Device Measurement Points

[boyu-dotcom]

"In my simulation file, I set up a measurement point for Mass Flux in Z Direction. As I understand it, flux represents a rate per unit area, so mass flux refers to the rate at which mass passes through a surface—expressed in kg/m²/s. If I want to convert the data into total mass in kg, what mathematical process should I apply? I assume I need to integrate over time to handle the 'per second' part, but I'm confused about the 'per square meter' part. Should I multiply by the total opening area or by the area of a single grid cell? Does anyone understand what I mean?"

[mcgratta]

I do. You should integrate over time and the area of the opening. If the mass flux is 2 kg/m²/s through an opening of 4 m² for 10 s, your total mass is 80 kg.

[boyu-dotcom]

Are you suggesting that in the unit of mass flux (kg/m²/s), the area component (m²) should correspond to the area of the window or opening I defined, rather than the mesh resolution?
Because if I set the mesh size to 0.2 m × 0.2 m, then the area would be 0.04 m².
If I consider the opening, the window I set is 1.6 m × 2 m, which means an area of 3.2 m². This has been bothering me for a long time.
I feel like the mesh cell size should be considered.

[Vojta-Salek]

Yes, the area should correspond to the area of window. From the window perspective, the same amount of mass will always be produced irrespective of the mesh resolution.

For instance, if you define a heat source as a surface with HRRPUA=X and you conduct a mesh sensitivity analysis, you have the same X for all different mesh sizes. This may be a more intuitive scenario where quantities related to area correspond to a defined surface, not cell size.