LiquidEvaporationBoil & LiquidEvaporation

amirhoshangm · August 26, 2016, 05:19

Hi,

I'm running a test case with sprayFoam. I have used two evaporation models "LiquidEvaporationBoil" and "LiquidEvaporation". The results are different. After some investigations, I figured out, if boiling does not occurs, theoretically two models should behave the same.

dMassPC[lid] in LiquidEvaporation is clear

Code:

dMassPC[lid] +=kc*(Cs - Cinf) *pi*sqr(d)*liquids_.properties()[lid].W()*dt

where kc is mass transfer coefficient and Cs is vapour concentration at surface of droplet

However I can not understand how dMassPC[lid] is calculated in LiquidEvaporationBoil (when there is not boiling)

Code:

         else
            {
                // evaporation

                // surface molar fraction - Raoult's Law
                const scalar Xs = X[lid]*pSat/pc;

                // molar ratio
                const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs);

                if (Xr > 0)
                {
                    // mass transfer [kg]
                    dMassPC[lid] += pi*d*Sh*Dab*rhos*log(1.0 + Xr)*dt;
                }
            }

amirhoshangm · August 26, 2016, 07:22

I found some information baout the evaporation part in the "LiquidEvaporationBoil" model. It is called "The Spalding evaporation model" (Spalding (1953)). you can find more information in the following link

Quote:

http://ethesis.inp-toulouse.fr/archi...a_sanchez2.pdf

pappo1890 · July 31, 2019, 05:03

I know the post is quite old but I have a question concerning the use of Xr in the expression:

dMassPC[lid] += pi*d*Sh*Dab*rhos*log(1.0 + Xr)*dt;

In literature this expression is always written using Bm, the Spalding mass number:
#mass ratio
const scalar Bm=(Ys-Yc)/max(SMALL,1.0-Ys)

#Molar ratio
const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs)

Does anybody know the rationale behind this choice in OpenFOAM?

August 26, 2016, 05:19	LiquidEvaporationBoil & LiquidEvaporation	#1
amirhoshangm New Member Amir Join Date: Feb 2012 Posts: 12 Rep Power: 14	Hi, I'm running a test case with sprayFoam. I have used two evaporation models "LiquidEvaporationBoil" and "LiquidEvaporation". The results are different. After some investigations, I figured out, if boiling does not occurs, theoretically two models should behave the same. dMassPC[lid] in LiquidEvaporation is clear Code: dMassPC[lid] +=kc(Cs - Cinf) pisqr(d)liquids_.properties()[lid].W()dt where kc is mass transfer coefficient and Cs is vapour concentration at surface of droplet However I can not understand how dMassPC[lid] is calculated in LiquidEvaporationBoil (when there is not boiling) Code: else { // evaporation // surface molar fraction - Raoult's Law const scalar Xs = X[lid]pSat/pc; // molar ratio const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs); if (Xr > 0) { // mass transfer [kg] dMassPC[lid] += pidShDabrhoslog(1.0 + Xr)dt; } }

July 31, 2019, 05:03	Spalding number in LiquidEvaporationBoil	#3
pappo1890 New Member Alessandro Join Date: Jul 2016 Posts: 11 Rep Power: 9	I know the post is quite old but I have a question concerning the use of Xr in the expression: *dMassPC[lid] += pidShDabrhoslog(1.0 + Xr)dt;* In literature this expression is always written using Bm, the Spalding mass number: #mass ratio const scalar Bm=(Ys-Yc)/max(SMALL,1.0-Ys) #Molar ratio const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs) Does anybody know the rationale behind this choice in OpenFOAM? zhangyan likes this.