Learning Forum

[nindiamelia107]

Why is the result of calculating the mass imbalance between [inlet] and [outlet] in the simulation that I did the result -1.1561628e-13 [kg/s], whereas in the video tutorial 2.09... [kg/s]? What are the causal factors?

[Raihan Lutfianto]

Hi Nindi. It may differ due to the iteration. Again, it does not have to be as exact as the tutorial. What you have to pay attention to is the physical meaning of the mass balance. What is it? It is really just mass_in = mass_out. Or we can write it as mass_in - mass_out = 0. Both values from your result and the tutorial are essentially zero.

[nindiamelia107]

But is it possible that the mass balance is negative? If it's not possible, what's wrong with the simulation?

[Raihan Lutfianto]

From what I understand, it is possible numerically. It is still considered close to zero. However, I recommend you to recheck:
- Inlet boundary condition
- Outlet boundary condition
- Solution methods setting
- Residual setting
- Mass balance report definition
- Any reversed flow inside your model

In my case, the solution is also negative. Again, if the overall physics does makes sense, then you do not have to worry about it.

[Welson Adi Putra Bancin]

Hi, Nindi and mas Raihan. The simulation i carried out also displayed the same results (-1.1561628e-13 [kg/s]). I agree with Mr. Raihan that the results of the simulation I carried out were essentially zero. Because in theory mass balance means mass_in = mass_out, but in practice there is something called the amount of mass accumulated in the system so it is possible that there is a small difference in mass in the pipe.