Thread: various cyclones design

All figures I have seen are up around 30%. We have been down this road before if you recall.

Originally Posted by Chris Parks

All figures I have seen are up around 30%. We have been down this road before if you recall.

We have?

Given a 20% increase in flow is a theoretical maximum I sense a problem when anyone gets more than this, as practice is almost always less than theory.

We now also know that many flow measurements are done incorrectly with a single reading in the middle of a duct using either an anemometer or a pressure reading.
The relative flow difference between 50 and 60Hz should not be that far out it appears that they might be because the flow rates do change.
BPs fudge factor when using single readings in the middle of a duct to determine air speeds is to simply deduct 10% but that is still not very accurate because the correction is not just proportional but a more complex function of air speed and duct diameter (and probably duct roughness). My experience with using single point readings in the middle of an air stream and comparing that to a full cross flow measurement and analysis is that the fudge factors required, range from 4% at less than 100 cfm in a 2" duct, slowly increasing to 10% at around the 800 cfm in a 6" duct, and then they shoot up to over 20% at around 1200 cfm in a 6" duct

Originally Posted by BobL

We have?

Given a 20% increase in flow is a theoretical maximum I sense a problem when anyone gets more than this, as practice is almost always less than theory.

We now also know that many flow measurements are done incorrectly with a single reading in the middle of a duct using either an anemometer or a pressure reading.
The relative flow difference between 50 and 60Hz should not be that far out it appears that they might be because the flow rates do change.
BPs fudge factor when using single readings in the middle of a duct to determine air speeds is to simply deduct 10% but that is still not very accurate because the correction is not just proportional but a more complex function of air speed and duct diameter (and probably duct roughness). My experience with using single point readings in the middle of an air stream and comparing that to a full cross flow measurement and analysis is that the fudge factors required, range from 4% at less than 100 cfm in a 2" duct, slowly increasing to 10% at around the 800 cfm in a 6" duct, and then they shoot up to over 20% at around 1200 cfm in a 6" duct

I don't know how the readings were done but yes we have. Figures were taken fro CV's forum and you concurred with them at the time. Are you saying you were wrong?

Originally Posted by Chris Parks

I don't know how the readings were done but yes we have. Figures were taken fro CV's forum and you concurred with them at the time. Are you saying you were wrong?

Could be. Most of the readings I have taken in the past (and by that I mean stuff I did a work for the last few decades) have been for rectangular ducts at low speeds so I although I was aware of the need for proper cross sectional air speed measurements I did not know exactly when the need for this really kicked in. In the last couple of years this has become a bit more obvious that a bit more care is needed to get reliable results.

Originally Posted by BobL

Could be. Most of the readings I have taken in the past (and by that I mean stuff I did a work for the last few decades) have been for rectangular ducts at low speeds so I although I was aware of the need for proper cross sectional air speed measurements I did not know exactly when the need for this really kicked in. In the last couple of years this has become a bit more obvious that a bit more care is needed to get reliable results.

BobL - this kind of duct and air movement - is that just for heating and cooling or can it be used for DC. I know nothing much really about DC so assume fast is what is needed?

Originally Posted by shedman

I am sorry you feel abandoned. I was waiting for a reply to my last email asking for your address so I can get a freight price to include with the quote. I have a shipment arriving on or about 22nd of this month.

If there is anyone else who feels ignored please let me know but I have had a problem with one person where my emails were going to his junk folder so you might want to check that.

Shedman
Steve

no worries Steve, will get in contact soon.

Originally Posted by BobL

They look like old cyclone designs - I would avoid these if you can.

thanks for the advice Bob. I wasnt too sure if they were newer design or older, dont have time to go through all the readings and developments...

So if you have one of the older design cyclones and it is outside the shed (and therefore venting outside) does it make much difference if the cyclone is less efficient. Does it simply mean a little less dust is collected in the cyclone and the remainder is vented into the breeze or does it have a significant effect on air flow through the system?

Tony

Originally Posted by tony_A

So if you have one of the older design cyclones and it is outside the shed (and therefore venting outside) does it make much difference if the cyclone is less efficient. Does it simply mean a little less dust is collected in the cyclone and the remainder is vented into the breeze or does it have a significant effect on air flow through the system?
Tony

Correct. The older cyclone designs have a higher back pressure so they don't have as much flow as the BP type designs.