Question

Saturated liquid-vapor mixture of water, called wet steam, in a steam line at 1500 kPa is throttled to 50 kPa and 100 C. what is the quality in the steam line?

Answer 1

Concepts and reason

Dryness fraction or quality:

Dryness fraction refers to the mass fraction of liquid and vapor in the saturated mixture. It is defined as the ratio of mass of vapor phase to the total mass of pure substance in the system. It is denoted by.

Compressed liquid:

The state of the water which comprises of only liquid phase at a time is known as compressed liquid.

Saturated liquid:

The state of the water which comprises of liquid phase and it will start to vaporize on further heating is known as saturated liquid

Saturated liquid vapor mixture:

The state of the water which comprises of both liquid and gaseous phases simultaneously at a time is known as saturated liquid vapor mixture.

Saturated vapor:

The state of the water which comprises of gaseous phase and it will start to condense into liquid on further cooling is known as saturated vapor.

Superheated vapor:

The state of the water which comprises of only gaseous phase at a time is known as superheated vapor.

Enthalpy:

Enthalpy is a measure of total energy in the system. Enthalpy is the summation of internal energy and work done by or on the fluid. It is denoted by the letter H.

Throttling process:

When the fluid flow is restricted through a passage to decrease the pressure of the fluid with constant enthalpy of the fluid is known as the throttling process.

Fundamentals

The expression for quality in terms of the specific enthalpy is as follows:

Here, specific enthalpy is, specific enthalpy of saturated liquid phase is , and specific enthalpy of saturated vapor phase is .

The enthalpy is constant through the throttling process.

Here, the enthalpy of fluid entering is and the enthalpy of fluid leaving is .

From Property tables, corresponding to pressure at state 1,

From Property tables, corresponding to pressure and temperature at state 2,

Find the specific enthalpy of the wet steam.

During throttling,

Ans:

The quality in the steam line is 94.42%