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-   -   Time unit in finite volume solution for diffusion problem. (http://www.cfd-online.com/Forums/main/77657-time-unit-finite-volume-solution-diffusion-problem.html)

alpha2beta June 30, 2010 02:05

Time unit in finite volume solution for diffusion problem.
 
Hi,

I am trying to solve diffusion problem with finite volume method. ( I am following Patankar book: Numerical heat transfer and fluid flow). I have written code for the eq(pg 58) to determine water diffusion after certain time interval. I am getting moisture distribution profile and it looks correct.

However, I am confused with the time term in the equation. The unit of diffusion coefficient is given in m2/s. I am interested to determine water diffusion in paper of 1 mm thickness after few hrs. so, I converted unit of diffusion coefficient in mm2/hr by multiplying it with (x1e6*60*60). When I compare the results in minutes and hrs, it shows completely different results. I am expecting that simulation after 120 min is same as simulation after 2 hrs. Is it correct way to do time conversion or is it something missing. Can u plz help me as I am new to this field of study.


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