Compressed water properties 1

[EdSPE]

Hello-

I was wondering if anyone had info on compressible water. I have a water system that is operating between 3000-4000psi. I'm using Pipe-Flo software to do my preliminary design and it is telling me that the fluid is changing state. The steam tables show a critical pressure of 3208psi @ 750deg. My fluid will be at most 80 deg.

 

[SirLotsaWatts]

A good and inexpensive source of properties, including compressed water, is NIST's REFPROP:

http://www.nist.gov/data/nist23.htm

I did a quick check and it looks like about 1% increase in density for water between atmospheric pressure and critical pressure at about 80F.

Above critical pressure, the fluid isn't really "liquid" any more since it can't boil, but below critical temperature it is also hard to call it a "gas." It is now a "supercritical fluid." So it could be that the software you are using is having a hard time classifying it, I don't know. Or maybe it is just an informational message and your run isn't stopping. But if the software lets you, you can still get away with calling it "incompressible liquid" as long as you don't go too much higher in pressure or temperature.

 

[dcasto]

Density at 4000 psia and 80F = 8.4172 lb/gallon at 3000 psia = 8.3926 2000 psig 8.3677, .6% change. Vicosity = .854 Cp @ 4000 and .855 Cp at 2000 psia.

 

[katmar]

At 4000 psi and 80 deg F water is not a supercritical fluid. The properties listed by dcasto are very similar to what my reference has. Enter these properties for your software rather than allowing it to calculate them for you. Pipe-Flo is not a thermodynamic simulator and you will find hiccups like this at the edges of the envelope. That doesn't stop it being a valuable piece of software for doing pressure drop calcs.

When you heat water/steam above a temperature of 705 F you can no longer liquify it by compressing it. The vapor pressure of water at 705 F is 3200 psi and these are called the critical properties. But water at this pressure and 80 F is still just water. This is the pressure you would find about 1.75 miles down in the sea. It would probably be a bit colder than 80 F, but it's still just water.

Katmar Software
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