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Consider water flowing in a pipe, and I don't know the direction of flow. How to determine the direction of flow? My approach- I can use a pitot tube but for that I have to drill a hole in the pipe and I can't use this approach for fluids whose leakage will create a severe problem.

What is the simplest way to determine the direction of flow?

Edit- Is it possible to determine the flow direction without using gauges or any specific instrument?

MechaTrex
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  • Pressure gauges at each end? – Solar Mike Jun 07 '22 at 14:19
  • @SolarMike No pressure gauges – MechaTrex Jun 07 '22 at 14:33
  • Why can't you fit them? they also work for many fluids... – Solar Mike Jun 07 '22 at 15:04
  • Actually I want to know, whether is it possible to determine the flow direction without using gauges or any specific instrument? – MechaTrex Jun 07 '22 at 15:08
  • this is an interesting problem. Usually people would go to the end and look at it or put their hand over the opening. – Tiger Guy Jun 07 '22 at 16:51
  • Hit the pipe using hammer on one end, and observe the sound coming on other end of pipe. Since, the sound wave travels faster in metal than in water, so there will be a delay. Now, switch the position of hammering to other end of pipe and then observe the sound. Direction of flow will be that one in which the delay is lesser. I think this should work. – Max Jun 08 '22 at 05:34
  • @max it won't work in general, given not all pipes are metal and not all material flows are fluids. Or maybe the fluid is, say Hg .... – Carl Witthoft Jun 08 '22 at 12:24

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Heat the pipe at some point, and find the direction in which heat transfers. This will give you the direction of the flow.

Caution: Don't do this for flammable fluids. Thanks to @Carl Witthoft for pointing this out.

Sina Atalay
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  • But if the pipe is made of some insulating material then? or if it is made of some material example- PVC then? – MechaTrex Jun 07 '22 at 14:46
  • ... or what if the heat causes an explosion. I wouldn't do this on a natural gas delivery pipe. – Carl Witthoft Jun 08 '22 at 12:21
  • @CarlWitthoft Yes, no one should do this for natural gas or the other flammable fluid delivery pipes. I edited the answer, thanks. – Sina Atalay Jun 08 '22 at 12:37
  • Even if its insulating, one side will get hotter than the other. You just need the measurement points far enough apart from each other that conduction through the pipe is negligible over how ever long you need to apply heat for (which could be a long time if it's insulating). If it's a closed loop then it might not work since the heat would be carried back around to the wrong measurement point. – Emily Conn Jun 10 '22 at 16:43
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Yes, purchase an ultrasonic flow meter.

Needs a straight length of pipe and very careful placing of the sensors. However, if done well one can get good results, if not then the results can be spectacularly poor.

Solar Mike
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If this is a pumped system, try measuring the reaction forces when you turn the system on. For example, if you're trying to measure the direction of fluid flow in a hermetically sealed "black box" type device, put the device on a turntable and turn the device on. Depending on the direction of rotation of the turntable, you will know if the fluid is flowing clockwise or counterclockwise.

Emily Conn
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Look at or develop a flow schematic of the system. A cursury examination should give most likely flow direction. Maybe some existing ancillary measurements could give you necessary info.

tckosvic
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