Variable orifice material

[Thomas Vaught]

Simple designs with stoppers are usually the most robust.

Tom V.

[Thomas Vaught]

I was playing around with a few ideas and had a question, I am at home so I do not have the calculations with me but from memory.

If I have a volumetric flow rate of 1094 cfm
and a hydraulic diameter of say 6.5 inches,
and I am using AIR at say 75 degrees F what is the
Kinematic Viscosity of the air and the reynolds number? Same deal for say 800 and 600 cfm through the same Dh.

Any help appreciated.

Tom V.

[DaveMcLain]

I think it will be interesting to see how this works out because it seems to me that any orfice style bench is rather sensitive to how the air approaches the actual measuring orfice, if it comes in at an angle or esspecially if there is some sort of lip around some or all of the orfice. This can radically change the calibration depending on the direction of flow and I do not think that this change is linear and easily factored out....

[SuperRunner]

Yes, that is why I decided against it.

I went with a standard replaceable orifice plate.

[Tony]

I am skeptical about anything other than a simple round, sharp edged orifice having a reasonably known and consistent Cd. Call me a cynic, but simplicity is a virtue.

As DaveMcLain says, the orifice entering air conditions are absolutely vital to getting consistent Cd from the orifice. And I am not at all sure that completely reversing the flow through the whole bench is really a very good idea.

If orifice flow (and the resulting depression) is always kept in the same direction it simplifies a whole lot of things, and getting a dead flat orifice turret to self seal against a dead flat surface is really easy, if it only ever sees a pressure drop in one direction.

The rubber stopper idea rather appeals to me too, if suitable access can be arranged to the stoppers.

I use a car steering wheel on the side of my bench to rotate my two foot diameter orifice turret, very fast and convenient.

[Erik]

I building a orificebench and plan to use two sliders with three orifices on each slider. I will move them with wires hoked up to a weel like a puch pull throttel on a motorcykle carb. I be glad for a second opinion.

This is my first post to the forum
Erik

[larrycavan]

Welcome to the forum Erik

You've ventured into rather unknown territory with your design choice. Keep us posted as to the progress and test results..

Larry C