Our fluid is bio slurry. We want to measure the vibration of this fluid when it will flow through the pipe. But my question is, What should be the minimum dia of pipe? If the dia of pipe is too thin, do we hear more the impact of wall more than the Fluid?
Hi Munshi
There are ways to do this.
You can insert pressure sensors to measure pulsation. Some use strain gauges to detect pulsation in pipes, other use stiff boxes and sense local pressure. Another approach is to use piezocables or long strips of piezofilm.
Piezocables can measure flow generated pulsation - these are very sensitive with a dynamic range of 200 dB.
http://www.te.com/usa-en/product-CAT-PFS0002.html
The smallest radial motion I have been able to detect using piezocables was in the ballpark 5E-12 m.
FYI - Piezocables work much better than one would at first assume and they outperform all the types of pressure sensors that I have tested with respect to sensitivity - also piezoelectric pressure sensors.
The method was, to the best of my knowledge, pioneered by R.S. Pinningon at ISVR in Southampton.
http://www.sciencedirect.com/science/article/pii/S0022460X84712430
Here is a discussion on pulsation measurement
http://qringtech.com/2014/01/28/how-to-measure-pulsation/
and here are some measurements made on a mix of oil, gas and water with- and without- slugging conditions for an oil well
http://qringtech.com/2017/05/20/slugging-pulsating-pressure-source-characteristic-measurement/
There is a company called CIDRA that use piezo cables for a clamp-on flow meter fitted with an array of piezocables. They use the correlation of the flow generated wall pressure variation from vortex whirls, e.g. http://www.cidra.com/resource-center/sonar-based-clampon-VF-Meter-gas-and-liquid-applications
You can get the flow velocity and the wave propagation speed from pulsation. From this information, you can make make educated guesses on the fluid properties.
Regarding the pipe - as Pinnington derives, the method works the best when used with a stiff fluid and a weak pipe, i.e. liquids and plastic or perspex piping is a good combo whereas gas and metal piping is the more difficult case (it works as well, but you must then compensate also for in-plane mechanical strain)
In the simplest case, there is a very straightforward relation between pulsation and hoop stress. https://en.wikipedia.org/wiki/Cylinder_stress
The major challenge in using piezocables is that you must find its sensitivity yourself whereas piezofilm comes with a known strain sensitivity. Piezofilm is costlier than piezocable though and not as robust for field work.
Last, most piezocables work well up to about 60 C above which they start to age. The cable melts at about 130 C.Ageing does not matter if your application is fluid properties as you then get away with transfer function measurement.
Hope this helps
Claes
Dear Dr. Fredo,
I'm still confused about your answer. We are trying to use Acoustic Sensors for measuring the vibration of fluid. My concern is will the dia of pipe will effect the vibration of fluid? or pipe properties? Some researcher has recommended that I should use Metal pipe rather than PVC pipe. As our fluid is slurry type. What should be our minimum dia? What should be our minimum velocity?
Hi Munshi
The piping material is secondary - it does not affect the flow. It is things like the flow velocity, wall smoothness, piping orientation and so on that matter.
Liquid flow almost always is turbulent. Velocity has to be very low for the flow to be laminar.
Turbulent flow makes its own noise which can be used to sense pressure oscillation (pulsation) in the flow.
Next you have to choose a method for sensing the fluid pulsation. If you use externally applied sensors, I suggest the use of piezocable or piezofilm. You can consider also te use of pressure sensors that protrude into the flow (or they will measure the wall turbulence rather than the pulsation).
Note that you must learn to discern between three kinds of pressure
- Line Pressure (ambient or static pressure)
- Kinetic Pressure ('wind pressure' - associated with flow velocity and transportation of matter)
- Pulsation ('sound' pressure - associated with wave propagation)
All three exist in your system and the choice of sensor react differently to these three.
See Figure 1 here for an example where a pressure sensor picks up both pulsation and Line Pressure. http://qringtech.com/2010/09/15/wave-steepening-increase-peak-pressure-piping-pumps/
I believe that you need to state your purpose (in terms of the quantities you want to derive and the boundary condition, e.g. temperature, pressure, corrosiveness and so on) to progress on the matter on sensor selection.
Sincerely
Claes
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