thermo objective

THERMODYNAMICS

6. Assertion (A) : For a mixture of solid, liquid and vapour phases of a pure substance in equilibrium, the
number of independent intrinsic properties needed is equal to one.
Reason (R): The three phases can coexist only at one particular pressure.
(a) BothAand R are individually true and R is the correct explanation ofA
(b) Both A and R are true but R is not the correct explanation of A
(c) Ais true but R is false
(d) Ais false but R is true

7. An adiabatic steam turbine receives dry saturated steam at 1.0 MN / m2 & discharge it at
0.1 MN/m2. The steam flow rate is 3 kg/s and the moisture at exit in negligible. if the ambient
temperature is 300K determine the rate of entropy production an the lost power. (G - 99)

8. Avessel of volume 1.0m3 contains a mixture of liquid water and steam in equilibrium at 1.0 bar. Given

that 90% of the volume is occupied by the steam, find the dryness fraction of the mixureAssume, at

1.0 bar, vf = 0.001 m3/kg and vs = 1.7 m3/kg. (GATE-ME-93)

9. In the vicinity of the triple point, the vapour pressures of liquid and solild ammonia are respectively

given by (GATE-ME-93)

In p = 15.16 - 3063/T and In p = 18.70 - 3754/T

Where p is in atmospheres and T is in Kelvin. What is the temperature at the triple point.

10. Constant pressure lines in the superheated region of the Mollier diagram will have (GATE-ME-95)

a)Apositive slope b)Anegative slope

c) Zero slope d) Both positive and negative slope

11. When wet steam flows though a throttle valve and remains wet at exit (GATE-ME-96)

a) Its temperature and quiality increase

b) Its temperature decreases but quality increases

c) Its temperature increases but quality decresses

d) Its temperature and quality decrease

12. Given below is an etract form steam tables (GATE-ME-05)

Specific enthalpy of water in kj/Kg at 150 bar and 450C is

a) 203.60 b) 200.53

c) 196.38 d) 188.45

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13. Water has a critical specific volume of 0.003155 m3/kg. A clossed and rigid steel tank of volume

0.025m3 contains a mixure of water and steam at 0.1 MPa. The mass of the mixture is 10 kg. The tank

is now slowly heated. The liquid level iside the tank. (GATE-ME-07)

a) will rise b)will fall c) will remainsame

d) may rise or fall depending on the amount of heat transferred

14, 15 & 16 Common Data Quesions :-

In the figure shown, the system is a pure substance kept in a piston - cylinder arrangement. The system

is initially a two-phase mixture containing 1 kg of liquid and 0.03 kg of vapour at a pressure of

100kPa. Initially, the piston rests on a set of stops, as shown in the figure. A pressure of 200 kPa is

required to exactly balance the weight of the piston and the outside atomsphereic pressure. Heat

transfer takes place into the system occurs in such a manner that the volume increases by 50%.Heat

transfer to the system in such a manner that the piston, when allowed to move, does so in a very slow

(quasistatic/quais-euqilibrium) process. The thermal reservoir from which heat is transferred to the

system is at 4000C. Average temperature of system boundary can be taken as 1750 C . The heat

transfer to the system is 1kJ, during which its entropy increases by 10J/K.

 atomsphereic

g pressure Piston



------ ----------- 
--- ---
Stop ---
---
System -----------

-----------

Specific volume of liquid (V ) and vapour (v ) phases , as well as volues of saturation temperatures,
fg

are given in the able below :

Pressure (kPa) Saturation temperature, Tsat(0C) Vf(m3/kg) Vg(m3/kg)
100 100 0.001 0.1

14. At the end of the process, which one of the following situations will be ture ? (GATE-ME-08)

a) superheated vapour will be left in the system

b) no vapur will be left in the system

c) a liquid + vapour mixture will be left in the system

d) the mixture will exist at a dry saturate vapour state

15. The work done by the sysstem during the process is (GATE-ME-08)

a) 0.1 kj b) 0.2 kj c) 0.3 kj d) 0.4 kj

16. The net entropy generation (considering the system and the thermal reserviour together) during the

process is closest to (GATE-ME-08)

a) 7.5 J/K b) 7.7 J/K c) 8.5 j/K d) 10 J/K

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7 PROPERTIES OF PURE SUBSTANCES

(PRACTICE QUESTIONS)

1. List - I gives some processes of steam whereas List - II gives the effects due to the processes. Match

list - I with list - II and select the correct answer using the codes given below the lists: (1995)

List - I List - II

A.As saturation pressure increases - 1. Entropy increases

B.As saturation temp. increases - 2. Specific volume increases

C. As saturation pressue decreases - 3. Enthalpy of evaporation decreases.

D.As dryness fraction increases - 4. Saturation temp. increases

ABCD

(a) 1 3 2 4

(b) 4 3 2 1

(c) 4 3 1 2

(d) 2 4 3 1

2. The ordinate and abscissa in the given fig. showing the throtting process of a pure substance

represent.

(a) temperature and pressure

(b) enthalpy and entropy Sat.
(c) pressure and volume Sat. Vapour
(d) pressure and enthalpy liquid

3. Assertion (A):At a given temperature, the enthalpy of superheated steam is the same as that of
saturated steam.
Reason (R): The enthalpy of vapour at lower pressures is dependent on temperature alone.
(a) BothAand R are individually true and R is the correct explanation ofA.
(b) Both A and R are true but R is not the correct explanation of A
(c) Ais true but R is false
(d) Ais false but R is true.

4. The given diagram shown as isochoric cooling process 1- 2 of a pure substance.

The ordinate and abscissa are respectively.
(a) pressure and volume
(b) enthalpy and entropy
(c) temperature and entropy
(d) pressure and enthalpy

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5. In which one of the following working substances, does the relation [(T2/T1) = (P2V1)0. 286] hold

good if the process takes place with zero heat transfer ?

(a) Wet steam (b) Superheated steam

(c) Petrol vapour and air mixture (d) Air

6. With increase of pressure, the latent heat of steam

(a) remains same (b) increases (c) decreases (d) behaves unpredictably

7. Assertion (A): Water is not a pure substance.

Reason (R): The term pure substance designates a substance which is homogeneous and has the same

chemical composition in all phases.

(a) BothAand R are individually true and R is the correct explanation ofA

(b) Both A and R are true but R is not the correct explanation of A

(c) Ais true but R is false (d) A is false but R is true

8. Match list - I with list List - II and select the correct

answer using the code given below the lists:

List - I List - II

A. Critical point - 1.All the three phase - solid, liquid and vapour coexits in equilibrium.

B. Sublimation - 2. Phase change form solid to liquid.

C. Triple point - 3. Properties of saturated liquid and saturated vapour are identical.

D. Melting - 4. Heating process where solid gets directly transformed to gaseous phase.

Codes:

ABCD

(a) 2 1 4 3

(b) 3 4 1 2

(c) 2 4 1 3

(d) 3 1 4 2

9. Which p- v diagram for steam illustrates correctly the isothermal process undergone by wet steam till

it becomes superheated ?

(a) (b)

(c) (d)

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10. Which one of the following is the fluid whose properties in all its three phases are made use of in

thermodynamics?

(a)Ammonia (b) Freon 12 (c) Helium (d) Water

11. For a pure substance, what are the numbers of the thermodynamic degrees of freedom for saturated

vapour and superheated vapour, respecitvely?

(a) 1 and 1 (b) 1 and 2 (c) 2 and 1 (d) 2 and 2

12. Which one of the following is correct ?
The specific volume of water when heated from 0oC

(a) First increases and then decreases. (b) first decreases and then increases.

(c) increases steadily (d) decreases steadily

13. Which one of the following is correct ?

At critical point the enthalpy of vaporization is

(a) dependent on temperature only (b) maximum

(c) minimum (d) zero

14. Consider the following:

1. Air 2. Gaseous combustion products

3. Steam

Which of these are pure substances, assuming there is no phase change ?

(a) 1 and 2 only (b) 1 and 3 only

(c) 2 and 3 only (d) 1, 2 and 3

15. Consider the following properties of vapour:

1. Pressure 2. Temperature

3. Dryness fraction 4. Specific volume

Which of these two properties alone are not sufficient to specify the condition of a vapour ?

(a) 1 and 2 (b) 1 and 3

(c) 2 and 3 (d) 3 and 4

16. A pure substance is

(a) two component system existing in one or more phases

(b) one component system existing in one phases

(c) two component system existing in one phases

(d) one component system existing in one or more phases

17. Saturated water at enthalpy 600 kJ/kg is injected into saturated steam at an enthalpy 2400 kJ/kg .

If mixing process accomplished at constant pressure & the mixing ratio of water to steam is 1:10 by

mass. The enthalpyof mixture is.

(a) 2218.36 kJ (b) 2236.36 kJ

(c) 3218.36 kJ (d) 1500 kJ

18. A large insulated vessel is divided into two chambers, one containing 2 kg. of dry saturated steam at

0.2MPa and the other 4 kg of steam, 0.8 quality at 0.5 MPa . If partition between chambers is

removed, the steam is mixed throughly and allowed to settle. what will be the mass of mixture.

(a) 3 kg (b) 4 kg (c) 5 kg (d) 6 kg

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19. At its critical point, any substance will

(A) exist in all three phase simultaneously

(B) change directly from solid to vapour.

(C) behave as an ideal gas

(D) loose phase distinction between liquid and vapour.

20. Consider the following statements :

When dry saturated steam is throttled from a higher pressue to a lower pressure, the

1. Pressure decreases and the volume increases

2. Temperature decreases and steam becomes superheated

3. Temperature & the dryness fraction increases

4. Entropy increases without any change in enthalpy

Which of these statements are correct?

(a) 1 and 4 (b) 1 , 2 and 4 (c) 1 and 3 (d) 2 and 4

********************

“Dream come true: without that possibility,
nature would not incite us to have them”

7. Properties of Pure Substances (Practice Questionsz) Ans. :
1-sol, 2-d, 3-b, 4-b, 5-sol, 6-c, 7-d, 8-b, 9-c, 10-d, 11-b, 12-b, 13-d, 14-c, 15-a, 16-sol., 17-sol,
18-sol, 19-sol, 20-sol.

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8 AIR CYCLES

(CLASS WORK OBJECTIVE)

1. The minimum pressure and temperature in an Ottocycle are 100 KPa and 270C.The amount of heat

added to the air per cycle is 1500kJ / kg. Determine the pressures and temperatures at all points of the

air standard Otto Cycle. also calculate the specific work and the thermal efficiency of the cycle for a

compression ratio of 8:1 [Take Cv (air) as 0.72 kJ / kg K and (G - 98)

Cp

= 1.4]

Cv air

2. A gas turbine cycle with infinitely large number of stages during compression and expansion leads to.

(a) Stirling cycle (b)Atkinson cycle (G- 94)

(c) Ericcson cycle (d)Brayton cycle.

3. A cycle consisting of two reversible isothermal processes and two reversible isobaric processes is

known as (G - 96)

(a)Atkinson cycle (b) Stirling cycle

(c) Brayton cycle (d) Ericsson cycle

4. In air - standard Otto cycle the terminal pressures at the end of compression, heat release and expan

sion are respectively P2, P3 and P4. If the corresponding values are P21, P31 and P41, taking into

account the effect of variable specific heat and dissociation of the working fluid, then.

[GATE-ME-89]

a) P2 <P21 and P3 > P31 b) P3 <P31 and P4 > P41

c) P2 >P21 , P3 > P31 and P4 > P41 d) P2 <P21 , P3 > P31

5. An air-standard diesel cycle consists of : (GATE-ME-90)

a) Two adiabatic and two constant volume processes

b) Two constant volume and two isothermal processes

c) One constant pressure, one constant volume and two adiabatic processes

d) One constant pressure, one constant volume and two isothermal processes

6. The Figure below shows a thermodynamic cycle undergone by a certain system. Find the mean

effective pressure in N/m2 P (GATE-ME-93)
bar

5 --------------------------
-------------------
2 -------

0.01 0.02 V(m2)

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7. A double acting single stage compressor running at 200 rpm has an average piston speed of 3m/s. Its

indicated horse power is 50 hp while compressing air from 1 bar to 6 bar with a compression index of

1.2. If the temperature of air at inlet is 200C, determine the dimension of the cylinder neglecting

clearance. (GATE-ME-91)

8. A four cylinder, four stroke compression ignition engine develops an indicated power output of

150 kw at 150 rpm. The stroke is 1.5 times the bore and the indicated mean effective pressure (imep)

is 6.0 bar find dimesions of cylander. (GATE-ME-90)

9. An air standard Otto cycle has a volumetric compression ratio of 6, the lowest cycle pressure of

0.1 MPa and operates between temperature limits of 270 C and 15690 C.

a) Calculate the temperature and pressure after the isentropic expansion (Ratio of specific heats = 1.4)

b) Since it is observed that values in (a) are well above the lowest cycle operating conditions, the

expansion process was allowed to continue down to a pressure of 0.1 MPa. Which process is

required to complete the cycle ? Name the cycle so obtained.

c) Determine by what percentage the cycle efficiency has been improved. (GATE-ME-94)

10. An engine working on air standard Otto cycle has a cylinder diameter of 10 cm and stroke length of

1.5 cm. The ratio of specific heats for air is 1.4. If the clearance volume is 196.3 cc and the heat

supplied per kg of air per cycle is 1800 kj/kg, then work output per cycle per kg of air is

(GATE-ME-04)

a) 879.1 kj b) 890.2 kj c) 895.3 kj d) 973.5 kj

11. A large diesel engine runs on four stroke cycle at 2000 rpm. The engine has a displacement of 25 liter

and a brake mean effective pressure of 0.6 MN/m2. It counsumes 0.018 kg/s of fuel (calorific value

= 42000 Kj/kg). Determine the brake power and the brake thermal effeiciency. (GATE-ME-99)

12. An isentropic air turbine is used to supply 0.1 kg/s of air at 0.1 MN/m2 and at 285 K to a cabin. The

pressure at inlet to the turbine is 0.4 MN/m2. Determine the temperature at turbine inlet and the power

developed by the turbine. Asuume CP = 1.0 Kj/kg K. (GATE-ME-99)

13. In a spark ignition engine working on the ideal Otto cycle, the compression ratio is 5.5. The work

output per cycle (i.e., area of the P-V diagram) is equal to 23.625 x 105 x VcJ, where Vc is the

clearance volume in m3. The indicated mean effective pressure is (GATE-ME-01)

a) 4.295 bar b) 5.250 bar c) 86.870 bar d) 106.300 bar

14. An ideal air standard Otto cycle has a compression ratio of 8.5. If the ratio of the specific heats of air
() is 1.4, what is the thermal efficiency (in percentage) of the Otto cycle ? (GATE_ME -02)

a) 57.5 b) 45.7 c) 52.5 d) 95

15. For an engine operating on air standard Otto cycle, the clearance volume is 10% of the swept volume.

The specific heat ratio of air is 1.4. The air standard cycle efficiency is (GATE-ME-03)

a) 38.3% b) 39.8% c) 60.2% d) 61.7%

16. In an air-standard Otto cycle, the compression ratio is 10. The condition at the begining of the

compression process is 100kPa and 270C. Heat added at constant volume is 1500 kj/kg, whcile

700 kj/kg of heat is rrejected during the order constant volume process in the cycle. Specific gas

constant for air = 0.287 kj/kgK. The mean effective pressure (in kPa) of the cycle is (GATE-ME-09)

a) 103 b) 310 c) 515 d) 1032

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17 & 18 Common Data Questions

In two air standard cycles - one operating on the Otto and the other on the Brayton cycle - air is

isentropically compressed from 300 to 450 K. Heat is added to raise the temperature to 600K in the

Otto cycle and to 550 K in the Brayton cycle. (GATE-EM-05)

17. If  and  are the efficiencies of the Otto and Brayton cycleds, the
0 B
   
a) 0 = 0.25, B = 0.18 b) 0 = B = 0.33

c)  = 0.5,  = 0.45
0 B

d) It is not possible to calculate the efficiencies unless the temperature after the expansion is given

18. If W0 and WB are work outputs per units mass, then (GATE-ME-05)

a) W0 > WB

b) W < W
0B

c) W0 = WB

d) It is not possible to calculate the work outputs unless the temperature after expansion is given

19. The comprression ratio of a gas power plant cycle corresponding to maximum work output for the

given temperature limits of Tmin and Tmax will be [GATE-ME-04]

 

a) Tmax ( - 1) b) Tmin ( - 1)
T
min Tmax

- 1 - 1

Tmax  d) Tmin 

c) T Tmax
min

20. An ideal Brayton cycle, operating between the pressure limits of 1 bar and 6 bar, has minimum and

maximum temperatures of 300 K and 1500 K. The ratio of specific heats of the working fluid is 1.4.

The approximate final temperatures in Kelvin at the end of the compression and expansion processes

are respectively. [GATE-ME-11]

a) 500 and 900 b) 900 and 500

c) 500 and 500 d) 900 and 900

21. In a gas turbine, hot combustion products with the specific heats CP = 0.98 kj/kg K, and
CV = 0.7538 kj/kg K enter the turbine at 20 bar, 1500 K and exit at 1 bar. The isentropic efficiency
of the turbine is 0.94. The work developed by the turbine per kg of gas flow is [GATE-ME-03]

a) 689.64 kj/kg b) 794.66 kj/kg

c) 1009.72 kj/kg d) 1312.00 kj/kg

22. A turbo-charged four-stroke direct injection diesel engine has a displacement volume of 0.0259 m3

(25.9 litres). The engine has an output of 950 kW at 2200 rpm. The mean effective pressure

(in MPa) is closet to (GATE-ME-10)

a) 2 b) 1 c) 0.2 d) 0.1

23. In an air - standard regenerative gas turbine cycle the pressure ratio is 5.Air enters the compressor at

1 bar, 300 K and leaves at 490 K. the maximum temperature in the cycle is 1000 K. Calculate the

cycle efficiencygiven that the efficiencyof theregenerator and the adiabatic efficiency of the turbine are

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THERMODYNAMICS

each 80%. Assume for air the ratio of specific heats is 1.4.Also, show the cycle on a T - s diagrams.

[GATE-ME-97]

24. Find the required air-fuel ration in a gas turbine whose turbine and comprressor efficiencies are 85%

and 80% respectively. Maximum cycle temperature is 8750C. The working fluid can be taken as air
(C = 1.00 kJ/kg, K , = 1.4) which enters the compressor at 1 atm and 270 C. The pressure ratio is

P

4. The fuel used has calorific value of 42000 kj/kg. T here is a loss of 10% of calorific value in the

combustion chamber. [GATE-ME-99]

25 In a gas turbine, hot combustion products with the specific heats CP = 0.98 kj/kg K, and
CV = 0.7538 kj/kg K enter the turbine at 20 bar, 1500 K and exit at 1 bar. The isoentropic efficiency
of the turbine is 0.94. The work developed by the turbine per kg of gas flow is [GATE-ME-03]

a) 689.64 kj/kg b) 794.66 kj/kg c) 1009.72 kj/kg d) 1312.00 kj/kg

26. A closed cycle ideal gas turbine plant operates between temperature limits of 8000 C and 300 C and

produces a power of 100 KW. The plant is designed such that there is no need for a regenerator.

A fuel of calorific value 45000 kJ/kg is used. Calculate the mass flow rate of air through the plant and

the rate of fuel consumption. (Assume CP = 1 kJ/kg K and the ratio of specific heats = 1.4)
[GATE-ME-94]

27 & 28 common data questions :-

A thermodynamic cycle with an ideal gas working fluid is shown below (GATE-ME-07)

P 3
400kPa

100kPa 1
2

1 m3 V V
1

27. The above cycle is represented on T-S plane by

a) T 3 b) T 3 1 c) T 3 1 d) T 3

< <
<
12 22 1
2

S SS
S
28. If the specific heats of working fluid are constant and the value of specific heat ratio  is 1.4, the

thermal efficiency (%) of the cycle is (GATE-ME-07)

a) 21 b) 40.9 c) 42.6 d) 59.7

**************************

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THERMODYNAMICS

8 AIRCYCLES

( PRACTICE QUESTIONS )

1. For maximum specific output of a constant volume cycle (Otto cycle)

(a) the working fluid should be air.

(b) the speed should be high.

(c) suction temperature should be high.

(d) temperature of the working fluid at the end of compression and expansion should be equal.

2 Consider the following statements regarding Otto cycle
1. It is not a reversible cycle.
2. Its efficiency can be improved by using a working fluid of higher value of ratio of specific heats.
3. The practical way of increasing its efficiency is to increase the compression ratio.
4. Carburetted gasoline engines working on Otto cycle can work with compression ratios more
than 12
(a) 1,3 and 4 are correct
(b) 1,2 and 3 are correct
(c) 1,2 and 4 are correct
(d) 2,3 and 4 are correct

3 Match list - I with list - II and select the correct answer using the codes given below the lists:

List - I - List - II
(cycles operating between fixed -
cycle temperature limits) - (Characteristic of
A. Otto cycle - Efficiency )
B. Diesel cycle - depends onlyupon temp. limits
C. Carnot cycle -  depends only on pressure limits
D. Brayton cycle  depends on volume compn ratio
 depends on cut-off-ratio and
ABCD
(a) 3 4 1 2 volume compression ratio.
(b) 1 4 3 2
(c) 3 2 1 4
(d) 1 2 3 4

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4 Match list - I (The T-S diagram of thermodynamic cycles ) with list - II (Names of cycles) and select

the correct answer using the codes given below the lists:

List - I List - II

A. 1. Brayton cycle

B. 2. Otto cycle
3. Stirling cycle
v=c 4. Ericssion cycle
v=c 5. Diesel cycle

C.

p=c
p=c

D.

p=c

p=c

ABCD
(a) 1 4 5 2
(b) 1 3 4 5
(c) 2 4 5 1
(d) 2 3 4 1

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5. Match list - I (name of cycles) with list - II (pv diagram) and select the correct answer using the codes

given below the lists:

List - I List - II

A. Stirling cycle 1.

Isothermal

B. Diesel cycle 2.

Adiabatic

C. Otto cycle 3. Adiabatic

D.Atkinson cycle 4. Adiabatic

Adiabatic

ABCD

(a) 2 3 1 5

(b) 1 3 2 5

(c) 2 3 1 4

(d) 1 3 2 1
6 In an air standard Otto cycle, r is the volume compression ratio and is an adiabatic index (Cp/Cv),

the air standard efficiency is given by. (b) = 1-[1 / (r)]
(a) = 1-[1 / (r)] (d) = 1-[1 / (r)]
(c) = 1-[1 / (r)]

7 The order of values of thermal efficiency of Otto, Diesel and Dual cycle, when they have equal

compression ratio and heat rejection, is given by.
(a)Otto >Diesel >Dual
(b) Diesel >Dual >Otto
(c)Dual >Diesel >Otto
(d) Otto >Dual >Diesel

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8 In an air- standard Diesel cycle; r is the compression ratio , is the fuel cut-off-ratio and is the

adiabatic index (Cp/Cv). Its air standard efficiency is given by.
(a) = 1-{(1/r)[(-1) / (-1)]} (b) = 1-{(1/r)[(-1) / (-1)]}
(c) = 1-{(1/r)[(-1) / (-1)]} (d) = 1-{(1/r)[(-1) / (-1)]}

9 A system comprising of a pure substance executes reversibly a cycle 1-2-3-4-1 consisting of two

isentropic and two isochoric processes as shown in the fig.1

2
3

14

Which one of the following is the correct representation of this cycle on the temperature - entropy
coordinates?

a) 4 b) T 1 2
4
T3 1 3
2 S S

c) T 2 d) T

1

43

S

10 A cycle consists of two reversible isothermal processes and two reversible isobaric processes is

known as.

(a)Atkinson cycle (b) Stirring cycle

(c) Brayton cycle (d) Ericsson cycle

11 An IC engine has a bore and stroke of 2 units each. the area to calculate heat loss can be taken as.

(a) 4 (b) 5 (c) 6 (d) 8

 An ideal air standard cycle is shown in the given temperature - entropy diagram.

3

21  Copyright : Ascent Gate Academy 64

The same cycle, when represented on the pressure -
volume coordinates takes the form .

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(a) THERMODYNAMICS 3
1
23 (b)

1 2

(c) (d)

2 2

3 3
1 1

13. Match list - I (details of process of the cycle) with list - II (name of the cycle) and select correct

answer using the codes given below the lists:

List - I List - II

A. Two isothermals and two adiabatic - 1. Otto

B. Two isothermals and two constant volumes - 2. Joule

C. Two adiabatics and two constant volumes - 3. Carnot

D. Two adiabatics and two constant pressures - 4. Stirling

Codes:-

ABCD

(a) 4 3 1 2

(b) 4 3 2 1

(c) 3 4 1 2

(d) 3 4 2 1

14. For the same maximum pressure and heat input, the least efficient cycle is. 2000

(a) otto cycle (b) Diesel cycle

(c) Brayton cycle (d) Dual combustion cycle

15. Match list - I and (Cycles) with list - II (Processes) and select the correct answer using the codes

given below the lists:- 2003

List - I List - II

A. Bell Coleman cycle - 1. One constant pressure, one constant volume and two is entropic.

B. Stirlingcycle - 2. Two constant pressure and two is entropic.

C. Ericsson cycle - 3. Two constant pressure and two isothermal

D. Diesel cycle - 4. Two constant volume and two isothermal.

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Codes:- 2007
ABCD
4
(a) 2 3 4 1
(b) 1 4 3 2
(c) 2 4 3 1
(d) 1 3 4 2
16

3

21

Thermodynamic cycle shown above on the temperature - entropy diagram pertains to which one of

the following ?

(a) Stirling cycle (b) Ericsson cycle

(c) Vapour compression cycle (d) Brayton cycle

17. An inventor says that his new concept of an engine, while working between temperature limits of
27oC and 327oC rejects 45% of heat absorbed from the source. His engine is then equivalent to

which one of the following engines? 2009

(a) Carnot engine (b) Diesel engine

(c)An impossible engine (d) Ericsson engine

18. Which cycle consists of two reversible isotherms and two reversible isobars?

(a) Carnot cycle (b) Stirling cycle

(c) Ericsson cycle (d) Brayton cycle

19.

v = const

T T v = const
1. S 2.

P = const S

T V = const T
3. 4. S

S

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The correct sequence of the given four cycles T-s plane in fig. (1), (2), (02), (3), (4) is

(a) Rankine, Otto, Carnot and Diesel (b) Rankine, Otto, Diesel and Carnot

(c) Otto, Rankine, Diesel and Carnot (d) Otto, Rankine, Carnot and Diesel

20. A gas turbine plant operates on the Brayton Cycle between Tmin = 300 K & Tmax = 1000K. The

cycle efficiencyis.

(a) 47% (b) 45.23% (c) 53% (d) 54.77%

21. Ratio of Bryton cycle efficiency to carnot cycle efficiency if both cycle operates between

Tmin = 300K & Tmax = 1000 K, is

(a) 1 (b) 0.8 (c) 0.65 (d) 0.52\

22. A gas turbine cycle operates on the Brayton cycle between 300K & 1073 K. The maximum work

done per kg of air is (if Cp = 1.005 kJ/Kg-K)

(a) 239.47 kJ/kg (b) 39.28 kJ/kg (c) 441.28 kJ/kg (d) 501.08 kJ/kg

23. Group 1 Group 2 (G- 2K)

1. Marine Diesel Engine - A Two stroke engine.

2.Air conditioning - B. Four stroke engine.

3. Steam Power plant - C. Rotary engine.

4. Gas Turbine Power Plant - D.Cooling and Dehumidification.

- E. Cooling Tower.

- F. Brayton Cycle.

- G. Rankine Cycle.

- H D- slide valve.

Codes:-

1234

(a) B E F H

(b) C F E G

(c) C F G E

(d) A D G F

************************

“The real oppportunity for success lies within the person
and not in the job”

8. Aircycles (Practice Ques.) Ans. :
1-d, 2-sol, 3-a, 4-d, 5-b, 6-a, 7-d, 8-c, 9-c, 10-d, 11-b, 12a, 13-c, 14-c, 15-c, 16-b, 17-c, 18-c,
19-b, 20-b, 21-c, 22-a, 23-d.

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9 RANKINE CYCLES

(CLASS WORK OBJECTIVE)

1. For a given set of operating pressure limits of a Rankinge cycle, the highest efficiency occurs for
(G- 94)

(a) Saturated cycle (b) Superheated cycle (c) Reheat cycle (d) Regenerative cycle.
2. Consider a Rankine cycle with superheat. If the maximum pressure in the cycle is increased without

changing the maximum temperature and the minimum pressure, the dryness fraction of steam after the
isentropic expansion will increase (T/F)......
3. Arankine cycle operators between pressures of 80 bar and 0.1 bar. The maximum cycle temperature
is 6000C . If the steam turbine and condensate pump efficiencies are 0.9 and 0.8, respectively,
calculate the specific work and thermal efficiency. Relevant steam table extract is given below.

(G - 98)
At 80 bar of 6000c, v = 0.486m3/kg, h = 3642 kj/kg, S = 7.0206kJ/kg k

P T Vf Vg h f hg Sf Sg

0.1 45.84 0.001003 14.68 191.9 2584.2 0.6488 8.1494

80 295.1 0.001385 0.0235 1317 2757.5 3.2073 5.7424

4. The efficiency of superheat Rankine cycle is higher than that of simple Rankine cycle is because.

(G- 2002)

(a) The enthalpy of main steam is higher for superheat cycle .

(b) The mean temperature of heat addition is higher for superheat cycle

(c) The emperature of steam in the condensor is high.

(d) the quality of stem in the condensor is low.

5. In a Rankine cycle, regeneration results in higher

efficiency because . (G- 2003)

(a) pressure inside the boiler increases

(b) heat is added before steam enters the low pressureturbine

(c) average temperature of heat addition in the boiler increases

(d) total work delivered by the turbine increases .

6. An economizer in a steam generator performs the function of : [GATE-ME-89]

a) Preheating the combustion air b) Preheaeting the feed water

c) Preheating the input fuel d) Raising the temperature of steam

7. In the Rankine cycle when superheated steam is used [GATE-ME-90]

a) Thermal efficiency increasses

b) Steam consumption decreases

c) Steam dryness after expansion increases

d)All of the above

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8. In a Rankine cycle heat is added [GATE-ME-91]

a) Reversibly at constant added

b) Reversiblyat constant volume

c) Reversibly at constant pressure and temperature

d) Reversibly at constant pressure

9. In a single heater regenerative cycle, steam enters the turbine at 30 bar, 3000C and condenser

pressure is 0.096 bar. The feed water heater is a direct contact type which operates at 5 bar. Draw

flow and h-s a diagrams considering the condition of steam at entry to the heater in mixture region.

Calculate steam extracted from hater to tubine in kg per kg of steam flow the cycle and cycle

efficiency. The enthalpies of steam at different locatios of the cycle are given in a table below. Pump

work may be neglected. [GATE-ME-91]

Location Entry to Entry to Entery to Exit from Exit from
h (k/kg) Turbine Heater Condenser Condenser heater

2993.5 2622.22 2056.39 188.45 640.23

10. Boiler rating is usually defined in terms of [GATE-ME92]

a) Maximum temperature of steam in Kelvin b) Heat transfer rate in kJ/hr

c) Heat transfer area in metre2 d) Steam ouput in kg/hr

11. In a steam power plant operating with simple Rankien cycle, the turbine is fed with steam at 100 bar

and 673 K. Determine the actual enthalpy and quality of the steam extracted at 14 bar if the turbine

stage efficiency is 90 percent. [GATE-ME-92]

12. For a given set of operating pressure limits of a Rankine cycle the highest efficiency occus for

[GATE-ME-94]

a) Saturated cycle b) Superheated cycle c) Reheat cycle d) REgenerative cycle

13. Dry saturated steam enters a frictionless adiabatic nozzle with negligible velocity at a temperaturee of

3000 C. It is expanded to a pressure of 5000 kPa. The mass flow rate is 1 kg/s. Calculate the exit

velocity of steam. [GATE-ME-95]

Properties of Steam

Sat temp Sat. press Enthalpy (kJ/Kg) Entropy (kJ/Kg/0C Specific volume
(0C) (kPa) (m3/Kg)

300 8593 Sat liq. Sat Vap. Sat liq. Sat Vap. Sat liq. Sat Vap.
263.91 5000 1345 2751 3.2552 5.7081 0.0014 0.0216
1154.5 2794.2 2.9206 5.9735 0.0012 0.0394

14. A steam power plant has the boiler efficiency of 92%,turbine efficiency (mechanical) of 94%,

generator efficiency of 95% and cycle efficiency of 44%. If 6% of the generated power is used to run

the auxilaries, the overall plant efficiency is [GATE-ME-96]

a) 34% b) 39%

c) 45% d) 30%

15. Consider an actual regenerative Rankine cycle with one open feed water heater. For each kg steam

entering the turbine, if m kg steam with a specific enthalpy of h1 is bled h3 the specific enthalpy of

saturated liquid leaving the heater is equal to [GATE-ME-97]

a) mh1 - (h2 - h1) b) h1 - m (h2 - h1)
c) h2 - m (h2 - h1) d) mh2 - (h2 - h1)

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16. An adiabatic steam turbine receives dry saturated steam at 1.0 MN/m2 and discharges it 0.1 Mn/m2.

The steam flow rate is 3kg/s and the moisture at exit in negligible. If the ambient temperature is 300K,

determine the rate of entropy production and the lost power. [GATE-ME98]

Steam properties :

P Tsat hf hg Sf Sg
MN/m2 0C
kJ/kg kJ/kg kJ/kg K kJ/kg K
10 179.9 762.8 2778.1
0.1 99.6 417.5 2675.5 2.139 6.586
1.303 7.359

17 & 18 Common Data Questions :

Consider a steam power plant using a reheat cycle as shown. Steam leaves the boiler and enters the

turbine at 4 MPa, 3500 C (h3 = 3095 kj/kg). After expansion in the turbine to 400 kPa

(h4 = 2609 kj/kg), the steam is reheated to 3500 C (h5 = 3170 kg/kg), and then expanded in a flow

pressure turbine to 10 kPa (h6 = 2165 kj/kg). The specific volume of liquid handled by the pump can

be assumed to be [GATE-ME-04]

h = 3095 kJ/kg
3

3

BOILER TURBINE
REHEATER

h = 2609 kJ/kg
4

( ) 4
(
h5 = 3170 kJ/kg

5 h = 2165 kJ/kg
6

2 6

PUMP h = 29.3 kJ/kg
1

CONDENSER

1

17. The thermal efficiencyof the plant neglecting pump work is

a) 15.8% b) 41.1%

c) 48.5% d) 48.5%

18. The enthalpy at the pump discharge (h2) is b) 3.33 kj/kg
a) 0.33 kj/kg

c) 4.0 kj/kg d) 33.3 kj/kg

19. Determine the correctness or otherwise of the followingAssertion (a) and the Reason (r).

Assertion (A) : In a power plant working on a Rankine cycle, the regenerative feed water heating improves

the efficiency of the steam turbine.

Reason (R) : The regenerative feed water heating raises the average temperature of heat addition in the

Rankine cycle.

a) Both A and R are true and R is the correct reason for A

b) Both A and R and true but R is NOT the correct reason for A

c) Both A and R are false

d) Ais false but R is true

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20. Which combination of the following statements is correct ? [GATE-ME-07]

The incorporation of re-heater in a steam power plant.

P : always increases the thermal efficiency of the plant

Q : always increase the dryness fraction of steam at condenser inlet.

R : always increases the mean tempeerature of heat addition

S : always increase the specific work output.

a) P and S b) Q and S c) P, R and S d) P, Q, R and S

21. Athermal power plant operates on a regenerative cycle with a single open feed water heater, as shown

in the figure. For the state points shown, the specific enthalpies are : h1 = 2800 kj/kg and

h2 = 200 kj/kg. The bleed to the feed-water heater is 20% of the boiler steam generation rate. The

specific enthalpy at state 3 is [GATE-ME-08]

a ) 720 kJ/kg Boiler > Boiler > Tur- >

Feed pump bine

b) 2280 kJ/kg 1 Condenser

3 <
<
c) 1500 kJ/kg << 2

<<

d) 3000 kJ/kg Open feed-water Condensate
COMMON DATA QUESION 22 & 23 heater extraction
pump

The inlet and the outlet conditions of steam for an adiabatic steam turbine are as indicated in the figure.

The notations are as usually followed.

h1 = 3200 kJ/kg <
V1 = 160 m/s <
Z1 = 10 m
P1 = 3 MPa

h2 = 2600 kJ/kg
V = 100 m/s

2

Z2 = 6 m
P2 = 70 K Pa
22. If mass flow rate of steam through the turbine is 20kg/s, the power output of the turbine (in MW) is

[GATE-ME-09]

a) 12.157 b) 12.941 c) 168.001 d) 168.785

23. Assume the above turbine to be part of a single Rankine cycle. The density of water at the inlet to the

pump is 1000 kg/m3. Ignoring kinetic and poterntial energy effects, t he specific work (in kJ/kg)

supplied to the pump is [GATE-ME-09]

a) 0.293 b) 0.351 c) 2.930 d) 3.510

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COMMON DATA FOR 24 & 25
In a steam power plant operating on the Ranking cycle,steam enters the turbine at 4 MPa, 3500 C and
exists at a pressure of 15 kPa. Then it enters the condenser and exists as saturated water. Next, a
pump feeds bakc the water to the boiler. The adiabatic efficinecy of the turbine is 90%. The thermo
dynamic states of water and steam are givene in table.

State h(kjkg - 1) s(kjkg-1 K-1) v(m3 Kg-1)
Steam 4MPa, 350 C 3092.5 0.06645
6.5821
Water : 15 Kpa Hf hg Vf Vg
225.94 2599.1 Sf Sg 0.001014 10.02

0.7549 8.0085

h is specific enthalpy, s is specific entropy and V the specific volume ; subscripts f and g denote

saturated liquid state and saturated vapour state. [GATE-ME-10]

24. The net work output (kj kg-1) of the cycle is

a) 498 b) 775 c) 860 d) 957

25. Heat supplied (kg kg-1) to the cycle is

a) 2372 b) 2576 c) 2863 d) 3092

*******

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9 RANKINE CYCLE

PRACTICE QUESTIONS

Level - 1

1. In an ideal steam power cycle with the same inlet pressure, the low dryness fraction of steam in the

laste staeg of expansion process can be avoided by

a) providing regeneration b) providing reheating

c) reducing the superheat d) lowering the condenser pressure

2. Assertion (A) : Air leaking into condenser of steam power plant reduces the output of the plant.

Reason (R) : Air inside condenser increases back pressure of steam turbine in the stem power plants.

a) Both A and R are true and R is the correct explanation of A

b) Both A and R are true but R is not a correct explanation of A

c) Ais true but R is false

d) Ais false but R is true

3. The function of an economizer in a steam power plant is to

a) increase the temperature of air supplied to a boiler

b) increase the enthalpy of feed water

c) condense the exhaust steam from the turbine

d) heat the fuel before combustion

4. The most efficient ideal regenerative steam power cycle is

a) Ranking cycle b) Carnot cycle c) Brayton cycle d) Joule cycle

5. In modern steam plants using pulverized fuel firing, the fuel gasses

a) Fist pass through air preheaters and then through economizer

b) First pass through economizer and then through air preheaters

c) Pass simultaneously through air preheaters and economizer which are connected in parallel

d) Pass through economizer only

Level - 2

6. Consider the following statements : The purpose of reheating the steam in a turbine power plant is to

1. increase specific output

2. increase turbine efficiency

3. reduce the turbine speed

4. reduce specific steam consumption

Which of these statements are correct ?

a) 2 and 4 b) 1 and 3 c) 1, 2 and 4 d) 1, 3 and 4

7. In a regenerative cycle, steam with enthalpy of 3514 kJ/kg is expanded in h.p. turbine to a state

corresponding to saturated enthalpy of water equal to 613 kJ/kg. If the pump work requirements in

high pressure and low pressure zones are respectively 3 and 1 kJ/kg , amount of heat transferred in

boiler is

a) 2897 kJ/kg b) 2898 kJ/kg c) 2904 kJ/kg d) 2905 kJ/kg

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8. Consider an actual regenerative Rankine cycle with one open feed water heater. For each kg steam

entering the turbine. For each kg steam entering the turbine, m kg steam with a specific enthalpy of

h1 is bled from the turbine. Specific enthalpy of water entering the heater is h2. The specific enthalpy of
saturated liquid leaving the heater is equal to

a) mh1 - (h2 - h1) b) h1 - m(h2 - h1)

c) h2 - m(h2 - h1) d) mh2 - (h2 - h1)

9. What is the efficiency of an ideal regenerative Rankine cycle power plant using saturated steam at

3270C and pressure 135 bar at the inlet to the trubine and condensing temperature of 270C

(corresponding saturation pressure of 3.6 kPa) ?

a) 92% b) 33%

c) 50% d) 42%

10. Which is the cause of reheat factor in a steam turbine ?

a) Reheating b) Superheating

c) Supersaturation d) Blade friction

11. In a steam power plant, what is the outcome of regenerative feed heating ?

1. Increase in specific output

2. Increase in cycle efficiency

3. Improved quality of exhaust steam

4. Reduced condenser load

Select the correct answer using the code given below :

a) 1 and 3 b) 2 only c) 2 and 4 d) 1, 2 and 3

COMMON DATA FOR 12 & 13
In a steam power plant operating on the Ranking cycle,steam enters the turbine at 4 MPa, 3500 C and
exists at a pressure of 15 kPa. Then it enters the condenser and exists as saturated water. Next, a
pump feeds bakc the water to the boiler. The adiabatic efficinecy of the turbine is 90%. The
thermodynamic states of water and steam are givene in table.

State h(kjkg - 1) s(kjkg-1 K-1) v(m3 Kg-1)
Steam 4MPa, 350 C 3092.5 0.06645
6.5821
Water : 15 Kpa Hf hg Vf Vg
225.94 2599.1 Sf Sg 0.001014 10.02

0.7549 8.0085

h is specific enthalpy, s is specific entropy and V the specific volume ; subscripts f and g denote

saturated liquid state and saturated vapour state. [GATE-ME-10]

12. The net work output (kj kg-1) of the cycle is b) 775
a) 498 d) 957
c) 860

13. Heat supplied (kg kg-1) to the cycle is b) 2576
a) 2372 d) 3092
c) 2863

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14. The correct representation of a simple Rankine cycle on a T - S diagram is.
(a) (b)

T2 3 T3 2
1 4 4 1
S
(c) 2 (d) S
1 3
T 4 T3 2
4 1

SS

15. Assertion (A): For the same limits of boiler pressure and temperature, the specific steam consumption

of ideal Carnot cycle is less than that of ideal Rankine cycle.

Reason (R): Fort the same limits of boiler pressure and temperature,Carnot cycle is more efficient than

Rankine cycle.

16. Consider the following statements regarding Rankine cycles.

1. It reduces the specific steam consumption.

2. It increases the dryness fraction of steam at the exhaust for the same value of condensor pressure.

3. It reduces the cycle efficiency.

(a) 1 and 2 are correct (b) 2 and 3 are correct

(c) 1 and 3 are correct (d) 1,2 and 3 are correct

17. Asuper heat Rankine cycle is shown in the given T-S diagram.Starting from the feed pump, the fluid

flow upto the boiler exit is represented by state-line

(a) ABCD

(b) BCDE

(c) ABDEFA T DE
(d) ABCDE C

B

AF

S

18. In the Rankine cycle lower limit on the condenser pressure is due to the .
(a) expansion limit in turbine
(b) condenser size
(c) air leakage into the condenser
(d) temperature of cooling water.

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19. Which one of the following modifications to a Rankine cycle would upgrade/enhance its efficiency so
as to approach that of Carnot cycle?
(a) Incomplete expansion of steam
(b) Reheating of steam
(c) Regenerative feed heating by steam
(d) Partial condensation of steam

20. The curve labeled 1- 2 in the given fig. refers to the
expansion process of a
(a) Rankine cycle
(b) modified Rankine cycle
(c) regenerative cycle
(d) reheat cycle

21. Consider the following statements:

Steam turbines are suitable for use as prime movers for large power plants because.

1. Asingle steam turbine can be designed for a capacity of 1000 MW or more.

2. much higher speed may be possible as compared to a reciprocating engine.

3. they are more compact when compared to a gas turbine power plant.

4. the maintenance cost and running cost may not increase with years of service.

Which of these statements are correct?

(a) 1,2 and 3 (b) 2,3 and 4 (c) 1,2 and 4 (d) 1,3 and 4

22. The most efficient ideal regenerative steam power cycle is.

(a) Rankine cycle (b) Carnot cycle

(c) Brayton cycle (d) Joule cycle

23. Consider the following statements:

The purpose of reheating, the steam in a steam turbine power plant is to.

1. increase specific output.

2. increase turbine efficeincy

3. reduce the turbine speed

4. reduce specific steam consumption.

Which of these statements are correct?

(a) 2 and 4 (b) 1 and 3 (c) 1,2 and 4 (d) 1,3 and 4

24. For a given set of operating pressure limits of a Rankine cycle the highest efficiency occurs for.

(a) Saturated cycle

(b) Superheated cycle

(c) Reheat cycle

(d) Regenerative cycle

25. For two cycles coupled in series, the topping cycle has an efficiency of 30% and the bottoming cycle

has an efficiency of 20%. The overall combined cycle efficiency is. (1996)

(a) 50 % (b) 44 % (c) 38 % (d) 55 %

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26. A steam power plant has the boiler efficiency of 92%, turbine efficiency (mechanical) of 94%, genera

tor efficiency of 95% and cycle efficiency of 44%. If 6% of the generated power is used to run the

auxiliaries, the overall plant efficiencyis (1996)

(a) 34 % (b) 39 % (c) 45 % (d) 30 %

IES Questions:-

1995

27. Consider the following statements with reference to gas turbine cycle.

1. Regeneration increases thermal efficiency.

2. Reheating decreases thermal efficiency.

3. Cycle efficeincy increases when maximum temp. of the cycle is increased.

Of these statements

(a) 1, 2 and 3 are correct (b) 2 and 3 are correct

(c) 1 and 2 are correct (d) 1 and 3 are correct

1997

28. In a Rankine cycle, with the maximum steam temperature being fixed from metallurgical consideration,

as the boiler pressure increases.

(a) The condenser load will increase.

(b) The quality of turbine exhaust will decreases.

(c) The quality of turbine exhaust will increases.

(d) The quality of turbine exhaust will remain unchanged

1999

29. Consider the following statements:

The efficiency of the vapour power Rankine cycle can

increased by.

1. Increasing the temperature of the working fluid at which heat is added.

2. Increasing the pressure of the working fluid at which heat is added.

3. Decreasing the temperature of the working fluid at which heat is rejected.

Which of these statements is / are correct ?

(a) 2 and 3 (b) 1 alone (c) 1 and 2 (d) 1 , 2 and 3

30 Consider the following processes:

1. Constant pressure heat addition.

2.Adiabatic compression

3.Adiabatic expansion

4. Constant pressure heat rejection

The correct sequence of these processes in Rankine cycle is:

(a) 1,2,3,4

(b) 2,1,3,4

(c) 2,1,3,4

(d) 1,2,4,3

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2001

31. The temp. - entropy diagram for a steam turbine power plant, operating on the Rankine cycle with

reheat and regenerative feed heating is shown in the given fig. If m denotes the fraction of steam bled

for feed heating, the work developed in the turbine per kg steam entering the turbine at state 5 is.

(a) (h5 - h4) + (1 - m) (h3 - h1)

(b) (h5 - h4) + (h3 - h2) + (1 - m) (h2 - h1)

(c) 2h5 - h4 - h1 + (1 - m) (h2 - h1)

(d) (h5 - h4) + (1 - m) (h3 - h2) T

53

6

7 m 4
8 2

9 1
10 S

2003

32. Assertion (A):An ideal regenerative Rankine cycle power plant with satureated steam at the inlet to

the turbine has same thermal efficiency as Carnot cycle working between the same temp. limits.

Reason (R): The change in entropy of steam during

expansion in the turbine is equal to the change in entropy of the feed water during sensible heating at

steam genera - tor pressure.

(a) BothAand R are individually true and R is the correct explanation ofA

(b) Both A and R are true but R is not the correct explanation ofA

(c) Ais true but R is false.

(d) Ais false but R is true.

33. Assertion (A): The efficiency of regerative cycle is greater than Rankine cycle.

Reason (R): mean temperature of regenerative cycle is greater than mean temperature of Rankine

cycle.

(a) BothAand R are individually true and R is the correct explanation ofA

(b) Both A and R are true but R is not the correct explanation ofA

(c) Ais true but R is false.

(d) Ais false but R is true.

34. In a rankine cycle, the enthalpies at the end of constant pressure, reversible adiabatic expansion, rev.

constant pressure and rev. adiabatic compression are 3165, 2216, 173 & 175 kJ/kg respectively. The

efficiency of cycle is.

(a) 30.02% (b) 31.65%

(c) 35.7% (d) 42.05%

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35. T - S diagram of power station with reheat has been shown.

T p1 = 150 bar o 1 3

550 C

p2 = 4.0 bar

6s p3 = 0.1 bar
5 4s
X

S

Enthalpier at state 1, 2S, 3, & 4S are 3465, 3065, 3566, 2300, 191, 83 & 206.83 kJ/kg. The cycle

efficiency is

(a) 30.3 % (b) 34.75% (c) 40.3% (d) 43.9%

36. Steam rate (in kg/kw-h) for above problem is

(a) 2.18 (b) 3.18 (c) 2.58 (d) 3.58

Note:- Consider the following problem related to regenerative cycle and select the correct answers
for question from Q. 37 to Q.41

30 bar 1

o

4010 kCg

Turbine

Boiler 5 bar 2 0.1 bar
m kg 3
Condenser
Heater

7 6 4
Pump 5

1 kg Pump

(1-m) kg

37. The quality of steam after expansion is

(a) 0.836 (b) 0.876 (c) 0.916 (d) 0.936
(c) 0.213 kg (d) 0.35 kg
38. The extracted amout of steam is (c) 36.1% (d) 39.5%

(a) 0.12 kg (b) 0.172 kg

39. Cycle efficiencyis

(a) 29.5% (b) 33.1%

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40. Mean temperature (with regeneration ) is

(a) 100oC (b) 211.7oC (c) 185.38oC (d) 238.94oC
(c) 185.38oC (d) 238.94oC
41. Mean temperature (without regeneration ) is (c) 4.5 (d) 4.9
(c) nearly 3% (d) nearly 4%
(a) 100oC (b) 211.7oC

42. Steam rate (without regeration) in kg/kw-h is

(a) 3.47 (b) 2.47

43. Increase in efficiency due to regeneration is

(a) nearly 1% (b) nearly 2%

*****************

“If you can imagine it, you can achieve it. If you can dream it,
you can become it”

UNIT 9 : RANKINE CYCLE (PRACTICE QUESTIONS ANS. )
1- b, 2-a, 3-b, 4-b, 5-b, 6-d, 7-a, 8-c, 9-c, 10-a, 11-c, 12-c, 13-c, 14-a, 15- F, T 16-c, 17-a, 18-a, 19-
c, 20-c, 21-a, 22-b, 23-d, 24-d, 25-b, 26-a, 27-d, 28-b, 29-d, 30-c, 31-b, 32-a, 33-a, 34-b, 35-d,. 36-
a, 37-a, 38 -b, 39-c, 40-d, 41-b, 42-a, 43-b.

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10 REFRIGERATION

( CLASS WORK QUESTIONS )

1. A reciprocating compressor produces 10 tons of refrigeration at an evaporator temperature of 50 C

and a condenser temperature of 350 C. Estimate how much cooling effect it can produce at an

evaporator temperature of -300 C, the condenser temperature remaining un-altered.

Given : Refrigerant : R - 12, clearance = 5%, index of comprression (in both cases) is 1.15. Extract from

refrigerant property tables : (GATE-ME-87)

Temp Pressure Specific volume (m3/kg) Enthalpy (Kj/Kg)
(bar)
-300c 1.005 Liquid x 103 vapour Liquid Vapour
+50 c 3.631
+350 c 8.501 0.672 0.1600 8.88 174.96

0.725 0.0478 40.81 190.88

0.787 0.0208 69.74 202.96

2. A Freon - 12 vapour compression system is operating at a condenser pressure of 9.6 bar (960 kPa)

and an evaporator pressure of 2.19 bar (219 kPa). Its refrigerating capacity is 15 tons. The values of

enthalpy at the inlet and the outlet of the evaporator arte 64.6 kj/kg and 195.7 kj/kg. The specific

volume at the inlet to reciprocating comprressor is 0.082 m3/kg. The index of compression (or

polytropic exponent) for the compressor is 1.13. (GATE-ME-88)

a) The power input in KW temperature the compressor

b) The coefficient of performance

3. A reciprocating compressor in a vapour compression refrigeration system has a clearance factor of

4 percent and a swept volume of 26 litres/second. If the mass flow of regrigerant is 0.46 kg/s and the

specific volume of vapour at compressor suction and discharge are 37 liters/kg and 12 liters/kg

respectively, calculate the clearance volumetric efficiency and the actual volumetric efficiency of the

compressor. (GATE-ME-89)

4. A refrigeration compressor, designed to operate with R 22 ______ (can/cannot) be operated with

R 12 because the condensing pressure of R 22 at any given temperature is ______ (higher/lower) than

that of R 12 (GATE-ME-92)

5. A refrigeration system of 15 tons capcityoperates on standard simple vapour compression cycle using
Refrigerant - 22 at an evaporator temperature 50C and condensing temperature of 500 C. Draw the
p-h diagram for the cycle. Calculate.
i) The refrigerant mass flow rate,and
ii) The compressor intake volume flow rate if the compressor volumetric efficiency is 0.72

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Use the refrigerant property data given in Table below (GATE-ME-93)

Temp. Pressur Enthalpy Volume
00C bar
Sat. Liquid Sat. Vapour Sat. Liquid Sat. Vapour
5 5.836
50 19.423 kJ/kg kJ/kg kJ/kg m3/kg

205.9 407.1 0.791 0.0404

263.3 417.7 0922 0.0117

6. Sketch the standard vapour compression refrigeration cycle on the enthalpy (y-axis) - entropy

(x-axis) plane, indicate the directions and processes clearly. (GATE-ME-94)

7. A refrigeration compressor of 50 mm bore and 40 mm stroke operates at a speed of 1460 rpm

between condensing and evaporating pressure limits of 1.219 MPa and 0.151 MPa. The clearance

ratio is 5%, ratio of specific heats of refrigerant is 1.18, specific volume of regrigerant at suction is

0.11 m3/kg and the enthalpy change of refrigerant in the evaporator is 93.7 kj/kg. Calculate the

refrigeration load the compressor can serve. (GATE-ME-94)

8. A refrigeration cycle uses Freon - 12 as working fluid. The temperature of the refrigerant in the

evaporator is - 100 C. The condensing temperature is 400 C. the cooling load is 150 W and the

volumetric efficiency of the compressor is 80%. The speed of compressor is 720 rpm. Calculating the

mass flow rate of the regrigerant and the displacement volume of thecompressor. (GATE-ME-95)

Properties of Freon - 12

Temperature Saturation Enthalpy (kJ/Kg) Specific volume
(0C) Pressure (m3/kg)
(MPa) Saturated
-10 0.22 Saturated vapour
40 0.96 Liquid Vapur 0.08
0.02
26.8 183.0

74.5 203.1

9. In a simple vapour compression cycle, following are the properties of the refrigerant R -12 at various

points : (GATE-ME-96)

Compressor inlet : h1 = 183.2 kJ/kg v1 = 0.0767 m3/kg
Compressor discharge : h2 = 222.6 kJ/kg ; v2 = 0.0164 m3/kg
Condenser exit : h3 = 84.9 kJ/kg ; v3 = 0.00083 m3/kg

The piston displacement volume for the compressor is 1.5 litres per stroke and its volumetric

efficiency is 80%. The speed of the compressor is 1600 rpm. Find (a) power rating of the

compressor (kW), (b) refrigerating effect (kW).

10. Clearance volume of a reciprocating compressor is 100 ml, and the volume of the cylinder at bottom

dead centre is 1.0 liter. The clearance ratio of the compressor is (GATE-ME-97)

a) 1/11 b) 1/10

c) 1/9 d) 1/1.1

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11. List - I List - II

A. Liquid to suction heat exchanger 1. Vapour abgsorption refrigeration

B. Constant volume heat addition 2. Vaopur compression refrigeration

C. Normal shock 3. Diesel cycle

D.Ammonia - water 4. Otto cycle

5. Converging nozzle

6. Converging - diverging nozzle

12. In a standard vapour compression refrigeration cycle, operating between an evaporator temperature
of 100 C and the condenser temperature of 400 C, the enthalpy of the regrigerant, Freon - 12 the end
of comprerssion is 220 kJ/kg . Show the cycle diagram on T - s plane. Calculate (a) the COP of the
cycle (b) the refrigerating capacity and the compressor power assuming a refrigerant flow rate of
1 kg/min. You may the extract of the Freon - 12 property table given below : (GATE-ME-97)

t(0C) p(MPa) hf(kJ/kg) hg (kJ/kg)

-10 0.2191 26.85 183.1

40 0.9607 74.53 203.1

13. An R-717 (ammonia) system operates on the basic vapour compression refrigration cycle. The

evaporator and the condenser pressure are 0.119 MPa and 1.389 MPa respectively. The mass flow

rate of refrigerant is 0.1 kg/s. If the volumetric efficiency of the compressor is 84%. Determine the

compressor displacement rate. If the COP of the cycle is 2, determine the power input to the

compressor. (GATE-ME-99)

Temp. Pressure Specific Enthalpy Kj/kg
(0C) (MPa) Volume
m3/kg Liquid Vapur
-30 0.119 0.9638
36 1.389 0.0930 63.9 1423.6
371.4 1488.6

14. In a vapour compression refrigeration system, liquid to suction heat exchanger is used to
(GATE-ME-00)

a) Keep the COP constant
b) prevent the liquid refrigerant from entering the compressor
c) sub-cool the liquid refrigerant leaving the condenser
d) sub-cool the vapour refrigerant from the evaporator

15. Global warming is caused by (GATE-ME-00)
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a) ozone b) carbon dioxide

c) nitrogen d) carbon monoxide

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16. In a 5 kW cooling capacity regrigeration system operating on a simple vapour compression cycle, the

refrigerant enters the evaporator with an enthalpy of 75 kJ/kg and leaves with an enthalpy of

183 kj/kg. The enthalpy of the refrigerant after compression is 210 kJ/kg, show the cycle on T - S or

P - h diagram. Calculate the following (a) COP (b) power input to compressor and (c) rate of heat

transfer at the condenser. (GATE-ME-00)

17. An ice making plant using refrigerant R - 12 is having an evaporator saturation temperature of -250C

and the condenser saturation temperature of 350 C. The vapour is leaving the compressor at 650 C.

The following table shows the properties of the refrigerant . (GATE-ME-02)

Temperature (0C) Pressure (kPa) Saturation Enthalpy kj/kg

Liquid vaopur

-25 123.7 13.3 176.5

35 850.0 69.6 201.5

Enthalpy of superheated refrigerant at 850 kPa and 65 C = 225.5 kj/kg

a) Calculate the Coefficient of performance (COP) of this system
b) If the capacity of the plant is 5 kW, calculate mass flow rate of refrigerant

18 & 19 COMMON DATA QUESTIONS

A refrigerator based on ideal vapour compression cycle operates between the temperature limits

of -200 C and 400 C. The refrigerant enters the condenser as saturated vaour and leaves as saturated

liquid. The enthalpy and entropy values for saturted liquid and vapour at these temperatures are given

in the table below : (GATE-ME-03)

T(0C) hf(kj/kg hg (kj/kg K) Sf (kj/kg K) Sg (kj/kg K)
-20 20 180 0.07 0.7366
40 80 200 0.3 0.67

18. If refrigerant circulation rate is 0.025 kg/s, the refrigeration effect is equal to

a) 2.1 kW b) 2.5 kW c) 3.0 kW d) 4.0 kW

19. The COP of the refrigerator is

a) 2.0 b) 2.33 c) 5.0 d) 6.0

20. In the window air conditioner, the expansion device used is (GATE-ME-04)

a) capillary tube b) thermostatic expansion value

c) automatic expansion value d) float value

21. Environment friendly refrigerant R134a is used is used in the new generation domestic refrigerators. It

chemical formula is (GATE-ME-04)

a) CH CIF2 b) C2 Cl3 F3 c) C2 Cl2 F4 d) C2 H2 F4

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22. A R - 12 refrigerant reciprocating coompressor operates between the condensing temperature of

300 C and evaporator temperature of -200 C. The clearance volume ratio of the compressor is 0.03.

Specific heat ratio of the vapour is 1.15 and the specific volume at the suction is 0.1089 m3/kg. Other

properties at various states are given in the figure. To realize 2 Tons of regrigeration, the actual volume

displacement rate considering the effect of clearnace is (GATE-ME-04)

a) 6.35 x 10-3 m3 / S 74 5 3 300 C 2

b) 63.5 x 10-3 m3 / S P Bar -200 C

150
4

c) 635 x 10-3 m3 / S 65 176 207
d) 4.88 x 10-3 m3 / S n kj/kg

23. The vapour compression refrigeration cycle is represented as shown in the figure below, with state
I being the exit of the evaporator. The coordinate system used in this figure is (GATE-ME-05)

a) p - h 2
b) T - s
c) p - s 3
d) T - h
<

V

41

24. In an ideal vapour compression refirgeration cycle, the specific enthalpy of refrigerant (in kj/kg) at the

following states is given as : (GATE-ME-09)

Inlet of condenser : 283 T
2

Exit of condenser : 116

Exit of evaporator : 232 3
4
The COP of this cycle is 1
S
a) 2.27 b) 2.75

c) 3.27 d) 3.75

*************

“There are many paths to the top of the mountain,
but the view is always the same”

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11 PSYCHROMETRY

( CLASS WORK QUESTIONS )

1. In an air conditioning system , air is to be cooled and dehumidified bymeans of a cooling coil. The data

are as follows : (GATE - ME - 88)

Initial conditon of the air at the inlet to the cooling

Dry bulb temperature = 250C

Partial pressure of water vapour = 0.019 bar

Absolute total presure = 1.02 bar (102 kPa)

Final condition of the air at the exit of the cooling coil :

Dry bulb temperature = 150C

Relative humidity= 90%

Absolute total pressure = 1.02 bar (102 kPa)

other data are as follows :

Specific gas constant for air = 287 J/kg K

Specific gas constant for water vapour = 461.5 J/kg K

Saturation pressure for water at 150C = 0.017 bar (1.7 kPa)

Enthalpy of dry air = 1.005 t kJ/kg.

Enthalpy of water vapour = (2500 + 1.88 t) kJ/kg. where t is temperature in 0C.

Determine

a) moisture removed from air per kg of dry air

b) Heat removed by the cooling coil per kg of dry air

2. Wet bulb depression, under saturated ambient air conditions : (GATE - ME - 89)

a) is always positive

b) is always negative

c) is always zero

d) May have a value depending upon the new point temperature

3. 20 kg/s of air at 300 C and a humidity ratio of 0.01 kg water vapur/kg air are mixed with 12 kg/s of air

at 380 C and a humidity ratio of 0.02 kg water vapour/kg air. If there is no external addition or

removal of moisture and heat, determine the temperature and humidity ratio of the resultant air steam

from first principles. Indicate the process on a psychometric chart (GATE - ME - 89)

4. Atmospheric air from 400C and 60 percent ralative humidity can be brought to 200C and 60 percent

relative himidityby: (GATE - ME - 90)

a) Cooling and dehumidification process

b) Cooling and himidification process

c)Adiabatic saturation process

d) Sensible cooling process

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5. In an air - conditioning system 200 m3/min air is cooled and dehumidified from 320C and specific

humidity 0.014 kg/kg of dry air to 160 C and specific humidity 0.011 kg/kg of dry air. Draw the

psycho-metric process and calculate the sensible heat factor. (GATE - ME - 90)

Average property values may be taken as :
Density of air,  = 1.2 kg/kg of dry air

Specific heat of air, C0 = 1.0216 kJ/kg K
Latent heat of water, h1 = 2500 kJ/kg

Draw the following characteristic

6. If moist air is cooled by sensible heat removal, which of thefollowing is true ? (GATE - ME - 91)
a) Neither relative humidity nor specific humiditychanges
b) Specific humiditychanges but not relative humidity
c) Both relative humidityand specific humiditychange
d) None of the above

7. At a location where the atmospheric pressure is 960 m bar, the temperature is 300 C and the relative

humidity 60%, calculate the humidity ratio, degree of saturation, enthalpy and dew point.Assume that

air and water vapour may be treated as perfect gases. The following data may be used :

(GATE - ME - 94)

Mair = 29 ; Mwater = 18 ;

Universal Gas constant = 8.314 kJ/kg mole K

Cp air = 1 k/kg JK

Cp water = 4.186 kJ/kg K

Vapur pressure of water follows the equation

In P = 19.013 - 5325 , P in kPa T in K

T

8. On the psychometric chart consider a point at a given dry and wet bulb temperature. At this point
show directions of
(GATE - ME - 95)
a) Sensible cooling
b) Sensible heating
c)Adiabatic saturation
d) Isothermal humidification
e) Cooling and dehumidification
f) Chemical dehumidification

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9. Select statements from List II matching the processes in List I. Entry your answer as D, C if the correct

choice for (1) is (D) and that for (2) is (C) (GATE - ME - 99)

List I List II

(1) Cooling and dehumidification (A) Dry bulb temperature increases

but dew - point temperature decreases

(2) Chemical dehumidification (B) Dew - point temperature increaes and

Dry temperature remains unchanged

(C) Dry - bulb and wet - bulb temperatures decrease

(D) Dry - bulb temperature decreases, but,

dew - point temperature increases

10. For air at a given temperature, as the relative humidity is increased isothermally, (GATE - ME - 01)

a) the wet bulb temperature and specific enthalpy increase

b) the wet bulb temperature and specific enthalpy decrease

c) the wet bulb temperature increaes and specific enthalpy decreases

d) the wet bulb temperature decreases and specific enthalpy increases

11. For air with a relative humidity of 80% (GATE - ME - 03)

a) the dry bulb temperature is less than the wet bulb temperature

b) the dew point-temperature is less than wet bulb temperature

c) the dew point and wet bulb temperatures are equal

d) the dry bulb and dew point temperatures are equal

12. During chemical dehumidification process of air

(GATE - ME - 04)

a) dry bulb temperature and specific humidity decrease

b) dry bulb temperature increases and specific humidity decreases

c) dry bulb temperature decreases and specific humidity increase

d) dry bulb temperature and specific humidity increase

13. Dew point temperature of air at one atmospheric pressure (1.013 bar) is 180C. The air dry bulb

temperature is 300C. The saturation pressure of water at 180C and 300C are 0.02062 bar and 0.04241

bar respectively. The specific heat of air and water vapour respectively are 1.005 and 1.88 kj/kg K

and the latent heat of vaporization of water at 00C is 2500 kj/kg. The specific humidity (kj/kg of dry

air) and enthalpy (kj/kg of dry air of this moist air respectively, are (GATE - ME - 04)

a) 0.01051, 52.64

b) 0.01291, 63.15

c) 0.01481, 78.60

d) 0.1532, 81.40

14. For a typical sample of ambient air (at 350C, 75% relative humidity and standard atmosheric pressure)

the amount of moisture in kg per kg of dry air will be approximately (Psat at 350C = 0.05622 bar)
(GATE - ME - 05)

a) 0.02 b) 0.027 c) 0.25 d) 0.75

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15. Water at 420 C is sprayed into a stream of air at atmospheric pressure, dry bulb temperature of 400 C

and a wet bulb temperature of 200 C. The air leaving the spray humidifier is not saturated. Which of the

following statements is true ? (GATE - ME - 05)

a)Air gets cooled and humidified b)Air gets heated and humidified

c)Air gets heated and dehumidified d)Air gets cooled and dehumidified

16. Various psychometric process are shown in the figure below (GATE - ME - 05)

Process in Figure Name of the process

P. 0 - 1 1. Chemical dehumidification 5
Q. 0 -2 2. Sensible heating 4
R. 0 - 3 3. Cooling and dehumidification
S. 0 - 4 4. Humidification with steam injection 1
T. 0 - 5 5. Humidification with water injection 0
32

The matching pairs are

a) P - 1, Q - 2, R - 3, S - 4, T- 5 b) P - 2, Q- 1, R - 3, S - 5, T - 4

c) P - 2, Q - 1, R - 3, S - 4, T - 5 d) P - 3, Q - 4, R- 5, S - 1, T- 2

17. Dew point temperature is the temperature at which condensation begins when the air is cooled at

constant (GATE - ME - 06)

a) Volume b) Entropy c) Pressure d) Enthalpy

18. The statements concern psychometric chart (GATE - ME - 06)

1. Constant relative humidity lines are uphill straight lines to the right

2. Constant wet bulb temperature lines are downhill straight lines to the right

3. Constant specific volume lines are downhill straight lines to the right

4. Constant enthalpy lines are coincident with constant wet bulb temperature lines

Which of the statements are correct ?

a) 2 and 3 b) 1 and 2 c) 1 and 3 d) 2 and 4

19. A thin layer of water in a field is formed after a farmer has watered it. The ambient air conditions are :

temperature 200 C and relative humidity 5% (GATE - ME - 06)

An extract of steam tables is given below :

Temp(0C) -15 -10 -5 0.01 5 10 15 20
Pressure 0.10 0.26 0.40 0.61 0.87 1.23 1.71 2.34
(kPa)

Neglecting the heat transfer between the water and the ground, the water temperature in the field after

phase equilibrium is reached equals

a) 10.30 C b) -10.30 C

c) -14.50 C d) 14.50 C

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20. Atmospheric air at a flow rate of 3 kg/s (on dry basis) enters cooling and dehumidifying coil with an

enthalpy of 85 KJ/kg of dry air and a humidity ratio of 19 grams/kg of dry air. The air leaves the coil

with an enthalpy of 43 kj/kg of dry air and a humidity ratio of 8 grams/ kgof dry air. If the condensate

wate leaves the coil with an enthalpy of 67 kj/kg, the required cooling capacity of the coil in kW is

(GATE-ME-07)

a) 75.0 b) 123.8 c) 128.2 d) 159.0

21. Moist air at a pressure of 100 kPa is compressed to 500 kPa and then cooled to 350 C in an after

cooler. The air at the entry to the aftercooler is unsaturated and become just saturated at the exit of the

aftercooler. The saturation pressure of water at 350 C is 5.628 kPa. The partial pressure of water

vapour (in kPa) in the moist air entering the compressor is closest to (GATE-ME-08)

a) 0.57 b) 1.13 c) 2.26 d) 4.52

22. Air (at atmospheric pressure) at a dry bulb temperature of 400 C and wet bulb temperature of 200 C is

humidified in an air washer operating with continuous water recirculation. The wet bulb depression

(i.e. the difference between the dry and wet bulb temperatures) at the exit is 25% of that at the inlet.

The dry bulb temperature at the exit of the air washer is closest to (GATE-ME-08)

a) 100 C b) 200 C c) 250 C d) 300 C

23. A moist air sample has dry bulb temperature of 300 C and specific humidity of 11.5 g water vapour

per kg dry air. Assume molecular weight of air as 28.93. If the saturation vapour pressure of at 300 C

is 4.24 kPa and the total pressure is 90 kPa, then the relative humidity (in %) of air sample is

(GATE-ME-10)

a) 50.5 b) 38.5 c) 56.5 d) 68.5

24. If a moist air in an airtight vessel is heated to a higher temperature, then (GATE-ME-11)

a) specific humidity of the air increases

b) specific humidity of the air decreases

c) Relative humidity of the air increases

d) relative humidity of the air decreases

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