This sample problem demonstrates two possible ways to model a mass flow controller (MFC) in the FloCAD® module of Thermal Desktop®.
If an MFC maintains the same mass or volumetric flow rate perfectly, a simple SetFlow device would be the answer. However, there are several reasons why a more complex method may be needed.
As a demonstration, two different types of MFC controllers are presented:
1. A SetFlow with a by-pass path for representing a lower control limit. (An upper limit could be added as an extension.) This is a simple representation, with minimal user logic:
2. A PID-controlled Orifice (valve model), which exhibits both upper and lower limits to its control, along with a finite response rate. It requires PID tuning and sizing of the orifice’s range of motion:
These examples represent just two possibilities. Many more methods are possible, especially if details of the valve construction, the flow measurement method, and the electronics and control algorithm are available.