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.