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HVAC Discussions - Heating, ventilation and air conditioning.
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Posted by Hareti on March 25, 2008, 4:06 pm
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?
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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