a few flowbench build questions

[vuurmuur]

Hello all,
i'm gathering information on building my own flowbench and i would like to discuss a few options.
Let me know what you guys think about it.
If someone has experience with one of the sensors please let me know what your findings are.
I have this list of options for my flow bench:

1. Use orifice plates for meassurement.
Pro's: -Relative easy way of building (especially with the PTS plans)
-Accurate
-Cheap
-Good repeat-ability (no temperature / weather corrections)
- Easy calibration
Con's: -Low turn down ratio (3:1 /5:1) (switching plates)
-Noise and flow restriction/ loss of flow capacity
-Harder to control test pressure due to turbulence etc.
Use a HFM hot film mass air flow sensor for measurement
Pro's: -Sensor can be mounted easily inside a pipe
-Can be verry accurate
-High turn down ratio
-No noise and flow restriction/ loss of flow capacity
-Better to control test pressure due to turbulence etc.

Con's:- Complex Electronic readout, it will need a flow/voltage map because the output voltage isn't linear.
- Possible needed to have temperature/humidity corrections.
NOTE: if built inside of bench is there still the need for temp/weather compensations?
- If it needs compensations than accuracy and more important repeat-ability can be compromised.
- Sensor element can get contaminated/damaged from particles sucked in to bench.
Use a PTS bench with an venturi sensor
Pro's: -Relative easy way of building
-Accurate
-Cheap
-Good repeat-ability (no temperature / weather corrections)
- Easy calibration (linear pressure/flow relation)
-High turn down ratio 10:1
-Low noise and flow restriction
-Better to control test pressure.

I want to read out the data through electronics (Blackbox/PTS DM etc) and electronically control test pressure.
I believe the most effective/fastest/accurate way is the venturi sensor inside a PTS bench.
What are your opinions?

[Hotz]

Welcome vuurmuur.

Good questions, I personally am 100% PTS system, but I believe that your topic will yield a good conversation.

[Tony]

Yes welcome to the Forum vuurmuur.

Orifice plate wins hands down in every respect, except for limited flow range caused by the rapidly reduced differential pressures generated at the low flow end.
If you plan to use a water manometer, this will mean multiple orifice plates will likely be required.
An electronic manometer is vastly more sensitive and only one sensibly selected orifice plate is needed during actual testing.
A PTS bench with the PTS electronic manometer will be the preferred solution once you really start looking more deeply into this.

Various types of hot wire air velocity sensors could be used, but never are.
The problems are endless.
Very high non linearity, only measures air velocity at one very small point in a pipe, hugely upset by turbulence or non laminar flow, needs extensive weather corrections to calculate an equivelant CFM figure.

A venturi sensor does not have a linear pressure/flow relationship.
In fact it COMBINES the worst features of both the orifice and hot wire sensor.

[vuurmuur]

Ok thanks for the answers so far.
I'm going for an orifice bench to avoid problems and development time.
But can someone explain why a venturi doesn't have a linear pressure flow relationship?

[Tony]

But can someone explain why a venturi doesn't have a linear pressure flow relationship?

I suggest you do an internet search on that, its a complex topic.
Its not a simple direct linear relationship.