# Direction of fluid flow

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?

• Pressure gauges at each end? Jun 7, 2022 at 14:19
• @SolarMike No pressure gauges Jun 7, 2022 at 14:33
• Why can't you fit them? they also work for many fluids... Jun 7, 2022 at 15:04
• Actually I want to know, whether is it possible to determine the flow direction without using gauges or any specific instrument? Jun 7, 2022 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. Jun 7, 2022 at 16:51

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.

• But if the pipe is made of some insulating material then? or if it is made of some material example- PVC then? Jun 7, 2022 at 14:46
• ... or what if the heat causes an explosion. I wouldn't do this on a natural gas delivery pipe. Jun 8, 2022 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. Jun 8, 2022 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. Jun 10, 2022 at 16:43

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.

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.

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.