Question: Why do we set Mass = 0 inside "Fluid States"

[mc1998]

Hello again,

I would like to clarify what this means. In Fluid Aspect Course 4.2.2: Fluid States we are instructed to "Leave Mass alone (zero)" with no explanation. However, we set a temperature (K). So are we defining the initial temperature of the fluid inside the pipes or the initial temperature of the surrounding walls?

If we set the mass > 0, will this be equivalent to having pre-existing fluid in the node? So if I have a fluid capacitor that connects to that node, will it initialize with a mass inside that volume?

(Similar question for TC State)

Thank you

[jasonlharvey]

The fluid state object defines the state of an infinitesimal amount (zero mass) of fluid, and then the nodes that contain that initial state compute the mass, according to their initial volume. The Fluid State's pressure & temperature correspond to an initial density by the fluid's state equation - that density gets computed by GUNNS from your P, T values and then multiplied by the node's volume to compute the initial mass inside each node -- thus we don't need to define mass in the Fluid State, and the same Fluid State can be reused in multiple nodes of differing volumes. The code class corresponding to the Fluid State has a mass term (that GUNNS ignores) because it was originally written to be reused by other fluid solvers besides GUNNS. We can look into maybe removing this mass term from the Fluid State draw.io object since it just adds confusion. I'll leave this issue open for now so we can look at it in the future.