water steam pressure at ambient temp
water steam pressure at ambient temp
(OP)
Talking about psichrometry
Given T in Kelvin or absolute temp
For Pws [presure water steam]
Is this formula valid ?
for Water air from 0 to 200 C degree
ln Pws= a/t + b+c*t+d*t^2+e*t^3+f*lnT
for the followings values
a -5800.2206
b -5.5162256
c -0.048640239
d 4.18E-05
e -1.45E-08
f 6.5459673
I used it for 100 C dgree and give
p mbar 1014.217979 mbar , that is a normal atmospheric pressure
My concern is if it is valid for the air ambient temperature
I wan to calc the Relative humidity by reading the DryBulb and WETbulb temperature.
I have 2 data loggers and I modify one of them to read wet bulb temperature, so I can charge the data from it to a spread sheet and get the HR % .
maybe it is not a conventional way of doing , but is it what I have and will have for ever. (lack of money to buy a HR datalogger)
Hope you can give me any advice.
PS I have the spread sheet done.
Given T in Kelvin or absolute temp
For Pws [presure water steam]
Is this formula valid ?
for Water air from 0 to 200 C degree
ln Pws= a/t + b+c*t+d*t^2+e*t^3+f*lnT
for the followings values
a -5800.2206
b -5.5162256
c -0.048640239
d 4.18E-05
e -1.45E-08
f 6.5459673
I used it for 100 C dgree and give
p mbar 1014.217979 mbar , that is a normal atmospheric pressure
My concern is if it is valid for the air ambient temperature
I wan to calc the Relative humidity by reading the DryBulb and WETbulb temperature.
I have 2 data loggers and I modify one of them to read wet bulb temperature, so I can charge the data from it to a spread sheet and get the HR % .
maybe it is not a conventional way of doing , but is it what I have and will have for ever. (lack of money to buy a HR datalogger)
Hope you can give me any advice.
PS I have the spread sheet done.
Pardal





RE: water steam pressure at ambient temp
M777182
RE: water steam pressure at ambient temp
http://webbook.nist.gov/cgi/cbook.cgi?Name=water&Units=CAL&cTP=on#Thermo-Phase
for the values of A, B, C in the equation
log10P(atm)= A - B/(T+C), where T is given in K in the Antoine equation.
RE: water steam pressure at ambient temp
RE: water steam pressure at ambient temp
Check this link,
http://www.uswcl.ars.ag.gov/exper/relhumeq.htm
Regards,
Eng-Tips.com : Solving your problems before you get them.
RE: water steam pressure at ambient temp
Tdb = dry bulb temp = 40C
Twb = wet bulb temp = 25C
From steam tables
sat press at Tdb = Pgd = 73.75mbar
sat press at Twb = Pgw = 31.66mbar
Atmos press = Pa
Partial press of vapour = Pv
= Pgw - ((Pa-Pgw)(Tdb-Twb)/(1537.778-Twb)) = 21.927mbar
Relative humidity = Pv*100/Pgd = 29.73%
Specific humidity = 0.622*Pv/(Pa-Pv) = 0.01376 kgH2O/kg dry air
athomas236
RE: water steam pressure at ambient temp
Pardal