4 Replies Latest reply on Jul 2, 2015 11:24 AM by Scott Rosoff

# Getting pressure drop AFTER tank fills up

Hello,

I'm currently working on a school project where I'm trying to calculate the pressure drop between the inlet and outlet after water's been flowing for a while so that the inlet/outlet tanks are nearly full. The system's geometry is pretty simple: there're two cubic tanks and 8 cylindrical pipes running in between the tanks. The first tank has a circular opening for the inlet, and likewise, the second tank has a circular opening for the outlet.

So far, I've ran several different tests (all internal) by modifying geometries, time-dependencies, and some other features, and the pressure drop is higher than empirically measured.

The problem then, I think, is that the pressure drop is being calculated immediately after water flows through the first couple of pipes instead of it calculating pressure after the inlet tank fills up. Looking at the flow trajectories and particle studies, my idea seems to be supported.

So my question: Is there a way to find the pressure drop after the water in the tank reached a certain point? This point is basically when the water has been flowing long enough so that the flow in the pipes has become steady.

Thanks,

Scott

• ###### Re: Getting pressure drop AFTER tank fills up

Are you trying to simulate the tank filling with a time-dependant problem? How did you set up your geometry and boundary conditions? I'm curious if you tried to set this up as  closed system, modeling both tanks and pipes (this would not give you a good answer).

• ###### Re: Getting pressure drop AFTER tank fills up

Hi Amit,

• I did try simulating it as a time-dependent problem, but that worked out worse than time-independent since I was getting a higher pressure drop.

• The geometry of the boundary is there's a small circular hole on the outside of each tank, for the inlet and outlet. The first hole (on first tank) was set up to be the inlet with volume flow of around 2000 in3/s. The second hole (on second tank) was set up to be the outlet with environmental pressure.

I did try setting this up as a closed, singular system with the tanks and pipes included. Why would this not work? Would the solution then be as simple as adding up the pressure drops across each individual component?

• ###### Re: Getting pressure drop AFTER tank fills up

I'm not sure I understand, maybe a diagram or a screenshot would be better.

If I get what you're saying, you have water from the environment coming into tank A, going through a pipe into tank B, and then leaving back to the environment?

• ###### Re: Getting pressure drop AFTER tank fills up

Yes, essentially a pump is constantly pumping water at some rate into tank A's inlet throughout the day, and tank B's outlet exits to some pipes.

Attached is a simplified diagram