properties of steam.pdf

7/27/2019 properties of steam.pdf

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Nitesh Kumar, Assistant Professor, Dept. of

Mech & Mfg. Engg.1

MechanicalMechanicalMMEE

SS

EngineeringEngineering

ScienceScience

2

MMechanicalechanical EEngineeringngineering SSciencecience

1. Properties of steam

2. Steam boilers

3. Steam turbines

4. Refrigeration5. I. C. Engines

6. Lubrication

1. Transmission of power

2. Machine tools

3. Casting

4. Forging5. Welding

6. Milling machine

7. Shaper

8. Grinding machine

Part APart A Part BPart B

ThermalThermal ProductionProduction


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InstructionsInstructions

Mark distribution:Mark distribution:

Test = 40 marksTest = 40 marksAssignment / surprise test = 10 marksAssignment / surprise test = 10 marks

EndEnd SemSem Exam = 50 marksExam = 50 marks

Test: 40 marksTest: 40 marks

There will be 2 Tests.

Each test is of 20 marks

Assignment / surprise test:

There will be 2/3 assignments / surprise tests.

Each assignment / surprise test is of 10 marks.

To award 10 marks, all are considered.Nitesh Kumar, Assistant Professor, Dept. of

Mech & Mfg. Engg.

4

Reference booksReference books

1. Mechanical Engineering Science: K.R.

Gopalakrishna, Subhas Publications

2. Elements of Mechanical Engineering:

Roy & Choudhury, Laxmi Publications Pvt. Ltd

3. Mechanical Engineering Science: B.K.

Mishra, Kumar & Kumar Publishers Pvt. Ltd

4. Mechanical Engineering Science: R.K

Rajput, Laxmi Publications Pvt. Ltd.


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Chapter 1:Chapter 1:

PROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAMPROPERTIES OF STEAM

Steam:

Vapour form of water is called STEAM.

Water in solid phase: We call it as ICEICE

Water in liquid phase: We call it as WATERWATER

Water in gaseous phase: We call it as STEAMSTEAM


Mech & Mfg. Engg.

Application of steam

Food processing industry

Cooking: hotels, restaurants etc

Used as working fluid in steam engines andsteam turbines

Used in industries for heating process

Petrochemical industries Washing, drying, sterilizing in hospitals

Health clinic and gym


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FORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENTFORMATION OF STEAM EXPERIMENT

(Constant Pressure)(Constant Pressure)

Consider 11 kgkg of water at 00ooCC

taken in a cylinder fitted

with a freely moving

frictionless piston as shown

in figure.

Cylinder

I kg of

water at

OoC

Pressure

P


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The initial condition of water at 0oC is represented by the point AAon

the Temperature Enthalpy graph

A

Temperature

Enthalpy

(h)

Temperature

(ToC)


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AA

Temperature

EnthalpyEnthalpy

(h)(h)

TemperatureTemperature

(T)(T)ooCC

TTSatSat BB

hhff

Sensible heatSensible heat

hhfgfg

Latent heatLatent heat

TTSupSup

AOSAOS

CC

DD

DOSDOS

Fig. 1

WW

WW

W

Fig. 2 Fig. 3 Fig. 4 Fig. 5

AA BB CC DD


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DefinitionsDefinitions

Sensible heatSensible heat(hf):: (Enthalpy of water)

It is the amount of heat required to raise the temperature of 1

kg of water from 0 0C to the saturation temperature Tsat0C a t a

given constant pressure P.

hf= m x Cpx Tsat kJ/kgkJ/kg

Where, m = mass of water in kg.

Cp = specific heat of water

= 4.1868 kJ/kg0K


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SaturationSaturation temperaturetemperature ((TTsatsat))::

It is the temperature at which the water begins to boil at the

stated pressure.

LatentLatent heatheat ((hhfgfg)):: (Enthalpy(Enthalpy ofof evaporation)evaporation)

It is the amount of heat required to evaporate 1 kg of water at

saturation temperature to 1 kg of dry steam at the same

saturation temperature and at the given constant pressure P.

SuperheatedSuperheated temperaturetemperature ((TTsupsup))::

It is the temperature of the steam above the saturation

temperature at a given constant pressure.


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AmountAmount ofof superheatsuperheat (AOS)(AOS):: (Enthalpy(Enthalpy ofof superheat)superheat)

It is the amount of heat required to raise the temperature of

dry steam from its saturation temperature to any desired

higher temperature at the given constant pressure P.

AOS = m x Csup (Tsup - Tsat) kJ/kgkJ/kg

DegreeDegree ofof superheatsuperheat (DOS)(DOS)::

It is the difference between the superheated temperature and

the saturation temperature.

DOSDOS == ((TTsupsup TTsatsat))


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Different states of steamDifferent states of steam

The steam as it is being generated can exist in threethree different

states,

1. Wet steam

2. Dry saturated steam (dry steam)

3. Superheated steam


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Wet Steam:Wet Steam:

A wet steam is defined as a twotwo--phasephase mixturemixture of finely

divided waterwater particlesparticles and steamsteam at the saturation

temperature corresponding to a given stated pressure.


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EnthalpyA

B C

Sensible

Heat

Latent Heat

hfg

Tsup

Temperature

Amount of

Superheat

Degree of Superheat

Ts

hf

D

Temperature

hg


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The quality of wet steam is specified by the drynessdryness fractionfraction

which indicates the amount of dry steam present in the given

quantity of wet steam and is denoted as xx.

The dryness fraction of a steam is defined as the ratio of mass of

the actual dry steam present in a known quantity of wet steam to

the total mass of the wet steam.

SteamWetofMassTotal

Steamin WetpresentSteamDryofMassxfraction,Dryness =


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Let,

mg = Mass of dry steam present in the sample quantity of wet

steam

mf= Mass of suspended water molecules in the sample quantity

of wet steam

The dryness fraction of wet steam is always lessless thanthan 11.

The dryness fraction of dry steam is equalequal toto 11.

g

f g

mx

m m=

+


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Dry Saturated Steam:Dry Saturated Steam:

(dry steam)(dry steam)

Dry saturated steam is the steam at saturation temperature

and at a given pressure having nono waterwater moleculesmolecules entrained

in it.


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SuperheatedSuperheated SteamSteam::

A superheated steam is defined as the steam at a temperature

higher than the saturation temperature at the given stated

pressure.


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Advantages of Superheated Steam:Advantages of Superheated Steam:

Superheated steam possess very high energy compared to dry

saturated steam or wet steam at the same pressure, hence its

capacity to do the work will be higher.

It doesnt create any problems like rusting or corrosion of

blades of turbine / engine cylinder.


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Disadvantages of Superheated Steam:Disadvantages of Superheated Steam:

The high superheated temperatures poses problems in thelubrication.

Higher initial cost.

EnergyEnergy contentcontent ofof steamsteam::

Superheated

steam

Dry saturated

steam

Wet

steam> >


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Enthalpy equations for different states of steamEnthalpy equations for different states of steam

a) Enthalpy of Dry saturated Steam (ha) Enthalpy of Dry saturated Steam (hgg):):

hg = hf+ hfg kJ/kg

EnthalpyA

B C

Sensible

Heat

Latent Heat

hfg

Tsup

Temperature

Amount of

Superheat

Degree of Superheat

Ts

hf

D

Temperature

hg


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b) Enthalpy of Wet Steam (h):b) Enthalpy of Wet Steam (h):

A

B C

Sensible

Heat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of

Superheat

Degree of Superheat

Tsat

hf

D

Temperature

h = hf+ x .hfgkJ/kg


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c) Amount of superheat (AOS):c) Amount of superheat (AOS): (Enthalpy of superheat)(Enthalpy of superheat)

A

B C

Sensible

Heat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of

Superheat

Degree of Superheat

Ts

hf

D

Temperature

AOS = Csup (Tsup - Tsat) kJ/kg

where, Csup = Specific heat of the superheated steam

= 2.25 kJ/kg0K


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d) Enthalpy of Superheatedd) Enthalpy of Superheated Steam (hSteam (hsupsup):):

A

B C

Sensible

Heat

Latent

Heat

hfg

Tsup

Temperature

Enthalpy

Amount ofSuperheat

Degree of Superheat

Tsat

hf

D

Temperature

hg

hsup

= hf

+ hfg

+ Csup

(Tsup

- Tsat

) kJ/kg


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e)e) Degree of superheat (DOS):Degree of superheat (DOS):

A

B C

Sensible

Heat

Latent

Heat

hfg

Tsup

Temperatur

Enthalpy

Amount of

Superheat

Degree of Superheat

Tsat

hf

D

Temperature

DOS = (Tsup - Tsat)0C


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a) Enthalpy of Dry saturated Steam:

hg = hf+ hfg kJ/kg

b) Enthalpy of Wet Steam:

h = hf+ x .hfg kJ/kg

c) Enthalpy of Superheated Steam:

hsup = hf+ hfg + Csup (Tsup - Tsat) kJ/kg

d) Degree of superheat (DOS):

DOS = (Tsup - Tsat)0C

e) Amount of superheat (AOS):AOS = Csup (Tsup - Tsat) kJ/kg


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Critical Temperature &Critical Temperature &Pressure.Pressure.

PPcc == 221.2 bar221.2 bar

TTcc == 374.15374.1500CC

At a particular pressure waterwater

is directly converted into drydry

steamsteam without going through

the phase of evaporation. i.e.,

hhfgfg == 00 . This point is called

criticalcritical pointpoint..

Temperature

Enthalpy

Tc

Pc

Pi

P3

P2

P1

hf hfghf


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CriticalCritical pressurepressure::

It is the pressure at which the water is directly converted into

dry steam without undergoing the state of evaporation.

CriticalCritical temperaturetemperature::

It is the corresponding temperature at the critical point.

properties of steam.pdf

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