# What are the Units for Souce Term?

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 May 7, 2006, 04:07 What are the Units for Souce Term? #1 Kali Sanjay Guest   Posts: n/a Hi! As per PHOENICS documentation, source term should be Kg/Sec if 'Cell' is specified in Patch. But I am solving for concentration and my equation is dc/dt = Source Term where 'c' is concentration not mass and units of dc/dt are coming to be moles/Volume-Sec. Will the Source term I specify in PHOENICS should be moles/Sec or Moles/Volume-Sec for 'Cell' type Patch? Thanks in Advance! Sanjay

 May 7, 2006, 04:30 Re: What are the Units for Source Term? #2 Kali Sanjay Guest   Posts: n/a Actually I tried to solve a simple diffusion equation for concentration and equation I formulated is dc/dt = d(D*dc/dx)dx with fixed boundary conditions. I tried to solve the problem using diffusion active in terms and secondly I tried to solve the RHS part as source term and I gave patch as 'East' and 'West'. I gave the patches as 'FIXFLU' and gave D*dc/dx at east wall as one source and -D*dc/dx at west wall as another source for all cells.....units of the source here are moles/area*sec and since I gave 'East' and 'West' in patch the units will be moles/Sec.....but the results are not matching for 2 cases..... What am I doing wrong? Thanks in advance! Sanjay

 May 9, 2006, 12:17 Re: What are the Units for Souce Term? #3 Mike Guest   Posts: n/a If you are solving for a concentration, say C1, with units of mol/m^3, how have you eliminated the density from the built-in transient term? If convection and diffusion are absent, setting the density to unity is probably sufficient. TYPE=cell means that PHOENICS will not apply any geometrical multiplier to your specified source term, which means that you must then supply the source (via CO & VAL) for each cell in units of mols/s. If it is a volumetric source, then one could use TYPE=VOLUME, and then set the source(via CO & VAL) in units of mols/m^3/s.

 May 9, 2006, 12:46 Re: What are the Units for Souce Term? #4 Kali Sanjay Guest   Posts: n/a Thnaks Mike! If I make RHO1 as unity will it not take care of density of diffusion and convection terms? Then my source can be moles/sec where I am solving for C1 whose units are moles/volume.

 May 10, 2006, 04:47 Re: What are the Units for Souce Term? #5 Mike Guest   Posts: n/a Yes, it will take care of the convection and diffusion terms in the generic built-in default transport equation, but my uncertainty is that I don't know the form of the convection and diffusion terms in your transport equation for the molar concentration. Well, not without resorting to a text book.

 May 10, 2006, 05:30 Re: What are the Units for Souce Term? #6 Kali Sanjay Guest   Posts: n/a Thank you Mike! My values calculated by diffusion active and solving same problem with diffusion as source term are matching provided RHO1 is set to unity.

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