More on mini cyclones - no need for cones hotline?

[ivan]

I have been experimenting with a very second hand mini cyclone vac originally sold for plaster dust (for use with wall chasers etc) This has a very short cone, so short it's only function appears to be getting the dust into the polybag designed to fix underneath.

Bill Pentz's small cyclone has a 2" outlet at the bottom, fine for dust, but tests suggest this may block when fed shavings from a big router bit, say. I think Barry too wrote of this problem last year.

I plan to try a length of 160 mm pvc soil pipe with no cone (or rather a "cone" of zero degrees, ie. parallel, standard pipe), and inlet of rectangular pvc cooker hood ducting, ramp cut from pvc sheet, air out by small round pvc drainpipe. This is all quite easy to glue together. Anyone tried something like this before?

I fould some bumf on line, re. cyclone vacs for cleaning up in radioactive environments. These had several very mini cyclones as per Dyson's root 8 design. These are appently capable of removing ciggie smoke particles :shock: fron the air, so should manage mdf dust.

Last time at the recycling centre there were several dead Dysons floating about. Mr D has spent quite a few quid at university research depts developing his machine, so perhaps we should go recycling for parts?

 

[tnimble]

A cyclone particle separator has very basic mathematics behind its working (well at least to me). Its form, all the dimensions of the various parts and relations between sizes coma from a mathematical modal. Because you can never build exactly as the model you have to round dimensions to a usable size and change some things to be able to create them.

You can also take real life measurements and put them in a simulation and see how close it is the the original mathematical model.

A cyclone works by rotating air at a high velocity through another air stream. The most important part is therefore the air intake, top cylinder and air ramp. The cone effects the rotating air streams velocity, the bottom of the cone deflects the down going rotating air into an upward stream of air.

Th angle of the cone and its top diameter more or less controls what sizes of particles are removed and how the air is deflected upward.

Reducing its angle should cause a reduction in the range of particle sizes separated and lowers efficiency.

Having no cone could work but with only a few particle (larger) sizes being removed.

I have actually worked for the Institute for Atomic and Molecular Physics a few years ago at finishing my education. There is no way you can clean an radioactive (contaminated) environment with a root 8. However when there is contaminated dust in that area you can vacuum up the dust with any vacuum cleaner. Only he root 8 would blow less of the particles out the vacum back into the environment. See the specs of the root 8 for the particle sizes it vacuums in your living room. That are the same type of particles vacuumed in a radioactive environment. After vacuming the environment remains radioactive only not so dusty as before. Being less dusty reduces the risk of spreading the radioactivity to other areas by taking dust with you as you pass thrugh the area or when wind can reach that area.

 

[ivan]

tnimble, both the "radioactive" environment vac, and the Dyson root 8 have a HEPA filter on the air outlet. The outlet air quality is ultimately specified by the HEPA filter, not the cyclones, whose job is to remove as much as possible to extend the life of the HEPA filter to reasonable proportions.

The paper referred to, tested various cyclone designs for the "radioactive" environment, being evaluated by the number of radioactive particles found in the HEPA filter at test end. The multi mini parallel cylone arrangement (similar in concept to Dyson root 8) trapped all radioactive partices at test end, none found in the filter. Obviously the actual Dyson design, however good it's cyclones may be, is not suitable for radioactive dust as apart from its "domestic" construction, you get a facefull back every time you empty it.

The idea of a pre vac cyclone in the workshop is to extend the life and capacity of your existing vacuum cleaner, so the filters in this will determine what's in the exhausted air. Axial industrial cyclones do not have a cone (often mounted horizontal) so I suspect my drainpipe suggestion above, with a bit of ex recycling centre Dyson on the outlet will be more effective than Bill Pentz's mini design and also much simpler to make.

It's true cyclones can be designed by rule of thumb, from simple mathematical models, but these do not predict at all well when the proportions are changed. Although continuous flow, it is often turbulent especially at the boundary of the falling and rising spirals, and about as easy to model as the weather. Gas and liquid phase cyclones are used for industrial separtion and there still appears to be sophisticated research underway, some of which can apparently map the trajectory of individual particles.

Incidentally, you might not have seen a tv programme some years ago where a university up north was commisioned to examine houshold vac contents in the general region of Winscale/Sellafield, (not workers' houses) finding plutonium partices in all samples. This was well before Dyson or indeed HEPA days. I think I'd quite like a hazardous environment vac that improved my air quality if I had to live in NW England!

 

[Nick W]

Why have I now got a mental image of a herd of Devonians hoovering the fields and byeways of the NorthWest? :?

 

[tnimble]

tnimble, both the "radioactive" environment vac, and the Dyson root 8 have a HEPA filter on the air outlet. The outlet air quality is ultimately specified by the HEPA filter, not the cyclones, whose job is to remove as much as possible to extend the life of the HEPA filter to reasonable proportions.

Indeed. Thats why one would use a ordinary vac in such areas. But with no vac an radioactive environments can be cleaned. When you need to remove dust from such an environment you need a special vac like a speciality vac or one such as the root 8.

The paper referred to, tested various cyclone designs for the "radioactive" environment, being evaluated by the number of radioactive particles found in the HEPA filter at test end. The multi mini parallel cylone arrangement (similar in concept to Dyson root 8) trapped all radioactive partices at test end, none found in the filter. Obviously the actual Dyson design, however good it's cyclones may be, is not suitable for radioactive dust as apart from its "domestic" construction, you get a facefull back every time you empty it.

That would not be a problem since working in such an environment already regulates using special respirators or oxygen tanks and a fully sealed suit. However you would have to start revacuuming.

The idea of a pre vac cyclone in the workshop is to extend the life and capacity of your existing vacuum cleaner, so the filters in this will determine what's in the exhausted air.

No entirely to suckup small particales and separate them a high velocity is required. When that velocity is not reached the filter does not filter them because they never reach the filter. Not reaching the velocity can be by having not enough suction capability or by a glogged filter. The cyclone or any other particle separator reduces the glog rate. But without enough vac capacity or the much loss in the piping, hose or what ever part no matter how good a filter is present you'll obtain a clean environment.

Axial industrial cyclones do not have a cone (often mounted horizontal) so I suspect my drainpipe suggestion above, with a bit of ex recycling centre Dyson on the outlet will be more effective than Bill Pentz's mini design and also much simpler to make.

Indeed a lot of types of particle separators do not have a cone. The efficiency of a system is both by loss in moved air, what range of particle sizes is removed from the air and by the number of particles of a particular size. Bill Pentz's his design with the cone extends the range of particle sizes for a extra loss in air moved.

It's true cyclones can be designed by rule of thumb, from simple mathematical models, but these do not predict at all well when the proportions are changed. Although continuous flow, it is often turbulent especially at the boundary of the falling and rising spirals, and about as easy to model as the weather. Gas and liquid phase cyclones are used for industrial separtion and there still appears to be sophisticated research underway, some of which can apparently map the trajectory of individual particles.

Calculating the amount of turbulence and the location of the turbulance is very simple. (don't pull out those pocet calculators yet, it would still fill multiple sheets) Only calculation participle trajectories is extremely hard and more or less unpredictable. The stream of particles is not hard.

Incidentally, you might not have seen a tv programme some years ago where a university up north was commisioned to examine houshold vac contents in the general region of Winscale/Sellafield, (not workers' houses) finding plutonium partices in all samples. This was well before Dyson or indeed HEPA days. I think I'd quite like a hazardous environment vac that improved my air quality if I had to live in NW England!

Even when doing this study 1000 years ago in a non populated area would turn up with radioactive particles in the filters. Radioactive particles are not dangerous , what makes it dangerous is the amount and wavelength spectrum of radiation emmited.

Having said all of the above. Your design would work only its properties would be different. Depending on the application and specification you want it to have it can be a good working design or a complete waste.

 

[Andy Pullen]

Rather than no cone why not buy a Wilko 18cm kitchen funnel, it'll fit straight on the end of the soil pipe and you can cut the spout to suit. This will allow the waste to go into a seperate container and out of the equasion.
Unlike you educated nuclear people I am a mere carpenter but I cant see why the whole body cannot be a funnel saving having to attach a cylinder to a cone in awkward sheet metal. I also have a problem seeing why you need the ramp, surely the best situation is to fire the waste around and down the cylinder and keep the inlet and outlet as far away as possible from each other so that the centrifuge and loss of draw makes the waste fall thru into a bin never to be seen again. Do we really need these rectangular inlets and ramps etc ?
I think what we all want is something that is relatively easy to build and effective and doesn't look like a bodge up.
There are a million things I would like to know about this so please carry on explaining the why's and wherefors. Regards Andy.

 

[TEP]

I'm with you on this Andy, I'm lost on the maths but wouldn't it be great if someone could design a simple unit that a humble turner like I could put together. :?