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max May 11, 2001 22:30

SOS!About water-vapor
Hi, everyone! IĄŻm modeling water-vapor flows through a converge-diverge nozzle using commercial code. For compressible flows, many commercial codes think the idea gas law is the appropriate density relationship. However, the water vapor IĄŻm using is 0.6Mpa, so in my opinion, it canĄŻt be thought as idea gas. Unfortunately, I couldnĄŻt find the UDF (User Defined Function) for density. Could anybody kind enough to give me some advices on how to set the physical properties. Anything about FLUENT, CFX, or ANSYS is welcome! All thanks given to you for your help!

Jin-Wook LEE May 17, 2001 03:02

Re: SOS!About water-vapor
For near 0.6Mpa, difference between real density(from steam table) and calculated density(from ideal gas law) is not so big. The difference becomes higher as temperature increases. However, near 1000Kelvin, the difference is about 3%. If you have another alternative for the exact density, I guess that ideal gas law is fairly good approach.

Sincerely, Jinwook

max May 17, 2001 05:04

Re: SOS!About water-vapor
Thank you for your concern! But i wonder whether the ideal gas law still do when the pressure vary from 366.6Pa to 0.6MPa?

Jin-Wook LEE May 18, 2001 03:14

Re: SOS!About water-vapor
1. Please refer steam-table.

2. For every gas, its behavior is similar to ideal gas at low pressure region. The difference is, as I posted, about 3% at P=0.6Mpa. When pressure becomes lower, e.g., 366Pa. the difference between ideal gas law and actual value becomes small. So, I recommend that you use ideal gas law if you can accept maximum error of about 3%(when P=0.6Mpa).

3. Ideal gas law is fairly good alternative till P = 1 ~ 2Mpa for many kind of gases.

Sincerely, Jinwook

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