Determination of Dryness Fraction Of Steam Using Separating And Throttling Calorimeter

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 DETERMINATION OF DRYNESS FRACTION BY USING SEPARATING & THROTTLING CALORIMETERS

AIM: -To determine dryness fraction of steam by using Separating throttling calorimeter

OBJECTIVE: 

The objective of this experiment is to study the determination of the dryness fraction of wet steam by

using 

1. Tank Calorimeter 

2. Separating Calorimeter 

3. Throttling Calorimeter 

4. Separating and Throttling Calorimeter 

DIAGRAM:

SEPARATING AND THROTTLING CALORIMETER

PROCEDURE:

The dryness fraction measured with the help of separating calorimeter is always higher than the actual.

This is because of incomplete separation of moisture by mechanical means. 

If the steam is highly wet (0.6 to 0.9), then its dryness fraction cannot be measured, by throttling calorimeter as it will not become superheated after throttling. Therefore the dryness fraction of highly wet steam is measured accurately by combining in series separating and throttling calorimeter. 

The arrangement of a separating and throttling calorimeter is shown in figure, where these calorimeters are placed in series. The steam from the sample tube is first passed through the separating calorimeter where major part of the water particles is removed and then it is passed on to throttling calorimeter.

The steam leaving the throttling valve comes out as superheated steam. The steam coming out of throttling calorimeter is condensed in a condenser and mass of the condensate is recorded. The mass of the water separated in separating calorimeter and the pressure and temperature of the steam leaving the throttle valve are recorded with the help of water manometer and mercury in glass thermometer.

Let:

ms= mass of steam condensed and collected from condenser. 

mw= mass of water collected from separating calorimeter. 

X= actual dryness fraction of steam in main pipe. 

X1= apparent dryness fraction of steam measured by separating calorimeter assuming that the

steam coming out of separating calorimeter is completely dry. 

X2= actual dryness fraction of steam entering in to the throttling calorimeter. 

The apparent dryness fraction is given by

Amount of water carried by the steam before entering into the calorimeter

= (1-x) (ms+mw) ---------------------- 2

Amount of water separated in separating calorimeter

= (1-x1) (ms+mw)  ---------------------- 3

And amount of carried by the steam in in to the throttling calorimeter

= (1-x2) (ms) ---------------------- 3

The mass of water in the steam given by the equation (2) must be equal to the quantities of water

given by equations (3) and (4).

(1-x) (ms+mw) = (1-x1) (ms+mw) + (1-x2) (ms)

Substituting the value in the above equation

(1-x) = (1-x1) + (1-x2) X x1 = 1-x1 + x1-x1x2

x = x1x2

This calorimeter gives very accurate value of the dryness fraction of the steam when it is considerably

wet and which cannot be measured accurately by any other method.

RESULT:

Hence we studied different calorimeters for determination of dryness fraction of steam.

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