Determination of Dryness Fraction

DETERMINATION OF DRYNESS FRACTION

The dryness fraction can experimentally be measured by using calorimeters. They are with four types.

1. Bucket or barrel calorimeter

2. Throttling calorimeter

3. Separating calorimeter

4. Combined separating and throttling calorimeter.

1. Bucket or barrel calorimeter:

The calorimeter is kept inside the vessel. The top cover is placed in position and the steam pipe is connected to the main steam pipe. The steam approaches the calorimeter when the steam is passed through the water. During contact of both steam and water, the steam gets condensed. The steam delivers its entire enthalpy of evaporation (latent heat) and part of its sensible heat to water. The water temperature increases at the expense of heat released by steam. This method of measuring the dryness fraction of steam is not exact method.

2. Throttling calorimeter:

This calorimeter is more suitable for finding dryness fraction of steam having very low portion of wet particles. It means, the steam is with high dryness fraction. It is well known that the total enthalpy remains constant before and after throttling process.

3. Separating calorimeter:

A separating calorimeter is used for measuring dryness fraction of very high wet steam. The calorimeter works on the principle of separating the water particles from steam and finding their mass fraction from the sample. The dryness fraction measured by this method provides an approximate value.

4. Combined separating and throttling calorimeter:

The problem of producing approximate value of dryness fraction by separating calorimeter is eliminated by the use of combined and throttling calorimeter. At the same time, the throttling calorimeter is not suitable for measuring the dryness fraction of steam which is having very high value of wetness fraction. The combined separating and throttling calorimeter can be successfully used by eliminating above said problems.