1. Theory of Steam Production
P M V Subbarao
Professor
Mechanical Engineering Department
The Impact of Heat Addition at High Temperature……..

2. A Deeper Study of Steam Production

3. The Microscopic View
When a liquid evaporates to a gas in a closed container, the molecules cannot escape.
Some of the gas molecules will eventually strike the condensed phase and condense back into it.
When the rate of condensation of the gas becomes equal to the rate of evaporation of the liquid or solid, the net amount of gas, liquid and/or solid no longer changes.
The gas in the container is in equilibrium with the liquid or solid.

4. Starting from Liquid State
Let's consider the results of heating liquid from 20°C
For Ammonia Pressure must be greater than 857.5kPa
For water Pressure must be greater than kPa
20C

5. State 1 Liquid Ammonia @ 1 MPa Liquid Water @ 100 kPa 20C
It is in a compressed liquid region or
Sub-cooled liquid region.
Start heating….

6. Constant Pressure Heating Process
Process from1-----:
The temperature and specific volume will increase from the compressed liquid, or subcooled liquid (state 1).
Proceed to reach the saturated liquid state.
state 2
Saturated Liquid 1 MPa &24.9C
Saturated Liquid 100 kPa & 99.62C

7. Further Heating from Saturated Liquid Vapour @ Constant Pressure
Process form 2---:
At state 2 the liquid has reached the temperature at which it begins to boil, called the saturation temperature, and is said to exist as a saturated liquid.
Properties at the saturated liquid state are noted by the subscript f and v2 = vf.
During the phase change both the temperature and pressure remain constant.
Water boils at 99.62°C when the pressure is 100kPa .
Ammonia boils at 24.99°C when the pressure is 1000 kPa.

8. State 3 : Saturated Vapour
Process 2-3:
At state 3 a saturated vapor exists and vaporization is complete.
The subscript g will always denote a saturated vapor state.
Note : v4 = vg.

9. Saturated Water Vs Saturated Steam
Temperature
Pressure
Specific Volume, m3/kg 0C
MPa
Saturated Liquid
Saturated Vapour
100
0.1013
1.673
120
0.1985
0.8919
150
0.4759
0.3928
200
1.554
0.1274
250
3.973
300
8.581

10. Saturated Liquid Ammonia Vs Saturated Vapour Ammnia
Temperature
Pressure
Specific Volume, m3/kg 0C
MPa
Saturated Liquid
Saturated Vapour
100
6.254
120
9.107
132.3
11.33

11. State 4 : Superheated Vapour
Process 3-4:
If the constant pressure heating is continued, the temperature will begin to increase above the saturation temperature.
State 4 is called a superheated state because T4 is greater than the saturation temperature for the pressure.
Superheated 1 MPa &300C
Superheated 100 kPa & 300C

12. Constant Pressure Process

13. The Theory of Producing Steam
Water and steam can be easily used as heat carriers in heating systems.
Water boils and evaporates at 100°C under atmospheric pressure.
By higher pressure, water evaporates at higher temperature - e.g. a pressure of 10 bar equals an evaporation temperature of ~179.90C.
At a constant pressure of 10 MPa the saturation temperature is C.

14. Wet Vapour
Wet vapour is a mixture of vapour and liquid water at same temperature and pressure.
Saturation pressure is the pressure at which the liquid and vapor phases are in equilibrium at a given temperature.
Saturation temperature is the temperature at which the liquid and vapor phases are in equilibrium at a given pressure.
Saturation Pressure is function of temperature or vice versa.
T = F(p)
The Wagner-Ambrose equation

15. Equations for Saturation Conditions of Water
Saturation Properties of Water :

16. Superposition of Many Constant Pressure Processes
If all of the saturated liquid states are connected, the saturated liquid line is established.
If all of the saturated vapor states are connected, the saturated vapor line is established.
These two lines intersect at the critical point and form what is often called the “steam dome.”
The critical point of water is oC, MPa
The critical point of ammonia is 132.3oC, MPa

17. Density of Saturated Liquid

18. Density of Saturated Vapour

19. Peculiar Nature of Wet Vapour
Pressure and temperature are not independent properties.
Either p & V or T& V are independent pair.
P & v or T & v can also be considered.
A new property is to be defined for steam for ease of design.
This is called Quality or dryness fraction of wet steam.

20. Quality and Saturated Liquid-Vapor (Wet) Mixture
Now, let’s review the constant pressure heat addition process for water shown in Figure.
The state 3 is a mixture of saturated liquid and saturated vapor.
How do we locate it on the T-v diagram?
To establish the location of state 3 a new parameter called the quality x is defined as

21. Quality or Dryness Fraction
The quality is zero for the saturated liquid and one for the saturated vapor (0x  1).
The average specific volume at any state 3 is given in terms of the quality as follows.
Consider a mixture of saturated liquid and saturated vapor.
The liquid has a mass mf and occupies a volume Vf.
The vapor has a mass mg and occupies a volume Vg.

22. Critical Point
The region to the left of the saturated liquid line and below the critical temperature is called the compressed liquid region.
The region to the right of the saturated vapor line and above the critical temperature is called the supercritical region.
At temperatures and pressures above the critical point, the phase transition from liquid to vapor is no longer discrete.

23. Heat Addition at sub-critical Pressure

24. Religious to Secular Attitude of Sustance

25. Thermodynamic Properties at Super Critical Pressures

26. Property Diagrams

27. Pressure Volume Diagram

28. Vapour
Temperature of the substance is higher than the saturation temperature at a given pressure.
Pressure of the substance is lower than the saturation pressure at a given temperature.
Molecules of substance move in random paths.
Weak inter-molecular forces.
Occupy entire volume of the container : No free surface.
Very low density
Highly compressible.

29. P – v- T Relation v = f (p,T) The specific volume of A vapour:
Greatest need for EoS of saturated and superheated steam.
R and a are constants.
The is called as Rankine’s Equation of state, 1849.

30. Pressure Volume Diagram

31. Van der Waals EOS
One of the oldest but most extensively used of the EOS of non ideal gases
Any EOS model must reproduce graphs such as that of the previous
a, b are the Van der Waals constants for the particular gas;
for water: a = J-m3/mole2; b = 3.049x10-5 m3/mole,

32. JO H A N N E S D . V A N D E R W A A L S The equation of state for gases and liquids Nobel Lecture, December 12, 1910
I intend to discuss in sequence:
(1) the broad outlines of my equation of state and how I arrived at it;
(2) what my attitude was and still is to that equation;
(3) how in the last four years I have sought to account for the discrepancies which remained between the experimental results and this equation;
(4) how I have also sought to explain the behaviour of binary and ternary mixtures by means of the equation of state.

33. Van der Waals EOS
a, b are the Van der Waals constants for the particular gas;
for water: a = J-m3/mole2; b = 3.049x10-5 m3/mole,

34. Van der Waals Coefficients
Gas
a (Pa m3)
B (m3/mol)
Helium
3.46 x 10-3
23.71 x 10-6
Neon
2.12 x 10-2
17.10 x 10-6
Hydrogen
2.45 x 10-2
26.61 x 10-6
Carbon dioxide
3.96 x 10-1
42.69 x 10-6
Water vapor
5.47 x 10-1
30.52 x 10-6

35. Van der Waals Isotherms

36. Isotherms of Real Gases

37. Improved Cubic Equations of State

38. The constants a, b, c, Ao, Bo varies with substance

40. The Ideal Gas Equation of State