basic pressure/flow physics question

[Tamal Paul]

Hey all! I having trouble wrapping my head around this. Take a look at the image I attached, which shows a very simple network. Lets assume no pipe friction loss.

If, at point A the pressure is 5 bar, then follow the main loop, point B is 5 bar (no pipe losses assumed).

However, If we take the red branch, point C has a loss of 2 bar, for example. Then we arrive at B, which should be ... what? 5 bar or 3 bar?

My question is part of a bigger more fundamental physics thought I am having: why does water flow at all in the red loop? After the red loop fills up with water, why does water even flow through it? Why doesnt the energy just push the water in the main loop, while the water in the red loop stay stagnant?

Thanks!

 

[Diehard]

Pressure differential!
Looks like a heating loop.
First off, you are talking with the pump running, of course.
You can't assume no friction loss since that is what determines how much flow is going in which direction. So there cannot be the same pressures at points A ans B, if there is flow.

So if you ignore the friction loss in the piping and introduce a pressure drop of 2 bar at point C, you would have close to 5 bar at point B but since the 5 bar was based on being fed with 2 lines(red and white lines) by introducing 2 bar pressure drop in one of those two lines you impacted the final pressure at point B(and made it slightly less).

The 2 bar pressure loss you introduced IS friction loss as well. Whether by a piece of equipment or by a valve. You can't completely ignore friction/pressure loss.

The thing is, the more restriction you add to the red line the less the flow through that line. But there should always be flow, however minute it may be.

There are heating loops similar to what you show that include, what I believe they call monoflow or venturi tees that direct a certain amount of the flow to the branches.

 

[FishScreener]

If you have any knowledge of electrical circuits, it is two resistors in parallel, with the pump head as the voltage.