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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Drum Roasters

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Page 1 of 2: 12

Exhaust Airflow
BobbyS	#1 Posted on 06/30/2017 2:32 AM
1/4 Pounder Posts: 179 Joined: July 02, 2011	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	#2 Posted on 06/30/2017 10:12 AM
1/4 Pounder Posts: 93 Joined: November 24, 2015	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	#3 Posted on 06/30/2017 3:51 PM
1/4 Pounder Posts: 179 Joined: July 02, 2011	this brings into question how much air intake open area is needed. too much and the flow would be very low


dmccallum	#4 Posted on 07/01/2017 4:11 AM
1/4 Pounder Posts: 93 Joined: November 24, 2015	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	#5 Posted on 07/01/2017 12:56 PM
Administrator Posts: 3650 Joined: February 23, 2010	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	#6 Posted on 07/03/2017 6:01 AM
1/4 Pounder Posts: 93 Joined: November 24, 2015	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: Edited by dmccallum on 07/03/2017 6:16 AM


BobbyS	#7 Posted on 07/04/2017 1:19 AM
1/4 Pounder Posts: 179 Joined: July 02, 2011	Good info Allen. Nice drawings dm Brings in the question of how large of openings for air in the burner area?


allenb	#8 Posted on 07/04/2017 4:55 PM
Administrator Posts: 3650 Joined: February 23, 2010	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	#9 Posted on 07/05/2017 1:28 AM
1/4 Pounder Posts: 179 Joined: July 02, 2011


renatoa	#10 Posted on 07/05/2017 11:05 AM
Administrator Posts: 2497 Joined: September 30, 2016	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 640g Moded commercial: 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: Flair, Kompresso, Rota Aeropress, Hario Cafeor dripper, Gaggia Mini


eschlukebir	#11 Posted on 07/06/2017 7:55 AM
Newbie Posts: 22 Joined: October 06, 2016	I think I saw that mill city's roasters now come with double wall drums also.


BobbyS	#12 Posted on 07/06/2017 7:55 PM
1/4 Pounder Posts: 179 Joined: July 02, 2011	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	#13 Posted on 07/09/2017 2:54 PM
1/4 Pounder Posts: 179 Joined: July 02, 2011	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	#14 Posted on 07/09/2017 6:52 PM
Administrator Posts: 3650 Joined: February 23, 2010	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	#15 Posted on 07/14/2017 5:20 PM
1/4 Pounder Posts: 179 Joined: July 02, 2011	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	#16 Posted on 12/22/2017 2:55 AM
Administrator Posts: 2497 Joined: September 30, 2016	Ordered yesterday this fan for my future, design in progress, machine, any thoughts ? https://www.ebay....2605258131


dmccallum	#17 Posted on 12/22/2017 4:03 AM
1/4 Pounder Posts: 93 Joined: November 24, 2015	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	#18 Posted on 12/22/2017 5:28 AM
Administrator Posts: 2497 Joined: September 30, 2016	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:


coffeeroastersclub	#19 Posted on 12/22/2017 3:22 PM
Pounder Posts: 535 Joined: May 26, 2009	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
	Web

renatoa	#20 Posted on 12/22/2017 3:58 PM
Administrator Posts: 2497 Joined: September 30, 2016	I see the main design difference, the motor is not in the airflow path...


coffeeroastersclub	#21 Posted on 12/22/2017 5:18 PM
Pounder Posts: 535 Joined: May 26, 2009	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
	Web

renatoa	#22 Posted on 12/23/2017 1:39 AM
Administrator Posts: 2497 Joined: September 30, 2016	Right, an impeller. Ok, will look for this motor type for next iteration, we are still in the prototyping phase.


hankua	#23 Posted on 12/25/2017 6:37 PM
Newbie Posts: 21 Joined: March 21, 2011	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
	Web

BobbyS	#24 Posted on 06/28/2018 1:06 AM
1/4 Pounder Posts: 179 Joined: July 02, 2011	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	#25 Posted on 06/28/2018 5:51 PM
Administrator Posts: 3650 Joined: February 23, 2010	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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