steam question ...

Question for the steam guys :

Pipe, 60mm diameter, contains steam at 8 bar and temperature 145 degrees C. Now cool the pipe to 25 degrees C and drop pressure to 0 bar (gauge).

How much condensate will be drained from the pipe per metre?

My thoughts : Trick question...

There shouldn't be any steam at this pressure since water at 8 bar will only boil once it reaches about 175 degrees.

Is my thinking correct?

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More of my thinking before I thought it was a trick question ...

The mass of steam = the mass of the water once it's completely condensed, so I started by looking for steam tables that would tell me this. If I could find the density of steam at given pressure and temperature I could work out the mass from the volume of the pipe. Trouble is, steam doesn't appear to exist at this temp and pressure.

Then I got to thinking, given the gas law ([p1v1]/t1 = [p2v2]/t2), you can work out pressure and temperature for a constant volume. So if you start at 8 bar and 145 degrees, and finish at 0 bar and 25 degrees, the gas law should agree. But maybe this gas law only works for one phase and doesn't take into account condensation. Maybe the t can only be sensible, or else the equation doesn't work.

I try to picture a pipe with 8 bar steam in it at 145 degrees C ( which isn't THAT hot ), then cool it to room temperature and open the pipe only to find the contents at atmospheric... must be a trick question....

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