Homework Help: Bernouilli's principle pipe flow problem

1. Jul 17, 2013

pianopanda

1. The problem statement, all variables and given/known data

On a horizontal pipe with flowing water on point 1 there is a vertical pipe with water up to some point. On another point 2, we have a pitot tube (L shaped) against the water flow and the lever on the vertical part is higher that on point 1. If the water flow stops what happens to the levels on the vertical tubes ?

2. Relevant equations

Bernouilli's equation : 1/2 ρv²+ ρgh+ P= constant

3. The attempt at a solution

On point 1 we only have the hydrostatic pressure. On point 2, the dynamic pressure is added to the hydrostatic pressure because of the shape of the tube so the water column will be higher. According to the principle that the total pressure should be conserved, then the dynamic pressure should completely change into hydrostatic pressure and the level on 1 should rise to the level on 2. This however seems quite counter intuitive to me so I would really appreciate your points of view! Thanks in advance

2. Jul 17, 2013

voko

Are you concerned with the situation when the flow is stopped abruptly, or when slowly?

3. Jul 17, 2013

pianopanda

from what i understood it was stopped abruptly

4. Jul 17, 2013

voko

You may want to read up on water hammer. You can experiment in your garden or kitchen, too.

5. Jul 18, 2013

pianopanda

I don't think it's the case of a water hammer. It's just a theoretical situation where we imagine the flow stopping "abruptly" but without the pressure wave.

6. Jul 19, 2013

voko

If it is abruptly, then there is a pressure wave - all that energy cannot just disappear. If there is no pressure wave, then it cannot be abruptly. You have to make a choice, you cannot have it both ways.