JNTU Previous Paper Questions Thermodynamics

Code No: 07A3EC08 R07 Set No. 2 II B.Tech I Semester Examinations,MAY 2011

THERMODYNAMICS Common to Mechanical Engineering, Aeronautical Engineering, Automobile

Engineering Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

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1. (a) What are the advantages associated with the diesel cycle as compared to theotto cycle?

(b) A gas engine working on Otto cycle has a cylinder of diameter 220 mm and

stroke 300 mm. The clearance volume is 1800 cc. Find the air-standard

efficiency. Assume Cp =1.004 kJ/kg.K and Cv = 0.718 kJ/kg.K for air. [6+10]

2. (a) Explain with a neat sketch P-V-T diagram. (Unit 4)

(b) 2 kg of steam expands adiabatically from 20 bar, 3000C to 0.5 bar in a steam

turbine such that the steam is dry and saturated at the end of expansion.

Calculate

i. the work done by steam, and ii. work lost due to irreversibility. [8+8]

3. (a) What is an equation of state?

(b) Air at 160C and 1.02 bar occupies a volume of 0.03 m3. The air is heated

at constant volume until the pressure is 4.3 bar and then cooled at constant

pressure back to the original temperature. calculate

i. The net heat flow to or from the air and ii. The net entropy change. [6+10]

4. (a) Explain with neat sketch the working of vapour compression refrigeration cycle

(b) Describe a binary vapour cycle with the help of schematic diagram of the plantand T-S diagram of the cycle. [8+8]

5. An engine working on Carnot cycle absorbs Q1 units of heat from a source at T1

and rejects Q2 units of heat to a sink at T2. Te temperature of the working fluid is

θ1 and θ2, where θ1 < T1 and θ2 > T2, If θ1 = T1-KQ1 and θ2 = T2+kQ2

where k is constant, then show that efficiency of the engine is given by: η = 1 − T2) [16]

T1 −2kQ1 . (Unit 3) 6. (a) Derive steady flow energy equation and simplify the equation when applied to

i. Gas turbineii. Compressors (Unit 2)

1

Work done by a substance in a reversible non-flow manner is in accordance

Code No: 07A3EC08 R07 Set No. 2 (b) A fluid system under goes a non-flow frictionless process following the pressure

volume relation as p=5/v +1.5 where p is in bar and v is in m3 and the system

rejects 42 kj of heat. Determine

i. change in internal energy ii. change in enthalpy. [8+8]

7. (a) Describe the method of dehumidification by cooling and show it on psychro-metric chart. Derive energy equation for this process.

(b) A thermally insulated vessel contains 3 kg mole of H2 and 1.5 kg mole of N2

each at 1 bar 270C initially they are separated by a partition wall. Determine

the change in entropy when the partition wall is removed and the two gases

mixes. [8+8]

8. (a) What are the different types of thermodynamic systems? Explain with exam-ples. Unit I

(b)

with = 150 m3, where p is in bar. Evaluate the work done on or by thep

system as pressure increases from 10 to 100 bar. Indicate whether it is a compression or expansion process. [8+8]

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2

Work do(e by a substance in a reversible non-flow manner is in accordance





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each at 1 bar 270C initially they are separated by a partition wall. Determinethe change in entropy when the partition wall is removed and the two gasesmixes. [8+8]



3. (a) What are the different types of thermodynamic systems? Explain with exam-ples. Unit I

(b) )with = 150 m3, where p is in bar. Evaluate the work done on or by the

p

system as pressure increases from 10 to 100 bar. Indicate whether it is acompression or expansion process. [8+8]





i. The net heat flow to or from the air and

ii. The net entropy change. [6+10]

5. (a) Derive steady flow energy equation and simplify the equation when applied to

i. Gas turbine ii. Compressors Unit II

(b) A fluid system under goes a non-flow frictionless process following the pressure




3

Code No: 07A3EC08 R07 Set No. 4 6. An engine working on Carnot cycle absorbs Q1 units of heat from a source at T1


θ1 and θ2, where θ1 < T1 and θ2 > T2, If θ1 = T1-KQ1 and θ2 = T2+kQ2 UNIT III

where k is constant, then show that efficiency of the engine is given by: η = 1 − T2 [16]

T1 −2kQ1 . Unit (III)7. (a) What are the advantages associated with the diesel cycle as compared to the

otto cycle?

(b) A gas engine working on Otto cycle has a cylinder of diameter 220 mm and stroke 300 mm. The clearance volume is 1800 cc. Find the air-standard efficiency. Assume Cp =1.004 kJ/kg.K and Cv = 0.718 kJ/kg.K for air. [6+10]

8. (a) Explain with a neat sketch P-V-T diagram. UNIT IV



Calculate

i. the work done by steam, and

ii. work lost due to irreversibility. [8+8]

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4





Answer any FIVE Questions All Questions carry equal marks

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mixes. [8+8]




where k is constant, then show that efficiency of the engine is given by: η = 1 − T2 [16]

T1 −2kQ1 .


(b) A gas engine working on Otto cycle has a cylinder of diameter 220 mm andstroke 300 mm. The clearance volume is 1800 cc. Find the air-standardefficiency. Assume Cp =1.004 kJ/kg.K and Cv = 0.718 kJ/kg.K for air. [6+10]



5. (a) What are the different types of thermodynamic systems? Explain with exam-ples.

(b) )with = 150 m3, where p is in bar. Evaluate the work done on or by the

p



(b) Air at 160C and 1.02 bar occupies a volume of 0.03 m3. The air is

heated at constant volume until the pressure is 4.3 bar and then cooled at

constant pressure back to the original temperature. calculate


5

Code No: 07A3EC08 R07 Set No. 1



i. Gas turbineii. Compressors

(b) A fluid system under goes a non-flow frictionless process following the pressure




8. (a) Explain with a neat sketch P-V-T diagram.



Calculate

i. the work done by steam, and ii. work lost due to irreversibility. [8+8]

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6






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1. (a) What are the different types of thermodynamic systems? Explain with exam-ples.

(b)

with =

)150p m3, where p is in bar. Evaluate the work done on or by the



(b) A gas engine working on Otto cycle has a cylinder of diameter 220 mm and stroke 300 mm. The clearance volume is 1800 cc. Find the air-standard efficiency. Assume Cp =1.004 kJ/kg.K and Cv = 0.718 kJ/kg.K for air. [6+10]







4. (a) Explain with a neat sketch P-V-T diagram.



Calculate

i. the work done by steam, and

ii. work lost due to irreversibility. [8+8]


i. Gas turbine ii. Compressors

(b) A fluid system under goes a non-flow frictionless process following the

pressure volume relation as p=5/v +1.5 where p is in bar and v is in m3 and the

system rejects 42 kj of heat. Determine

i. change in internal energy

7

Code No: 07A3EC08

ii. change in enthalpy.

R07 Set No. 3

[8+8]


(b) Describe a binary vapour cycle with the help of schematic diagram of the plant and T-S diagram of the cycle. [8+8]




where k is constant, then show that efficiency of the engine is given by:η = 1 − T2

T1 −2kQ1 .[16]





mixes. [8+8]

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8

Code No: R05210304 R05 Set No. 2 II B.Tech I Semester Examinations,November 2010

THERMODYNAMICS Common to Mechanical Engineering, Automobile Engineering

Time: 3 hours Max Marks: 80Answer any FIVE Questions

All Questions carry equal marks

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1. (a) Explain the important components of a simple vapour compression refrigera-tion system. Also discuss the functions of each component.

(b) Discuss the effect of sub cooling on C.O.P.of the vapour compression refriger-ation cycle. Would you derive large sub cooling and why? [8+8]

2. (a) Deduce the relation ship between absolute temperature and pressure in anpolytropic process.

(b) 0.3m3 of air at pressure 8 bars expands to 1.5m3 . The final pressure is 1.3

bar. Assuming the expansion to be polytropic, calculate the heat supplied and

change of internal energy. Take [7+9]

3. A cycle consists of three processes. The first is a constant pressure compression at

200 KPa from an initial volume of 0.7 m3 to a final volume of 0.2 m3. The second

process takes place at constant volume with the pressure increasing to 600 KPa.

The third process to the beginning of the first process. Sketch the cycle on P-v

coordinates, and calculate the net work transfer. [16]

4. (a) Make an energy analysis of the steam nozzle and heat exchanger.

(b) Refrigerant vapour enters the condenser of a refrigeration plant with enthalpy

223.75 KJ/kg and leaves with enthalpy 64.6 KJ/kg. Cooling water enters at

150C and leaves at 200C. Calculate the mass flow rate of water per unit flow

rate of refrigerant. Take for water Cp = 4.186 KJ/Kg-K. [8+8]

5. (a) List out different colorimeters used to find the quality of wet steam, Explainany one of them.

(b) In a steam engine the steam at the beginning of the expansion process is at

7 bar, dryness fraction 0.98 and expansion follows the low P v1.1 = constant

,down to a pressure of 0.34 bar, calculate The work done during expansion per

kg of steam. [7+9]

6. (a) State the Kelvin-Plank and Clausius statements of the second law of thermo-dynamics and establish equivalence between them.

(b) Determine the power required to run a refrigerator that transfers 2000 KJ/min

of heat from a cooled space at 00C to the surrounding atmosphere at 270C.

The refrigerator operates on reversed Carnot cycle. [10+6]

7. An engine with 200mm cylinder diameter and 300mm stroke works on diesel cycle.

The initial pressure and temperature of air used are 1 bar and 270C. The cut-off

is 8% of the stroke. Determine:

1

Code No: R05210304 R05 Set No. 2

(a) Temperatures and pressures at all salient points

(b) Air standard efficiency. [16]

8. (a) Write shoot notes on

i. By pass factor ii. Degree of saturation iii. Adiabatic mixing iv. Humidification

(b) 200m3 of air per minute at 150C DBT and 75 Find

i. R. it of heated air ii. Wet bulb temperature of heated air

iii. Heat added to air per minute [8+8]

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2





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3. (a) List out different colorimeters used to find the quality of wet steam, Explainany one of them. UNIT IV




kg of steam. [7+9]

4. (a) Make an energy analysis of the steam nozzle and heat exchanger.UNIT II

(b) Refrigerant vapour enters the condenser of a refrigeration plant with enthalpy223.75 KJ/kg and leaves with enthalpy 64.6 KJ/kg. Cooling water enters at150C and leaves at 200C. Calculate the mass flow rate of water per unit flowrate of refrigerant. Take for water Cp = 4.186 KJ/Kg-K. [8+8]

5. (a) Deduce the relation ship between absolute temperature and pressure in anpolytropic process. UNIT II



change of internal energy. Take γ= 1.4 [7+9]







3

Code No: R05210304

i. By pass factorii. Degree of saturationiii. Adiabatic mixingiv. Humidification

R05 Set No. 4


i. R. it of heated air ii. Wet bulb temperature of heated air iii. Heat added to air per minute [8+8]

8. (a) State the Kelvin-Plank and Clausius statements of the second law of thermo-dynamics and establish equivalence between them. UNIT III




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4




All Questions carry equal marks⋆ ⋆ ⋆ ⋆ ⋆




change of internal energy. Take γ= 1.4 [7+9]









(b) Refrigerant vapour enters the condenser of a refrigeration plant with enthalpy

223.75 KJ/kg and leaves with enthalpy 64.6 KJ/kg. Cooling water enters at

150C and leaves at 200C. Calculate the mass flow rate of water per unit flow

rate of refrigerant. Take for water Cp = 4.186 KJ/Kg-K. [8+8]






i. By pass factor ii. Degree of saturation iii. Adiabatic mixing iv. Humidification


i. R. it of heated air

5

Code No: R05210304 R05 Set No. 1

ii. Wet bulb temperature of heated airiii. Heat added to air per minute [8+8]





kg of steam. [7+9]






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6





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2. An engine with 200mm cylinder diameter and 300mm stroke works on diesel cycle.The initial pressure and temperature of air used are 1 bar and 270C. The cut-offis 8% of the stroke. Determine:







kg of steam. [7+9]


(b) 0.3m3 of air at pressure 8 bars expands to 1.5m3 . The final pressure is 1.3bar. Assuming the expansion to be polytropic, calculate the heat supplied andchange of internal energy. Take γ= 1.4 [7+9]


(b) Refrigerant vapour enters the condenser of a refrigeration plant with enthalpy223.75 KJ/kg and leaves with enthalpy 64.6 KJ/kg. Cooling water enters at150C and leaves at 200C. Calculate the mass flow rate of water per unit flowrate of refrigerant. Take for water Cp = 4.186 KJ/Kg-K. [8+8]


(b) Discuss the effect of sub cooling on C.O.P.of the vapour compression refriger-

ation cycle. Would you derive large sub cooling and why? [8+8]


7

Code No: R05210304

i. By pass factorii. Degree of saturationiii. Adiabatic mixingiv. Humidification

R05 Set No. 3


i. R. it of heated air ii. Wet bulb temperature of heated air iii. Heat added to air per minute [8+8]






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8

Code No: 43141/43142 R07 Set No - 1 II B.Tech I Semester Regular Examinations,Nov/Dec 2009




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1. (a) Explain a heat engine cycle performed by a steady flow system with line dia-gram. (Unit III)

(b) Show by second law that the dissipation of electrical work into internal energyor heat is irreversible. [8+8]

2. (a) Energy is a point function. Explain and prove. (Unit II)

(b) Prove that heat and work are path functions. [8+8]

3. (a) What are adiabatic and diathermic walls? (Unit II)

(b) The flow energy of 0.124 m3/min of a fluid crossing a boundary to a system is 18 KW. Find the pressure at this point. [6+10]

4. A gas refrigerating system using air as a refrigerant is to work between -11oC

and 26oC using an ideal reversed Brayton cycle of pressure ratio 6 and minimum

pressure l atm, and to maintain a load of 11 tonnes. Find

(a) the COP

(b) the air flow rate in kg / s

(c) the volume flow rate entering the compressor in m3/s and

(d) the maximum and minimum temperatures of the cycle. [16]

5. For air conditioning a room in winter, atmospheric air at 6 oC and relative humidity

22% is first heated in a heating coil. It is then passed through a spray water till

the relative humidity becomes 90%. The humidified air is again heated sensibly

to the conditioned state in the room at 21.5oC and 32% relative humidity. If the

atmospheric pressure is 1 bar, determine per kg of dry air

(a) the amount of heat required during the process, and

(b) the amount of water evaporated in the spray water unit respectively.

Compute also the humidifying efficiency of the spray water unit. Plot the

process on the psychrometric chart. [16]

6. (a) Explain the significance of Vander walls equation and its limitations

(b) A tank of volume 1.3 m3 is filled with argon at 6 bar and 260oC. If the gas

within the tank changes its state isentropically when it flows from the tank

until the pressure drops to the atmospheric pressure of 1 bar, determine the

mass of the gas that has left the tank during the process. [6+10]

1

Code No: 43141/43142 R07 Set No - 1 7. A dual combustion cycle operates with a volumetric compression ratio rk

= 12, and with a cut-off ratio 1.615. The maximum pressure is given by Pmax

= 54 P1

where P1 is the pressure before compression. Assuming indices of compression and

expansion of 1.35, show that the m.e.p. of the cycle Pm= 10 P1 Hence evaluate

(a) temperatures at cardinal points with T1 = 335 K, and

(b) cycle efficiency. [16]

8. (a) What is normal boiling point and explain its significance.

(b) Steam flows in a pipe line at 1.5 Mpa. After expanding to 0.1 Mpa in throttling

calorimeter, the temperature is found to be 1200 C. Find the quality of steam

in the pipe line. What is the maximum moisture at 1.5 Mpa that can be

determined with this set-up it at least 50c of super heat is required after

throttling for accurate readings? [6+10]

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2





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1. A slow-speed reciprocating air compressor with a water jacket for cooling approxi-

mates a quasi-static compression process following a path pv1.35 = constant. If air

enters at a temperature of 23oC and a pressure of 1.1 bar, and is compressed to 6.5

bar at a rate of 1050 kg/h, determine the discharge temperature of air, the power

required and the heat transferred per kg. [16]

2. (a) Demonstrate, using the second law, that free expansion is irreversible.

(b) A domestic food freezer maintains a temperature of -150 C with ambient tem-

perature of 300C. If heat leaks into he freezer at the continuous rate of 1.75

kJ/s, What is the least power necessary to pump this heat out continuously.

[8+8]

3. (a) What is an air standard cycle? Why are such cycles conceived?

(b) Find the air standard efficiencies for Otto cycles with a compression ratio of 6using ideal gases having specific heat ratios 1.35, 1.43 and 1.62. What are theadvantages and disadvantages of using helium as the working fluid? [6+10]

4. (a) Explain microscopic and macroscopic approach with examples.

(b) A pump forces 1.2m/min of water horizontally from an open well to a closed

tank where the pressure is 0.9 Mpa. Compute the work the pump must do

upon the water in an hour just to force the water into the tank against the

pressure. [6+10]

5. Air at 28 oC, 78% RH is cooled by spraying in water at 10 oC. This causes saturation,

followed by condensation, the mixing being assumed to take place adiabatically and

the condensate being drained off at 17.5oC. The resulting saturated mixture is then

heated to produce the required conditions of 55% RH at 23oC. The total

pressure is constant at 101 kPa. Determine the mass of water supplied to the

sprays to provide 12 m3/h of conditioned air. What is the heater power required?

[16]

6. A 6 ton ideal vapour compression refrigerator works between the condensing pres-

sure of 12 bar and evaporating pressure of 3.3 bar. The refrigerant is dry saturated

vapour before it enters the compressor. Saturated liquid refrigerant enters into the

expansion valve from the condenser. The average specific heat of the superheated

refrigerant vapour at constant pressure is 1.7 kJ /kg K. Compute the temperature

of the refrigerant before it enters the condenser, the refrigerating effect per kg of

refrigerant, the COP, the mass flow rate of the refrigerant per minute and power

3

Code No: 43141/43142

input into the compressor.

R07 Set No - 2

The properties of the refrigerants are:

Pressure bar Sat. Temperature 0C Enthalpy kJ/kg Entropy kj/kg KSat. liquid Sat. liquid Sat. vapour

(hf ) (Sf ) (Sg )12 30 84.5 0.312 0.93.3 -12 31 0.125 0.95

[16]

7. A rigid vessel contains 1 Kg of a mixture of saturated water and saturated steam

at a pressure of 0.15 Mpa. When the mixture is heated, the state passes through

the critical point. Determine the volume of the vessel, the mass of the liquid and

vapour in the vessel initially, the temperature of the mixture when the pressure has

risen to 3Mpa, and the heat transfer required to produce the final state.[16]

8. (a) Explain what is PMMI?

(b) Steam enters a steam turbine with a volocity of 16 m/s and specific enthalpy

2990 kJ/kg. The steam leaves the turbine with a velocity of 37 m/s and

specific ethalpy of 2530 kJ/kg. The heat lost to the surroundings is 25 kJ/kg

with the steam flow rate of 3,60,000 kg/w. Calculate the turbine work output

in kW. [4+12]

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4

p2





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1. (a) Explain the air standard Otto cycle with the help P-V and T-S diagrams.

(b) In an Otto cycle, the upper and lower limits for absolute temperatures are

respectively T3 and T1. Show that for maximum work, the ratio of compression

should have the value r = (T3 / T1)1.25 Take γ = 1.4 [8+8]

2. (a) Write the unit of temperature and explain the International fixed points.(Unit II)

(b) Explain in detail the ideal gas temperature scale. [8+8]

3. Two containers p and q with rigid walls contain two different monoatomic gases

with masses mp and mq gas constants Rp and Rq , and initial temperatures Tp and

Tq respectively, are brought in contact with each other and allowed to exchange

energy until equilibrium is achieved. Determine:

(a) the final temperature of the two gases and

(b) the change of entropy due to this energy exchange. [16]

4. (a) Show that the adiabatic mixing of two fluids is irreversible. (Unit III)

(b) Show that if two bodies of thermal capacities C1and C2 at temperatures T1

and T2 are brought to the same temperature, T by means of a reversible heat

engine, then In T= C1 ln T1 +C2

ln T2 [8+8]C1 +C2

5. (a) What are the advantages and disadvantages of air refrigeration systems overthe other?

(b) Determine the temperature ratio (T2 / T1) (where T2 = source temperature

and T1 = sink temperature) for a Carnot refrigerator whose COP is 5. Also

calculate the refrigeration capacity of the machine in tons of refrigeration if the

power consumption is 8 kW. If the cycle is used as heat pump, find the COP

for heating cycle and the quantity of heat pumped assuming same temperature

range. [6+10]

∫ 6. (a) Show that the work done during a flow process is − vdp (Unit II)

p1

(b) A certain mass of sulphur dioxide (S02) is contained in a vessel of 0.145 m3

capacity, at a pressure and temperature of 24.2 bar and 20oC respectively. A

5

Code No: 43141/43142 R07 Set No - 3

valve is opened momentarily and the pressure falls immediately to 7.8 bar.Sometime later the temperature is again 20oC and the pressure is observed tobe 10.2 bar. Estimate the value of specific heat ratio. [6+10]

7. (a) What is principle of operation of an electrial calorimeter?

(b) A vessel of 0.04 m3 contains a mixture of saturated water and saturated steam

at a temperature of 250 0C. The mass of the liquid present is 9 Kg. Find the

pressure, the mass, the specific volume, the enthalpy, the entropy and internal

energy using steam table only. [6+10]

8. (a) Explain the work interaction between a system and the surroundings.

(b) The pistion of an oil engine, of area 0.0045 m2, moves downwards 75 mm,

drawing in 0.0028 m3 of fresh air from the atmosphere. The pressure in the

cylinder is uniform during the process at 80 kPa, while the atmospheric pres-

sure is 101.325 kPa, the difference being due to the flow resistance in the

induction pipe and the inlet valve. Estimate the displacement work done by

the air finally in the cylinder. [6+10]

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6





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1. Two tanks are connected by a valve. One tank contains 1.5 kg of CO gas at 75 oC

and 0.9 bar. The other tank holds 7.5 kg of the same gas at 25oC and 1.4 bar. The

valve is opened and the gases are allowed to mix while receiving energy by heat

transfer from the surroundings. The final equilibrium temperature is 45oC. Using

the ideal gas model, determine

(a) the final equilibrium pressure,

(b) the heat transfer for the process. [16]

2. (a) Define the specific heats at constant volume and at constant pressure.

(b) 1.5 Kg of liquid having a constant specific heat of 2.5 KJ/kg K is stirred ina well insulated chamber causing the termerature to rise by 150C. Find thechange in the internal energy and wotk done for the process. [6+10]

3. (a) What do you understand by the terms refrigeration effect and ton of refriger-ation?

(b) An ideal refrigeration system working on Carnot cycle operates between the

temperature limits of -25 oC and 30oC. Find the ideal COP and the power

required from an external source to absorb 4 kW at low temperature. If the

system operates as a heat pump, determine the COP and the power required

to discharge 4 kW at high temperature. [6+10]

4. The usual cooking gas (mostly methane) cyclinder is about 20 cm in diameter and

100 cm in height. It is charged to 11.5 MPa at room temperature of 25 oC.

(a) Assuming the ideal gas law, find the mass of gas filled in the cyclinder.

(b) Explain how the actual cyclinder contains nearly 15 kg of gas.

(c) If the cylinder is to be protected against excessive pressure by means of a

fusible plug, at what temperature should the plug melt to limit the

maximum pressure to 15 MPa? [16]

5. (a) Distiguish between open system and closed system. (Unit I)

(b) A gas at a pressure of 138 kN/m2 is having volume of 0.112 m3. It is com-pressed to 690 kN/m2 according to the law pv1.4=constant.Calcuate the final volume of the gas. [6+10]

6. (a) Explain with the help of a line diagram the cyclic refrigeration palnt.(Unit III)

7

Code No: 43141/43142 R07 Set No - 4

(b) Prove the equivalence of Kelvin planck and clausius statement. [8+8]

7. Two streams of steam one at 2 Mpa, 3000 C and the other at 2 Mpa, 4000 C mix in

a stedy flow adiabatic process. The rates of flow of the two streams are 3 Kg/min,

2kg/min respectively. Evaluate the final temperature of the emerging stream, if

there is no pressure drop due to the mixing process. What would be the rate of

increase in the entropy of the universe? This stream with a negligible velocity now

expands adiabatically in a nozzle to a pressure of 1Kpa. Calculate the exit velocity

of the stream and the exit area of the nozzle. [16]

8. For an air standard Otto cycle with fixed intake and maximum temperatures, T1

and T3, find the compression ratio that renders the net work per cycle a maximum.

Derive the expression for cycle efficiency at this compression ratio. If the air intake

temperature, T1, is 305 K and the maximum cycle temperature, T3, is 1300 K,

compute the compression ratio for maximum net work, maximum work output

per kg in a cycle, and the corresponding cycle efficiency. Find the changes in

work output and cycle efficiency when the compression ratio is increased from this

optimum value to 8. Take Cv = 0.718 kJ/kg K. [16]

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8

Code No: 07A3EC08 Set No. 1 II B.Tech I Semester Regular Examinations, November 2008

THERMODYNAMICS ( Common to Mechanical Engineering, Aeronautical Engineering and

Automobile Engineering) Time: 3 hours Max Marks: 80


⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Explain the control volume and its significance. (Unit I)

(b) If a gas of volume 6000 cm3 and at a pressure of 100 kPa, is compressedquasistatically to pV2=constant until the volume becomes 2000 cm3. Calcuatethe final pressure and the work transfer. [6+10]

2. (a) Constant pressure gas thermometer-explain in detail.(Unit II)

(b) The readings tA and tB of two celsius thermometers A and B agree well at ice

point (00 C) and steam point (1000). At other points between these two, the

temperatures are related by tA=p+qtB +rt2 B , Where p,q and r are constants.

When the two thermometers are immersed in a well stirred oil bath, while A reads 51, B reads 50.

i. Determine what A reads when B reads 30.

ii. Discuss the question of which thermometer is correct. [6+10]

3. (a) Explain the causes of Irreverisbility.(Unit III)

(b) An invertor claims to have developed an engine that takes in 105 MJ at atemperature of 400k, rejets 42 MJ at a temperature of 200 k, and delivers15 Kwh of mechanical work. Listing out all the reasons, suggest your adviceinventing money to put this engine in the market. [8+8]

4. (a) Explain the significance of Tripple point in case of pure substance.

(b) Explain in detail the formation of steam with the help of T-H diagram indi-cating the salient points. [8+8]

5. An ideal gas cycle of three processes uses Argon (Mol. wt.40) as a workingsubstance. Process 1-2 is a reversible adiabatic expansion from 0.015 m3, 650 kPa, 270oC to 0.066 m3. Process 2-3 is a reversible isothermal process. Process 3-1 is a constant pressure process in which heat transfer is zero. Sketch the cycle in the p-v and T-s planes, and find

(a) the work transfer in process 1-2,

(b) the work transfer in process 2-3, and

(c) the net work of the cycle. Take γ= 1.67. [16]

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Code No: 07A3EC08 Set No. 1 6. A vessel is divided into three compartments (a), (b), and (c) by two partitions. Part

(a) contains Oxygen and has a volume of 0.15 m3, (b) has a volume of 0.25 m3 and contains Nitrogen, while (c) is 0.05 m3 and holds Carbon diaoxide. All three parts are at a pressure of 2.5 bar and a temperature of 150C. When the partitions are removed and the gases mix, determine the change of entropy of each constituent, the final pressure in the vessel and the partial pressure of each gas. The vessel may be taken as being completely isolated from its surroundings. [16]

7. (a) What are cyclic and non-cyclic heat engines? Give examples.

(b) State the four processes that constitute the Ericsson cycle. Show that the re-

generative Ericsson cycle has the same efficiency as the Carnot cycle. Mention

the merits and demerits of the Stirling and Ericsson cycles. [6+10]

8. For an ideal vapor-compression refrigerating system using R134a and dry compres-

sion, the refrigerated region is to be kept at 3oC, and the ambient air to which

heat is rejected is at 30oC. The rate of heat removal from the refrigerated region

is 200 kJ/min. A minimum temperature difference of 10 degree Celsius is to be

maintained for heat transfer at the condenser and at the evaporator. For a fixed

condensation temperature of 40oC, plot coefficient of performance and refrigerant

flow rate versus temperature difference between the evaporating refrigerant and the

refrigerated space in the range of 10 degree Celsius to 30 degree Celsius. [16]

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THERMODYNAMICS( Common to Mechanical Engineering, Aeronautical Engineering and

Automobile Engineering)Time: 3 hours Max Marks: 80


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1. (a) Energy is a point function. Explain and prove. (Unit I )

(b) Prove that heat and work are path functions. [8+8]

2. (a) State the first law of thermodynamics and prove that for non flow process itleads to Q=W+ΔU. (Unit II)

(b) Define PMMI and the relevance of it. [8+8]

3. (a) Show that the COP of heat pump is greater than the COP of a refrigeratorby unity. (Unit III)

(b) Prove that the efficiency of a reversible engine operating between two givenconstant temperatures is the maximum. [8+8]

4. (a) Why cannot a throttling calorimeter measure the quality if the steam is verywet? (Unit IV)

(b) Find the enthalpy, entropy and volume of steam at 1.4 Mpa, 3800 C. Usingsteam tables only. [6+10]

5. (a) Write down the van der Waals equation of state. How does it differ from theideal gas equation of state?

(b) A gas occupies 0.034 m3 at 600 kPa and 85oC. It is expanded in the non-flow

process according to the law pV1.2 = constant to a pressure of 60 kPa after

which it is heated at constant pressure back to its original temperature. Sketch

the process on the p-v and T-s diagrams, and calculate for the whole process

the work done, the heat transferred. Take Cp = 1.047 and Cv = 0.775 kJ/kg

K for the gas. [6+10]

6. A gaseous mixture contains 23 % by volume of Nitrogen, 45% by volume of Hy-

drogen, and 32% by volume of Carbon-dioxide. Calculate the Molecular weight

of the mixture, the characteristic gas constant R for the mixture and the value of

the reversible adiabatic index γ. (At 10oC, the cp values of Nitrogen, Hydrogen,

and Carbon dioxide are 1.04, 13.95, and 0.85 kJ/kg K respectively.) A cyclin-der contains 0.095 m3 of the mixture at 1.1 bar and 10oC. The gas undergoes a reversible non-flow process during which its volume is reduced to one-fifth of its original value. If the law of compression is Pv1.25 = constant, determine the work and heat transfers in magnitude and direction and the change in entropy.[16]

7. (a) Derive the expression for efficiency of air standard Otto cycle

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Code No: 07A3EC08 Set No. 2

(b) An engine equipped with a cylinder having a bore of 12 cm and a stroke of 40cm operates on an Otto cycle. If the clearance volume is 1600 cm3, computethe air standard efficiency. [8+8]

8. (a) Derive the expression for COP of Bell Coleman cycle when the compressionand expansion are isentropic

(b) An air refrigerating plant operates between 1.6 bar and 8 bar. The capacity

of the plant is 5.5 ton. The temperature of the air entering the compressor

and into an air engine is -4oC and 29oC respectively. The compression and

expansion processes are polytropic with exponent n = 1.35. Determine the

COP and the net power input for the plant. [8+8]

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1. (a) What do you understand by state function and path function? (Unit I)

(b) Prove that work is a path function and properties are point functions. [6+10]

2. (a) Why should specific heat not be defined in terms of heat transfer? (Unit II)

(b) During one cycle, the working fluid in an engine engages in two work interac-tions: 15 KJ to the fluid and 44 KJ from the fluid, and three heat interations,two of which are 75 kJ of the fluid and 40 KJ from the fluid. Evalute themagnitude and direction of the third heat transfer. [6+10]

3. (a) Explain the concept of heat pump ealborately. (Unit III)

(b) A heat engine performs many cycles during which it develops 21 kJ work andreceives 85 kJ heat from the source. Evaluate the thermal efficiency and theheat rejected by the engine. [8+8]

4. (a) Define sensible heat and dry steam. (Unit IV)

(b) A spherical shell of diameter 50 cm contains steam at a pressure of 40 bar and0.85 dryness fraction. Calculate the mass of water and steam. [6+10]

5. (a) Explain the significance of Vander walls equation and its limitations

(b) A tank of volume 1.3 m3 is filled with argon at 6 bar and 260oC. If the gas

within the tank changes its state isentropically when it flows from the tank

until the pressure drops to the atmospheric pressure of 1 bar, determine the

mass of the gas that has left the tank during the process. [6+10]

6. A system consisting of three tanks, all interconnected by pipes and valves, contains

Nitrogen, Oxygen, and Argon. One tank contains 5 kg of Nitrogen at 650 kPa,

23oC; another 3.5 kg of Argon at 450 kPa, 48oC; and the third 7 kg of Oxygen at

300 kPa, 80oC. After the valves are opened and the system is allowed to come to

equilibrium, compute for the mixture

(a) the temperature

(b) the apparent molar mass

(c) the constant-pressure specific heat

(d) the gas constant

(e) the pressure and

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Code No: 07A3EC08

(f ) the partial pressure of each constituent.

Set No. 3

[16]

7. A four - cylinder petrol engine working on an air - standard Otto cycle has a swept

volume of 2000 cm3 and the clearance volume in each cylinder is 60 cm3. Determine

the cycle efficiency. If the air at the beginning of the compression stroke is at 100

kpa and 300k, and the maximum cycle temperature is 1650 k, determine the mean

effective pressure of the cycle. [16]

8. A R-12 vapour compression refrigeration system is operating at a condenser pres-

sure of 10 bar and an evaporator pressure of 2.2 bar. Its refrigeration capacity is

14 tonnes. The values of enthalpy at the inlet and outlet of the evaporator are

650 and 200 kJ/kg. The specific volume at inlet to the reciprocating compressor is

0.085 m3/kg. The index of compression for the compressor is 1.15. Determine:

(a) the power input in kW required for the compressor and

(b) the COP. Take 1 tonne of refrigeration as equivalent to heat removal at the rate of 3.517 kW. [16]

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1. (a) Differentiate the cyclic process and non cyclic process.(Unit I)

(b) A vacuum gauge connected to a tank reads 30 Kpa at a location where thebarometer reads 755 mm Hg. Calcuate the absolute pressure in the tankassuming density of Hg to be 13,590 kg/m3. [6+10]

2. (a) Derive the expression for stedy flow energy equation.(Unit II)

(b) A blower handles 1 kg/sec of air at 20 0C and consumes a power of 15 kw.The inlet and outlet velocities of air are 100 m/s and 150 m/s respectively.Find the exit air temperature, assuming adiabatic conditions. [8+8]

3. (a) State and prove carnot theorems. (Unit III)

(b) A rerversible reversed heat engine operates between -13 0C and 370

C. Calcu-late its coefficient of performance as a refrigerator and as a heat

pump. [8+8]

4. (a) Why do the isobars on mollier diagram diverge from one another? (Unit IV)

(b) Find the enthalpy and entropy of steam when the pressure is 2 Mpa and the specific volume is 0.09 m3/kg. Use the steam table only. [6+10]

5. A gas in a cylinder fitted with a piston undergoes a cycle composed of three

processes. First, the gas expands at constant pressure with a heat addition of

42.0 kJ and a work output of 12.0 kJ. Then it is cooled at constant volume by a removal of 48 kJ of heat. Finally, an adiabatic process restores the gas to its initial state. Determine

(a) the work of the adiabatic process and

(b) the stored energy of the gas at each of the other two states if its stored energy in the initial state is assigned the value of zero. [16]

6. The number of moles, the pressures, and the temperatures of gases a, b, and c aregiven as followsGas m (kg mol) p (kPa) t (0C)N2 1 330 95CO 3 410 190O2 2 680 285

If the containers are connected, allowing the gases to mix freely, find

(a) the pressure and temperature of the resulting mixture at equilibrium, and

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Code No: 07A3EC08 Set No. 4

(b) the change of entropy of each constituent and that of the mixture. [16]

7. (a) What is an air standard cycle? Why are such cycles conceived?

(b) Find the air standard efficiencies for Otto cycles with a compression ratio of 6

using ideal gases having specific heat ratios 1.35, 1.43 and 1.62. What are the

advantages and disadvantages of using helium as the working fluid? [6+10]

8. A food-freezing system requires 22 tonnes of refrigeration at an evaporator tem-

perature of - 30oC and a condenser temperature of 27oC. The refrigerant, R-12, is

subcooled 3oC before entering the expansion valve, and the vapour is superheated

4oC before leaving the evaporator. A six-cylinder single-acting compressor with

stroke equal to bore is to be used, operating at 1550 rpm. Determine

(a) the refrigerating effect

(b) the refrigerant flow rate

(c) the theoretical piston displacement per sec

(d) the theoretical power required in kW

(e) the COP

(f ) the heat removed in the condenser, and

(g) the bore and stroke of the compressor. [16]

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