|Jun23-04, 01:52 PM||#1|
I have a question for you all, say you have a pressurized cylinder with water in it, it is at 200*F and at a pressure of 300psig. Now you open a drain valve on the bottom to the atomosphere.
Will it flash to stream or just come out as hot water or a combo of the two?
What equations and info do tyou use to figure this out?
|Jun23-04, 04:59 PM||#2|
Here is a calculation for flash steam:
% flash steam = (100 * (hf1 - hf2)) / hfg2
hf1 = enthalpy of liquid at pressure p1
hf2 = enthalpy pf liquid at pressure p2
hfg2 = latent heat of vaporization at pressure p2
This calculation is from ASHRAE Systems 2004.
Now if I'm interpretting this correctly, that equals
% flash steam = (100 *(393.84 - 180.07)) / 970.3 =
% flash steam = (100 *(213.7)) / 970.3 =
% flash steam = 21377.00 / 970.3 = 22.03%
So approximately 22% should flash to steam.
Do not try this experiment at home!
|Jun24-04, 07:11 AM||#3|
what units are you using? I used 80*F as the ambient temp.
I got hf1=169 BTU/lb, hf2=49 BTU/lb and hfg2 970 BTU/lb.
so I came up with 12% steam.
|Jun24-04, 07:41 AM||#4|
Sat. Liquid Enthalpy hf of 393.84 at 300 psi Abs Pressure and 180.07 at atmospheric pressure of 14.696 psi Abs Pressure.
I'm not positive that I am right, but the formula calls for the hf at the given pressure, not the given temperature. Maybe someone else can verify this.
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