Thread: Cut size dpc calculation vs Bill Pentz expt data

Regarding the inputs and results...
I adjusted inputs a little and added some information...

The inputs for cyclones.pdf and Cyclone_Design_Calculation_Tool_Simplified.xls I set the same.

Flow rate ...1100CFM (1869m/s) to give the Vi (inlet velocity that BP likes, 3798FPM (19.3m/s). Close to his 4000FPM anyway.

The dpc result from these spreadsheets is 9.5 and 8.9 microns respectively. The first one matches my manual calculation very well.

Just for interest's sake, the pressure drop from the cyclone with no neutral vane was 3.18 and 5.12 in w.g. respectively.
For the first s.sheet a version with neutral vane is also calculated...pressure drop was 1.49 in w.g.

Some other thoughts
Just intuitively, it's hard to get my head around how few variables there are in those equations (1) and (2) above.
And the common equation for number of turns N, my instincts say it should contain inlet velocity and inlet inclination.

These two s.sheets assume the top of the cyclone cylinder is flat and there is no Bill Pentz style spiral vane inside the cylinder.

(Greg, I've PMed you a link to my collection of relevant documents that I've culled from the internet over the last few years.)

Before you get too wrapped up in trying to make calculations align with BP claims there are a couple of points to keep in mind.

First, all of the analytical methods are only estimates, they are far from exact. The Lapple equation you posted dates to 1951 and is really only the first attempt at that kind of calculation. There's been a lot of work done since and the subject is still fodder for graduate student projects. Most of that appears to done now using simulation rather than analysis.

Second, the BP "data" of 99.9% greater than 4.7 micron really doesn't tell you anything without specifying the velocity and especially the size distribution of the test material. That kind of claim is more marketing fluff than engineering data.

Also, not trying to be picky, but

(by definition, particles at or below the cut size will be collected with 50% efficiency)

particles at the cut size are collected with 50% efficiency. Smaller are collected with less than 50% and larger more than 50%. See the chart on p9 of the pdf you linked.

This paper has some good information.

My limited experience with commercial cyclone vendors is that they have some clever empirical models they use, then tweak the feed pressure to control cut size. Not something you do with a home dust collector system, but clearly there are limits to basic equations like this.
I'm sure they use CFD modelling too... Beyond the reach of most of us!

Originally Posted by dmorse

(Greg, I've PMed you a link to my collection of relevant documents..............
...... the analytical methods are only estimates....... The Lapple equation you posted dates to 1951 and is really only the first attempt at that kind of calculation.....now using simulation rather than analysis.

...the BP "data" of 99.9% greater than 4.7 micron really doesn't tell you anything without specifying the velocity and especially the size distribution of the test material...

Also, not trying to be picky, but particles at the cut size are collected with 50% efficiency. ....)

Hey Dave,
I downloded that package of files. Really useful stuff. Thanks again
I'm happy to be pulled up on the cut size definition. That's just me being too loose, imprecise and in a hurry. It's a new field for me (excuses, excuses).

Skimming through Cyclone Collection Efficiency: Comparison of Experimental Results with Theoretical Predictions from your collection, there is really useful expt data, and some calculation models that look better than Lappele's (Barth).

I would love to have a go modeling the cyclone behaviour with Fluent CFD but there is just too much to learn and I can't go down that rabbit hole right now. I do have a friend with a bootleg Fluent and a grunty old workstation though..

Cheers,
Gregg.