Static Head in Circuit

[jor1492]

What is the static head in a system were discharge vessel is not at the highest point in the circuit?
Highest point in the circuit is at 11 m from pump discharge.
Discharge vessel is at 0 m from pump discharge.

 

[LittleInch]

11m

There are some variables but if at the start your pump doesn't deliver at least 11m you won't have any flow when pumping into an empty line.

There are some syphon effects here which complicates things.

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Also: If you get a response it's polite to respond to it.

 

[TiCl4]

As LittleInch said, 11m of liquid. I recently dealt with a recirculation loop that ran into the same design consideration. When starting the pump into an empty line, flow will be limited by the increase in static pressure needed to fill the line at the highest elevation.

Once the pipe is full all the way to the receiving tank, the pump will only need to overcome the differential height between the pump and the discharge height. In my case, I had 3-way valves at various elevations that were drawing material off. In this case, the static head is still the same rho*g*h calculation to determine pressure at a point. If the vessel nozzle has a height difference of 0, then you will have a 0 static head to overcome when actually flowing into the vessel.

However, you will need to be careful to ensure the down-leg piping is liquid-full. If your flow rate is low enough that air can flow up the down-leg, coutner-current to your liquid flow, you will lose the siphon effect. This could end up making your pump have to deal with the static head and flow less than you designed. Also, given just the right conditions, I think this could cause flow to cycle (high->low->high, etc) if you enter into slug flow regime, causing a temporary siphon that is then relieved when the slug is passed.

I'm not actually sure how to check to see if the pipe will be liquid full. There are calculations for self-venting pipes and the like for gravity flow, but I'm not sure how making it a pumped system affects it.

 

[jor1492]

thanks gentlemen