Hello Wang,
Yes, I confirm that Q=pS assumes that p is isotropic, and therefore cannot be applied next to 100% sticking pumps.
As mentioned in the previous message, pressure shouldn’t be measured on pump facets, since these facets don’t exist in reality: the mechanical definition of pressure - force exerted on a wall - can’t be applied as there’s no wall.
Molflow still shows a pressure on these facets, assuming that sticking particles lose their momentum, or in other words, come to a standstill (and thus contribute half of the pressure compared to rebounding ones). Therefore I can’t answer “does this mean that the pressure calculated by Molflow for a sticking facet is not accurate? Specifically, when sticking = 1, does the pressure calculated in the formula editor only represent half of the actual pressure?” - there is no physical quantity “pressure” in a pump facet, as there is no wall, and the pressure is not isotropic, therefore pressure can only be defined as a vectorial - direction-dependent quantity.
I’ve checked your file, but didn’t find info about your calculation method in the Formula Editor, so I assume you still measure pressure on the end caps (the pumps) directly.
Textbooks usually calculate the pressure from the ideal gas equation (pV=NkT), and in the real worlds vacuum gauges also measure density, then they convert it to pressure electronically. You can do the same in Molflow, as Molflow’s density quantity is isotropic, even near strong pumps.
You can also read this relevant thread, which was folowed up by a Zoom call, and we concluded that when there’s a stream of particles, defining pressure isn’t straightforward: How do you calculate Pressure on transparent surfaces?