BHARATHIDASAN ENGINEERING COLLEGE, NATTRAMPALLI – 635854.

DEPARTMENT OF MECHANICAL ENGINEERING

ME 6404 – THERMAL ENGINEERING

QUESTION BANK

UNIT I - GAS POWER CYCLES

PART-A

1. State any 4 major difference between Otto cycle and diesel cycle. (Dec. 2016)

2. When compression ratio is kept constant, what is effect of cut off ratio on the efficiency of diesel

cycle? (Dec. 2015)

3. Differentiate any 4 major difference between otto and diesel cycle. (Dec. 2015)

4. What are the assumptions made in air standard cycles? (May 2015) (June 2016) (Dec. 2016)

5. Draw the Otto cycle on the p-v and t-s diagrams.

6. Draw the Diesel cycle on the p-v and t-s diagrams.

7. Draw the Dual cycle on the p-v and t-s diagrams.

8. Draw the Brayton cycle on the p-v and t-s diagrams. (May 2015)

9. For same compression, compare the efficiency of Otto, diesel and Dual Cycles.

10. Draw the actual p-v diagram of the 2 stroke engine. (Dec. 2014)

11. What is meant by mean effective pressure? (Dec. 2014)

12. What is an air standard efficiency? (May 2014)

13. Define a) compression ratio b)cut-off ratio. (May 2014)

14. For a given compression ratio the otto cycle is more efficient than diesel cycle. Justify? (Dec. 2013)

15. What is meant by mean effective pressure? Show that on a p-v diagram.(Dec. 2013) (June 2016)

16. Define the terms actual thermal efficiency and relative efficiency. (Dec. 2012)

17. What is an air-standard cycle? Why such cycles are conceived? (Dec. 2012)

PART-B

1. In a gas turbine plant working on the Brayton cycle the air at the inlet is at 27oC, 0.1 MPa. The

pressure ratio is 6.25 and the maximum temperature is 800oC, the turbine and compressor

efficiencies are each 80%. Find (i) the compressor work per kg of air (ii) the turbine work per kg

of air (iii) the heat supplied per kg of air (iv) the cycle efficiency, and (v) the turbine exhaust

temperature. (Dec. 2016)

2. The compression for a single-cylinder engine operating on dual cycle is 9. The maximum pressure

in the cylinder is limited to 60 bar. The pressure and temperature of the air at the beginning of the

cycle are 1 bar and 30oC. Heat is added during constant pressure process upto 4% of the stroke.

Assuming the cylinder diameter and stroke length as 250mm and 300mm respectively. Determine:

(i) The air standard efficiency of the cycle, (ii) the power developed if the number of working cycles

is 3 per second. (June 2016)

3. The swept volume of a diesel engine working on dual cycle is 0.0053m3 and clearance volume is

0.00035m3. The maximum pressure is 65 bar. Fuel injection ends at 5% of the stroke. The

temperature and pressure at the start of the compression are 80oC and 0.9 bar. Determine the air

standard efficiency of the cycle. Take γ for air as 1.4. (June 2016) (Dec. 2016)

4. Fuel supplied to an SI has a calorific value 42000kJ/kg. The pressure in the cylinder at 30% and

70% of the compression stroke are 3bar and 2.6bar respectively. Assuming that the compression

follows the law pv1.3 = constant. Find the compression ratio. If the relative efficiency of the engine

compared with the air standard efficiency is 50%. Calculate the fuel consumption in kg/kWh. (Dec.

2015)

5. An air standard dual cycle has a compression ratio of 10. The pressure and Temperature at the

beginning of the compression are 1bar and 27oC. The maximum pressure reached is 42 bar and

maximum temperature is 1500oC. Determine (i) the temperature at the end of constant volume heat

addition (ii) cut off ratio (iii) work done per kg of air (iv) cycle efficiency. (Dec. 2015)

6. An engine with 200mm cylinder diameter and 300mm stroke works on theoretical diesel cycle. The

initial pressure and temperature of air used are 1bar and 27oC. The cut off if 8% of the stroke.

Determine (i) the pressure and temperature at all salient points (ii) theoretical air standard efficiency

(iii) mean effective pressure (iv) Power of the engine if the working cycles per minute are 380.

Assume that compression ratio is 15 and working fluid is air. (May 2015)

7. Air enters the compressor of the gas turbine plant operating on Brayton cycle at a1bar, 27oC. The

pressure ratio in the cycle is 6. If WT =2.5 x WC. Calculate the maximum temperature and the cycle

efficiency. (May 2015)

8. An engine works on Otto cycle. The initial pressure and temperature of the air 1bar and 40oC. 825

kJ of heat is supplied per kg of air at the end of the compression. Find the temperature and pressure

at all salient points if the compression ratio is 6. Also find the efficiency and mean effective pressure

for the cycle. Assume air is used as working fluid and take all ideal conditions. (Dec. 2014)

9. A Gas turbine works on an air standard brayton cycle. The initial condition of air is 25oC and 1bar.

The maximum pressure and temperature are limited to 3bar and 650oC. Determine the following i)

cycle efficiency ii) heat supplied and rejected per kg of air iii) work output iv) exhaust temperature.

(Dec.

2014)

10. An air standard diesel cycle Hs compression ratio of 8 and heat transferred to the working fluid is

1800KJ/kg. The pressure and temperature at the beginning of the compression stroke are 1bar and

300K respectively. Calculate i)the pressure and temperature of each point of the cycle. ii) the air

standard efficiency iii) mean effective pressure. (May 2014)

11. Derive an expression for an air standard efficiency of dual combustion cycle. (May 2014)

12. An air standard diesel cycle has a compression ratio of 18. The pressure at the beginning of the

compression stroke is 1bar and the temperature is 30oC. The heat supplied is 1800kJ/kg. Determine

i) The efficiency ii) pressure and temperature at the salient points iii) heat rejected iv)mean

effective pressure.

(Dec. 2013)

13. An Otto cycle has a compression ratio of 7. The initial pressure and temperature at the beginning

of compression stroke is 1bar and 40oC. The heat supplied is 2510kJ/kg. Find i) the maximum

temperature and pressure ii) work done per kg of air iii) the cycle efficiency iv)mean effective

pressure. (Dec. 2013)

14. A spark ignition engine working on ideal otto cycle has the compression ratio 6. The initial pressure

and temperature of air are 1 bar and 37oC. The maximum pressure in the cycle is 30bar. For unit

mass flow, calculate (i) p,V and T at various salient points of the cycle and (ii) The ratio of heat

supplied to the heat rejected. (Dec. 2012)

15. An air standard dual cycle has a compression ratio of 18, and compression begins at 1 bar, 40oC.

The maximum pressure is 85 bar. The heat transferred to air at constant pressure is equal to that at

constant volume. Estimate: (i) The pressures and temperatures at the cardinal points of the cycle.

(ii) the cycle efficiency and (iii) the mean effective pressure of the cycle. (Dec. 2012)

UNIT – II - INTERNAL COMBUSTION ENGINES

PART-A

1. What is the antifreeze solutions used in water cooling systems? (Dec. 2016)

2. What is meant by motoring test? (Dec. 2016)

3. Show the valve overlapping of a typical 4-stroke petrol engine on valve timing diagram. (June 2016)

4. Define the phenomenon ‘knocking’ in spark ignited engines. (June 2016)

5. Write the important requirements of fuel injection system. (Dec. 2015)

i) The beginning as well as end of injection should take place sharply.

ii) Inject the fuel at correct time in the cycle throughout the speed range of the engine.

iii) Atomize the fuel to the required degree. iv) Distribute the fuel throughout the

combustion chamber for better mixing.

6. State the purpose of thermostat in an cooling system. (Dec. 2015)

A thermostat valve is used in the water-cooling system to regulate the circulation of water in system

to maintain the normal working temperature of the engine parts during different operating

conditions.

7. What are the functions of a flywheel? (May 2015)

Flywheel serves as a energy reservoir. It stores energy during power stroke and releases during

other strokes.

8. What are the advantages of 4 stroke cycle engine over 2 stroke cycle engines? (May 2015)

i) Thermal efficiency is high. ii)

Volumetric efficiency is more. iii)

Overall efficiency is more.

iv) Specific fuel consumption is less because of separate exhaust stroke. v)

More compression ratio.

9. What is meant by valve overlapping period? (Dec. 2014)

10. What do you understand by ignition delay? (Dec. 2014)

Ignition delay in CI Engines is time interval between start of injection and start of combustion.

11. What is a carburetor? State any 2 functions of carburetor. (May 2014) A Carburetor is a device

which vaporizes the fuel and mixed it with the air.

Functions:

i) It atomizes and vaporizes the fuel.

ii) It prepares a mixture of petrol and air in

correct proportions. iii) It supplies a fine

spray of petrol.

12. Define the term brake power. (May 2014)

Brake power is defined as the power available at the crankshaft. It is always less than the indicated

power.

13. What is a unit injection system? (Dec. 2013)

14. What do you mean short circuiting in 2 stroke engine? (Dec. 2013)

15. What are the characteristics of an efficient cooling system? (Dec. 2012)

i) It reduces friction between moving parts.

ii) It reduces wear and tear of moving

parts. iii) It minimizes power loss

due to friction.

iv) It provides cooling effect: - During circulation, it carries heat from the hot moving parts and

delivers it to the surrounding through radiator.

16. The bore and stroke of a water-cooled, vertical, single cylinder, four-stroke diesel engine are 80mm

and 110mm respectively and the torque is 23.5Nm. Calculate the mean effective pressure of the

engine. (Dec. 2012)

1.

PART-B

(i) Explain the pressure lubrication system with a neat sketch.

(ii) Explain the bosch fuel injector with a neat sketch. (Dec. 2016)

2. Air consumption for a four stroke petrol engine is measured by means of a circular orifice of

diameter 3.5 cm. The coefficient of discharge for the orifice is 0.6 and the pressure across the orifice

is 14 cm of water. The barometer reads 760 mm of Hg. The temperature of air in the room is 24oC.

The piston displacement volume is 1800 cm3. The compression ratio is 6.5. The fuel consumption

is 0.13 kg/min and calorific value is 44,000 kJ/kg. The brake power developed at 2500 rpm is 28

kw. Determine (i) Air fuel ratio (ii) Volumetric efficiency on the basis of air alone (iii) Brake mean

effective pressure (iv) Relative efficiency on brake thermal efficiency basis. (Dec. 2016)

3. Describe with suitable sketches the following system of a modern carburetor:

(a)Main metering system (b) idling system (c) economizer system (d) acceleration pump system

(e) choke. (June 2016)

4. (i) With a neat sketch, explain the principle of work of diesel fuel injector.

(ii) A four-stroke, four-cylinder gasoline engine has a bore of 60 mm and a stroke of 100 mm. On

test it develops a torque of 66.5 Nm when running at 3000rpm. If the clearance volume in each

cylinder is 60 cc, the relative efficiency with respect to brake thermal efficiency is 0.5 and the

calorific value of the fuel is 42 MJ/kg, determine the fuel consumption in kg/h and the brake mean

effective pressure. (June 2016)

5. A 4 cylinder 4 stroke oil engine 10cm in diameter and 15cm in stroke develops a torque of 185Nm

and 2000rpm. The oil consumption is 14.5 litres per hour. The specific gravity of oil is

0.82 and calorific value of oil is 42000kJ/kg. If the imep taken from the indicated diagram is 6.7bar.

Find i) mechanical efficiency ii)brake thermal efficiency iii)brake mean effective pressure iv)

specific fuel consumption in litres on brake power basis. (Dec. 2015)

6. Write a note on lubrication system for an I.C. engine in detail with relevant sketches of various

types. (Dec. 2015)

7. Discuss the difference between theoretical and actual valve timing diagrams of a diesel engine.

(May 2015)

8. Explain the phenomenon of knocking in diesel engines. What are the different factors which

influence the knocking? (May 2015)

9. Explain the working principle of diesel injector with a neat sketch. (Dec. 2014)

10. Calculate the diameter and length of the stroke of a diesel engine working on four stroke constant

pressure cycle from the following data. Indicated power = 18.75 kW, rotation per minute = 220,

compression ratio = 14, fuel cut off = 1/20th of the stroke, index of expansion = 1.3, index of

PART-B

1.

compression = 1.35, length/diameter = 1.5 Assume the pressure and temperature of the air at the

inlet are 1 bar and 40oC respectively. (Dec. 2014)

11. Draw a neat sketch of an injector of diesel engine and explain its working. (May 2014)

12. What are the different methods of lubricating IC Engine? Explain the pressure system of lubrication

with a neat sketch. (May 2014)

13. Discuss the construction and working principle of a four stroke engine with sketch. (Dec. 2013)

14. Explain the construction and working principle of Battery coil ignition system with neat sketch.

(Dec. 2013)

UNIT – III - STEAM NOZZLES AND TURBINES

PART-A

1. What is the effect of super saturation in the nozzles? (Dec. 2016)

2. Define stage efficiency. (Dec. 2016)

3. Draw the shape of supersonic nozzle. (June 2016)

4. Distinguish between impulse and reaction principles. (June 2016)

5. What is the need for compounding in steam turbines? (Dec. 2015)

6. What is effect of friction on the flow through a steam nozzle? (Dec. 2015)

7. What is supersaturated flow? (May 2015)

8. What is pressure compounding? (May 2015)

9. Define co-efficient of velocity in nozzle. (Dec. 2014)

10. Define degree of reaction. (Dec. 2014)

11. What are the effects of friction on the flow through a steam nozzle? (May 2014)

12. Define degree of reaction. (May 2014)

13. Define coefficient of friction in nozzle. (Dec. 2013)

14. Define the term – critical pressure ratio. (Dec. 2013)

15. Define critical pressure ratio. Calculate the value of critical pressure ratio for saturated and

supersaturated steam. (Dec. 2012)

16. What is the effect of supersaturated flow in steam nozzle? (Dec. 2012)

A convergent divergent nozzle required to discharge 2 kg of steam per second. The nozzle is

supplied with steam at 7 bar and 180oC and discharge takes place against a back pressure of 1 bar.

The expansion up to throat is isentropic and the frictional resistance between the throat and the exit

is equivalent to 63 kJ/kg of steam. Take approach velocity of 75 m/s and throat pressure 4 bar,

estimate (i) suitable areas for the throat and the exit, and (ii) overall efficiency of the nozzle based

on the enthalpy drop between the actual inlet pressure and the temperature and the exit pressure.

(Dec. 2016)

2. In a stage of impulse reaction turbine operating with 50% degree of reaction, the blades are identical

in shape. The outlet angle of the moving blade is 19o and the absolute discharge velocity of steam

is 100 m/s in the direction 70o to the motion of the blades. If the rate of flow through the turbine is

15000 kg/hr, calculate the power developed by the turbine. (Dec. 2016)

3. (i) Define critical pressure ratio of a nozzle and discuss why attainment of sonic velocity determines

the maximum discharge through steam nozzle.

(ii) Explain the metastable expansion of steam in a nozzle with help of h-s diagram. (June 2016)

4. A simple impulse turbine has one ring of moving blades running at 150 m/sec. The absolute velocity

of steam at exit from the stage is 85 m/sec at an angle of 80o from the tangential direction. Blade

velocity co-efficient is 0.82 and the rate of steam flowing through the stage is 2.5 kg/sec. If the

blades are equiangular, determine: (i) Blade angles, (ii) Nozzle angle, (iii) Absolute velocity of

steam issuing from the nozzle, (iv) Axial thrust. (June 2016)

5. Dry saturated steam at a pressure of 8bar enters a convergent divergent nozzle and leaves it at a

pressure of 1.5bar. The flow is isentropic and if the corresponding expansion index is 1.133, find

the ratio of cross sectional area at exit and throat for maximum discharge. (Dec. 2015)

6. The steam at 4.9bar and 160oC is supplied to a single stage impulse turbine at a mass flow rate of

30kg/min, from where it is exhausted to a condenser at a pressure of 19.6kPa. The blade speed is

300m/sec. The nozzle are inclined as 25o to the plane of wheel and the outlet blade angle is 35o.

Neglecting friction losses, determine i) theoretical power developed by the turbine ii) diagram

efficiency iii)stage efficiency. (Dec. 2015)

7. Dry saturated steam at a pressure of 11 bar enters a convergent-divergent nozzle and leaves at a

pressure of 2 bar. If the flow is adiabatic and frictionless, determine: (i) the exit velocity of steam

(ii) ratio of cross-section of exit and that at throat. (May 2015)

8. In a De Laval turbine steam issues from the nozzle with a velocity of 1200m/s. The nozzle angle is

20o, the mean blade velocity is 400m/s and the inlet and outlet angles of blades are equal. The mass

of steam flowing through the turbine per hour is 1000kg. Calculate (i) blade angles (ii) relative

PART-B

1.

velocity of steam entering the blades (iii) tangential force on the blades (iv) power developed (v)

blade efficiency. Take blade velocity co-efficient as 0.8. (May 2015)

9. Steam at a pressure of 10.5bar and 0.95dry is expanded through a convergent divergent nozzle. The

pressure of steam leaving the nozzle is 0.85 bar. Find the velocity of steam at throat for maximum

discharge. Take n=1.135. Also find the area at the exit and the steam discharge if the throat area is

1.2cm2. Assume the flow is isentropic and there are no friction losses. (Dec 2014)

10. Explain the pressure and velocity compounding diagram of multi stage turbine with a neat sketch.

(Dec. 2014)

11. Steam enters the blade row of an impulse turbine with a velocity of 600m/s at an angle of 25o to the

plane of rotation of the blades the mean blade speed is 250m/s. The blade angle at the exit side is

30o. The blade friction loss is 10%. Determine (i) the blade angle inlet (ii) the work done per kg of

steam (iii) blade efficiency. (May 2014)

12. The flow rate through steam nozzle with isentropic flow from pressure of 13 bar was found to be

60kg/min. steam is initially saturated. Determine the throat area. If the flow is super saturated,

determine the increase in the flow rate. (May 2014)

13. Steam expands isoentropically in a nozzle from 1 MPa, 250oC to 10kPa. The flow rate of the steam

is 1 kg/s. Find the following when the inlet velocity is neglected (i) Quality of steam (ii) velocity

of steam at exit of the nozzle (iii) exit area of the nozzle. (Dec. 2013)

14. Explain the pressure and velocity compounding diagram of an multi-stage turbines with sketch. (Dec. 2013)

UNIT – IV - AIR COMPRESSOR

PART-A

1. Write the difference between centrifugal and axial compressors? (Dec. 2016)

2. Define volumetric efficiency of an air compressor. (June 2016)

3. State the conditions which lower the volumetric efficiency of an air compressor. (June 2016)

4. What is meant perfect intercooling? (Dec. 2015)

5. List out the factors limit the delivery pressure in a reciprocating compressor. (Dec. 2015)

6. Define the terms: free air delivery and volumetric efficiency compression. (May 2015)

7. What are the advantages of multistage compression? (May 2015)

8. What is effect of intercooling in multistage compressor? (Dec. 2014) (Dec. 2016)

9. Define isometric efficiency of reciprocating compressor. (Dec. 2014)

10. Draw the p-v diagram of a 2 stage reciprocating air compressor. (May 2014)

11. What is meant by intercooler? (May 2014)

12. List the effects of inter-cooling in a multi stage compression process. (Dec. 2013)

13. Give the classification of compressor based on movement of piston. (Dec. 2013)

14. What do you mean by perfect intercooling? (Dec. 2012)

15. Define free air delivery. (Dec. 2012)

The free air delivery of a single cylinder, single stage reciprocating air compressor is 2.5 m3/min.

The ambient air is at STP condition. The delivery pressure is at 7 bar. The clearance volume is 5

percent of stroke volume. Both compression and expansion are according to the law PV1.25 =

constant. Stroke length is 20% more than that of the bore. Compressor runs at 150 rpm. Determine

the mass of air per second, indicated power, indicated effective pressure, bore and stroke of

cylinder. (Dec. 2016)

2. Explain the construction and working principle of centrifugal compressor and axial flow

compressor with neat sketches. (Dec. 2016)

3. A two-stage air compressor consists of three cylinders having the same bore and stroke. The

delivery pressure is 7 bar and the free air delivery is 4.3 m3/min. Air is drawn in at 1.013 bar, 15oC

and an intercooler cools the air to 38oC. The index of compression is 1.3 for all three cylinders.

Neglecting clearance calculate: (i) The intermediate pressure (ii) The power required to drive the

compressor (iii) The isothermal efficiency. (June 2016)

4. With a neat sketch, describe the construction and working of a single-stage single acting

reciprocating air compressor. Also derive the equation for work done with clearance and without

clearance. (June 2016)

5. A single acting air compressor takes in atmospheric air (atm condition 101.325kPa, 27oC) and

delivers it at 1.4MPa. The compressor runs at 300rpm and has cylinder diameter of 160mm and

stroke 200mm, clearance volume is 4% of stroke volume. If the pressure and temperature of the air

at the end of suction are 100kPa and 47oC, the law of compression and expansion is pv1.2=C.

determine i) mass of the air delivered per minute ii)volumetric efficiency iii)driving power required

if ηm=0.85. (Dec. 2015)

6. A 3 stage air compressor with perfect intercooling takes 15m3 air per minute at 95kPa and 27oC,

and delivers the air at 3.5MPa. If the compression process is polytropic (pv1.3=C). determine i)

power required if mechanical efficiency if 90% ii) heat rejected in the intercooler per minute iii)

isothermal efficiency iv)heat rejected through cylinder walls per minute. (Dec. 2015)

7. A single-stage single acting air compressor delivers 0.6 kg of air per minute at 6 bar. The

temperature and pressure at the end of suction stroke are 30oC and 1 bar. The bore and stroke of the

compressor are 100 mm and 150 mm respectively. The clearance is 3% of the swept volume.

Assuming the index of compression and expansion to be 1.3, find: (i) Volumetric efficiency of the

compressor (ii) Power required if the mechanical efficiency is 85% and (iii) speed of the compressor

(rpm). (May 2015)

PART-B

1.

8. In a single-acting two-stage reciprocating air compressor 4.5kg of air per min. are compressed from

1.013 bar and 15oC through a pressure ratio of 9 to 1. Both stages have the same pressure ratio, and

the law of compression and expansion in both stages is pV1.3=C. Calculate (i) the indicated power

(ii) the cylinder swept volumes required. Assume that the clearance volumes of both stages are 5%

of their respective swept volumes and that the compressor runs at 300rpm.

(May 2015)

9. Derive the expression for volumetric efficiency of reciprocating air compressor. (Dec. 2014)

10. Explain the construction and working of Multi stage compressor and discuss the perfect and

imperfect inter cooling with a neat sketch. (Dec. 2014)

11. Derive an expression for volumetric efficiency of an air compressor. (May 2014)

12. Explain the working principle of a intercooler with neat sketch and Explain the working principle

of an axial flow compressor. (May 2014)

13. In a two stage compressor in which inter-cooling is perfect, prove that work done in the compressor

is minimum when the pressure in the intercooler is geometric mean between the initial and final

pressure. Draw the P-V & T-S diagram for Two Stage Compression. (Dec 2013)

14. Explain the construction and working principle of Multi stage compressor and discuss the perfect

and im-perfect intercooling with neat sketch. (Dec. 2013)

UNIT – V - REFRIGERATION AND AIR CONDITIONING

PART-A

1. Name any 4 commonly used refrigerants? (Dec. 2016)

2. What is meant by ERSHF?

3. Show the simple vapour compression cycle on pressure-enthalpy diagram. (June 2016)

4. List out the basic elements of an air conditioning system. (June 2016)

5. Distinguish the summer and winter air conditioning. (Dec. 2015)

6. How does humidity effect the human comfort? (Dec. 2015)

7. Define tonne of refrigeration? (May 2015)

8. Define the terms gross sensible factor and effective sensible heat factor. (May 2015)

9. What is room sensible heat factor? (Dec. 2014)

10. State the unit of refrigeration and any 2 properties of good refrigerant. (May 2014)

11. Define RSHF, RTH. (May 2014)

12. List out the components in the vapour absorption refrigeration system. (Dec. 2013)

13. List 2 desirable properties of refrigerants. (Dec. 2013) (Dec. 2014)

14. What are the expansion devices used in a vapour compression plant? When are they used? (Dec.

2012)

15. What is sensible heating or cooling? (Dec. 2012)

A food storage locker requires a refrigeration capacity of 50 kW. It works between a condenser

temperatures of 35oC and an evaporator temperature of -10oC. The refrigerant is ammonia. It is

sub-cooled by 5oC before entering the expansion valve by the saturated vapour leaving the

evaporator. Assuming a single cylinder, single-acting compressor operating at 1000 rpm with

stroke equal to 1.2 times the bore. Determine (i) power required (ii) The cylinder dimensions. (Dec.

2016)

2. (i) Explain centralized air-conditioning system with a neat sketch.

(ii) 100 m3 of air per minute at 15oC DBT 80% RH is heated until its temperature is 22oC. Calculate

heat added to air per minute, RH of the heated air and wet bulb temperature of the heated air.

(Dec. 2016)

3. Describe the following refrigeration systems with layout: (i) Ammonia water system (ii)

Lithiumbromide water system. (June 2016)

4. (i) Describe the working principle of a centralized air conditioning system and enumerate the need

for it.

(ii) List the loads that contribute to the overall cooling load. (June 2016)

5. Air enters the compressor of an air craft of an cooling system at 100kPa and 183K. Air is now

compressed to 2.5bar with an isentropic efficiency of 72% after being cooled to 320K at constant

pressure in a heat exchanger, the air is then expand in a turbine to 1bar with a isentropic efficiency

of 75%.The cooling load of the system is 3 tonnes of refrigeration after absorbing heat at constant

pressure, the air reenters the compressor which is driven by turbine. Find then COP of the

refrigerator, driving power required and air mass flow rate. (Dec. 2015)

6. An air conditioning plant is required to supply 50m3 of air minute at a DBT of 22oC and 50% RH.

The atmospheric condition is 32oC with 65% RH. Determine the mass of moisture removed and

capacity of cooling coil, if the required effect is obtained by dehumidification and sensible cooling

process. Also calculate sensible heat factor. (Dec. 2015)

7. An ammonia refrigerator operates between evaporating and condensing temperatures of -16oC and

50oC respectively. The vapour is dry saturated at the compressor inlet, the compression process is

PART-B

1.

isentropic and there is no undercooling of the condensate. Calculate: (i) the refrigerating effect per

kg. (ii) the mass flow and power input per kW of refrigeration and (iii) COP. (May 2015)

8. Saturated air leaving the cooling system of an air-conditioning system at 14oC at a rate of 50m3/min

is mixed adiabatically with the outside air at 32oC and 60% relative humidity at a rate of 20m3/min.

Assuming that the mixing process occurs at a pressure at 1atm, determine the specific humidity, the

relative humidity, the dry-bulb temperature and the volume flow rate of the mixture. (May 2015)

9. Explain the construction and working of vapour absorption refrigeration system. (Dec. 2014)

10. Explain the desirable thermodynamic properties and environmental safety aspects of alternative refrigerants. ( Dec. 2014)

11. Explain briefly simple vapour absorption system. Give the comparison between vapour

compression system and vapour absorption system. (May 2014)

12. An office is to be air-conditioned for 50 staff when the outdoor conditions are 30oC DBT and 75%

RH if the quantity of air supplied is 0.4m3/min/person, find the following (i) the capacity of the

cooling coil in tons of refrigeration. (ii) capacity of the heating coil in kW. (iii) Amount of water

vapour removed per hour assume that required air inlet conditions are 20oC DBT and 60%RH. Air

is conditioned first by cooling and dehumidifying and then by heating. (iv) if the heating coil surface

temperature is 25oC, find the by-pass factor of the heating coil. (May 2014)

13. The temperature limits of Ammonia Refrigeration system are 25oC and -10oC. If the gas is dry at

the end of compression. Calculate the COP of the cycle assuming no under-cooling of the liquid

ammonia. The properties of Ammonia are given below.

Temperature in oC Liquid heat Latent heat Liquid entropy

25 298.90 1166.94 1.2420

-10 135.37 1297.68 0.5443

14. Explain the construction and working of Vapour compression refrigeration system with neat sketch.

(Dec. 2013)