Dryness Fraction Question

[dcann213]

Have researched and cant really find any answers?

A separating and throttling calorimeter can be used to determine the dryness fraction of steam in a system. It operates by taking a sample of wet steam, separating the water from the steam, and collecting the water for weighing. The steam is then passed through a throttle which drops the pressure down to atmospheric, whereupon the steam is condensed and collected for weighing. The weights of the separated water and the condensed steam can then be used to calculate the dryness fraction. Unfortunately the separator is never 100% efficient, so it is necessary to calculate the dryness fraction of the steam after it has passed through the separator in order to accurately determine the dryness fraction of the original steam sample.

Wet steam is bled from a system at a pressure of 6 bar (gauge) and passed through the separator which collects water at a rate of 0.1kg/min. The remaining steam passes through the throttle which reduces the steam to atmospheric pressure, where the steam temperature is measured as 132.9oC. This steam is then condensed and collected at a rate of 0.9kg/min

Calculate the dryness fraction of the steam between the separator and the throttle, and hence the dryness fraction of the steam being bled from the system.

 

[25362]

Enthalpy of steam at atm. pressure and 132.9^oC is 655.46 kcal/kg (NIST).

Assuming same enthalpy at 6 barg (upstream nozzle), make a mass balance using the enthalpies of water and steam at these conditions.

 

[dcann213]

what do you think of this solution where 2743 is the specific enthalpy of water at 100kpa and 139.2 degrees Celcius, sorry forgot to denote that

 

[25362]

Student's homework is not allowed. Anyway,

Enthalpy of wet steam: 2743 kJ/kg
Pressure: 7 bar
Enthalpy of water: 697 kJ/kg
Enthalpy of dry steam: 2763 kJ/kg (must be > 2743 kJ/kg)

Dry component: (2743-687)/(2763-697) = 0.99
Then, multiply by whatever factor results from drying, in your case 0.9.