Does any one know what the difference between these two options in the plot settings is?
the solidworks help file says: Inlet and Outlet. Presents how the flow moves inside the part as viewed from the inlet or outlet perspective.
this seems a little ambiguous to me, are they saying it is colouring the pipes with relation to the inlet velocity or outlet velocity?
It's exactly what i'm asking to myself.
Have you had any answer ?
Welcome to SW forums both of you.
This is basically to represent the flow of fluid inside the part. Check the two video here Viewing Results Click on this icon 
after you open the link to play the video for both of these options.
It works like this: take the inlet surface for example and divide its area by the number of trajectories, take the center of each "sub" area and then trace that point across the domain till you reach the outlet. The same applies for the other direction. You do not get the same view of the flow field. In the ball valve example you have uniform inlet flow (more or less) and a jet crossing the outlet biased to one side due to the constriction. This produces a big recirculation zone of flow coming in the "outlet". see images below.
I put the other image together just to highlight the complexity of the flow in something as simple as the ball valve example. It shows the horseshoe vortex due to upstream constriction particularly well.
Im a still a bit confused. See my attached images. Why do only (2) of the vertical pipes have water going through it on the "Outlet" plot setting? The "Inlet" settings looks more realistic.
it has to do with the distance travelled - the paths shown in the outlet end somewhere before they make it back to the inlet.
With the inlet flow being more streamlined the particles will quickly enter a small tube. After that the slow flows and becomes more turbulent and the particles are bumped around to a varying degree (you can see how some seem to get stuck in eddy currents).
When you look at the particles starting at the exit though, they have a very random path that they followed - some bounced around so much in the larger tube that the distance travelled in the large tube is longer than the limit of the graphical representation. In full Flow simulation you can define how long it should attempt to follow particles before ending the line. If you were to look closely at the exit you would find that the lines simply end somewhere and the length of that line from end to end is the same for all the lines that do not make it to the inlet surface. I am not sure what the length limit is with FloXpress, I've never used it.
If you increase the number of lines you'll start to get the inlet and outlet to look more similar. It depends on what you are trying to evaluate as to which is more important - do you care where the gas you put in ends up or where the gas that exits came from? Inlet evenly distributes the traces based on where the gas goes in, outlet evenly distributes them based on where they exit.
