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Doing the math on a home made CF. Can anyone help?
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I'm gonna try my hand at putting together a home made centrifuge and I was wondering if anyone could help me do the math.

The bowl will be 14 inches in diameter and 4 inches tall. It'll be spun by a 1750 RPM motor.

Based on those numbers, what gravity number will I achieve, and what flow rate should I set?

Any help would be greatly appreciated


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Location: On my computer at this moment :) | Registered: October 13, 2007Reply With QuoteReport This Post
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You can do a search online for G Force Calculator and come up with some online calculators that you just plug in the numbers like radius of the bowl (half diameter) and rpm and it gives you the g force. Here's an example:
http://www.geneinfinity.org/sp/sp_rotor.html

With the size/RPM you mention, it says you'll be getting about 609 G's which is not really that high. You might consider finding a way to raise the RPM a bit if you can (just be careful not to over spin a large diameter bowl - for safety reasons obviously)

I built a centrifuge, and it almost worked but I used the wrong material for the bowl (tried a composite resin like material that was CNC machined... but it didn't take the heat) Also tried a metal bowl but never got it balanced well enough. Then I ended up buying a simple centrifuge which I've been really happy with. I like their design with the feed cone and although it's not necessarily the fastest centrifuge in the world it does what I'm looking to accomplish. One of the problems I found with building my own centrifuge was that I didn't have a clean, smooth bowl and the result was that it created a lot of wind/turbulence and pretty much vaporized the oil coming out and would take a long time to go clear again so I couldn't tell if the oil was coming out clean because it stayed cloudy for a LONG time, even though it went in clear. I was using a bowl diameter of about 15" but had it spinning over 3000 RPM. Never did find a good flow rate on that one but I run about 3 gallons/hour at 140* F through my "simple centrifuge" setup and have always had good results.

To determine feed rate you need to determine how long the oil will be in the centrifuge for (figure out volume of how much oil will be in the bowl at any given time and how long it would be in there for at any given flow rate. I don't know exactly what is recommended but I believe the guys at simple centrifuge told me to aim for about 1/2 million g-seconds. (figure out g-seconds by multiplying time in seconds the oil is in the bowl for by how many g's its under) obviously the more g force your centrifuge puts up the less time the oil needs to be in it to pull the heavy stuff out and the faster you can push the feed rate.

I'd encourage you to also check out some videos on youtube about the feed cone idea. I remember seeing videos showing how you could have a basic centrifuge and how fast "new" oil going in may come out - not having stayed in as long as you'd think. That's why the feed cone idea appeals to me because it forces the oil to the outside of the bowl and go under the most g-forces and stay in the bowl longer than it would by just dropping oil into the middle of an open rotor.

Hope all this helps.


1986 vw jetta 2 tank SVO conversion
1992 vw golf 2 tank SVO conversion
1998 2500 12 valve Cummins diesel with 2 tank SVO conversion
Making biodiesel in the back yard and running WVO in the vehicles with 2 tanks
 
Location: Burk's Falls, Ontario, Canada | Registered: July 05, 2003Reply With QuoteReport This Post
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VWpickup -
I have the early SimpleCF bowl version that is bolted to a Baldor 1/3 hp @ 3450 rpm . The settled WVO is introduced into the CF bowl via 1/2" PVC pipe, flattened out to spread out the oil in a ribbon flow, to about 1/4" off the bottom of the bowl. I run the settled WVO at 140F @1/2 gal/min. As far as the vapor/mist can be over addressed by adding additional drains along the bottom where the good CF'd oil exits the outer bowl. IMHO, I would suggest any 3450 RPM electric motor that can be bolted directly to the CF bowl.
 
Registered: October 30, 2005Reply With QuoteReport This Post
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Wow, that's 30 GPH... Maybe I run my oil through too slow but since I'm not in a rush I don't mind slowing the feed rate down.
Anyways I agree that the basic centrifuge design (without feed cone) will work too. And for Pir8Darryl that's up to you how complicated you want to get with the centrifuge. I just thought I'd mention the feed cone idea as I really like the design of it.
I also agree it's probably going to give better results to run a 3450 RPM motor direct driving the CF bowl. It's the easiest way and works well. When I built my centrifuge I used a belt drive setup so that the CF bowl would be supported both top and bottom of the shaft but then had to devise a way to seal against the shaft and make a way to access into the bowl to clean it up... for the bit I used it I never did find a good enough seal.


1986 vw jetta 2 tank SVO conversion
1992 vw golf 2 tank SVO conversion
1998 2500 12 valve Cummins diesel with 2 tank SVO conversion
Making biodiesel in the back yard and running WVO in the vehicles with 2 tanks
 
Location: Burk's Falls, Ontario, Canada | Registered: July 05, 2003Reply With QuoteReport This Post
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The trick for getting the WVO somewhat clean is to allow it to settle for a few days. I use a 60 gal. cone barrel and fill it with approx. 45- 50 gals of WVO and allowed to settle for about a week at ambient temps in the two car garage. I built a separate cleaning room with a 350 cfm bathroom fan to suck out the "smell". The settled oil is gravity fed into an unheated steel 55 gal drum, then pumped up to a white 55 gal poly drum laying on its side, then through a gate valve to regulate the flow, then gravity feed to two 1200 watt hot water heater elements controlled through a hot water thermostat set at 140, then the oil drops into the top of the CF. The oil is rather dirty from the restaurant, therefore the cone to settle. I've run several trials to see how many cycles were needed to get the VO the cleanest. I've run the same 45 gals through once and cleaned the bowl of dark sludge; a second time the cf bowl had only slight amount of very fine sludge what wasn't worth cleaning out (although I did clean it out), the third time there was almost nothing but a very slight film. The short of it was run it once and clean out the CF. The proof of how clean the VO is can be summed up with how many miles are driven before the VO filter is changed. I drive about 14K a year. I have not had a plugged VO filter in two years. Had the filtered VO tested via Sandy Brea Water testing system. Raw WVO had 750 ppm of water; CF'd at 1/2 gal/min @140F tested our as 75ppm. I rest my case... IMHO, purchasing a CF bowl and 1/3 hp Baldor motor, 10 qt pressure cooker (really seals off the smell/vapor) for the container and some 1" aluminum pipe. As far as a seal for the motor shaft, check out Forsheda Shaft Seal Corp. "V" Ring #4209-54 or a "V"-16A. Mic the electric motor's shaft for the correct dia. They can be found at 404 Wl Rowland Ave, Santa Ana, CA 92707 800-556-5054.....
Hope this above helps.
 
Registered: October 30, 2005Reply With QuoteReport This Post
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