Antoine Equation coefficients for water
 

Hi
I'm modeling liquid evaporation and I have some problem with coefficients that have been used in tutorial. in spray dryer tutorial the coefficients are as below:

Antoine Enthalpic Coefficient B = 1687.54 [K]*ln(10)
Antoine Pressure Scale = 1 [bar]
Antoine Reference State Constant A = 5.11564*ln(10)
Antoine Temperature Offset C = (230.23-273.15) [K]

but in references(like below) the coefficients are different:

http://ddbonline.ddbst.com/AntoineCa...ulationCGI.exe

I know that the units are different. but when I use tutorial coefficients, the water particles(diameter 2 micro) evaporate immediately in inlet. here is some information about my simulation:

reference pressure: 20 kPa
inlet temp: 303 Kelvin
inlet vel : 0.1 m/s

does anybody know why this problem happen?its related to coefficients (does anybody checked the accuracy of these coefficients?)
or its because of the size of particles(I also used particles with 70 micro diameter and it didn't evaporate immediately!)?

another question. in spray dryer tutorial, the Buoyancy Model for gas mixture was Non Buoyant. is it a correct? (for example for a 100 kelvin temp difference in domain.)

I am actually struggling through some similar modeling issues, and the Antoine coefficients were part of my problem (so far) so maybe I can contribute.

The coefficients you are using from your reference are similar to the ones I am using (referenced to 1 mm Hg). There is an Ansys tutorial out there somewhere that uses this form of coefficients. Here is the form I think you need:

A = 8.07131 * ln(10)
B = 1730.63 * ln(10) [K]
C = (233.426 - 273.15) [K]
p scale = 1 [mm Hg]

You should validate that these do in fact calculate the saturation pressure for your conditions and compare against thermo tables or similar. I believe the default that comes with the H2Ovl material is valid, but agreeably the form is a bit confusing. My issue was that my temperatures are higher than 100C and so these coefficients were way off for my simulation.

Not sure about your buoyancy question.

Good luck,
Charlie

Actually I figured the problem for Antoine coefficients. here is a reference that the units are kelvin and bar. but you are right. these coefficients must be used for proper conditions(temp and pressure range).
http://www.separationprocesses.com/D.../DT_Chp01h.htm
you just need to multiply the A and B by ln(10).

about the high temperature you said. I think its because of NASA format of H2O. It can make divergence in simulation.