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ChΕ CαΙcuΙαΤions > Chemical Thermodynamics > Flashcards

Chemical Thermodynamics Flashcards

1
Q

Collection of matter within prescribed and identifiable boundaries. Either an open one, or a closed one, referring to whether mass transfer or does not take place across the boundary.

A

ANSWER: System

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2
Q

Is usually restricted to those particles of matter external to the system which may be affected by changes within the system, and the surroundings themselves may form another system.

A

ANSWER: Surroundings

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3
Q

A physical or imaginary surface, enveloping the system and separating it from the surroundings.

A

ANSWER: Boundary

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4
Q

Is any quantity whose changes are defined only by the end states and by the process.

A

ANSWER: Property

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5
Q

The normal force exerted per unit area of the surface within the system.

A

ANSWER: Pressure

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6
Q

Is the degree of hotness or coldness of the system.

A

ANSWER: Temperature

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7
Q

The property of a system covering all forms of energy arising from the internal structure of the substance.

A

ANSWER: Internal Energy

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8
Q

A property of the system conveniently defined as h = u + PV where u is the internal energy.

A

ANSWER: Enthalpy

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9
Q

The microscopic disorder of the system. It is an extensive equilibrium property.

A

ANSWER: Entropy

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10
Q

Is the state of the substance such as solid, liquid, or gas.

A

ANSWER: Phase

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11
Q

It is possible that phases may be mixed, eg ice + water, water + vapour etc.

A

ANSWER: Mixed Phase

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12
Q

The ratio of the mass of pure vapour present to the total mass of the mixture (liquid and vapour).

A

ANSWER: Dryness Fraction (x)

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13
Q

Is a vapour whose dryness fraction is equal to zero. It has a quality of 100% or a dryness fraction of one.

A

ANSWER: Saturated State

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14
Q

A gas when its temperature at a given pressure is greater than the saturated temperature at that pressure, ie the gas has been heated beyond its saturation temperature.

A

ANSWER: Superheated Vapour

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15
Q

The difference between the actual temperature of a given vapour and the saturation temperature of the vapour at a given pressure.

A

ANSWER: Degree of Superheat

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16
Q

Is described as undercooled when its temperature at a given pressure is lower than the saturated temperature at that pressure, ie the liquid has been cooled below its saturation temperature.

A

ANSWER: Subcooled Liquid

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17
Q

The difference between the saturation temperature and the actual temperature of the liquid is a given pressure.

A

ANSWER: Degree of Subcool

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18
Q

A state point in which all solid, liquid, and vapour phases coexist in equilibrium.

A

ANSWER: Triple Point

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19
Q

A state point at which transitions between liquid and vapour phases are not clear.

A

ANSWER: Critical Point

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20
Q

A thermodynamic process wherein there is no heat transfer from or to the fluid.

A

ANSWER: Adiabatic

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21
Q

A thermodynamic process wherein there is no change in temperature of the fluid.

A

ANSWER: Isothermal

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22
Q

A thermodynamic process wherein there is no change in volume of the fluid.

A

ANSWER: Isochoric

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23
Q

A thermodynamic process wherein there is no change in entropy of the fluid.

A

ANSWER: Isentropic

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24
Q

A thermodynamic process wherein there is no change in pressure of the fluid.

A

ANSWER: Isobaric

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25
Q

A thermodynamic process wherein there is no change in enthalpy of the fluid.

A

ANSWER: Isenthalpic

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26
Q

Self-ignition would occur in the engine using certain brand of petrol if the temperature due to compression reached 350°C. Calculate the highest ratio of compression that may be used to avoid pre-ignition if the law of compression is

PV 1.3 = c
PV 1.4 = c
Calculate the final pressure in each case. Assume inlet condition of 27°C and 1bar.

A

ANSWER: Pi=23.5 bar; Pii= 12.8 bar

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27
Q

Calculate the density of Ethane at 171 bar and 458K; assume for Ethane:

Tc=305 K
Pc=48.80 bar
R = 319.3 J/kg-K

Assuming it behaves as a perfect gas

A

ANSWER: ρ =117 kg / m3

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28
Q

Find the specific volume for H2O at 10 MPa and 500°C using: Compressibility chart

A

ANSWER: V = 0.032 m3/kg

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29
Q

Determine the pressure of water vapour at 300°C, if its specific volume is 0.2579 m3/kg, using the following methods:
a) Ideal gas equation
b) Van-der-Waals equations

A

ANSWER: P(ideal) = 1.025 MPa ; P(vdw)= 1.006 MPa

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30
Q

An unknown gas has a mass of 1.5 kg contained in a bottle of volume 1.17 m3 while at a temperature of 300 K, and a pressure of 200 kPa. Determine the ideal gas constant and deduce the gas?

A

ANSWER: R= 520 J/kg-K M= 15.99

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31
Q

A 6 m3 tank contains helium at 400K is evacuated form atmospheric pressure of 100kPa to a final pressure of 2.5kPa.
Determine
a) the mass of helium remaining in the tank;
b) the mass of helium pumped out;
c) if the temperature of the remaining helium falls to 10oC, what is the pressure in kPa?

A

ANSWER: a) 0.018 kg b) 0.722 c) 1763 Pa

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32
Q

A motorist equips his automobile tyres with a relief-type valve so that the pressure inside the tyre will never exceed 220 kPa (gauge). He starts the trip with a pressure of 200 kPa (gauge) and a temperature of 23oC in the tyres. During the long drive the temperature of the air in the tyres reaches 83oC. Each tyre contains 0.11 kg of air. Determine:
a) the mass of air escaping each tyre,
b) the pressure of the air inside the tyre when the temperature returns to 23oC.

A

ANSWER: a) 0.0094 kg b) 183 kPa

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33
Q

300 kg/minute of steam at 3 MPa and 400oC is supplied to a steam turbine. determine the potential heat released from steam if it is condensed at constant pressure. Can you deduce the specific heat of the steam under this condition?

A

ANSWER:Q= 2133.5 kW; Cp=4.18 kJ/kg-K

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34
Q

Self-ignition would occur in an engine using certain brand of petrol if the temperature due to compression reaches 350 oC; when the inlet condition is 1 bar, 27oC.
Calculate the highest compression ratio possible in order to avoif self-ignition, if the compression is according to
a) adiabatic, with index of 1.4; and
b) polytropic, with index of 1.3

A

ANSWER: a) 6.2 b) 11.4

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35
Q

The gas in an internal combustion engine, initially at a temperature of 1270oC; expands polytropically to five times its initial volume and one-eights its initial pressure. Calculate:
a) the index of expansion, n, and
b) the final temperature.

A

ANSWER: a) 1.292 b) 689K

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36
Q

Determine using Steam Tables, the volume occupied by 2 kg of steam at 500 kPa, under the following conditions and specify the state of steam.
a) pure liquid state
b)when it is in a pure vapour state
c) 20% moisture content
d) 20% dry.

A

ANSWER: a) 0.00218m3 b) 0.7498m3 c)0.557m3 d)0.152m3

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37
Q

The model ‘6SE-TCA3 Perkins’ diesel engine have a stroke of 190 mm and a bore of 160 mm. If its clearance volume is 5% of the swept volume, determine the pressure and temperature at the end of compression when the inlet condition is 1 bar, 27oC.

A

ANSWER: P= 67.2 bar T=956k

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38
Q

A closed rigid container has a volume of 1 m3 and holds air at 345 kPa and 20 °C. Heat is added until temperature is 327 °C. Determine the change in Internal Energy:-
a.) Using an average value of the specific heat.
b.) Taking into account the variation of specific heat with temperature.

A

ANSWER: a.) ΔU = 932 kJ; b.) ΔU = 1018.7 kJ

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39
Q

An adiabatic steam turbine expands steam from a pressure of 6 MPa and a temperature of 500°C to a pressure of 10 KPa The isentropic efficiency of the turbine is 0.82 and changes in kinetic and potential energy may be neglected. Determine the state of the steam at exit from the turbine and the specific work transfer.

A

ANSWER: W = 849 kJ/kg

40
Q

Show that for a polytropic process, the change in entropy may be expressed as:

A

ANSWER: S2-S1=m.Cv[(Y-n)/(n-1)].Ln(T1/T2)

41
Q

Steam at 1.0 MPa, 0.95 dry is throttled to 10 kPa. What is the quality of the steam after throttling?

A

ANSWER: h2 = h1 = 2677.24 kJ/kg = Superheated condition

42
Q

A steam turbine receives steam at 2 MPa and 250 oC, and exhausts at 0.1 MPa, 0.85 dry.
Neglecting heat losses and changes in ke and Pe, estimate the work output per kg steam.
If, when allowance is made for friction, radiation, and leakage losses, the actual work obtained is 80% of that estimated in (a), calculate the power output of the turbine when consuming 600 kg of steam per minute.
Saturated table extract for P = 100 KPa

A

ANSWER: a.) Wideal = 539 kJ/kg; Power = 4.31 MW

43
Q

A boiler receives feed water at 40oC and delivers steam at 2 MPa and 500oC. If the furnace is oil fired, the calorific value of oil being 42000 kJ/kg and 4000 kg oil are burned while 45000 kg of steam are produced, determine:
the heat supplied in the boiler.
the efficiency of the boiler.

Assume the values of enthalpies at the two state points as:
h1 = hf@40°C = 169.33 kJ/kg at 2 MPa , 500 °C, h = 3467.6 kJ/kg

A

ANSWER: a.) 1.484 x 108 kJ; b.) Boiler Efficiency = 88%

44
Q

An air compressor receives air at 27oC and delivers it to a receiver at the rate of 0.5 kg/s. It is driven by an electric motor which absorbs 10 kW and the efficiency of the drive is 80%.

Water jacket cooling is used at the rate of 6 kg/min while its temperature rises from 10oC to 20oC. Estimate the temperature of the air delivered.
Data : Cpw = 4.186, and Cpa = 1.005 kJ/kg.K

A

ANSWER: 43.5 °C

45
Q

Air at 27oC receives heat at constant volume until its temperature reaches 927oC. Determine the heat added per kilogram? Assume for air CV = 0.718 kJ/kg.K.

A

ANSWER: 646.2 kJ/kg

46
Q

An insulated, constant-volume system containing 1.36 kg of air receives 53 kJ of paddle work. The initial temperature is 27oC. Determine
the change of internal energy
the final temperature.

Assume a mean value Cv = 0.718 kJ/kg.K.

A

ANSWER: a.) ΔU = -W = +53 kJ;
T2 = 81.3 °C

47
Q

An ideal gas occupies a volume of 0.5 m3 at a temperature of 340 K and a given pressure. The gas undergoes a constant pressure process until the temperature decreases to 290 K. Determine
the final volume,
the work if the pressure is 120 kPa,

A

ANSWER: V2 = 0.426 m3 ; W = -8.88 kJ

48
Q

30 kg/s steam at 3 MPa, 300oC expands isentropically in a turbine to a pressure of 100 kPa. If the heat transfer from the casing to surrounding air represents 1 per cent of the overall change of enthalpy of the steam, calculate the power output of the turbine. Assume exit is 2 m above entry and that initial velocity of steam is 10 m/s whereas exit velocity is 1 m/s.

A

ANSWER: W = +19 kW

49
Q

A piston and cylinder mechanism contains 2 kg of perfect gas. The gas expands reversibly and isothermally from a pressure of 10 bar and a temperature of 327 ∘ C to a pressure of 1.8 bar.

the work transfer,
the heat transfer,
the specific change in enthalpy of the gas.

Take R=0.3 kJ/kg K and n=1.4

A

ANSWER:
a.) W = 617 kJ;
b.) Q = W = 617 kJ ;
c.) Δh = Cp .ΔT = 0

50
Q

The gas expanding in the combustion space of a reciprocating engine has an initial pressure of 50 bar and an initial temperature of 1623 ∘C. The initial volume is 50000 mm 3 and the gas expands through a volume ratio of 20 according to the law pV 1.25 = constant. Calculate

a. the work transfer
b. heat transfer in the expansion process.

Take R = 270 J/Kg K and C v = 800 J/Kg K.

A

ANSWER: a.) W = 527 J; b.) Q = 136 J

51
Q

Air, which may be considered a perfect gas, enters an adiabatic nozzle with negligible velocity. The entry pressure is 6 bar and the exit pressure is 1 bar; the entry temperature is 760 K. The flow throughout the nozzle is reversible and the mass flow rate is 2 kg/s. Calculate the exit velocity.

Take Cp = 1004.5 J/kg K and n = 1.4

A

ANSWER: 782 m/s

52
Q

A reciprocating compressor delivers 0.1 kg/s of air at a pressure of 12 bar. The air enters the compressor at a pressure of 1 bar and a temperature of 15 ∘ C. Calculate the delivery temperature of the air, the work transfer rate and the heat transfer rate in the compression process for:
reversible polytropic compression, PV 1.2 = constant;
reversible adiabatic compression;
reversible adiabatic compression;

Air - R = 0.287 kJ/kgK, C p = 1.005 kJ/kg K 2 C v = 0.718 kJ/kgK and n = 1.4.

A

ANSWER: a.) Q = -10.6 kW; b.) Q = 0; c.) Q = W = -20.5 kW

53
Q

A reciprocating internal combustion engine has a clearance volume of 0.0001m3 and a compression
ratio (volume ratio) of 10. The pressure and temperature of the combustion gases when the piston
is at top dead centre are 4000 kN/m2 and 1800ºC respectively.
Assuming that the expansion process follows PV1.3 = constant, calculate:
a) the work transfer in this process, and
b) the temperature of the gases at the end of the process.

A

ANSWER: V2 = 0.001m 3 T2=1039k

54
Q

A reciprocating steam motor is supplied with dry saturated steam at a pressure of 1.6MPa ( specific
volume = 0.1238 m3/kg). The stroke of the motor is 0.8m and the bore is 0.3m. The clearance
volume is negligible. The steam enters the cylinder, expands at constant pressure for ¼ of the
stroke and then expands reversibly according to a law PV = constant, til the end of the stroke.
Calculate
a) the mass of the steam,
b) the work transfer and the heat transfer in the process?

A

ANSWER:
V1 = 2 = 0.0141m 3,
Q = W = 31.3kJ

55
Q

A piston and cylinder mechanism has its piston fixed so that the volume contained is 0.0025m3.
The mechanism is filled with wet steam at a pressure of 2 bar. The steam is heated until it reaches
the critical point. The piston is released and the steam expands adiabatically to a pressure of 2 bar
and a volume of 0.5m3. Calculate:
a) the mass of steam in the mechanism,
b) the dryness fraction of the steam after expansion.

A

ANSWER: m= 0.788kg, x3 = 0.715

56
Q

A mass of gas occupying 0.08m3 at 6kN/m2 and 80°C is expanded reversibly in a non-flow process
according to a law PV1.2 = constant. The pressure at the end of expansion is 0.7kN/m2. The gas is
then heated at constant pressure to the original temperature. The specific heat capacities at
constant pressure and constant volume are 1.00 and 0.74 kJ/kg K respectively. Determine:a)
a) the work transfer in the expansion process;
b)the heat transfer in the expansion process;
C) the volume at the end of the heating process;
d)the change in internal energy during the heating process.

A

ANSWER: m= 5.23 x10 −3 kg, Q=+0.312kJ v3=0.685m3, ∆U−0.411kJ

57
Q

An ideal centrifugal air compressor takes in air at 1 bar, 15ºC and compresses it reversibly and adiabatically to a pressure of 4 bar. a) (Calculate the delivery temperature of the gas. b) (If kinetic energy and potential energy changes are negligible calculate the specific work transfer in the compression process. Air may be assumed to be a perfect gas with specific heat capacity at constant pressure Cp = 1.005kJ/kg K and n = 1.4.

A

ANSWER: T2= 428 K, W = -140.7 kJ/kg

58
Q

A reversible adiabatic air turbine drives a small generator which requires a power of 2kW. The air
supply for the turbine is provided by a reservoir and the pressure and temperature at turbine entry
may be considered constant at 9 bar, 20ºC respectively. The velocity of the air at inlet to the
turbine is small and may be neglected but at exit the velocity is 55m/s. The exit pressure is 1.2 bar.
Calculate:
a) the air temperature at exit from the turbine, and
b) the mass flow rate of air stating any assumptions made.
Air may be considered a perfect as for which the specific heat capacity at constant pressure Cp =
1.005 kJ/kg K and n = 1.4.

A

ANSWER: T2 = 164.76 K, m= +0.0157 kg / s

59
Q

Steam at a pressure of 2 MPa and a temperature of 240ºC enters a nozzle with a velocity of 15m/s.
The steam expands reversibly and adiabatically in the nozzle to a pressure of 100 kPa and a dryness
fraction of 0.9. Calculate the velocity of the steam at exit from the nozzle,
Saturated table extract for P = 100 KPa
p

A

ANSWER: V2= 715m / s

60
Q

A one pass steam generator receives saturated water at 20 bar, and converting it into steam at
400ºC. The mass flow rate of steam is 1200 kg/h, calculate the heat transfer in the generator.
Enthalpy of Superheated Steam (kJ/kg)
Pressure
(bar)

A

ANSWER: Q= 2799

61
Q

1kg of gas occupies a volume of 0.4m3 at a pressure of 100 kN/m2. The gas is compressed
isothermally to a pressure of 450 kN/m2. Determine the work of compression, and the change in
entropy of the gas during the compression. Assume for the gas R = 300 J/kgK
Solution:
a) For an isothermal process, the work is given by
b) the change of Entropy is given by:

A

ANSWER:∴W = - 60 kJ, ∆s= −0.451 kJ / kgK

62
Q

A gas contained in a closed system at a pressure of 1 bar and temperature of 15ºC. A mass of 0.9kg
of the gas is heated at constant pressure to raise its temperature from 15ºC to 250ºC. Determine the
work done, and during the process. R = 0.185 kJ/kgK

A

ANSWER:V2= 0.871m

63
Q

The cylinder of an engine has a stroke of 300mm and a bore of 250mm. The volume ratio of
compression is 14:1. Air in the cylinder at the beginning of compression has a pressure of 96
kN/m2 and a temperature of 93 ºC. The air is compressed for the full stroke according to the law
PV1.3 = C. Determine the work transfer per unit mass of air. Assume air R = 287 J/kgK.

A

ANSWER:W =-424 kJ/kg

64
Q

A mass of air at 330ºC, contained in a cylinder expanded polytropically to five times its initial
volume and 1/8th its initial pressure which is 1 bar. Calculate:
a) the value of the expansion index,
b) the work transfer per unit mass.

A

ANSWER:n= 1.292, V2= 8.653m 3

65
Q

Steam at a pressure of 10 bar and dryness fraction of 0.96 expands adiabatically to a pressure of 2
bar according to PV1.12 = constant. Determine the work done during expansion per unit mass of
steam.

A

ANSWER: W = 246 kJ / kg

66
Q

A nuclear reactor generates 3000 MW of heat. The heat is transferred in a heat exchanger of
energy transfer efficiency 75% into steam which is expanded in a turbine in order to produce a
power output. The steam is condensed in a condenser, releasing 1800 MW of heat, and pumped
back through the heat exchanger by a feed pump which requires 3% of the power output from the
turbine. Determine:
a) The net power output from the plant.
b) The power output from the turbine.
c) The overall thermal efficiency of the plant.

A

ANSWER: Wt= 463.9, MW W net = 450, MW η= 15%

67
Q

Milk initially at 30ºC is to be kept in a chilled tank at 5ºC. If the total volume of milk is 100 litres,
its density is 1100kg/m3 and the specific heat capacity of 4.2kJ/kgK.
a) Determine the heat extraction rate assuming the chiller to be perfectly insulated
b) What would be the chiller consumption if heat transfer through the chiller body is?
i.
+ 5kW gain in summer, ii) -5kW loss in winter

A

ANSWER: Q = 11.55kW Qchiller = 6.55kW in winter

68
Q

You have a 200 gram cup of coffee at 100 C, too hot to drink.
a) How much will you cool it by adding 50 gm of water at 0 C?
b) How much will you cool it by adding 50 gm of ice at 0 C?
for ice assume hi = -333.5
and hf = 417 kJ/kgK

A

ANSWER: tc2 = 80oC, tc2 = 64oC

69
Q

Determine for a unit mass of air, the change in enthalpy when heated from zero C to 100 OC if:
i. Cp = 1 kJ/kgK constant

ii.Cp = 0.95 + 0.00002 * T – 0.03x10-6 xT2

A

ANSWER:dh= 100 kJ/kg ∆h = 96.09 kJ / kg

70
Q

A burner heats air from 20 to 40oC at constant pressure. Determine the change in entropy for a unit
mass of air going through the heater, assuming that for air
Cp = 1 kJ/kgK

A

ANSWER: ∆S= 0.03356 kJ / kgK

71
Q

In a non -flow process there is heat transfer loss of 1055 kJ and an internal energy increase of 210 kJ. Determine the work transfer and state whether the process is an expansion or compression

A

ANSWER: -1265 kJ, compression

72
Q

In a non -flow process carried out on 5.4 kg of a substance, there was a specific internal energy decrease of 50 kJ/kg and a work transfer from the substance of 85 kJ/kg. Determine the heat transfer and state whether it is gain or loss.

A

ANSWER: 189 kJ, gain

73
Q

During the working stroke of an engine the heat transferred out of the system was 150 kJ/kg of the working substance. If the work done by the engine is 250 kJ/kg, determine the change in internal energy and state whether it is decrease or increase.

A

ANSWER: -400 kJ/kg, decrease

74
Q

Steam enters a cylinder fitted with a piston at a pressure of 20 MN/m2 and a temperature of 500 deg C. The steam expands to a pressure of 200 kN/m2 and a temperature of 200 deg C. During the expansion there is a net heat loss from the steam through the walls of the cylinder and piston of 120 kJ/kg. Determine the displacement work done by one kg of steam during this expansion.

A

ANSWER: 168.6 kJ/kg

75
Q

A closed rigid system has a volume of 85 litres contains steam at 2 bar and dryness fraction of 0.9. Calculate the quantity of heat which must be removed from the system in order to reduce the pressure to 1.6 bar. Also determine the change in enthalpy and entropy per unit mass of the system

A

ANSWER: -38 kJ

76
Q

2 kg of air is heated at constant pressure of 2 bar to 500 o C. Determine the change in its entropy if the initial volume is 0.8 m3

A

ANSWER: 2.04 kJ

77
Q

A boiler is designed to work at 14 bar and evaporate 8 kg/s of water. The inlet water to the boiler has a temperature of 40 deg C and at exit the steam is 0.95 dry. The flow velocity at inlet is 10 m/s and at exit 5 m/s and the exit is 5 m above the elevation at entrance. Determine the quantity of heat required. What is the significance of changes in kinetic and potential energy on the result?

A

ANSWER: 20.186 MW

78
Q

Steam flows along a horizontal duct. At one point in the duct the pressure of the steam is 1 bar and the temperature is 400°C. At a second point, some distance from the first, the pressure is 1.5 bar and the temperature is 500°C. Assuming the flow to be frictionless and adiabatic, determine whether the flow is accelerating or decelerating.

A

ANSWER: Decelerating

79
Q

Steam is expanded isentropically in a turbine from 30 bar and 400°C to 4 bar. Calculate the work done per unit mass flow of steam. Neglect changes in Kinetic and Potential energies.

A

ANSWER: 476 kJ/kg

80
Q

A compressor takes in air at 1 bar and 20°C and discharges into a line. The average air velocity in the line at a point close to the discharge is 7 m/s and the discharge pressure is 3.5 bar. Assuming that the compression occurs isentropically, calculate the work input to the compressor. Assume that the air inlet velocity is very small.

A

ANSWER: -126.6 kJ/kg

81
Q

Air is expanded isentropically in a nozzle from 13.8 bar and 150°C to a pressure of 6.9 bar. The inlet velocity to the nozzle is very small and the process occurs under steady-flow, steady-state conditions. Calculate the exit velocity from the nozzle knowing that the nozzle is laid in a horizontal plane and that the inlet velocity is 10 m/s.

A

ANSWER: 390.9 m/s

82
Q

A rotary air compressor takes in air (which may be treated as a perfect gas) at a pressure of 1 bar and a temperature of 20°C and compresses it adiabatically to a pressure of 6 bar. The isentropic efficiency of the processes is 0.85 and changes in kinetic and potential energy may be neglected. Calculate the specific entropy change of the air. Take R = 0.287 kJ/kg K and C p = 1.006 kJ/kg K.

A

ANSWER: 0.07 kJ/kg K

83
Q
A
84
Q

Oxygen has a molecular weight of 32 and a specific heat at constant pressure of 0.91 kJ/kg K.
Determine the ratio of the specific heats.
Calculate the change in internal energy and enthalpy if the gas is heated from 300 to 400 K.

A

ANSWER: 1.4, 65 kJ/kg, 91 kJ/kg

85
Q

A steam turbine inlet state is given by 6 MPa and 500°C. The outlet pressure is 10 kPa. Determine the work output per unit mass if the process:-
a) is reversible and adiabatic (ie 100% isentropic),
b) such that the outlet condition is just dry saturated,
c) such that the outlet condition is 90% dry.

A

ANSWER: 1242.7 kJ/kg, 837.5 kJ/kg, 1076.8 kJ/kg

86
Q

Determine the volume for carbon dioxide contained inside a cylinder at 0.2 MPa, 27°C: -
a) assuming it behaves as an ideal gas
b) taking into account the pressure and volume associated with its molecules

A

ANSWER: 0.2833m3 /kg

87
Q

A cylindrical storage tank having an internal volume of 0.465 m3 contains methane at 20°C with a pressure of 137 bar. If the tank outlet valve is opened until the pressure in the cylinder is halved, determine the mass of gas which escapes from the tank assuming the tank temperature remains constant.

A

ANSWER: 20.972 kg

88
Q

Find the specific volume for H2O at 1000 kN/m2 and 300°C by using: -
the ideal gas equation assuming
R = 461.5 J/kg K
b) steam tables

A

ANSWER: 0.264m3/kg, 0.258 m3/kg

89
Q

Determine the specific volume of steam at 6 MPa using the steam tables for the following conditions:-
dryness fraction x = 0
dryness fraction x = 0.5
dryness fraction x = 1
its temperature is 600C

A

ANSWER: 0.001319, 0.01688, 0.03244, 0.06525 m3/kg

90
Q

Steam at 4 MPa, 400C expands at constant entropy till its pressure is 0.1 MPa. Determine: a) the energy liberated per kg of steam
b) repeat if the process is 80% isentropic

A

ANSWER: 758 kJ/kg, 606 kJ/kg

91
Q

Steam (1 kg) at 1.4 MPa is contained in a rigid vessel of volume 0.16350 m3 . Determine its temperature.
If the vessel is cooled, at what temperature will the steam be just dry saturated?
If cooling is continued until the pressure in the vessel is 0.8 MPa; calculate the final dryness fraction of the steam, and the heat rejected between the initial and the final states.

A

ANSWER: 250C, 188C, 0.678; 8181 kJ

92
Q

Steam (0.05 kg) initially saturated liquid, is heated at constant pressure of 0.2 MPa until its volume becomes 0.0658 m3 . Calculate the heat supplied during the process.

A

ANSWER: 128.355 kJ

93
Q

Steam at 0.6 MPa and dryness fraction of 0.9 expands in a cylinder behind a piston isentropically to a pressure of 0.1 MPa. Calculate the changes in volume, enthalpy and temperature during the process.

A

ANSWER: 1.1075 m3, -276 kJ/kg, -59C

94
Q

The pressure in a steam main pipe is 1.2 MPa; a sample is drawn off and throttled where its pressure and temperature become 0.1 MPa, 140C respectively. Determine the dryness fraction of the steam in the main stating reasonable assumptions made!

A

ANSWER: 0.986, assuming constant enthalpy

95
Q

A boiler receives feed water at 20 kPa as saturated liquid and delivers steam at 2 MPa and 500C. If the furnace of this boiler is oil fired, the calorific value of oil being 42000 kJ/kg determine the efficiency of the combustion when 4.2 tonnes of oil was required to process 42000 kg of steam.

A

ANSWER: 96%

96
Q

10 kg/s steam at 6 MPa and 500 C, expands isentropically in a turbine to a pressure of 100 kPa. If the heat transfer from the casing to surroundings represents 1 per cent of the overall change of enthalpy of the steam, calculate the power output of the turbine. Assume exit is 5 m above entry and that initial velocity of steam is 100 m/s whereas exit velocity is 10 m/s.

A

ANSWER: 96%

ChΕ CαΙcuΙαΤions (2 decks)

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