Hi everybody,

Is it true that The Mass Flow Rate from a small volumen to a bigger volumen has always be positive.

But the realised result of my calculation is negativ. Although the absolute value are the same in comparison with an other calculation.

How now? or is it a problem of setting/definition?

thanks Hai Duc

It could be because the outward normal is in the opposite direction of the normal velocity component resulting in a negative flux calculation (dot product of Vnorm and area vector in calculating mass flow across the boundary.)