steam data

[kagadpencil]

I am looking at steam table data for specific volume (ft3/lb) of superheated steam in the range 500 F to 1400 F. I am ok with data at 14.7 psi but I will like to incorporate the effect of variation of pressure. The variation is not much -- May be 2"wg at the most, do you think I should at all be worrying about the effect of variation of pressure of steam in this case ? Or should I just fit a linear curve for data at 14.7 psi between the temperatures 500 F and 1400 F and use that equation?

 

[lilliput1]

The 2" wg is +/-0.072 psig. The Keenan & Keys Superheat Vapor Tables (1964)show the following"

At 14.0 psia, 400°F v=34.61 h=1240.0 s = 1.8796
At 14.696 psia, 400°F v=34.68 h=1239.9 s=1.8743
At 15.0 psia, 400°F v =33.97 h=1239.9 s=1.8719

At 14.0 psia, 1400°F v=79.11 h=1745.5 s=2.2657
At 14.696 psia, 1400°F v=75.37 h=1745.5 s=2.2603
At 15.0 psia, 1400°F v=73.84 h=1745.5 s=2.2580

Where v=specific volume cu. ft. per lb
h=enthalphy Btu/lb
s=entropy Btu/(°F-lb)

 

[25362]

You may visit

http://webbook.nist.gov/chemistry/name-ser.html

for water (fluid properties) and verify whatever properties you are after.

 

[siretb]

Why not add a correction in 14.7/p, where p is pressure if you want to use a simple formula.
I rely on tables.
You may try the following empirical formula
v(ft3/lb)=18.293+0.0410 t -1.913e-7 t^2)*14.7/p

t in °F P in psia it's OK in your range

 

[lilliput1]

Siretb,
Please correct your formula. The open parenthesis is missing. It is not clear what must be multiplied by 14.7/p

 

[TD2K]

I took a quick look at the steam tables at 500F and 1500F and 15 psia, you match the data pretty well just assuming ideal gas behavior (which is what I would expect at these conditions).

I wouldn't worry about 2" WG, that's less than 0.5% of the pressure assuming 14.7 psi you give is absolute. Or you could correct the specific volume just based on the inverse ratios of the absolute pressure.

The key question is here, what accuracy do you need?

 

[MariusChE]

Look for the Excel addin called Water97_v13.XLA on the Internet. It is a free IAPWS download and it allows you get all the thermodynamic steam- and water data that you would ever need. You can also get a very good commercial program at

http://www.tencon.nl

remove.marius@mailbox.co.za

 

[siretb]

Missing parenthesis added. Sorry about that Lilliput1.

v(ft3/lb)=(18.293+0.0410 t -1.913e-7 t^2)*14.7/p

t in °F p in psia