Thermo

Question 1

γ = ?/?

Answer 1

Cp / Cv

Question 2

Cp = _ + _

Answer 2

Cp = Cv +R

Question 3

Diatomic Cp

Answer 3

Cp, dia = 7/2 R

Question 4

Diatomic Cv

Answer 4

Cv, dia = 5/2 R

Question 5

γ, Dia

Answer 5

1.4

Question 6

Cp, mono

Answer 6

5/2R

Question 7

Cv, mono

Answer 7

3/2 R

Question 8

γ, mono

Answer 8

1.67

Question 9

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 using an average value of the specific heat.

Answer 9

932 KJ

Question 10

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 variation of the specific heat.

Answer 10

1018

Question 11

reciprocating compressor

Answer 11

is always a closed system
But a “compressor” is an open system

Question 12

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

Answer 12

S = 0.03356 KJ/ kgK

Question 13

A solid metallic block weighing 5 kg has an initial
temperature of 500C. 40 kg of water initially at 25C is contained
in a perfectly insulated tank. The metallic block is brought into
contact with water. Both come to equilibrium. Specific heat of
block material is 0.4 kJ/kg-K. Ignoring the effect of expansion and
contraction and also the heat capacity to tank, the total entropy
change in kJ/kg-K.

Answer 13

1.25 answer BUT 0 in indiabix

Question 14

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/kg-K.

Answer 14

424 kJ

Question 15

Latent heat of fusion at 0C of water (Lambda f)

Answer 15

80 cal/g

Question 16

Latent heat of vaporization at 100C of water (Lambda v)

Answer 16

540 cal/g

Question 17

Phase change is called

Answer 17

latent heat

Question 18

Constant phase, but temperature changes

Answer 18

sensible heat

Question 19

Specific heat of water in english units

Question 20

specific heat of water in SI units

Question 21

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.

Answer 21

A 450 MW
B 464 MW
C 15%

Question 22

Worked Example 3.19:
A reciprocating internal combustion engine has a
clearance volume of 0.0001 m3 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
1800°C respectively.
Assuming that the expansion process follows PV1.3
= constant, calculate:
c) The work transfer in this process; and
d) The temperature of the gases at the end of the
process.

Answer 22

[Answer: 66.7 J; 1039 K]

Calculations in the book did not match the final
answer given for part (a).

Question 23

Steam at a pressure of 2 MPa and a temperature of
240°C enters a nozzle with a velocity of 15 m/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.

Answer 23

Answer: 715 m/s]

Question 24

clearance volume of 0.0001 m3 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
1800°C 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.

Answer 24

[Answer: 66.7 J; 1039 K]

Question 25

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 PV1.3 = c PV1.4 = c Calculate the final pressure in each case. Assuming inlet conditions of 27°C and 1 bar.

Answer 25

[Answers: 11.36, 6.19, 23.5 bar, 12.8 bar]

Question 26

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 a) Assume it behaves as a perfect gas. b) Using the compressibility chart.

Answer 26

[Answers: 117 kg/m3, 146 kg/m3]

Question 27

Worked Example 3.1: A closed rigid container has a volume of 1 m3 and holds air at 345 kPa and 20°C. heat is added until the 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

Answer 27

answer: 932 kJ; 1018.7 kJ]

Question 28

Worked Example 3.19: A reciprocating internal combustion engine has a clearance volume of 0.0001 m3 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 1800°C 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.

Answer 28

[Answer: 66.7 J; 1039 K]

Question 29

The cylinder of an engine has a stroke of 300 mm and a bore of 250 mm. 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°C. 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/kg-K

Answer 29

Answer: -424 kJ/kg

Question 30

Worked Example 3.30: A mass of air at 330°C, contained in a cylinder expanded polytropically to fuve 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.

Answer 30

[Answer: 1.292; +222 kJ]

Question 31

Worked Example 3.32: 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.

Answer 31

Answer: 463.9 MW; 450 MW; 15%

Question 32

Milk initially at 30°C is to be kept in a chilled tank at 5°C. If the total volume of milk is 100 litres, its density is 1100 kg/m3 and the specific heat capacity of 4.2 kJ/kg-K. 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. ii. + 5 kW gain in summer – 5 kW loss in winter

Answer 32

Answer: a) 11.55 kW; b) i. 16.55 kW; ii. 6.55 kW

Question 33

Worked Example 3.34: 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 ice at 0°C? For ice: assume hi = -333.5 and hf = 417 kJ/kg-K

Answer 33

[Answer: 80°C; 64°C]

Question 34

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.

Answer 34

[Ans: -38 kJ]

Question 35

important Worked Example 3.36: A burner heats air from 20 to 40°C 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/kg-K.

Answer 35

[Answer: 0.03356 kJ/kg-K] Tarik used T2 = 30°C in the solution hence the answer derived is different. The correct answer using 40°C is 0.066 kJ/kg-K

Question 36

imp A boiler receives feed water at 20 kPa as saturated liquid and delivers steam at 2 MPa and 500oC. 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.

Answer 36

[Ans: 96%] Correct answer should be 76%.

Question 37

imp 10 kg/s steam at 6 MPa and 500oC, 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.

Answer 37

[Ans: 96%] Question being asked is the power output, however, percentage was given as the answer

Question 38

imp Worked Example 2.8: 300 kg/minute of steam at 3 MPa and 400°C 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?

Answer 38

[Answer: Q = 2133.5 kW; Cp = 4.009 kJ/kg-K]

Question 39

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

Answer 39

[Answer: 1.292; 698K] Solution provided for (b) actually came out as 964.31K. The final answer provided however is close to the value when converted to Celsius.

Question 40

imp Worked Example 3.2: 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.

Answer 40

[Answer: Mixed phase with dryness factor x = 0.917; 849 kJ/kg] Dryness factor is actually 0.831 when calculated. The solution provided by Tarik will also derive 0.831 however, 0.917 was encoded as the final answer.

Question 41

imp Worked Example 3.15: Steam at a pressure of 6 MPa and a temperature of 500°C enters an adiabatic turbine with a velocity of 20 m/s and expands to a pressure of 50 kPa, and a dryness fraction of 0.98. The steam leaves with a velocity of 200 m/s. The turbine is required to develop 1 MW. Determine c) The mass flow rate of steam required, when KE is neglected, and d) What is the effect of KE on the answer?

Answer 41

[Answer: 1.216 kg/s; 1.187 kg/s or an error of 2.4%] Answer must be 1.247 kg/s. The solution derived 1.247 but the answer provided was 1.187

Question 42

Worked Example 3.19: A reciprocating internal combustion engine has a clearance volume of 0.0001 m3 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 1800°C respectively. Assuming that the expansion process follows PV1.3 = constant, calculate: c) The work transfer in this process; and d) The temperature of the gases at the end of the process.

Answer 42

[Answer: 66.7 J; 1039 K] Calculations in the book did not match the final answer given for part (a).

Question 43

Worked Example 3.25: Steam at a pressure of 2 MPa and a temperature of 240°C enters a nozzle with a velocity of 15 m/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.

Answer 43

[Answer: 715 m/s]