different methods of humidifying the air? Explain the working of

any one of the atomizing the water type humidifier

[8]

b) With a neat sketch explain the working of a coil type dehumidifier [7]


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a) What are the advantages and disadvantages of steam jet refrigeration system over other types of refrigeration system [6] b) A steam jet refrigeration system is to supply 1200 kg

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