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renatoa
03/25/2024 12:38 PM
coffee drink, Ramper?

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03/24/2024 12:10 PM
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03/23/2024 3:02 PM
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Exhaust Airflow
BobbyS
Mill City has a lot of info on their site about their roasters. I was surprised at the low max exhaust airflow. On their 2k roaster the max was about 41 cfm.
 
dmccallum
That's interesting to know and thanks for pointing this out.

If they're referring air draw from the roasting chamber, then I've been wondering what a typical commercial roasters metric would be and relevant to my build.
 
BobbyS
this brings into question how much air intake open area is needed. too much and the flow would be very low
 
dmccallum
Have wondered about that also, but assumed you'd be more concerned about the orifice being too small and wind up sucking bean out owing to the increased air velocity ?
 
allenb

Quote

BobbyS wrote:

Mill City has a lot of info on their site about their roasters. I was surprised at the low max exhaust airflow. On their 2k roaster the max was about 41 cfm.


Optimum exhaust air flow on a drum roaster depends on the desired ratio of the two primary heat transfer sources; air and radiant heat from the drum wall. On most Probat current models with dual drum wall construction, they've gone for a higher convection heat transfer versus drum radiant to bean which necessarily requires more air flow than is necessary to just get the chaff and smoke pulled from the drum. If one will be using a single wall design then there's no need to pull more exhaust than necessary to effectively remove the chaff and smoke which is less CFM than most would imagine.

For my 1lb gas drum, I'm guessing I'm not pulling more than around 15 to 20 CFM and there's never a problem with removal of chaff and smoke.

For a 2kg drum with single wall construction, 40 should be more than adequate from my experience.

On air intake area exiting the top front of the drum for 40 CFM I would not go less than 2 1/2" diameter to ensure velocity was low enough to not pull the beans out of the drum. Unfortunately, it's very difficult to measure CFM without setting up proper test conditions and without lab grade tools. It's probably best to go a little over on the design and include an adjustable damper to back it off if velocity is too high.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
dmccallum

Quote


On air intake area exiting the top front of the drum for 40 CFM I would not go less than 2 1/2" diameter to ensure velocity was low enough to not pull the beans out of the drum.

Allen


You had me scared for a moment. For my 2kg drum I'm running with a 1 3/4" exhaust pipe to the cyclone, but I'd increased the roast chambers front plate orifice behind the hopper to what looks like 2 3/4" and I do plan to implement a damper.

Quite a tricky topic this one as it's not easy to measure airflow. Might be a useful guideline for "Links and Formulas Drum Roaster Building" ?
dmccallum attached the following images:
roaster_exhaust_area.jpg roaster_exhaust_area_1.jpg

Edited by dmccallum on 07/03/2017 6:16 AM
 
BobbyS
Good info Allen.

Nice drawings dm

Brings in the question of how large of openings for air in the burner area?
 
allenb
Always leave ample area around the burners for air to flow up, alongside them at very low velocity to ensure you don't cause irregular combustion. There's no known formula that I know of to determine this. You'll know if you have insufficient surface area for the opening if the flame is tossed back and forth and has trouble staying lit.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
BobbyS
ThumbsUp
 
renatoa
I don't see the OP 41cfm figure in the 2kg roaster page... :confused:

https://millcityroasters.com/shop/coffee-roasters/2kg-gas-coffee-roaster/
Roasters: DIY: TO based IR 200-640g
Moded commercial: Skywalker, Dieckmann RoestMeister, Nesco, popper(s).
Electrics: TC4ESP, MS6514, USB/Artisan/Apps, PID controllers
Grinders: Arco, Xeoleo ghost burrs, Krinder, vintage PeDe Dienes, MBK Feldgrind
Brew/presso: ALM pour over, Arin lever, Staresso Mirage, Hario Cafeor dripper, Flair, Kompresso, Rota Aeropress, Gaggia Mini
 
eschlukebir
I think I saw that mill city's roasters now come with double wall drums also.
 
BobbyS

Quote

renatoa wrote:

I don't see the OP 41cfm figure in the 2kg roaster page... :confused:

https://millcityroasters.com/shop/coffee-roasters/2kg-gas-coffee-roaster/


It is shown as 70 m3/h and converted/ 41.2cfm
 
BobbyS
What type of tubing are folks using on exhaust air from the drum on out to the chaff collector? Seems most thin-wall stuff I see is zinc coated or such and I don't know if that would be toxic or if it matters on exhaust.
 
allenb
Doesn't matter at all for that location. For there to be any potential health risk in that location, you would have to be hitting near melting point of zinc which is way over any roasting temperatures you'll ever expose it to.

On the other hand, health guidelines from most agencies do not allow zinc coated metal surfaces to be in contact with food regardless of temperature but with your use of it in the exhaust stream, you should be good to go.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
BobbyS
Thanks Allen! I'm thinking of using EMT conduit since it is easy to find in my area. where I live here in NM we are the end of the pipeline when it comes to supplies..
 
renatoa
Ordered yesterday this fan for my future, design in progress, machine, any thoughts ?

https://www.ebay....2605258131
 
dmccallum
Great price. Main concern I'd have is will it cope with the heat as it appears to be intended for air-con.
Will be interesting to see if it suffices.
 
renatoa
Full metal, what could go wrong ?
Possible paint to burn/peel in the entrance area...
Should worry about motor windings, expect to have 100C degrees in motor area, if placed in (hot) airflow ?

PS: wish I have more smilies, like "thinking", :confused: Grin
 
coffeeroastersclub

Quote

renatoa wrote:

Ordered yesterday this fan for my future, design in progress, machine, any thoughts ?

https://www.ebay....2605258131


Due to coffee oils from the roasting process and the high exhaust heat the fan will fail, maybe not immediately, but it will. Following would be a decent fan for the exhaust application:
https://www.ebay....2227282606
Sometimes you can find them for alot less expense. I purchased 2 a few years ago from surpluscenter.com for around $30 if my memory serves me correct.

Len
"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
 
renatoa
I see the main design difference, the motor is not in the airflow path...
 
coffeeroastersclub
It does not use a squirrel cage fan either, plus there is an outer fan that attaches to the motor shaft (you can see it in the caged area under the motor prior to main fan housing) that keeps that area cool.
"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
 
renatoa
Right, an impeller.

Ok, will look for this motor type for next iteration, we are still in the prototyping phase.
 
hankua
Here?s another photo of what a heat resistant blower for a coffee roaster looks like:
(Sorry photo not uploading)

https://1drv.ms/i...DGnBdHsg-w

Update: This particular fan is perfect for DIY projects as it?s a 24V version with a built in 5V control wire. They sell an inexpensive control board with a knob, so all you have to do is supply 24V DC. There are a couple of different fan blades available for it as well. I?ve got one on a 400g roaster and have seen one on a 1K roaster and thought it was a stretch but worked well according to his Magnehelic gauge.
Edited by hankua on 06/28/2018 10:44 PM
 
BobbyS

Quote

allenb wrote:

Always leave ample area around the burners for air to flow up, alongside them at very low velocity to ensure you don't cause irregular combustion. There's no known formula that I know of to determine this. You'll know if you have insufficient surface area for the opening if the flame is tossed back and forth and has trouble staying lit.

Allen


do you think air from the bottom would be enough for two pipe burners, or would it also need side venting?
 
allenb
Shouldn't need any side venting and I would recommend against it to lessen chances of unwanted turbulence across the flame. See this post showing a typical Probat with bottom updraft makeup air.

https://forum.hom...post_52286

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
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