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Presenting a power point presentation on

Steam formation, Throttling Process and

Bucket Calorimeter.

space for your information

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2Information which we like to share in this presentation…

Steam formation.

Graphical representation of steam formation.Types of steam (detailed information).Throttling process.Bucket calorimeter.Model (picture) prepared by Nquare GROUP.

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SOURCE (information taken from).

Totally EME Book (Books

India Publication).

One picture of

calorimeter is taken from

Google.

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Steam formation

PISTON

W

WATER

1

vfConsider a cylinder fitted with a piston which can move freely upwards and downwards in it.

Vf: volume of water

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PISTON

W

WATERts

3

Consider 1Kg of water at 0 degree C under the piston.

ts: Boiling point

PISTON W

WATER

Wet steam

2

Now if the heat is supplied to water ,a rise in temperature will be noticed and this rise will continue till boiling point is reached.

Ts: boiling point

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WPISTON

Dry statured steam

ts

4

vg

Vg-v

fThe temperature at which water boils , depends on the pressure acting on it.

Vg: volume of dry and stratured.

Vf: volume of water

PISTON W

5

Vsup

Ts: boiling point

Supe

r hea

ted

stea

m

tsup

Vsup: volume of super heated steamTsup: temperature of super heated steam

When boiling point of water reached ,there will be a slight increase in in the volume of water

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A

C

D

Tsup

Ts

P=C

B

A

P=C

xhfg

Sensible heat hf

Latent heat hfg

Enthalpy of super heat

D

Temperature

Enth

alpy

C

P=C

Graphical representation of steam formation

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Advantages of superheated

steamDisadvantages of

superheated steamHigh temperature can cause the problems of lubrication.

Maintenance costs of high.

Contains more heat energy.

Capacity to do work is higher.

It reduces the condensation in extreme cases.

It improves the thermal efficiency of the boiler.

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Types of steam

Wet steam Dry saturated steam Superheated steam Both the water molecules and steam coexist to form a two phase mixture.

A steam at the saturation temperature corresponding to a given pressure and having no water molecules in it.

When a dry statured steam heated further at the give constant pressure, its temperature rises beyond its saturation temperature.

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Dryness fraction

x=ms/(ms+mw)

mass of dry steam mass of water molecules in wet steam

It is defined as the ratio of the weight of dry steam actually

presents to the weight of total wet steam which contains it. It is

denoted by x. Thus

Dryness fraction of

wet steam is always less

than 1.

Dryness fraction of dry

and superheated

is always unity.

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wetness fraction It is the ratio of the weight of water/ moisture in suspension in a wet steam sample to the total weight of wet steam.

It is calculated by subtracting x from 1

wetness fraction = 1-x = mw/ (ms+mw).

Priming: When wetness fraction is expressed in percentage, it is known as priming.

So Priming= 100(1-x)

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Enthalpy of steam

Enthalpy of liquid(hf)

hf = Cpw (tf-0) kJ/kg

where Cpw =specific heat of water in kJ/kgK

Tf =temperature of water in °C

. Enthalpy of dry saturated steam(hg)

hg= hf+ hfg kJ/kg

where hfg= heat required to convert the same water from B.P.to dry saturated steam at constant temperature Ts

Enthalpy of wet steam(h)

. h= hf+ xhfg kJ/kg

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Enthalpy of superheated steam(hsup)

hsup = hg+ hfg+ Cps (Tsup-Tsat)

Cps=specific heat of superheated

steam

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Throttling process

It’s a type of expansion process , in which steam passes through a narrow passage and expands with a full pressure without doing any external work.

In this process there is no exchange of heat.

During this process the enthalpy remains constant therefore this process is also called constant enthalpy process.

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Orifice

Throttling Process1

1

2

2

ORIFICE

LOW PRESSURE FLIUD

HIGH PRESSURE FLUID

Throttling process

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h1+(v1*v1)/2+gz1+q=h2+(v2*v2)/

2+gz2+WSteady flow energy equation is

No work is done during throttling hence W=0

No change in elevation so z1=z2

Change in K.E. is negligible so v1=v2 So h1=h2

Initial enthalpy = Final enthalpy

Throttling is a steady flow process hence, the steady flow energy equation applicable.

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Bucket or barrel calorimeter

Construction

The top cover is made of wood

bottom ring

The thermometer

copper

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working

1. Measure the weight of calorimeter.

2. Specific heat of copper.

3. Water equivalent to calorimeter is calculated.

4. Note initial temperature.

5. Connect steam pipe to main steam pipe.

6. Steam contact with water.

7. Temperature of water increases.

8. Mass of water also increases .

9. Closed the valve.

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MODEL OF BUCKET CALORIMETER MADE BY N SQUARE GROUP

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