BASIC CONCEPTS, ZEROTH LAW & WORK
Note- 1)One or more options may be correct 2) Choose the nearest answer
1)Which of the following is/are correct about an open system –
a) both mass and energy can cross the system boundary.
b) work cannot cross the system boundary.
c) it is also-called control volume system.
d) mass cannot be stored.
e) flow is always steady.
2) Which of the following is/are correct about a closed system –
a) only mass can cross the system boundary.
b)work cannot cross the system boundary.
c) it is also-called control mass system.
d) the mass inside the system may increase or decrease.
e) there is no boundary.
3) Which of the following is/are correct about a pure substance –
a) it can remain in one phase only.
b) it has same chemical composition throughout.
c) liquid gas mixture of air is not a pure substance.
d) water is always a pure substance.
4) Which of the following is/are correct about Degree of freedom of a system a)it denotes No. of dependent intensive properties to define state
b)it denotes No. of independent intensive properties to define state
c)For a three phase one component system degree of freedom is zero.
d) A system containing air has two degree of freedom.
5) Which of the following is/are correct about a cyclea) Final and initial states are same
b)Change in all properties in a cycle is zero.
c) entropy can change during a cycle
d)Only two processes one isothermal and one adiabatic can make a cycle
6) Which of the following is/are correct about a reversible processa) During a reversible process there is no change in system and surrounding
b) Reversible process is the most efficient process
c) Reversible process can be completely reversed
d)During the process all states are equilibrium states
7)Change 212ºC into Fahrenheit
a) 415F
b)413.6 F
c) 422.7 F
d) cannot be done
8) Which of the following represent triple point of watera) .01ºC
b) 273 K
c) 273.16K
d) All of these
9)In a mercury thermometer length of mercury column is 5 cm when
temperature is 100ºC & 2 cm when temperature is 30ºC . What will be the
length of mercury column at 0ºC.
a)0.71 cm
b)0.62 cm
c)0.93 cm
d)none
10)In a constant volume thermometer the pressure measured at triple point of
water is 0.1 bar. What will be the measured temperature if the pressure inside
the thermometer is 0.2 bar
a)0.02ºC
b)273.17ºC
c).02K
d) 273.17K
𝟐
11)The equation W=∫𝟏 𝑷𝒅𝒗 is applicable for
a) Only open system
b) closed system
c) all systems
d) isolated system
12) The equation W=∫Pdv is applicable for
a) all substances
b)ideal gases
c) only gases
d)only liquids and gases
13) For an open system work done is given by
2
2
2
a) -∫1 𝑣𝑑𝑝
b)∫1 𝑣𝑑𝑝
c) ∫1 𝑝𝑑𝑣
d) none of these
14)A gas(air) is contained in a cylinder piston arrangement. The mass of the gas
is 2 kg, press 2 bar and specific volume 0.1m³/kg. Due to expansion the
volume of the gas changes to .4 m³. Find out work done by the gas ifi) the pressure of the gas remains constant at 2 bar
a) 80KJ
b) 50 KJ
c) 40 KJ
d) 90 KJ
ii) the gas expands isothermally
a) 27.72 KJ
b) 26.52 KJ c) 19.45 KJ d) None of these
iii) the gas expands adiabatically
a)36 KJ
b)24 KJ
c)96 KJ
d)none of these
15) In a compressor air enters at 5 bar 27ºC. After compression the pressure
becomes 25 bar.
i) Work done on air per kg if process is isothermal
a) -135KJ
b) -138.6 KJ
c)+135 KJ
d)+138.6 KJ
ii) Work done on air per kg if process is adiabatic
a)-175.9 KJ b)-177.5 KJ c) -26.9 KJ d)none of these
16) 5 Kg of Hydrogen with specific volume 0.5 m³/kg & temperature 50ºC is
filled in a cylinder piston arrangement. Find the final pressure and volume ifi) the temperature increases to 100ºC & volume remains constant
a)58.96bar,2.5m³
b)31 bar,2.5m³
c) 36 bar,3.5m³
d) None
ii)the temperature increases to 100ºC & pressure remains constant
a)26.8 bar, 5m³
b) 26.8 bar, 2.9 m³ c) 58.6 bar,5m³
d) none
iii)the volume is doubled isothermally
a)13.4 bar,2.5m³
b)13.4 bar, 5m³
c) 28bar,10m³
d) none
iv) the temp becomes 100ºC adiabatically
a)80bar,1.74m³
b)450 bar,.22m³
c) 120bar,.66m³
d)none
Answers
1.a,c
2.c
3.b,c,d
10.b
11.b
12.a
13.a
4.b,c,d
5.a,b
6.b,c,d
7.b
8.a,c
14.i)c ii)a
iii)b
15.i)b ii)a
16.i)b ii)b
9.a
iii)b
iv)a
CLOSED & OPEN SYSTEM WORK
1)A cylinder contains 2 kg of air. Heat is transferred to the gas at constant volume & the
temperature rises by 30 ºC. The gas is brought to it’s initial state & the temperature is
again increased by 30ºC but now at constant pressure. What is the difference in heat
transfer in both the processes.
a)17.22 KJ
b)8.61 KJ
c) 9.42 KJ
d)None of these
2) In a cycle 1-2-3-4 in the process 1-2, 60 KJ is transferred to the system and 20 KJ
work is done by the system. In the process 2-3, 30 KJ work is done by the system and 10
KJ heat is taken out of the system. If in the process 3-4, 60 KJ heat is taken out of
system and 20 KJ of work is done on the system find the heat given/taken to/from the
system in the process 4-1 if it is given that there is no work transfer in the process 4-1.
a) +60 KJ
b) +40 KJ
c) -40 KJ
d) -60 KJ
3)A cylinder contains 2 Kg of air. It undergoes a process 1-2 in which 60 KJ of heat is
added to the gas. What is the rise in it’s temperature.
a)41.78 K
b) 4.178 K
c) 417.8 K
d) 417 K
4)A cylinder piston arrangement is kept vertically in equilibrium. If the weight of the
piston is 20 N, cross section area of piston is 5 cm² then findi) Pressure inside the cylinder if atmospheric pressure is 1 bar.
a)2.8 bar
b)1.7 bar
c) 1.4 bar
d) data insufficient
ii) How much heat is to be added to raise the temp of inside air by 40K if mass of air is 1
Kg
a)40.2 KJ
b) 60.8 KJ
c)314.56 KJ
d) none of these
5)A cycle 1-2-3-4-1 with ideal gas as working fluid consists of two isothermal processes 12 & 3-4 and two adiabatic processes 2-3 & 4-1. In the isothermal 1-2 the heat given to
the system is 50 KJ
i) what is the work done during process 1-2
a) 100 KJ
b) +50 KJ
c)-50 KJ
d) insufficient data
ii)What is the change in internal energy of gas during process 1-2
a)Zero
b) +50 KJ
c) -50 KJ
d) None
iii) In the adiabatic process 2-3 if work done by the system is 60 KJ, then heat transfer is
a)+ 60 KJ
b) -60 KJ
c)zero
d)None
6) In a polytropic process with index n=1.3 and 3 kg air as working fluid the heat transfer
to the system during process is 100KJ. What is the change in temperature of aira) +139.27K
b) -139.27K
c) +39.27K
d) -39.27K
7) In a steady flow process the inlet air has specific enthalpy 100KJ/kg and velocity 50
m/s. 600 KJ heat is added to the system and 40 KJ is received as shaft work. If the
outlet velocity is 100m/s find the specific enthalpy of outlet air given that mass flow
rate is 3 kg/sec.
a) 364.2KJ/Kg
b)339.4 KJ/Kg
c)282.9 KJ/Kg
d)none
8)In a turbine with air as flowing fluid the entering air has temperature 400K and exiting
air has temperature 200 K. Find the specific work produced by the turbine
a) 200KJ/kg
b) 300 KJ/Kg
c)305 KJ/Kg
d) 201 KJ/kg
9)In a throttling process the inlet enthalpy is 600 KJ & inlet press is 5 bar. The outlet
fluid has pressure of half the inlet pressure and volume .5m³. Find
i)Work done in the process
a)zero
b) 2.5 MJ
c) 60 KJ
d)insufficient data
ii) The internal energy of fluid at outlet
a) 250 KJ
b)350 KJ
c) 80 KJ
d) 475 KJ
10) In a bottle filling process with no heat transfer the entering ideal gas(γ=1.67) has
temperature of 300K. If the bottle is filled upto the press of supply mains what is the
temp of fluid in the bottle neglecting K.E. & P.E.
a) 501K
b)420 K
c) 300K
d) none
11) An insulated box containing .5 Kg of a gas having Cv=.98KJ/KgK falls from a balloon
4 km above the earth’s surface. What will be the temperature rise of the gas when the
box hits the grounda) 0K
b)20 K
c) 40 K
d)60 K
12) The internal energy of certain system is a function of temperature alone & is given
by the formula E=25+0.25t KJ. If this system executes a process for which work done by
it per degree temperature increase is 0.75KN-m then the heat interaction per degree
temperature increase in KJ isa)-1.00
b)-0.50
c)0.50
d)1.00
Ans-1)a 2)b 3)a 4)i-c,ii-a
5)i-b,ii-a,iii-c 6)b 7)c 8)d
9)i-a,ii-d 10)a 11)c
12)d
SECOND LAW OF THERMODYNAMICS
1.A reversible engine is working between source temperature 727ºC & sink temperature
T. If the engine takes 500KJ/s as input and rejects 200KJ/s to sink then find
temperature T.
a)227ºC
b)127ºC
c) 300K
d) 180K
2.A reversible engine working between source temperature T1 & sink temperature T2 has
an efficiency η1 if the source temperature is increased to T3 where T3> T1 then
a) the efficiency of the engine will remain the same b) the efficiency will increase
c)the efficiency will decrease
d) nothing can be said with certainity
3. A heat pump working between temperature limits 300K and 600K has a COP of 1.5.
We can conclude thata) it follows an irreversible cycle
b) it follows a reversible cycle
c) such heat pump is impossible to construct
d)none
4. A refrigerator has COP of 5 and works between environment at 27ºC & storage
temperature T. what is the minimum possible temperature of T
a)-15ºC
b)-33ºC
c)0ºC
d) None
5. In a Carnot cycle operating between temperature limits of 1000K & 300K. If 1kg of air
is used in the cycle at initial pressure 5 bar & the heat taken by the system is 100 KJ.
Find
i) work done during the isothermal heat addition
a) 100 KJ
b) 50 KJ
c)-100 KJ
d)80 KJ
c)89 KJ
d) 703.5 KJ
ii) work done during the cycle
a)301.5 KJ
b) 70 KJ
6. A reversible engine is to be used as a thermometer. It is found that when operating
between one reservoir at triple point of water & other at temp T the heat taken by the
engine from the reservoir at temp T is 100 KJ and work done by the engine is 70 KJ. Find the
temp T.
a) 1500 K
b)910.5 K
c)1100.82 K
d) none
7. A reversible engine operating between temperature limits of 1000K & 300 K drives a
heat pump which operates between temperature limits of 500 K & 1200 K. If the heat
taken by the engine is 5 KJ/s how much heat is being pumped to 1200 K reservoir.
a)6 KW
b) 9 KW
c)15 KW
d) none
8. A reversible heat engine works between 3 reservoirs A,B &C at temperatures 1000K,
700 K & 300K resepectively by taking heat both from reservoirs A& B & rejecting it to
C.If heat taken by reservoir A is 700 KJ and total heat rejected to reservoir C is 500 KJ
then heat taken by reservoir B & total work done is
a) 676.6,875.7
Ans-1)b
b)987.6,567.8
2)b
3)a
4)b
c) 876,567
5)i)a ii)b
6)b
d) none
7)a
8)a
ENTROPY
1.The value of δQ/T for a cycle isa) always greater than zero
c)always less than or equal to zero
b) always less than zero
d) always greater than equal to zero
2. Which of the following is termed as entropy change ds
a)(δQ/T)rev
b)(δQ/T)irrev
c) either a or b
d) none
3. A system changes from state 1 to state 2 through an irreversible path 1-a-2
with net heat exchange δQirrev & through a reversible path 1-b-2 with net heat
exchange δQrev . Which of the following is/are correcta) Change in entropy ‘ds’ will be same both for reversible and irreversible path
b) The value of change in entropy can be either δQrev/T or δQirrev/T
c)ds irr >(δQ/T )irr & ds rev >(δQ/T )irr
d)ds irr< δQ/T )irr & ds rev >(δQ/T )rev
4. A system undergoes a process 1-2
a) It’s entropy can only increase
b) it’s entropy can only decrease
c) there will be no change in entropy if the process is reversible
d) entropy can
either increase or decrease or remain same
5. The entropy of universe or isolated system
a) always remains constant
same but never decrease
b) always increases
c) can increase or remain
d) nothing could be said without certainty
6. A system undergoes an irreversible process 1-2 . It’s entropy will always
a) increase b) decrease c) can increase , decrease or remain same depending on δQ&I
7.Which of the following is/are correct
a) An isentropic process is always reversible b) A reversible adiabatic process is
always isentropic c) An adiabatic process is always isentropic
d) An isentropic
process is always adiabatic
8. The area of T-S diagram in a cycle 1-2-3-4-1 shows
a) work done
b) heat supplied
c) heat rejected
d) entropy change
9. Tds equations are applicable for
a) all processes & systems
process e) Only open System
b) only reversible process d) Only irreversible
f) Only closed system
10. The slope of a constant volume line on T-S diagram where temperature is
27ºC & working fluid is air would bea)30º
b)22.7º
c)28.8º
d) none
11. i)The state of air(m=5kg) in a container changes from 5bar & 0.5m³ to 10 bar
in a isothermal process . Find the change in entropy of the gas
a)-.994KJ/K
b)-.198KJ/K
c)+.994KJ/K
d)+.198KJ/K
ii) If the change of state takes place through a polytropic process n=1.2 then the
change in entropy would bea)-.407 KJ/K
b)-2.03 KJ/K
c)+.407 KJ/K
d)-.45 KJ/K
iii) If in the polytropic process n=1.4 then change in entropy would bea)zero
b)-2.86 KJ/K
c)+3.25 KJ/K
d) none
12.Water at 20ºC is heated to steam at 100ºC at atmospheric pressure. If the
latent heat of vaporization of water is 540 Kcal/KgK then find
i) change in entropy of water when 20ºC water is converted to 100ºC water
a)1 KJ/Kg K
b) 2 KJ/KgK
c) 5 KJ/KgK
d) none
ii) change in entropy when water at 100ºC is converted into steama)5 KJ/KgK
b)6.05 KJ/KgK
c) 8 .09KJ/KgK
d)none
iii) If the steam at 100ºC is converted in water reversibly to atmospheric
temperature of 20ºC by extracting heat then the maximum work which can be
obtained isa) 800KJ/Kg
b)630KJ/kg
c)526 KJ/Kg
d)none
13. Two similar blocks of mass 2 kg and specific heat 0.1 KJ/kgK are at
temperatures 300 ºC & 50 ºC respectively. If a reversible engine is operated
between them then
i) the final temperature obtained by both the blocks would be
a)157.2ºC
b)314.4 ºC
c) 188 K
d)none
ii) The work achieved in the process isa)7.12 KJ
b)8.24 KJ
c)15.32 KJ
d)none
Ans-1.c 2.a 3.a,c 4.d 5.c 6.c 7.b 8.a 9.a 10.b 11.i)a ii)a iii)a 12.i)a ii)b iii)c 13.i)a ii)a
Availability & Irreversibility
1.Find the available energy in case of a reversible engine absorbing 1000 KJ of
heat at 1000K & rejecting it to the environment at 300K.
a)500 KJ
b) 600 KJ
c) 700 KJ
d) 800 KJ
2.Find the loss of available energy if 1000 KJ of heat is transferred from 400ºC
to 200ºC & environment is at 30ºC.
a) 190.36 KJ
b) 85.62 KJ
c) 184.56 KJ
d) 88.59 KJ
3. A reversible cyclic engine has 20 kg of air as working fluid. If the heat
absorption process is isobaric and the max cycle temp is 400ºC what is the
maximum work possible if environment is at 300 K.
a) 12.5 MW
b) 10.91 MW
c) .55 MW
d) 6.8 MW
4. Availability is dependent on
a) state of system
b) atmospheric condition c) type of process
d) is constant
5. Availability is defined as
a) maximum useful work b) maximum work c) actual work
d) irreversible work
6. The state of a gas(air) in a cylinder changes from 5 bar 100ºC to 3 bar 50ºC.
Find the change in availability if mass of the gas is 2 kg & environment is at 1
bar 27ºC
a)26.98 KJ
b) 53.98 KJ
c) 44.29 KJ
d) 52.25 KJ
7. In an irreversible turbine the inlet air has a pressure & temperature of 10 bar
& 100ºC whereas the outlet air has a pressure & temperature of 5 bar & 50 ºC. If
the environment is at 1 bar and 27ºC find(i) Change in availability of air
a)15.87 KJ/kg
b)30.74 KJ/kg
c)90.75 KJ/kg
d)none
c)90.75 KJ/kg
d)none
(ii) Maximum possible work
a)15.87 KJ/kg
b)30.74 KJ/kg
(iii) Actual work done if the heat transfer from turbine to the environment is 40
KJ/Kg during expansion
a)10.25 KJ/Kg
b) 15.44 KJ/Kg
(iv) Irreversibility of the process is
c) 199.96 KJ/Kg
d) none
a)5.62 KJ/Kg
b) 11.22 KJ/kg
c) 9.65 KJ/kg
d)8.66 KJ/Kg
(v) Maximum work if the expansion from 10 bar 100ºC to 5 bar is reversible &
isentropic
a)67.34 KJ/Kg
b)96.42 KJ/Kg
c) 99.96 KJ/Kg
d) 42.42 KJ/Kg
(vi) The isentropic efficiency or first law efficiency of turbine
a)15.22 KJ/kg
b)30.44 KJ/kg
c)98.76 KJ/kg
d)none
(vii) The second law efficiency of turbine
a)64.58%
b)98.22%
c)96.88%
d) none
(8) If the second law efficiency of a compressor is 90% & work input to
compressor is 100 KJ find the irreversibility of the process
a)10 KJ
b) -10 KJ
c) 100KJ
d) -100 KJ
(9) Find the irreversibility of the process if 5kg of water at temperature 90ºC is
mixed with 10kg of water at temperature 50 ºC with no heat transfer to
environment while the environment is at 27ºC & 1 bar.
a)45.63 KJ/Kg
b)28.53 KJ/Kg
c) 96.93 KJ/Kg
d) zero
(10) A heat engine is operating between temperature limits of 100ºC & 20ºC has
efficiency of 30%. Find the second law efficiency of engine
a)21.44 %
b) 71.49%
c) 37.5%
d) engine is impossible
(11) In a boiler the furnace temperature is 800 ºC whereas the steam
temperature is 540ºC. If 100MW heat is supplied to boiler and 10 MW is lost to
the surroundings at 27ºC then the second law efficiency of boiler would be
a)78.8%
b)86.5%
c) 98.99%
d) none
Ans-1.c
2.a
4. a,b
5.a
9. b
11.a
10.d
3.b
6.b
7. a( for all sections)
8.a
Thermodynamic Relations
1.If U=f(p,v) then (∂U/∂P)v(∂P/∂V)u(∂V/∂U)p will be
a)1
b)-1
c)0
d)none
2.From Maxwell relation the value of (∂S/∂V)T for ideal gas is
a)R/P
b)R/V
c)-R/P
d) none
3.Which of the following is/are correct
a) Cp≥Cv always
temperature
b) Cp=Cv at T=0
c) Value of Cp & Cv does not change with
d)For water Cp=Cv at 4ºC
4.Internal energy & enthalpy of an ideal gas is a function of
a) temperature only
b) temperature & pressure
c)entropy
d)none
5. Find the coefficient of volume expansion β for air at pressure 5 bar& specific
volume 2 m³/kg.
a)0.287x10ˉ³ /K
b).0562/K
c) .0096/K
d).0287/K
6.For air at pressure 5 bar the coefficient of isothermal compressibility per bar
would be
a)1/5
b)1/10
c)-1/5
d)none
7.For air find the value of adiabatic compressibility per bar if isothermal
compressibility Kt=1/10 per bar
a)1/10
b)1/14
c)1/28
d)none
8.An ideal gas boils at 76ºC at 101 Kpa. The latent heat of vaporization is 195
KJ/Kg & characteristic gas constant is .055 KJ/Kg-K . Assuming latent heat of
vaporization to be constant the boiling point of liquid at 202 Kpa is
a)274.54 K
b)374.54 K
c)274.54 K
d)574.54K
9.For a gas at 27ºC if dP/dT= 8 Kpa/K, Vg=.04 m³/kg & Vf<<Vg then the latent
heat of vaporization of gas at this temperature would be
a) 84 KJ/Kg
b)96 KJ/Kg
c)100 KJ/Kg
d)none
10.For a substance if latent heat of vaporization is 5000 KJ/Kg & latent heat of
sublimation is 6000 KJ/Kg then latent heat of fusion would be
a)11000 KJ/Kg
b) 2000KJ/Kg
c) 1000 KJ/Kg
d)none
11.Which is/are correct for a gas undergoing throttling
a)It is irreversible
b) It is reversible
c) If µj>0 temperature of gas will decrease
d) If µj>0 temperature of gas will increase
e) For ideal gas µj is always zero
12.For a substance at temperature 300 K with Cp= 1.2 KJ/Kg K & specific
volume .02 m³/Kg if it is found experimentally that (∂V/∂T)p=.001 then the
value of Joule Kelvin coefficient is
a).224
b)-.224
c).682
d)none
13. The Joule Kelvin Coefficient is given by
a)(∂T/∂P)h
Ans-1.b
11.a,c,e
b)(∂P/∂T)h
2.b
c) )(∂P/∂T)s
3.a,b,d
4.a
12.a
13.a
5.a
6.a
d)none
7.b
8.b
9.b
10.c
Pure Substances & Gas Mixtures
1.In a steam water mixture of 2 kg mass the mass of water is .25 Kg then the
dryness fraction of steam would be
a).8
b).875
c).82
d)none
2.In a boiler steam exists at 100 bar & 350ºC. If saturation temperature
corresponding to 100 bar is 311ºC then degree of super heat would be
a)36ºC
b)39ºC
c)48ºC
d)none
3. In a throttling process wet steam at pressure P1 is throttled to dry saturated
state at press P2 with enthalpy 1800 KJ/Kg. If the enthalpy of liquid water at
pressure P1 is 100 KJ/Kg and latent heat of vaporization at pressure P1 is 2000
KJ/Kg then the dryness fraction of steam would bea).95
b).75
c).85
d).65
4. Steam in superheated state at pressure P1 is at temperature 400ºC. At this
pressure the enthalpy of saturated liquid is 100 KJ/Kg , entropy is .5KJ/Kg K &
latent heat of vaporization is 1800 KJ/Kg. If the saturation temperature is
127ºC & Cp of superheated steam is taken as 2.8 KJ/Kg then
(i) enthalpy of steam would be
a)2664.4 KJ/Kg
b)2627.2 KJ/Kg
c)2564.4KJ/Kg
d)none
(ii)entropy of steam would be
a)6.46 KJ/KgK
b)5.25 KJ/KgK
c)9.87 KJ/Kg K
d)none
5. The critical pressure & critical temperature for water is
a) 180 bar 370 ºC
b) 221.2 bar & 374.15ºC
c) is not fixed d) is same as triple point
6. The slope of fusion curve for water in P-T diagram is
a)positive
b)negative
c)zero
d) changes from positive to negative
7.Which of the following is/are correct about Mollier diagram
a) Isothermal & Isobaric lines coincide in two phase region
b)The slope of isothermal & isobaric lines are constant in two phase region
c) Isobars converge in two phase region
d)In superheated region isotherms bend towards right whereas the isobars bend
towards left
8. In a combined separating & throttling calorimeter the intake of steam water
mixture is 5 kg. The water collected in the separator is .5 Kg. If the quality of
steam after partial moisture separation is .9 then the the dryness fraction of
incoming steam is
a).85
b).92
c).81
d).95
9. 20 kg Carbon dioxide is mixed with 14 Kg of Oxygen & 18 Kg of Nitrogen then
i) mole fraction of Nitrogen would be
a).52
b).42
c).62
d).72
ii) The characteristic gas constant for the mixture in KJ/Kg K would be
a).245
b).287
c)8.314
d)none
iii) If total pressure of mixture is 5 bar then the partial pressure of Nitrogen
would be
a)2.1 bar
b)3.2 bar
c)4.6 bar
d)none
10.If superheated steam is at a pressure of 15 bar & 400ºC then the value of
reduced properties Pr & Tr would be
a) .0678,1.04
b).0952,9.2
c)1.5,3.2
d)none
11. Which of the following is/are correct about generalized compressibility
charta)All isotherms start at Z=1
b) The minimum value of Zc is 3/8
c) Tr=1 for critical isotherm
d)It can be used for all gases
Ans-1.b
10.a
2.b
3.c
11. All are correct
4.i)a (ii) a
5.b
6.b
7.a,b,d
8.c
9.i)b (ii)a(iii)a
Vapor Compression Cycle
1.The refrigeration unit ‘ton’ refers to
a) quantity of heat removed from storage space
space
c) work done by compressor
b) rate of heat removal from storage
d)rate of work done by compressor
2.If the refrigerant entering into storage space has enthalpy of 200 KJ/Kg & the
leaving refrigerant has enthalpy 450 KJ/Kg .Then the refrigerating capacity of
unit for 0.1 Kg/s mass flow rate would bea)250 KJ
b)250 KJ/Kg
c)25 KJ/s
d) 25 KJ
3. If in problem 2 the enthalpy of refrigerant at compressor outlet is 600 KJ/Kg
then power input to the compressor isa)150 KJ
b)400 KW
c)15 KW
d)150 KW
4.In a reciprocating compressor if clearance volume is .01m³,stroke length 60.2
cm & dia 46 cm then find
i) volume of refrigerant gas in the cylinder when the crank is at bottom dead
center
a).1 m³
b).11m³
c).09m³
d).01m³
ii)the clearance ratio would be
a)1
b)10
c).1
d).09
iii) If the pressure ratio of the compressor is 3 & index of compression 1.3 then
the volumetric efficiency of the compressor isa)86.72%
b)98.23%
c)100%
d)none
iv) If the specific volume of refrigerant at inlet to compressor is .1m³/kg then
the mass flow rate of refrigerant if the compressor rpm is 300a)50 kg/s
b)4.3 kg/s
c)14.92 kg/s
d)25 kg/s
5.In a simple VC cycle if the power consumed by compressor is 5 KW, enthalpy
of refrigerant leaving the condenser is 400 KJ/kg & enthalpy of refrigerant
leaving the evaporator is 600 KJ/kg then for mass flow rate of .1 kg/s the COP
of cycle is
a)6
b)5
c)4
d)3
6.Superheating at evaporator in VC cycle causes
a)Increase in refrigerating effect b)decrease in compressor work
volumetric efficiency
d) decrease in COP for R-12
c) increase in
7.In a VC cycle the refrigerant is dry saturated at the end of compression with
entropy 5.045 KJ/Kg. If at inlet to compressor the dryness fraction of
refrigerant is .912 & at inlet temperature the entropy of saturated liquid
refrigerant is .5443 KJ/Kg & latent heat of vaporization is 1297.68 KJ/kg then
the temperature of evaporator is
a)-20ºC
b)-10ºC
c)273 K
d)290 K
8.In a simple VC cycle the compressor discharge temperature is 50ºC whereas
temperature of refrigerant at compressor inlet is 10ºC. If specific heat of vapor
refrigerant is .6KJ/Kg & COP of cycle is 5 then the refrigerating effect produced
per Kg of refrigerant flow isa)150KJ
b)140 KJ
c)120 KJ
d)none
9.In a VC cycle operating between evaporator & condenser at -10ºC & 30ºC
respectively the vapor at compressor inlet was superheated by 10ºC whereas the
liquid at condenser outlet was subcooled by 5ºC. The enthalpy of saturated vapor
at evaporator pressure is 350 KJ/Kg & Cp of vapor is .6 KJ/Kg K. The enthalpy
of saturated liquid at condenser pressure is 150 KJ/Kg and Cp of liquid
refrigerant is .9 KJ/KgK. If mass flow rate of refrigerant is 0.1 kg/s then find
i) refrigerating capacity of system in tons of refrigeration
a)4 ton
b) 5 ton
c)6 ton
d)none
ii)If the specific volume of saturated vapor at evaporator pressure is .07m³/kg
then specific volume in m³/kg of refrigerant at compressor inlet assuming ideal
gas
a).073
b).06
c).086
d)none
iii)If the entropy of saturated vapor at evaporator pressure is 1.56 KJ/KgK then
entropy at compressor inlet in KJ/Kg K isa)1.55
b)1.58
c)1.60
d)none
iv)If the compression is isentropic & entropy of saturated vapor at condenser
pressure is 1.54 KJ/KgK then compressor outlet temperature isa)323.9K
b)435 .3K
c)423.8K
d)none
10.In a VC cycle with liquid vapor regenerative heat exchanger operating
between evaporator & condenser temperature of 35ºC & -10ºC the refrigerant
leaves evaporator in a saturated state with enthalpy 1450 KJ/Kg. The liquid at
condenser outlet is saturated with enthalpy 300 KJ/kg & is subcooled by this
vapor to 30ºC. If Cp of vapor is 2.5 & Cp of liquid is 4.5 then find
i) Refrigerating effect per Kg of refrigerant
a)1200 KJ
b)1172.5 KJ
c)1325.2 KJ
d)none
ii)The temperature of vapor after leaving the regenerative heat exchanger in ºC
a)-5
b)-2
c)-1
d)none
11.In an evaporator of a ice plant water at 35ºC is converted to ice at -8ºC at the
rate of 5 kg/minute. If latent heat of ice is 80 cal/gram & Cp of ice is 2.26
KJ/KgK & COP of plant is 4 then power input to compressor is
a) 10.4 KW
b) 8.6 KW
c) 41 KW
d)none
12.In a simple VC cycle at condenser pressure the enthalpy & entropy of
saturated vapor is 150KJ/Kg & .68 KJ/KgK respectively. These values at 50 ºC
superheat at condenser pressure are 190 KJ/Kg & .75 KJ/KgK respectively. If
enthalpy & entropy at inlet to compressor are 120 KJ/Kg & .7 KJ/Kg K then
find the work done by compressor per Kg of refrigerant flowa)60.23 KJ
b)41.43 KJ
c)92.98 KJ
d)none
13.In a cascade refrigeration system the COP of 1st & 2nd stage is 1.2 & .9. If the
heat removal rate from the storage space is 50 KJ/S then the power
consumption of the plant isa)143.5 KW
b) 155.2 KW
Ans-1.b
2.c
iv)a
10.i)b ii)c
3.c
11.a
c)176.9 KW
4.i)b ii)c iii)a iv)b
12.b 13.a
5.c
d)none
6.a
7.b
8.c
9.i)c ii)a iii)b
Multi Pressure Systems
1.In a two stage VC cycle without any super heat or subcooling operating
between condenser & evaporator temperature of 30ºC & -5ºC flash gas is removed
at a temperature of 15ºC & enthalpy of saturated vapor is 130 KJ/Kg at this
temperature. If the mass flow rate of refrigerant in condenser is .9 Kg/s & flash
gas removal rate is .1 Kg/s then findi)Refrigerating capacity if the enthalpy of saturated liquid at 15ºC is 80 KJ/Kg,
at 30ºC is 90 KJ/Kg & enthalpy of saturated vapor at -5ºC is 120 KJ/Kg
a)36 KW
b)32 KW
c)40 KW
d)none
ii)The power input required if the lower stage compressor has enthalpy of
refrigerant at compressor exit 140 KJ/Kg & higher stage compressor has
enthalpy of refrigerant at exit 160 KJ/Kg
a)35 KW
b)40KW
c)50 KW
d)none
iii)The COP of the system is
a).91
b)1.09
c)2.54
d)none
2.In a two stage VC cycle with flash intercooling only(no flash gas removal) the
rate of refrigerant flow in condenser is .9 Kg/s. At the intermediate stage 0.1
Kg/s of refrigerant is used to cool the superheated refrigerant of lower stage
compressor outlet to saturated state .If the enthalpy of liquid refrigerant at
condenser outlet is 80 KJ/Kg & at evaporator outlet is 120 KJ/Kg then find
i) refrigerating capacity
a)32 KW
b)27 KW
c)36 KW
d)none
ii)Enthalpy at lower stage compressor outlet if the enthalpy of saturated vapor at
intermediate stage is 140 KJ/Kg
a)105 KJ/Kg
b)147.5 KJ/Kg
c)102.5 KJ/kg
d)none
iii)Power required by compressor if the upper stage compressor outlet
temperature is 160KJ/Kg
a)40 KW
b)60 KW
c)80 KW
d)none
iv)COP of plant
a)1.5
b)1.2
Ans-1.i)b ii)a iii)a
c).8
d)none
2.i)a ii)b iii)a iv)c
Properties Of Moist Air
1.To completely define the state of moist air number of independent intensive
properties needed are
a)1
b)2
c)3
d)4
2. The mass of a moist air sample is 1 Kg & the mass of moisture content is 0.1
Kg then the specific humidity of the mixture in Kg vapor per kg dry air is –
a) 0.1
b)0.2
c)0.22
d)0.11
3. In an air vapor mixture the mass of dry air is 1 Kg & mass of moisture is 0.3
Kg. If the total atmospheric pressure is 1 bar & molecular weight of dry air is 29
then the partial pressure of water vapor in the mixture isa).225 bar
b).326 bar
c).492 bar
d)none
4.In moist air having total pressure of 1 bar & partial pressure of dry air 0.9 bar
the humidity ratio in Kg v/Kg da would be
a)0.069 bar
b)0.075 bar
c)0.123 bar
d)none
5. In an air vapor mixture the mass of water vapor is 0.1 Kg with partial pressure
0.01 bar. Moisture is added to the mixture at the same temperature such that
the partial pressure becomes 0.02 bar while the total pressure remains at 1 bar.
The amount of moisture added in air in Kg isa).2 kg
b).1 Kg
c).5 Kg
d).05 Kg
6.If for a sample the partial pressure of water vapor is .01 bar & the partial
pressure of vapor when the air is saturated at the same temperature is .02 bar &
atmospheric pressure is 1 bar then
i) The RH of the sample is
a)70%
b)50%
c)40%
d)30%
ii) The degree of saturation of the sample is
a)49.5%
b)50%
c)50.5%
d)none
7.A saturated air sample has DBT of 30ºC. The WBT & DPT in degree Celsius will
respectively be
a)35,45
b)30,30
c)carrier eqn is needed
d)steam table is needed
8. An unsaturated air sample having partial pressure of vapor 0.01 bar is cooled
in such a way that the air becomes saturated. The partial pressure of vapor at
this state will bea).02 bar
b).03 bar
c).01 bar
d) steam table is needed
9.From steam table it is known that at P pressure boiling point of water is 30ºC.
In a moist air sample at 30 ºC moisture is added so that it becomes saturated at
the same temperature. Then the partial pressure of water vapor in the mixture
would bea)P
b)P/2
c)P/3
d) cannot be determined
10.Air having DBT of 30ºC & WBT of 20ºC is kept in a cylinder having pressure 1
atm. If the saturation pressure of air at 20ºC is 0.023 bar then the partial
pressure of moisture in the air using carrier eqn isa)0.0164 bar
b).02435 bar
c).01114 bar
d)none
11. A moist air at 30ºC has specific humidity .023 Kg v/Kg da. The specific
enthalpy of the sample in KJ/ per kg da would be
a)88.94
b)54.72
c)67.95
d)none
12. Unsaturated air at temperature 30ºC having specific humidity .023 Kg V/Kg
da is flowing over water in an adiabatic chamber having enthalpy of liquid water
100 KJ/Kg. The rate of evaporation of water is 0.03 Kg V/Kg da due to which
the air becomes saturated at outlet. If there is no change in temperature of
water due to vaporization the thermodynamic wet bulb temperature in ºC would
bea)25
Ans-1)c
12)b
b)27
2)d
3)b
c)24
4)a
5)b
d)none
6) i)b ii)a
7)b
8)c
9)a
10)a
11)a