I am trying to set up a simple 2D convection-diffusion problem where oxygen diffuses from a small cirlce into a larger circle. The larger circle (which represents brain tissue) is consuming oxygen at a certain rate.
My boundary condition for O2 concentration in the small circle is in mL / L. What should be my units for the reaction rate, R, in the large circle? I understand that the Toolbox generally does not assume units, but it surely has to assume a unit of time? Should I use mL / L / second, mL / L / minute, etc.?
I understand that the Toolbox generally does not assume units, but it surely has to assume a unit of time?
Hi, thanks for trying the toolbox.
How and in what unit you interpret d/dt is entirely up to you (and what other units you have chosen). But the general recommendation is to stick to a unit system (for example SI) to make it simple. For the convection-diffusion physics mode you would for example typically use the following SI units:
Concentration, c [mol/m3]
Diffusion coefficient, D [m2/s]
Reaction rate, R [mol/(m3/s)]
Velocities u, v, w [m/s]
Boundary flux, N [mol/(m2/s)]
But you could just as well substitute the time unit s to minutes if you like, as long as it is consistent.