Physics Help Forum Determining length of a tube with applied pressure

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 Aug 9th 2019, 12:48 PM #1 Junior Member   Join Date: Aug 2019 Posts: 4 Determining length of a tube with applied pressure Hi folks, I have a question. Imagine i'm blowing air through a duct that is capped in one side. The tube is made of plastic and has a 14mm external radius and an internal readius of 10mm. If I apply a constant pressure of 16 bar, and it takes 30 seconds for the air to come out on the origin, what is the lenght of the tube? Thank you in advance. Regards Attached Thumbnails
 Aug 11th 2019, 03:46 AM #2 Senior Member   Join Date: Apr 2017 Posts: 513 There are many errors , just in the question! For a start the blowing machine ... You cannot say this applies a constant pressure of 16 bar .... It maybe able to achieve a max pressure of 16 bar , this will be with no air flow . Once connected to your tube the pressure will dramatically drop ... We need to know the flow rate of air (liters per sec) your pump can deliver at different back pressure ... Is this a practical problem ?? Give more information. topsquark likes this.
 Aug 11th 2019, 04:37 AM #3 Junior Member   Join Date: Aug 2019 Posts: 4 Yes, it is a pratical problem. We want to blow a cable from point A to point B. Before blowing the cable we blow air to see if it's all good, but in this case we have a blockage somewhere. I was trying to find a way to determine the blockage, since we already know that takes 30seconds for the air to come out.
 Aug 11th 2019, 04:41 AM #4 Junior Member   Join Date: Aug 2019 Posts: 4 I'll try to know the air flow rate...
Aug 11th 2019, 01:34 PM   #5
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 Originally Posted by joaoortinsbrito Yes, it is a pratical problem. We want to blow a cable from point A to point B. Before blowing the cable we blow air to see if it's all good, but in this case we have a blockage somewhere. I was trying to find a way to determine the blockage, since we already know that takes 30seconds for the air to come out.
Ah ... I see .. In that case I would just take off the end cap and connect the blower , 16bar is considerable pressure it should clear any blockage .

 Aug 12th 2019, 01:15 AM #6 Junior Member   Join Date: Aug 2019 Posts: 4 That's the problem. The cap is underground. We'll need to dig to find it...
 Aug 12th 2019, 02:49 AM #7 Senior Member   Join Date: Apr 2017 Posts: 513 Phew this is hard work ... So the pipe is buried underground , it has a cap on the end , but you don't know where the end is ??? But you want to blow a cable from one end of the pipe to the other ??? It seems the first job is to find where the end is and dig it up If you have a rigid piece of wire or rod you could push it down one end of the pipe till it hits the end cap (or the obstruction) . Then take this length of wire out ,lay it on the ground roughly above the pipe and this will tell you where to dig.
 Aug 12th 2019, 03:13 AM #8 Senior Member   Join Date: Oct 2017 Location: Glasgow Posts: 474 Water utilities usually use water pressure sensors to determine where leaks/blockages occur. Without access to the whole pipe, it's going to be difficult to figure out where the blockage is. If it's a straight pipe, maybe echolocation might work? Pass a sound pulse-wave along the air column and then record the time taken for the reflected wave to return?

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