Vapor Pressure and Specific Gravity of Water

[CraigDSellers]

Has anyone developed or is anyone aware of emperical equations for the vapor pressure and specific gravity of water? The temperature and pressure range of interest is 60 - 250 F and 5 - 75 psia.

 

[MJCronin]

Craig,

Yup old buddy, you are in luck, they have......

And they are called ASME Steam tables...... They have properties of water too !!!

"Keenan and Keys" are the originals in publishing detailed values. You may find a copy at the library, I did......... Many texts have abbreviated versions of the tables.

The reciprocal of the specific volume can be used to find the SG at a specific temperature and pressure.

Vapor pressure is also typically listed.

Try also Crane technical manual #410

MJC

 

[nbucska]

If you find only the abbreviated table, you can fit a
polynomial on the given points and you have an eguation ! <nbucska@pcperipherals.com>

 

[gunnarhole]

Craig,

A year or so ago I downloaded an Excel add-in called Water_97.xla from the Chemical Engineering Magazine website that can provide the thermodynamic and transport properties for water/steam for temperatures between 273.15 K and 1073.15 K and pressures between 0 and 1000 bar. It is based upon industrial standard IAPWS-IF97. Check it out.

Regards,

Gunnar

 

[jproj]

CraigDSellers:

There are several emperical expressions you can use to calculate vapor pressure. In college we usually used the Antoine equation:

log P(sat) = A - [B/(T+C)]

Where A, B, and C are constants, P(sat) is the vapor pressure at a temperature, T.

From Perry's:
A = 8.07131
B = 1730.630
C = 233.426
This is valid from 34ºF - 212ºF (.096 psi to 14.7 psi).
P(sat) is in torr, T is in ºC.

Another equation you can use to calculate Vapor pressure (also from Perry's) is as follows:

P(sat) = exp[C1 +(C2/T) + C3*ln(T) + C4*T^(C5)]

where:
C1 = 73.649
C2 = -7258.2
C3 = -7.3037
C4 = 4.1653E-06
C5 = 2

Temperature (T) is in Kelvin and Vapor pressure (P(sat)) is in Pa. This equation is valid from 32ºF to 705.2ºF (0.09 psi to 3208 psi).

I am not aware of an emperical expression specifically for specific gravity, but there is one for density:

density = C1/C2^[1+(1-T/C3)^C4]

with density in kmol/m3. To convert to lb/ft3, multiply by 1.12466

for temperatures from 32ºF to 140ºF use the following:
C1 = 5.459
C2 = 0.30542
C3 = 647.13
C4 = .081

for temperatures from 140ºF to 266ºF use the following:
C1 = 4.9669
C2 = 0.27788
C3 = 647.13
C4 = .1874

for temperatures from 266ºF to 705.2ºF use the following:
C1 = 4.391
C2 = 0.2487
C3 = 647.13
C4 = .25340

Specific gravity can then be calculated by using a reference density (say H2O at 40ºF):

SG = Calculated Density / Reference Density

There are also conversions to units like degrees API (ºAPI) or degrees Twaddell (ºTw) that are given in Perry's. I'm sure (although I haven't checked) that these are online as well.

There are tables with all this stuff in Perry's Chemical Engineers Hanbook if you need them.

Hope this helps!

Jproj