# ReactingFoam specie transport equation

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 August 28, 2007, 19:15 During a discussion on IRC. a #1 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,907 Rep Power: 27 During a discussion on IRC. a doubt about reactingFoam implementation came out. In reactingFoam, the transport equation for the specie mass fration contains the diffusional term in the form: fvm::laplacian(turbulence->muEff(), Yi) which means that the effective specie diffusivity is assumed to be equal to the effective viscosity: Deff = D_lam + D_turb = nu_lam/Sc_lam + nu_turb/Sc_turb = nu_lam + nu_turb which means that Sc_lam = Sc_turb = 1 Why this assumption is done? For example, in a laminar calculation, if we consider water, the viscosity of the fluid and the diffusivity of a specie, for example the oxygen, can be very different. At 25°C we have: D_02 ~ 2.0 * 10^-10 m^2/s nu_H20 ~ 1.0 * 10^-4 m^2/s In turbulent flows, the turbulent Schmidt number is set to 0.7 in other codes, but however it can change too. For example, in a pipe with passive transport it's between 0.6 and 0.9. Thanks in advance for any clarification. With kind regards, Alberto __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 March 27, 2009, 08:44 #2 New Member   Lu,Y. Join Date: Mar 2009 Posts: 2 Rep Power: 0 I guess the reason is that when dealing with turbulent combustion, the molecular transport are often small compared to their tubulent counterparts and so are neglected. But I think it is very important of you to have pointed it out that when dealing with laminar combustion with OpenFoam, special attention may have to be paid to the issue. But I am not very sure about this.

 March 27, 2009, 13:22 #3 Member   M. Mahdi Salehi Join Date: Mar 2009 Location: Vancouver, BC, Canada Posts: 50 Rep Power: 9 You are right alberto, I usually use fvm::laplacian(turbulence->muEff()/Sc, Yi) and set Sc=0.7.

December 4, 2010, 13:03
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 Originally Posted by alberto During a discussion on IRC. a doubt about reactingFoam implementation came out. In reactingFoam, the transport equation for the specie mass fration contains the diffusional term in the form: fvm::laplacian(turbulence->muEff(), Yi) which means that the effective specie diffusivity is assumed to be equal to the effective viscosity: Deff = D_lam + D_turb = nu_lam/Sc_lam + nu_turb/Sc_turb = nu_lam + nu_turb which means that Sc_lam = Sc_turb = 1 Why this assumption is done? For example, in a laminar calculation, if we consider water, the viscosity of the fluid and the diffusivity of a specie, for example the oxygen, can be very different. At 25°C we have: D_02 ~ 2.0 * 10^-10 m^2/s nu_H20 ~ 1.0 * 10^-4 m^2/s In turbulent flows, the turbulent Schmidt number is set to 0.7 in other codes, but however it can change too. For example, in a pipe with passive transport it's between 0.6 and 0.9. Thanks in advance for any clarification. With kind regards, Alberto
dear alberto
i have a problem and i think you can help me.
my problem is mass transfer from solid to liquid with electrochemical method and i want simulate this problem with openfoam and i cant find solver for it.
use a solver or write a code for it.
if you write a code : can i have your code?