Hi Decoy - You have started me down the path of reviewing my uni stuff. There are a few theories used to design cyclones and these days you can do it with CFD as vorticity is now handled quite well. Here is an article with some of the maths and the link that I thought I had included. I have been helping the local mens shed set up a new dust extraction system. Initially it was going to be a filter tower 5.5m high 1.2x2m footprint. I thought this was over the top. So the search for cyclones started. I have settled on one that does not need a filter, is highly recommended by users and fits a space that we would prefer it to be rather then create a skyscraper at our front door. Peter

https://www.youtube.com/watch?v=1SsbSxbalFo

https://clearvueoz.com.au/clearvue-cvmax/