Submerged Pipe Discharge Force

[Swifty358]

I need to calculate the downward vertical force exerted on a section of tubing that is submerged and discharging a cold water flow into hot water.

The tubing is 27.125 inches long and is connected to a water supply on one end w/ a flow rate of 3 GPM. The other end is open to a tank of hot water. I am assuming the tube is completely submerged in water. The tube has ID 0.58" and OD 0.65". The tube material is smooth plastic. The flow cycles on and off, so I am assuming the greatest force will be when it first turns on, similar to the jolt felt when a firehose or garden hose first turns on.

I have calculated several different forces several ways (including shear stress along the tube inner wall and momentum flux at the outlet) and everything I get is of minimal value, always <0.1 lbf.

Any sort of help is appreciated.

 

[rb1957]

are you discharging downwards, or upwards ?

i suspect downwards. in that case you first have to overcome the static pressure difference, about 15psi on 0.25in2 (internal area) = 4 lbs.

now 1 gallon = 4.54liters = 4540cc = 277in3 = 0.16ft3
3 gpm = 831in3/min = 14in3/sec
so the flow rate is 56in/sec = 4.5ft/sec
and 3 gpm = 30 lbf/min = 0.5 lbf/sec = 0.0155 lbm/sec
so that the momentum rate (force) = 0.0155*4.5 = 0.07 lbf
(alot smaller than i'd've thought)

 

[hydtools]

You are correct. There is not much force. You can experience the effect by using a garden hose and bucket of water. Run water through the garden hose and while the water is running submerge the hose end in the bucket of water. You will notice the force pushing the hose up and out is very low compared to the force when the hose is out of the bucket of water.

Ted