Properties of Steam and Gas
Exam Duration: 45 Mins Total Questions : 30
The given diagram shows the throttling process 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
Match List I (Some process of steam) with List II (Effect due to the processes) and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
P. As saturation pressure increases | 1. Entropy increases |
Q. As saturation temperature increases | 2. Specific volume increases |
R. As saturation pressure decreases | 3. Enthalpy of evaporation decreases |
S. As dryness fraction increases | 4. Saturation temperature increases |
- (a)
P Q R S 1 3 2 4 - (b)
P Q R S 4 3 2 1 - (c)
P Q R S 3 4 1 2 - (d)
P Q R S 2 4 3 1
Consider the following statements:
A real gas obeys perfect gas law at very
1. high temperatures.
2. high pressures.
3. low pressures.
Which of these statements is/are correct?
- (a)
Only 1
- (b)
1 and 3
- (c)
Only 2
- (d)
Only 3
Which one of the following phenomena occurs when gas in a piston-in-cylinder assembly expands reversibly at constant pressure?
- (a)
Heat is added to the gas
- (b)
Heat is removed from the gas
- (c)
Gas does work from its own stored energy
- (d)
Gas undergoes adiabatic expansion
Consider the phase diagram of a certain substance as shown in the given figure. Match List I (Process) with List II (Curves/lines) and select the correct answer using the codes from the lists.
List I | List II |
---|---|
P. Vaporization | 1. EF |
Q. Fusion | 2. EG |
R. Sublimation | 3. ED |
- (a)
P Q R 1 3 2 - (b)
P Q R 1 2 3 - (c)
P Q R 3 2 1 - (d)
P Q R 3 1 2
Match List I with List II and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
P. Critical point | 1. All the three phases solid, liquid and vapour coexists in equilibrium |
Q. Sublimation | 2. Phase change from solid to liquid |
R. Triple point | 3. Properties of saturated liquid and saturated vapour are identical |
S. Melting | 4. Heating process where solid gets directly transformed to gaseous phase |
- (a)
P Q R S 2 1 4 3 - (b)
P Q R S 3 4 1 2 - (c)
P Q R S 2 4 1 3 - (d)
P Q R S 3 1 4 2
Which one of the following is the characteristic equation of a real gas?
- (a)
(p + a / V2) (V- b) = RT
- (b)
(p - a/V2) (V + b) = RT
- (c)
pV = RT
- (d)
pV = nRT
Consider the four processes A, B, C and D shown in the graph given below:
Match List I (Processes shown in the graph) with List II (Index n in the equation pVn = C) and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
A | 1. zero |
B | 2. 1 |
C | 3. 1.4 |
D | 4.Infinite |
- (a)
P Q R S 4 2 3 1 - (b)
P Q R S 1 2 3 4 - (c)
P Q R S 1 3 2 4 - (d)
P Q R S 4 3 2 1
Assertion (A) The constant pressure lines are steeper than the constant volume lines for a perfect gas on the T-S plane.
Reason (R) The specific heat at constant pressure is more than the specific heat at constant volume for a perfect gas.
- (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 the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
Assertion (A) Thermodynamic work is path dependent except for an adiabatic process.
Reason (R) It is always possible to take a system from a given initial state to any final state by performing adiabatic work only.
- (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 the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
Assertion (A) For a mixture of solid, liquid and vapour phases of a pure substance are in equilibrium and the number of independent intrinsic properties needed is equal to one.
Reason (R) The three phases can coexist only at one particular pressure.
- (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 the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
Assertion (A) An adiabatic process is always a constant entropy process.
Reason (R) In an adiabatic process there is no heat transfer.
- (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 the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
There is shown a T-S diagram for a two-phase mixture. Some points are located and some data are given as-
P (in bar) |
Ts (in ° C) |
h1 (in kJ/kg) |
hg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sg (in kJ/kg-K) |
Vg (in m3/kg) |
---|---|---|---|---|---|---|
1.0 | 100 | 417.5 | 2675.4 | 1.3027 | 7.3598 | 1.694 |
2.0 | 120 | 504.7 | 2706.3 | 1.530 | 7.126 | 0.885 |
Now, determine the condition or position of this mixture in given diagram on the basis of following questions.
If P = 2.0 bar and h = 2675.4 kJ/kg.
- (a)
Point a
- (b)
Point b
- (c)
Point c
- (d)
Between a and b
There is shown a T-S diagram for a two-phase mixture. Some points are located and some data are given as-
P (in bar) |
Ts (in ° C) |
h1 (in kJ/kg) |
hg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sg (in kJ/kg-K) |
Vg (in m3/kg) |
---|---|---|---|---|---|---|
1.0 | 100 | 417.5 | 2675.4 | 1.3027 | 7.3598 | 1.694 |
2.0 | 120 | 504.7 | 2706.3 | 1.530 | 7.126 | 0.885 |
Now, determine the condition or position of this mixture in given diagram on the basis of following questions.
For p = 2.0 bar mixture has a temperature of 120°C at
- (a)
Only point a
- (b)
Only point b
- (c)
all points between a and b
- (d)
at point a and b
There is shown a T-S diagram for a two-phase mixture. Some points are located and some data are given as-
P (in bar) |
Ts (in ° C) |
h1 (in kJ/kg) |
hg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sg (in kJ/kg-K) |
Vg (in m3/kg) |
---|---|---|---|---|---|---|
1.0 | 100 | 417.5 | 2675.4 | 1.3027 | 7.3598 | 1.694 |
2.0 | 120 | 504.7 | 2706.3 | 1.530 | 7.126 | 0.885 |
Now, determine the condition or position of this mixture in given diagram on the basis of following questions.
If mixture has a temperature 100°C and p = 1.0 bar with entropy = 7.126 kJ/kg-K, then it exist at
- (a)
point f
- (b)
point b
- (c)
point e
- (d)
Data is insufficient
There is shown a T-S diagram for a two-phase mixture. Some points are located and some data are given as-
P (in bar) |
Ts (in ° C) |
h1 (in kJ/kg) |
hg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sg (in kJ/kg-K) |
Vg (in m3/kg) |
---|---|---|---|---|---|---|
1.0 | 100 | 417.5 | 2675.4 | 1.3027 | 7.3598 | 1.694 |
2.0 | 120 | 504.7 | 2706.3 | 1.530 | 7.126 | 0.885 |
Now, determine the condition or position of this mixture in given diagram on the basis of following questions.
If pressure = 1.0 bar and T = 120°C, then steam is
- (a)
saturated liquid
- (b)
dry saturated steam
- (c)
superheated steam
- (d)
wet steam
There is shown a T-S diagram for a two-phase mixture. Some points are located and some data are given as-
P (in bar) |
Ts (in ° C) |
h1 (in kJ/kg) |
hg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sg (in kJ/kg-K) |
Vg (in m3/kg) |
---|---|---|---|---|---|---|
1.0 | 100 | 417.5 | 2675.4 | 1.3027 | 7.3598 | 1.694 |
2.0 | 120 | 504.7 | 2706.3 | 1.530 | 7.126 | 0.885 |
Now, determine the condition or position of this mixture in given diagram on the basis of following questions.
Temperature of point c, if Vc = 0.934 m3/kg is
- (a)
123.72°C
- (b)
110.43°C
- (c)
131.05°C
- (d)
141.75°C
A wet steam at pressure of 15 kg/cm2 has dryness fraction 0.06. It is given that at 15 bar. Given, Vg= 0.1317 m3/kg, hf= 844.7 kJ/kg hfg= 1945.2 kJ/kg Vf = 0.001154 m3/kg, Sf= 2.315 kJ/kg-K, Sfg = 4.126 kJ/kg-K Then, internal energy of steam is
- (a)
1081.02 kJ/kg
- (b)
729.91 kJ/kg
- (c)
949.35 kJ/kg
- (d)
961.4 kJ/kg
Determine the entropy of 1 kg of wet steam at a pressure of 6 bar and 0.8 dry, reckoned from freezing point (0°C). Given, at p = 6 bar, ts = 158.8°C, hfg = 2085 kJ/kg.
- (a)
5.7 kJ/kg-K
- (b)
3.4 kJ/kg-K
- (c)
2.9 kJ/kg-K
- (d)
7.2 kJ/kg-K
Two vessels A and B, each of volume 3 m3 may be connected together by a tube. Vessel A contains air at 7 bar and 95°C while B contains air at 3.5 bar, 205°C. The change of entropy when A is connected to B. Assume the mixing to be complete and adiabatic.
- (a)
5.62 kJ/K
- (b)
5.09 kJ/K
- (c)
0.52 kJ/K
- (d)
3.28 kJ/K
Tank A has volume 0.1 m3 and contains steam at 200° C 10% liquid and 90% vapour by volume while tank B is evacuated. If valve is opened, the tank eventually come to same pressure as 4 bar. Steam temperature does not change during the process.
Given, T = 200°C, Vf = 0.00157 m3/kg,
Vg = 0.12736 m3/kg, p= 4 bar, Ts= 200°C, V= 0.534 m3/kg Volume of tank B is
- (a)
4.99 m3
- (b)
9.34 m3
- (c)
4.89 m3
- (d)
0.53 m3
In a simple steam power cycle water enters the pump as a saturated liquid at 40°C and is pumped to 2 bar. Then, it evaporates in the boiler at this pressure and enters the turbine as saturated vapour. A the turbine exhaust the conditions at 40°C and 10% moisture. The flow rate is 150 kg/h.
ts (in °C) |
Ps (in bar) |
ht (in kJ/kg) |
hfg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
---|---|---|---|---|---|
40°C | 0.07 | 167.57 | 2406.7 | 0.5725 | 7.501 |
- | 2 | 504.7 | 2201.6 | 1.530 | 5.596 |
Isentropic efficiency of turbine is
- (a)
80%
- (b)
76%
- (c)
85%
- (d)
70%
In a regenerative cycle, the steam enters the turbine at 30 bar, 400°C (h = 3230.9 kJ/kg, S = 6.92kJ/kg-K) and exhaust pressure is 0.10 bar. Feed water heater operates at 5 bar.
p (in bar) |
hf (in kJ/kg) |
hfg (in SkJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
---|---|---|---|---|
0.1 | 191.8 | 2392.8 | 0.649 | 7.501 |
5 | 640.1 | 2155.9 | 1.86 | 5.06 |
Mass of bled steam is
- (a)
0.723 kg
- (b)
0.828 kg
- (c)
0.546 kg
- (d)
0.172 kg
Schematic diagram of a power plant is shown below.
Condition of steam is given as
P3 = 15 bar, T3 = 250 °C, h3 = 2920 kJ/kg
h4 = 2660 kJ/kg, h5 = 2960 kJ/kg, h6 = 2335 kJ/kg
Based on these data the work obtained by turbine is
- (a)
725 kJ/kg
- (b)
795 kJ/kg
- (c)
300 kJ/kg
- (d)
885 kJ/kg
In a reheat cycle, steam enters to high pressure turbine at 150 bar, 550°C (h = 3448 kJ/kg, S = 6.520 kJ/kg-K). It is reheated at constant pressure of 40 bar to 550 °C (h = 3050 kJ/kg, s = 7.21 kJ/kg-K) and expands upto a condenser pressure 0.1 bar. Also given
p (in bar) |
hf (in J/kg) |
hfg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
Vf (in m3/kg) |
Vf (in m3/kg) |
---|---|---|---|---|---|---|
150 | 1611 | 1004 | 3.685 | 1.632 | .00016 | .0103 |
40 | 1087.4 | 1712.9 | 2.796 | 3.724 | .00012 | 0.049 |
0.1 | 192.6 | 2392.4 | 0.652 | 7.495 | .00101 | 14.54 |
Cycle efficiency is
- (a)
30%
- (b)
35%
- (c)
49%
- (d)
40%
In a reheat cycle, steam enters to high pressure turbine at 150 bar, 550°C (h = 3448 kJ/kg, S = 6.520 kJ/kg-K). It is reheated at constant pressure of 40 bar to 550 °C (h = 3050 kJ/kg, s = 7.21 kJ/kg-K) and expands upto a condenser pressure 0.1 bar. Also given
p (in bar) |
hf (in J/kg) |
hfg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
Vf (in m3/kg) |
Vf (in m3/kg) |
---|---|---|---|---|---|---|
150 | 1611 | 1004 | 3.685 | 1.632 | .00016 | .0103 |
40 | 1087.4 | 1712.9 | 2.796 | 3.724 | .00012 | 0.049 |
0.1 | 192.6 | 2392.4 | 0.652 | 7.495 | .00101 | 14.54 |
Steam rate in kg/kW-h, is
- (a)
2.52
- (b)
1.32
- (c)
0.57
- (d)
3.12
Analyse the schematic diagram of a power plant based on regeneration and reheat cycle
Properties and conditions of steam are as
h1 = 2985 kJ/kg, h2 = 2520 kJ/kg, h6 = 317.7 kJ/kg,
h7 = 697.1 kJ/kg, h3 = 3170 kJ/kg, h4 = 2555 kJ/kg
If capacity of power plant is 110 MW. Then,
boiler generating capacity is
- (a)
104 kg/s
- (b)
117 kg/s
- (c)
113 kg/s
- (d)
121 kg/s
Analyse the schematic diagram of a power plant based on regeneration and reheat cycle
Properties and conditions of steam are as
h1 = 2985 kJ/kg, h2 = 2520 kJ/kg, h6 = 317.7 kJ/kg,
h7 = 697.1 kJ/kg, h3 = 3170 kJ/kg, h4 = 2555 kJ/kg
If capacity of power plant is 110 MW. Then,
thermal effiviency of cycle is
- (a)
34%
- (b)
29.1%
- (c)
37%
- (d)
42.04%
In an ideal regenerative reheat steam cycle, steam enters the HP turbine at 80 par, 500°C and expands till it becomes saturated vapour. Some of the steam then goes to feed later heater and the balance is reheated to 400°C after which it expands in the LP turbine to 0.07 bar. Given, at 80 bar, 500°C, h = 3398.3 kJ/kg, S = 6.72 kJ/kg-K
p (in bar) |
hf (in kJ/kg) |
hfg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
---|---|---|---|---|
15 | 844.7 | 1945.2 | 2.314 | 4.126 |
6.6 | 686.8 | 2072.7 | 1.968 | 4.756 |
0.07 | 163.4 | 2409.1 | 0.559 | 7.717 |
Reheat pressure is
- (a)
0.07 bar
- (b)
15 bar
- (c)
Cannot be determined
- (d)
None of these
In an ideal regenerative reheat steam cycle, steam enters the HP turbine at 80 par, 500°C and expands till it becomes saturated vapour. Some of the steam then goes to feed later heater and the balance is reheated to 400°C after which it expands in the LP turbine to 0.07 bar. Given, at 80 bar, 500°C, h = 3398.3 kJ/kg, S = 6.72 kJ/kg-K
p (in bar) |
hf (in kJ/kg) |
hfg (in kJ/kg) |
Sf (in kJ/kg-K) |
Sfg (in kJ/kg-K) |
---|---|---|---|---|
15 | 844.7 | 1945.2 | 2.314 | 4.126 |
6.6 | 686.8 | 2072.7 | 1.968 | 4.756 |
0.07 | 163.4 | 2409.1 | 0.559 | 7.717 |
If power output of steam cycle is 80 MW, then steam flow rate is
- (a)
59.36 kg/s
- (b)
73.29 kg/s
- (c)
67.23 kg/s
- (d)
Data is insufficient