# How to increae diffusion in flow?

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 February 12, 2020, 12:10 How to increae diffusion in flow? #1 Member   Abdullah Arslan Join Date: Apr 2019 Posts: 87 Rep Power: 2 Good day, Can we increase diffusion in a fluid flow, say by Lewis number (if there is any option)? My flow is laminar with thermal energy on. I don't want to change either density, heat capacity or thermal conductivity. I am using also real gas mixture from library. The reason I want to increase it, just to see its effect without changing the 3 mentioned parameters. Regards

 February 12, 2020, 13:02 #2 Senior Member   Gert-Jan Join Date: Oct 2012 Posts: 1,025 Rep Power: 16 Diffusion is for molecules. So, if you have a massfaction equation for a component that you want to diffuse in the continuous phase, than you can add a kinematic diffusion coefficient in the tab Fluid Models/Component Models. Goenitz likes this.

 February 12, 2020, 16:06 #3 Senior Member   Join Date: Jun 2009 Posts: 1,127 Rep Power: 22 May I ask what you mean by diffusion? Momentum diffusion is through molecular viscosity, mu Thermal diffusion is through thermal conductivity, k Mass diffusion is through mass diffusivity, density * D, where D is the kinematic Diffusivity What are you trying to achieve? Lewis number is the ratio of thermal diffusion to mass diffusion, i.e. Le = [k/(rho Cp) ] / D which relates the energy equation respect to the mass diffusion equations. Similarly, you can use the Schmidt number as the ration between momentum diffusion, and mass diffusion, i.e. Sc = mu / (rho D) which diffusion are you trying to modify or study? As you can see, there are 5 parameters so far: Density, rho Specific Heat, Cp Thermal Conductivity, k Dynamic Viscosity, mu Kinematic Diffusivity, D and you want to fix the first 3, you are only left with changing viscosity and kinematic diffusivity. I would fix the viscosity, vary the Schmidt number and compute the corresponding input kinematic diffusivity, D = Dynamic Viscosity / Density / Schmidt Number Hope the above helps, Goenitz likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.