Flow straighteners

[pmcenroe]

Hello,

I've recently taken an interest again in getting my early flow bench efforts to work better than before. I had been unhappy with the maonometer readings I was getting and decided to use some DAQ technology to provide a flow reading directly.

While this has been a great learning experience, in lots of ways, if I was unhappy with pressure readings before, I'm even more unhappy now... The physical characteristics of liquid manometers have a lot to recommend them in this sort of application; inertia, damping etc.

I've gotten my hands on the PTS flow bench plans (thanks Bruce) and while I don't plan to build that bench yet, it has given me some ideas for improvements.

I have been using a pipe and orifice setup to measure flow, but from my reading of the forum this is probably the most difficult method to get accurate readings given the dimensions of pipe and orifice I had been using.

I intend to build a flow measuring box, for the want of a better term, to provide a large settling volume. I intend to provide a baffle on the inlet and I'm also considering a flow settling/straightening mechanism as well in front of the orifice plate. I have seen honeycomb section (somewhere) being used as a flow straightener but I was wondering if the air filters I have might do the job.

I've attached pictures of the air filters. They are from a Mercedes E500 so should be able to handle considerable flow.

I'm hoping that the filter pleating would provide an element of straightening and that the perforated back section would also help.

Is a straightening element required?

Would these filters act as a straightening element?

Regards

Paschal

[Tony]

I'm also considering a flow settling/straightening mechanism as well in front of the orifice plate.

Paschal

Don't do it !!

The natural way air tries to flow through an orifice, is that it approaches radially from all directions, and spills over the edge, and falls into the hole. It does not rush towards the hole from straight in front.

Anything that blows air directly towards the orifice such as a pipe or flow straightener, just interferes with the natural flow coefficient.
The best way is a settling chamber, with a baffle plate placed directly in front of the orifice, as shown in Bruce's plans.
It is simple, and it works.

[jfholm]

Another thing to consider with the air filters is that most add more restriction then you would think. How would that influence the accuracy of your readings?

While flow testing air filters I had to stack a 14" round one until I had 6" height before I lost my restriction.

John

[pmcenroe]

Thanks for the feedback.

In terms of flow to the orifice, I would intend to have settling volume in front of the orifice and after the straightener element. I would hope that the straightener would provide a more consistent pattern of flow to the settling volume and orifice and hence provide a more consistent environment for the measurement. If it doesn't provide any advantage over a baffle (which I would use as well) then I would be happy to omit it.

In terms of accuracy, I would using pressure taps after the straightener so hopefully it wouldn't affect accuracy. In terms of restriction, I was hoping that for the flows rate I'm considering (120 CFM max), the restriction would not be great, given that these filters are sized for a 5-litre engine.

As above, I would be happy to omit them if they aren't going to provide any additional accuracy.

Thanks,

Paschal

[Brucepts]

Don't make it more complicated than it needs to be, as simple as the plans are when you look at them, believe it or not the damn thing works quite well if I do say so myself

[dusty]

Hello Newbi Here

I have been looking around the site and am quite impressed with everything here.

I have been thinking about building myself a flow bench too.

On Flow Straitening.

I have been looking around for something to reduce the air turbulence while flowing through the bench.

Some Ideas:

Perforated plate (Small to Med Holes)

Aluminum Grease Trapping Mesh like above the Stove in the Range Hood

Furnace Filters, (Simple to Fancy) they could also help filter the Shop Air of allot of Contaminating Dust Etc.

Also Cheaper than Automotive/Truck Air Filters

Just my 2 Cents

And a great site

Take Care

Dusty

[blaktopr]

No need for flow straighteners, period.