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 crevoise February 20, 2012 09:26

Dropro.f subroutine for multi-component droplets

Helo all.

I am trying to compute the evaporation process of AdBlue (UWS) droplets along a pipe.
I am defining the droplets as a mixture of two components (urea and water), with one evaporating to water(g) and the other one to urea(g).

I wish to know few detailed in order to write my subroutine in a proper way. For the moment, the computation is running, but the results are not satisfactory. The urea should evaporate only once the water totally evaporated; however, I am getting some vapor urea at the same as water vapor.

About the bulk properties, the subroutine should be ok, as I tested these datae from a single component droplet.
The concern is about the datae definition of the components, especially the vapor pressure, as this one is of main importance in my case:
1/ While defining the data, I am using this way:
if ico 1 (water), then pvH2O= .... , and finish with pv=pvH20
if ico 2 (urea), then pvurea= .... , and finish with pv=pvurea

Is it done in the right way? It seems that Star will then manage my two components in independent way, so will compute their evaporation in parallel? Can't it be return to Star a pv1 and pv2?

2/ About the same vapor pressure, I was wondering if I need to write in dropro.f the Raoult's law - thus to write pv=0.6664 * pvH20 ? (with 0.6664 the water mass fraction)

3/ Together with the fact evaporation of urea is happening too early, the droplets remains at 320K (which is the evaporation temperature of the problem one using only pure water)
Trying solving this point, I have wrote in the subroutine to start computing the vapor pressure of urea, only once the water mass fraction was 0 (if DRMFR(1) .le. 0), then...)
However, the droplet temperature is then increasing without stopping to the urea 'boiling' point

So the question is, do I need to define for every component a boiling temperature, or the bulk boiling temperature is enough?
If so, how to do it?

4/ I was wondering if using the mixture model was appropriated to this problem. Does anybody think I need to use a emulsified mixture?

5/Does anybody knows where to find some advice or supplementary note about the definition of user subroutine in StarCD, to get deeper knowledge on them?