Calculating friction loss (fluid dynamics)?

[preet]

Hey all...

My scenario is as follows: I have a pump that provides a certain rate of flow in my system. The pump is connected to a spraybar, a pipe with holes drilled through at evenly spaced intervals. Each of these holes is fitted with a 90 degree nozzle (effectively a miniature 90 degree elbow). Assume that I measure the flow rate by collecting the water discharged by the nozzles into a fixed volume and timing it. Let's say I arrive at a flow of "X" GPM.

a) Is the flow from each nozzle pretty much the same (ie, X/#nozzles GPM)? (assume that the spraybar is connected from both ends and not only from one side, so pressure isn't lost as the water travels along the spraybar)

b) How do I go about finding the combined friction loss from the nozzles? Do I find the friction loss of each nozzle and add them up? Or do I just use the friction loss at one nozzle (I've heard about doing this, but I want to know why).

The friction loss from the nozzle depends on the GPM, so if I use "X" as my GPM, with one nozzle, would the friction loss be equivalent If I used "X/#nozzles" as my GPM and then multiplied the friction loss I obtain by the # of nozzles? Or is everything I'm saying totally wrong?

Would appreciate any input...

Thanks,
Preet

 

[Chestermiller]

Hey all...

My scenario is as follows: I have a pump that provides a certain rate of flow in my system. The pump is connected to a spraybar, a pipe with holes drilled through at evenly spaced intervals. Each of these holes is fitted with a 90 degree nozzle (effectively a miniature 90 degree elbow). Assume that I measure the flow rate by collecting the water discharged by the nozzles into a fixed volume and timing it. Let's say I arrive at a flow of "X" GPM.

a) Is the flow from each nozzle pretty much the same (ie, X/#nozzles GPM)? (assume that the spraybar is connected from both ends and not only from one side, so pressure isn't lost as the water travels along the spraybar)

If the spray-bar has a large diameter, the frictional pressure loss in the spray bar will be negligible, and the flow rate out the nozzles will be approximately uniform.

b) How do I go about finding the combined friction loss from the nozzles? Do I find the friction loss of each nozzle and add them up? Or do I just use the friction loss at one nozzle (I've heard about doing this, but I want to know why).

The nozzles are in parallel, so all you need to do is find the friction loss for one nozzle (assuming uniform flow).

The friction loss from the nozzle depends on the GPM, so if I use "X" as my GPM, with one nozzle, would the friction loss be equivalent If I used "X/#nozzles" as my GPM and then multiplied the friction loss I obtain by the # of nozzles? Or is everything I'm saying totally wrong?

No. As I said, the nozzles are in parallel, so the all have the same friction loss (pressure drop).