this slide content what is steam its types and various formula and introduction to steam table

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STEAM DEFINITION
PROPERTIES OF STEAM
STEAM TABLE

3. STEAM:- the vapor into which water is converted when heated, forming a white
mist of minute water droplets in the air.
Or
Steam is the hot mist that forms when water boils
Steam is water in the gas phase. It is commonly formed by boiling or evaporating
water. Steam that is saturated or superheated is invisible;
Formation of steam:
DEFINITION
Steam can be formed by boiling water in a vessel. But to use it effectively as a
working or heating medium, it has to produce in a closed vessel under pressure.
Steam formed at a higher pressure has higher temperature and can be made to flow
easily through insulated pipes from steam generator to point of use. A simple
arrangement of formation of steam at constant pressure is shown.

4. Consider 1 kg of ice at temperature -100C which is below the freezing point. Let it
be heated at constant pressure P. The temperature of ice starts increasing until it
reaches the melting temperature of ice i.e., 00C and during this course ice absorbs
its sensible heat. On further addition of heat, ice starts melting, its temperature
remains constant at 00C and it absorbs latent heat of fusion and converts completely
into water at 00C.

5. On further addition of heat, the temperature of water starts rising until it reaches the
boiling temperature or saturation temperature corresponding to pressure P. This heat
absorbed by water in sensible heat.

6. After the boiling temperature is reached, it remains constant with further addition
of heat and vaporization take place. The water absorbs its latent heat and converts
into dry saturated steam remaining at same saturation temperature. The
intermediate stage of water and dry saturated steam is wet steam, which is actually
a mixture of steam and water. If further the heat is added, the temperature of this
dry saturated steam starts rising from saturation temperature and it converts into
superheated steam. This heat absorbed is again the sensible heat. The total rise in
temperature of superheated steam above the saturation temperature is called degree
of superheat. We must know here that the saturation temperature, latent heat and
other properties of steam remain same at constant pressure but varies with the
variation of pressure.
Pressure –Temperature Relationship of Water & Steam:
If water is heated beyond the boiling point, it vaporizes into steam, or water in the
gaseous state. However, not all steam is the same. The properties of steam vary
greatly depending on the pressure and temperature to which it is subject.
Saturated (dry) steam results when water is heated to the boiling point (sensible
heating) and then vaporized with additional heat (latent heating). If this steam is
then further heated above the saturation point, it becomes superheated steam
(sensible heating).

7. TRIPLE POINT is the temperature and pressure at which solid, liquid, and vapor
phases of a particular substance coexist in equilibrium. It is a specific case of
thermodynamic phase equilibrium.
The term "triple point" was coined by James Thomson in 1873.

8. CRITICAL POINT a point on a phase diagram at which both the liquid and gas
phases of a substance have the same density, and are therefore indistinguishable.
In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 221.5
bar
Qualities of Steam:
1. Produced from water.
2. Clean, odorless, and tasteless.
3. Easily distributed and controlled.
4. Heat can be used over and over.
5. High usable heat content.
6. Gives up its heat at constant temperature.
7. Well-known characteristics. Pressure, temperature, volume.
Types of steam:
Steam has following type as per moisture content.
 Wet Steam
 Dry steam
 Superheated steam

9. Wet Steam :-
When the moisture present in the steam it is known as wet steam. This is the most
common form of steam actually experienced by most plants. When steam is generated
using a boiler, it usually contains wetness from non-vaporized water molecules that
are carried over into the distributed steam. Even the best boilers may discharge steam
containing 3% to 5% wetness. As the water approaches the saturation state and begins
to vaporize, some water, usually in the form of mist or droplets, is entrained in the
rising steam and distributed downstream.
Dry steam:-
Dry Steam is saturated steam that has been very slightly superheated. This is not
sufficient to change its energy appreciably, but is a sufficient rise in temperature to
avoid condensation problems, given the average loss in temperature across the steam
supply circuit. Dryness fraction x = 1.
Superheated Steam:-
Superheated steam is created by further heating wet or saturated steam beyond the
saturated steam point. This yields steam that has a higher temperature and lower
density than saturated steam at the same pressure. Superheated steam is mainly used
in propulsion/drive applications such as turbines, and is not typically used for heat
transfer applications.

10. IMPORTANT TERM RELATING STEAM FORMATION:
 SPECIFIC HEAT:-
The specific heat is the amount of heat per unit mass required to raise
the temperature by one degree Celsius. The relationship between heat and
temperature change is usually expressed in the form shown below where c is the
specific heat. The relationship does not apply if a phase change is encountered,
because the heat added or removed during a phase change does not change the
temperature. The equation is
Q= m c ΔT
We have:
Q: Sensible heat
m: Mass of the body
ΔT: Change of the temperature
c: Specific heat coefficient of the material
The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is
higher than any other.

11.  SENSIBLE HEAT OF WATER:
It is defined as the quantity of heat absorbed by 1 kg of water when it is heated from
0°C (freezing point) to boiling point. It is also called total heat (or enthalpy) of water.
If 1 kg of water is heated from 0°C to 100°C the sensible heat added to it will be
4.18 × 100= 418 kJ
but if water is at say 20°C initially then sensible heat added will be
4.18 × (100 – 20)= 334.4 kJ.
This type of heat is denoted by letter hf and its value can be directly read from the
steam tables.
 LATENT HEAT (L):
It is defined as the amount of thermal energy (heat, Q) that is absorbed or released
when a body undergoes a constant-temperature process. The equation for specific
latent heat is:
L = Q / m
where:
L is the specific latent heat
Q is the heat absorbed or released
m is the mass of a substance

12. The most common types of constant-temperature processes are phase changes, such
as melting, freezing, vaporization, or condensation. The energy is considered to be
"latent" because it is essentially hidden within the molecules until the phase change
occurs.
It is "specific" because it is expressed in terms of energy per unit mass. The most
common units of specific latent heat are joules per gram (J/g) and kilojoules per
kilogram (kJ/kg).
Specific latent heat is an intensive property of matter. Its value does not depend on
sample size or where within a substance the sample is taken.
Types of Latent Heat:
• Latent Heat of Fusion: Latent heat of fusion is the heat absorbed or released
when matter melts, changing phase from solid to liquid form at a constant
temperature.
• Latent Heat of Vaporization: The latent heat of vaporization is the heat
absorbed or released when matter vaporizes, changing phase from liquid to gas
phase at a constant temperature.

13. Latent Heat of Fusion
Latent Heat of
Vaporization:

14. Table of Specific Latent Heat Values:
Material Melting Point (°C) Boiling Point (°C) SLH of Fusion
kJ/kg
SLH of Vaporization
kJ/kg
Ammonia −77.74 −33.34 332.17 1369
Carbon Dioxide −78 −57 184 574
Ethyl Alcohol −114 78.3 108 855
Hydrogen −259 −253 58 455
Lead 327.5 1750 23.0 871
Nitrogen −210 −196 25.7 200
Oxygen −219 −183 13.9 213
Refrigerant R134A −101 −26.6 — 215.9
Toluene −93 110.6 72.1 351
Water 0 100 334 2264.705
Examples of Latent and Sensible Heat
Daily life is filled with examples of latent and sensible heat:
 Boiling water on a stove occurs when thermal energy from the heating element
is transferred to the pot and in turn to the water. When enough energy is
supplied, liquid water expands to form water vapor and the water boils. An
enormous amount of energy is released when water boils. Because water has
such a high heat of vaporization, it's easy to get burned by steam.

15.  Similarly, considerable energy must be absorbed to convert liquid water to ice in
a freezer. The freezer removes thermal energy, allowing the phase transition to
occur. Water has a high latent heat of fusion, so turning water into ice requires
the removal of more energy than freezing liquid oxygen into solid oxygen, per
unit gram.
 Latent heat causes hurricanes to intensify. Air heats as it crosses warm water and
picks up water vapor. As the vapor condenses to form clouds, latent heat is
released into the atmosphere. This added heat warms the air, producing
instability and helping clouds to rise and the storm to intensify.
 Sensible heat is released when soil absorbs energy from sunlight and gets
warmer.
 Cooling via perspiration is affected by latent and sensible heat. When there is a
breeze, evaporative cooling is highly effective. Heat is dissipated away from the
body due to the high latent heat of vaporization of water. However, it's much
harder to cool down in a sunny location than in a shady one because sensible
heat from absorbed sunlight competes with the effect from evaporation.

16. x =
Ms
Ms +Mw
 DRYNESS FRACTION:
The term dryness fraction is related with wet steam. It is defined as the ratio of the
mass of actual dry steam to the mass of steam containing it. It is usually expressed
by the symbol ‘x’ or ‘q’.
If
Ms=Mass of dry steam contained in steam considered and
Mw=weight of water particles in suspension in the steam considered
Then
 SPECIFIC VOLUME :
Gases (steam is a gas) occupy less space under higher pressure than under lower
pressure. This means 1 kilogram of steam occupies different volumes, depending
upon its pressure. The term specific volume refers to the volume that one kg of
steam occupies at a given pressure and temperature.
VS = V/M
VS = V
Where V = Volume in m3
M= 1kg or unit mass

17. Specific volume of saturated water (vf)
It is defined as volume of 1kg of water at saturation temperature corresponding to the
given pressure. It is denoted by vf. It can be calculated experimentally. It slightly
increases with increase in saturation temperature and hence the pressure. The
reciprocal of sp-volume is equal to density.
Specific volume of dry saturated steam (vg)
It is defined as volume of 1kg of dry saturated steam corresponding to the given
pressure. It is denoted by vg and can be calculated experimentally. As dry saturated
steam is a gas, its specific volume decreases with increase in pressure or the
saturation temperature.
Specific volume of wet steam of quantity x
It is the volume of 1kg of wet steam and is denoted as = x.vg
Where
x = Dryness fraction
vg = Specific volume of dry saturated steam
Specific volume of Superheated Steam (vsup):
It is the volume of 1kg of superheated steam and can be determined by assuming that
the steam behaves as a perfect gas i.e., obeys the gas laws.
It is denoted by

18. Vsup = vg . Tsup
ts
Let P = pressure under which steam is superheated. Since, P = constant,
tsup =temperature of superheated steam
vg = Specific volume of dry saturated steam
ts = saturation temperature at pressure P.
Table of Common Specific Volume Values
Engineers and scientists typically refer to tables of specific volume values. These
representative values are for standard temperature and pressure (STP), which is a
temperature of 0 °C (273.15 K, 32 °F) and pressure of 1 atm.
Substance Density Specific Volume
(kg/m
3
) (m
3
/kg)
Air 1.225 0.78
Ice 916.7 0.00109
Water (liquid) 1000 0.00100
Salt Water 1030 0.00097
Mercury 13546 0.00007

19.  ENTHALPY:
The total heat content of a substance is called enthalpy, so the total heat content by
steam is termed as its enthalpy. It is denoted by ‘H’. SI unit is KJ
‘h‘ is generally used term which represents specific enthalpy, unit for which is KJ/Kg.
Enthalpy of wet steam is given by:
h = hf + xhfg
Where
hf = sensible heat of saturated liquid.
hfg = Latent heat of vaporization
x= Dryness fraction
Enthalpy of dry steam is given by:
h = hf + hfg =hg
Where
hf = sensible heat of saturated liquid.
hfg = Latent heat of vaporization
x= Dryness fraction = 1

20. Enthalpy of superheated steam is given by:
hsup = hf + hfg + cps(Tsup - Ts)
Where
hf = sensible heat of saturated liquid.
hfg = Latent heat of vaporization
hsup = Enthalpy of Superheated steam.
Tsup = Superheating temperature
Cps = specific heat
Ts = saturation temperature
 ENTROPY OF STEAM:
Specific entropy of saturated water (sf)
The specific entropy of saturated water at a particular pressure P and saturation
temperature Ts is given as the change in entropy during conversion of one kg of water
at 00C into saturated water at that pressure. The water at freezing point 00C or 273 K
is considered as datum where, absolute entropy is taken as zero. If CW is specific heat
of water then the change in entropy of 1kg water during temperature change from
273 K to TK is given as

21. As the Initial entropy at 273 K is zero, so this change in entropy above 273 K is taken
as entropy of water at temperature T. In case of Saturated Water, T= Ts
Change in specific entropy during evaporation, (sfg)
During evaporation heat added = hfg = Latent heat of water
Temperature remains constant during evaporation and is equal to saturation
Temperature Ts.
Specific entropy of wet steam:
Specific entropy of wet steam is equal to sum of specific entropy of saturated water
and change in specific entropy during evaporation of dry fraction of steam.
s = sf + xsfg
Where
sf = specific entropy
Sfg = specific entropy during evaporation.

22. Specific entropy of dry saturated steam (sg)
It is the entropy of one kg of dry saturated steam and is given as the sum of entropy
of 1kg of saturated water and entropy change during evaporation.
It is denoted by sg. Thus sg = sf + sfg
Specific entropy of superheated steam (ssup)
It is the sum of specific entropy of dry saturated steam and entropy change during
superheating from saturation temp Ts to superheated temp Tsup.
Change in entropy during superheating
Total specific entropy of superheated steam

23. STEAM TABLE
In engineering problems for any fluid which is used as working fluid, the six basic
thermodynamic properties required are:
1. Pressure,
2. Temperature.
3. Volume.
4. Internal energy.
5. Enthalpy.
6. Entropy.
These properties must be known at different pressure for analyzing the
thermodynamic cycle used for work producing devices.
The values of these properties are determined theoretically or experimentally and are
tabulated in the form of table which are known as STEAM TABLE.
Following are the thermodynamic properties of steam which are tabulated in the
form of table:

24. p = absolute pressure in bar
ts = Saturation temperature 0C
hf = Specific enthalpy of saturated water (kJ/kg)
hfg = Latent heat of evaporation (kJ/kg)
hg = Specific enthalpy of dry saturated steam (kJ/kg)
vf = Specific volume of saturated water (liquid). (m3/kg)
vg = Specific volume of saturated steam (gas). (m3/kg)
sf = Entropy of saturated liquid (kJ/kg.Kelvin)
sg = Entropy of saturated vapor (kJ/kg.Kelvin)
sfg = Entropy of vaporization (kJ/kg.Kelvin)
Also
hfg = hg -hf change of enthalpy during evaporation.
sfg = sg -sf change of entropy during evaporation.
vfg = vg -vf change of volume during evaporation.
The above mentioned properties at different pressure and temperature are
tabulated in the form of steam table.

25. Two Formats: Pressure Based and Temperature Based
Since saturated steam pressure and saturated steam temperature are directly related
to one another, saturated steam tables are generally available in two different
formats: based on pressure and based on temperature. Both types contain the same
data that is simply sorted differently.
Pressure based table: in this types of table pressure given in the first column and
then corresponding values based on it.
PRESS.
(GAUGE)
TEMP.
SPECIFIC
VOLUME
SPECIFIC ENTHALPY
kPaG °C m3/kg kJ/kg
P T Vf Vg Hf Hfg Hg
0 99.97 0.0010434 1.673 419.0 2257 2676
20 105.10 0.0010475 1.414 440.6 2243 2684
50 111.61 0.0010529 1.150 468.2 2225 2694
100 120.42 0.0010607 0.8803 505.6 2201 2707

26. Temperature based table: in this type of table temperature given in the first column and
then corresponding values based on it.
TEMP.
PRESS.
(GAUGE)
SPECIFIC VOLUME SPECIFIC ENTHALPY
°C kPaG m3/kg kJ/kg
T P Vf Vg Hf Hfg Hg
100 0.093 0.0010435 1.672 419.1 2256 2676
110 42.051 0.0010516 1.209 461.4 2230 2691
120 97.340 0.0010603 0.8913 503.8 2202 2706
130 168.93 0.0010697 0.6681 546.4 2174 2720
140 260.18 0.0010798 0.5085 589.2 2144 2733
150 374.78 0.0010905 0.39250 632.3 2114 2746

27. How to use steam table:
1. First things we have to understand how much values given in the question.
Pressure based values or temperature based values on which other properties
depends.
2. If pressure given in the question and all the properties we have to find on the
basis of it. Then go to steam table find values in S.I. Units.
3. Then find Pressure Based Saturated Steam Table and search given pressure say
20 kpa or bar then find the corresponding values of T, hf, hg, hjg , vf, vg, or if
required sf, sg, sfg.
4. Simliary find Temperature Based Saturated Steam Table and search given
temperature say 100 then find the corresponding values of p, hf, hg, hjg , vf, vg,
or if required sf, sg, sfg.
Please see in the table provided in previous slide.