Mass-averaged and Volume-averaged problems...

frodooon · May 21, 2009, 08:57

Hi !

I am running a simulation of ammonia combustion in a ICE. I wanted to plot average pressure, temperature, and species concentration during the cycle.
I used for that the option "volume-averaged" in solve==> monitors ===> volume...
But i don't really know the difference between this and "mass-averaged" . I know it already has been discussed, and it seems that for compressible fluids, "volume averaged" is ok for pressure... but what for the species concentration ?

I mean, i want to compare for example exhaust NO mole fraction with existing results, should i use "mass-averaged" ?

Thanks a lot !

barzzin · April 22, 2024, 03:42

When you want to calculate temperature or pressure in a section of your geometry in fluent, it's better that you use volume-average; but when you want to calculate mole or mass fraction of species, what you should use depends on your objective.
1 - If you're interested in the actual amount of the species, it's better that you use mass-average.
2 - If you're interested in the spatial distribution of the amount of species, it might be better to use volume-average.

Mass-average weights each cell's contribution to the average by its mass and volume-average weights each cell's contribution to the average by its volume.

May 21, 2009, 08:57	Mass-averaged and Volume-averaged problems...	#1
frodooon New Member Join Date: May 2009 Posts: 12 Rep Power: 16	Hi ! I am running a simulation of ammonia combustion in a ICE. I wanted to plot average pressure, temperature, and species concentration during the cycle. I used for that the option "volume-averaged" in solve==> monitors ===> volume... But i don't really know the difference between this and "mass-averaged" . I know it already has been discussed, and it seems that for compressible fluids, "volume averaged" is ok for pressure... but what for the species concentration ? I mean, i want to compare for example exhaust NO mole fraction with existing results, should i use "mass-averaged" ? Thanks a lot !

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April 22, 2024, 03:42		#2
barzzin New Member Barzin Banan Join Date: Aug 2023 Posts: 1 Rep Power: 0	When you want to calculate temperature or pressure in a section of your geometry in fluent, it's better that you use volume-average; but when you want to calculate mole or mass fraction of species, what you should use depends on your objective. 1 - If you're interested in the actual amount of the species, it's better that you use mass-average. 2 - If you're interested in the spatial distribution of the amount of species, it might be better to use volume-average. Mass-average weights each cell's contribution to the average by its mass and volume-average weights each cell's contribution to the average by its volume.