mixture average diffusion coefficient calculation

[Yu Li]

Hi:

    I'm not a specialist in diffusion coefficient calculation. but I need to calculate the mixture average diffusion coefficient for next step research.

    I use the command below but the result looks weird (too small), so I want to see if someone can help check my code.

    the input is mass fraction, temperature, and pressure. my code is:

    

    g=Solution('test.cti')

    set(g,'Y',mass_frac,'T',T,'P',P/101325*oneatm)

    mix_ave_D=mixDiffCoeffs(g).

    Thanks for the help.

Li

[Bryan W. Weber]

Yu,

Can you let us know what are the values you expected? Also, can you include your test.cti? Note that the results returned will be in SI units, so they may be in units you're not used to seeing.

Best,

Bryan

[Yu Li]

please see attached .cti.

Thanks!
Yu

[Yu Li]

Hi:

    thanks for your reply.

    in the CFD code I used, in order to reduce the computatinal cost, the code calculate D using viscosity / Schmidt  number, which means the D is equal for all species. however, after I calculate the D use the mixture average method, it is totally different. the units are the same. please see cut plane below:

    the mixture average D is about 4-5 order's of magnitude less than constant D, and the distribution is different. so if the calculation is right, the use of constant D may cause significant difference.

Thanks!

Yu

On Friday, March 23, 2018 at 5:21:40 PM UTC-4, Bryan W. Weber wrote:

[Ray Speth]

Yu,

What conditions are you calculating these properties for? Where are you getting your values for the kinematic viscosity? Mixture-averaged diffusion coefficients in the range of 10^-7 to 10^-4 m^2/s are perfectly reasonable for gases at elevated pressures. On the other hand, you would have to have some pretty extreme conditions to get a kinematic viscosity of 0.1 m^2/s.

Regards,

Ray