Question

Hello! In Ansys Fluent, how can I calculate the molar concentration (kmol/m^3) of a species and molar fraction (dimensionless) of a species in fluent after I put an exact amount of the mass (kg) of a species at a boundary? Thank you, I will thumb you up!

Answer 1

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molar concentration is defined as the number of moles per litre of solutuon. For example if we take 5 gm of formaldehyde and and mix this into 1 litre of water than molar concentration can be cacaluated as :

Molar gram of HCHO = 1.008 + 12+ 1.008 + 16

= 30.016

Moles in 5 gm of HCHO = 5/30.016 ==0.166578 mol

So molar concentration =( 0.166578/ 1 )

= 0.166578 mol/litre Ans

Molar fraction- it is defined as the ratio of number of moles of the species to the total moles in the solution.

For example - in the solution of acetic acid there are one moles of acetic acid and twol moles of water so the molar fraction is

( no of mole of acetic acid/ no.of moles of water )

= 1/2

= 0.5 Ans .

It is a dimensioless quantity..

The given formulas can be used in the ansys for the formulation of an expression with the help of macros based on the concentration which translates to molar fraction.in the fluent you can make a user defined functions based on application or using the new fluent expression capabilities.

You can use the macro define_profile as the macro for the problem.