August 19, 2018 21:13:40


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3d Printed Fluid Bed Roaster
Great circulation. How long did the 12oz roast take with your single element? Was it 1600W or did you change it?
I believe it's a 1680W element. The roast took 14 minutes, but ran at only an average of 940 watts. I used a ramp programmed to slowly bring the beans up to temp over 14 minutes, so it seems that it could have been quicker with a more aggressive ramp.

This design may be slightly more efficient than others, as the element is encased in insulating refractory material rather than heat conducting metal. Similarly, the bowl of the roast chamber itself is insulating and has a high heat capacity, it is room temp where it meets the plastic base, and only reaches about 130 degrees near the joint with the Pyrex tube. Additionally, the topper increases internal pressure in the roast chamber and prevents hot air from venting out the top too quickly.

Cupped today and happy with the result. Fuller body than my previous attempts with these Brazilian beans.

When the heat element is switched off the beans are cooled to 100c within 15 seconds and 40c within a minute or so. I do need a good way to eject and am wondering if the vacuum pressure would be enough to do so if I capped the top with a tube inserted into the bean mass.
Edited by Linnaeus on 02-20-2018 03:50
A quick modification - I added an aluminum plate to the rear of the chamber. Beans were circulating well in the front but we're stalling quite a bit in the rear. The new / steeper wall is giving a much better motion to the bed.

In the future I would not experiment with an off axis inlet unless all of the walls were significantly steeper than they are in my roast chamber.

Great efforts. I would be interested to buy from you the ready roasting chamber as you already have the molds. it is not wrong to sell them to cover your costs. but the size is too small. thanks
Thanks Husamka - I'm not sure that it's really ready for mass production, but maybe I'll make a few batches once it's optimized.

In other news, I added a small disc in the center of the roast chamber inlet to agitate the air and fluidize the whole bed a bit more (rather than spouting just in the center). This has made the roasts more even and predictable, but has reduced the maximum roast volume down to 180g or so.

The issue is airflow and the 120W vacuum just isn't enough. I've printed some parts to add a 6W 80mm fan to the vacuum intake. Curious to see if an Axial/Radial combo will be more efficient. At the very least, the benefit is that I can turn off the vaccuum motor (which is obnoxious) and just leave the 80mm fan running while the roaster cools off (after ejecting the beans).

So this would be an axial compressor into a radial compressor. The thinking is that the radial compressor is optimized for high pressure, but maybe not high airflow. Adding an axial fan to the inlet will drive SLIGHTLY more air into the radial compressor, hopefully raising the static pressure (bean mass) at which it stalls. They may have an interesting interaction... the axial fan stalls readily with any back pressure, but in this configuration it will actually have a pressure deficit... I have no idea what impact this will have on the performance characteristics, because all the charts I can find show a positive static pressure at the fan outlet.

At the worst, it's just additive - which would have a minimal impact as the pressure capabilities of the axial fan are so poor.

I'm no this is really some bunk science going on here. I'll let the results speak for themselves once this is testable.

Edited by Linnaeus on 03-27-2018 06:46
So, no surprise...there is no magical pressure gain in stacking an axial and radial fan in series. The axial fan had almost literally no effect.

Then I remembered that I had a few 24V - 0.83A squirrel cage fans lying around. I printed up a quick adapter for one and added it to the intake before the vacuum motor. This did have a noticeable effect, allowing me to loft approximately 20% more beans by weight.

Lesson learned - compressor pressure is roughly summed in series. The exception is when a compressor is outside of its "stable" pressure rating (static pressure too high) - in which case the compressor will be stalling. Adding another compressor in series will bring it out of stall and then the gains will be much greater.

Another fun discovery: A bowl of water makes a surprisingly good chaff collector:
Added a conical separator for chaff management.

Nice! Is that one of the small cyclones from ebay?
Yep, looks as mine, different cased but same.
eBay search terms: "Aluminium Cyclone Separator"
It is - works really well too. I used a paint can from home depot as an outer housing. Allows it to be mounted to the top of a mason jar. I just cut a hole in the bottom and bolted on a mason jar top minus the inner sealing plate.
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