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## Homework Statement

In a sample of wet steam at 11 bar, 75% of the total internal energy is contained in the vapour portion. Calculate the dryness fraction of the steam to 3 decimal places.

## Homework Equations

u(kJ/kg) = (1-x)uf + x*ug

x - dryness fraction

f - saturated liquid state

g - saturated vapour state

## The Attempt at a Solution

I have done the following to no avail:

At 11 bar using steam tables uf = 780 kJ/kg and ug = 2568 kj/kg

Assuming u = 75% of ug.

u = (1-x)uf + x*ug

0.75*ug = (1-x)uf + x*ug

0.75*2568 = (1-x)*(780) + x*(2568)

x = 0.642

Therefore, dryness fraction is equal to 0.642.

However this is incorrect and I'm unsure what I'm doing wrong. Possibly interpreting the 75% of total internal energy wrong.

Could it be that I need to use u = 0.25*uf + 0.75*ug?

Thanks for your help, it's appreciated.