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 Air Roaster
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| zena13 |
Posted on 02/06/2008 2:29 PM
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 Newbie  Posts: 18 Joined: February 06, 2008 |
I am a newby but have been reading numerous posts on this site and have found lots of great information. I have been considering building a fluidized bed roaster for some time now and have read many posts and articles about the subject. Many have talked about building their own heating elements. Would it not be possible to use a tubular dryer heating element. Maytag for example uses an element that is inside a 6 inch diameter duct. These units are 220v and produce 4,000-5,000 watts. That should be plenty of heat. My idea is to attach a vacuum motor to the lower end of the element and roasting chamber at the upper end. The heater could be controlled by a thermocouple in the roasting area connected to a digital heat controller. This should cycle the element off and on to maintain a constant temperature. Am I over simplifying things ? |
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| Justin Marquez |
Posted on 02/06/2008 4:39 PM
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Newbie Posts: 31 Joined: December 31, 2007 |
Quote zena13 wrote: I am a newby but have been reading numerous posts on this site and have found lots of great information. I have been considering building a fluidized bed roaster for some time now and have read many posts and articles about the subject. Many have talked about building their own heating elements. Would it not be possible to use a tubular dryer heating element. Maytag for example uses an element that is inside a 6 inch diameter duct. These units are 220v and produce 4,000-5,000 watts. That should be plenty of heat. My idea is to attach a vacuum motor to the lower end of the element and roasting chamber at the upper end. The heater could be controlled by a thermocouple in the roasting area connected to a digital heat controller. This should cycle the element off and on to maintain a constant temperature. Am I over simplifying things ? My HySys process simulator says that with a 5 KW heat input, 60 deg F air to be heated up to 750 deg F (arbitrary guess) that you need about 22 cubic feet per minute of air flow (about 100.7 lb/hr) to make it all balance out. Now that is one big hot-air popcorn popper! Safe Journeys and Sweet Music!
----------------------------------- Coffee gear: HG/DB and RK Drum, Solis Maestro Plus, Cuisinart 975 Drip, Presspot, Aeropress and "cowboy coffee" |
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| seedlings |
Posted on 02/06/2008 5:08 PM
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 1 1/2 Pounder  Posts: 4226 Joined: June 27, 2007 |
Great post, zena13! If you have enough air blowing to move the beans and enough heat to hit at least 450F, you have a roaster. The basics are that simple. I've always had trouble in the excruciating details it takes to connect the simple things together! Things like how to make the hopper, or how to connect the blower permanently. And, don't forget to overengineer. In other words, use more air flow and more heat than you think you'll need. You can always turn down the heat or the motor. The other side of overengineering is to lessen the amount of beans you'd like to roast. What quantaty of beans would you like this roaster to handle? Great ideas! CHAD Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| zena13 |
Posted on 02/06/2008 6:37 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
Yes, my feelings were that the dryer element is readily available and you can cycle it off and on to maintain temperature. Round duct is also very easy to work with. |
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| Kaffee Bitte |
Posted on 02/07/2008 12:09 AM
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 1 1/2 Pounder Posts: 613 Joined: May 11, 2007 |
Very interesting thoughts on the air roaster theme. And welcome zena13. I will be watching avidly as you work up your roaster!
Lynn
"Some days it's spice, other days it's bitter dirt." |
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| seedlings |
Posted on 02/07/2008 8:40 AM
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1 1/2 Pounder Posts: 4226 Joined: June 27, 2007 |
Quote zena13 wrote: Yes, my feelings were that the dryer element is readily available and you can cycle it off and on to maintain temperature. Round duct is also very easy to work with. Just be sure you don't use any galvanized ductwork. The galvanized coating can burn off into your coffee. Not healthy. But, never fear, aluminum is always near! Find the duct you'd like to use, but be sure it's aluminum, then you don't have to worry. (my first air roaster used galvanized ductwork. I learned this info from the experts who informed me about safety) Here's to engineering success! CHAD Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| Dan |
Posted on 02/07/2008 9:06 AM
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 1 1/2 Pounder Posts: 1662 Joined: October 24, 2005 |
zena13, I think you are on to something! Some motors are dual voltage, and PIDs can work at 220V, too. You might be able to make the whole thing run on 220V without having to resort to multiple power input (a safety issue). |
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| nhamilto40 |
Posted on 02/07/2008 9:03 PM
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 Newbie Posts: 31 Joined: December 05, 2007 |
You may have problems using a dryer element. These elements are usually living right on the edge. They are designed with the assumption of plenty cool air flow. Reduce the amount of air/raise its temperature and the element may fail. |
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| zena13 |
Posted on 02/07/2008 9:18 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
I have built a mock up using 6" round air duct and the vacuum motor has plenty of flow to raise 2 lbs. of beans. Too much in fact so I will need to throttle it down. I picked a new dryer element on eBay for around 30.00 to test. If it fails it will be on to plan B, finding a heavier duty element. |
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| seedlings |
Posted on 02/07/2008 10:31 PM
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1 1/2 Pounder Posts: 4226 Joined: June 27, 2007 |
Pictures, Z, pictures! Let's see your mock up, pretty please? CHAD Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| dBndbit |
Posted on 02/08/2008 7:21 PM
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 1/2 Pounder  Posts: 268 Joined: January 13, 2007 |
Great thread! Maybe I can stir the broth too. I'm working on a similar build and I agree with nhamilto40's cautionary words. One way to look at a specific heating element is that it was designed to raise the temperature of air flowing at a specific rate by a certain number of degrees using some standard volts and watts. And we all know appliance designers are never allowed to over-design the products. They can do what they need to do and not much more. Normal clothes dryers and hair driers raise air temps something like 100F. In roasting coffee we need to raise air temp by 500F. That's a 5x rate of climb faster than designed. The rate of increase looks a little more achievable if you convert to Kelvin where the change looks like about a 2x increase. But how is that going to happen? Something needs to be physically 2-times better than it was in the original equipment. If nothing else changes, the air would have to move 2x slower. The amount of necessary improvement won't be exactly 2, but that's the general idea. We're asking a lot. All the parameters above work together and affect each other. More air flow needed to loft the beans means lower air temp unless you can compensate by improving something else even more. However, I wanted to suggest that there is one additional parameter: the physical arrangement of the coil in the air flow. It might be a big help to re-make the heating tube so the air is forced to get much closer to the coils and longer so the air has more time to pick up heat. Not sure how much help it will be, but it's something to think about. One other detail. I've been playing with numbers and I think it might take hot air (561K) moving at 114 ft/s to loft coffee beans. But that's just my (high-end) guess. It was calculated assuming coffee beans have the same drag coefficient as a smooth sphere (0.1). If I assume a bean is more like a bullet, the drag is 0.295 and the necessary air velocity becomes 66 ft/s. I'd be really interested to hear what anyone thinks about air speed. The trouble with predicting moving air performance is that Reynolds numbers and drag coefficients are impossible to guess. I think I'll check the US Department of Agriculture website to see if they publish the drag coefficients for peas, beets, and green coffee beans. Probably it's better science (and more fun) to just build something and try it. Got a fire extinguisher? Edited by dBndbit on 02/08/2008 8:36 PM |
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| zena13 |
Posted on 02/08/2008 9:36 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
I agree that a dryer is manufactured to operate at a temperature well under the temperature require to roast coffee beans. I also believe that a 5kw element will produce a temperature in excess of 500 degrees if regulated in a different manner. The question is at what point will it fail. In a dryer application the thermostat cycles the element off and on. There is a high limit switch that shuts down the element if temperature exceeds a certain temperature. My memory tells me it is something like 240 degrees. A dryer is not designed to operate at 500 plus degrees because it is not required to do the job. If left on for a longer period of time I think the element will produce more heat within the chamber. |
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| Justin Marquez |
Posted on 02/08/2008 9:40 PM
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Newbie Posts: 31 Joined: December 31, 2007 |
Quote zena13 wrote: I agree that a dryer is manufactured to operate at a temperature well under the temperature require to roast coffee beans. I also believe that a 5kw element will produce a temperature in excess of 500 degrees if regulated in a different manner. The question is at what point will it fail. In a dryer application the thermostat cycles the element off and on. There is a high limit switch that shuts down the element if temperature exceeds a certain temperature. My memory tells me it is something like 240 degrees. A dryer is not designed to operate at 500 plus degrees because it is not required to do the job. If left on for a longer period of time I think the element will produce more heat within the chamber. There's not much magic in a heater element. All the KW goes into heating the element first and then the air passing over it. More air flow = lower temps on both the element and in the airflow. To get higher air temps, reduce the airflow. Do that radically enough and the element melts! Safe Journeys and Sweet Music!
----------------------------------- Coffee gear: HG/DB and RK Drum, Solis Maestro Plus, Cuisinart 975 Drip, Presspot, Aeropress and "cowboy coffee" |
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| Dan |
Posted on 02/09/2008 6:46 AM
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1 1/2 Pounder Posts: 1662 Joined: October 24, 2005 |
Some heating elements are designed to only be used with air flow and will indeed 'fuse'. Others are designed to be used in still air and will never overheat, your kitchen toaster for example. It all depends on its design. I wish I knew more about that topic, but I'll leave it to others to figure out. |
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| zena13 |
Posted on 02/11/2008 7:28 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
Well, I tested the dryer element today and some of you that posted were pretty much dead on. With unrestricted air flow from the vacuum motor out the top of the 6 inch pipe the coils barely glowed. The temperature was about 190 degrees. When I switched off the vacuum the coils immediately began to glow red. I think I need to add a temperature controller to see if the current coils can withstand 450 degrees with little or no air flow. If not I may need to restring the coils with some that are rated at a higher temperature. As for air flow I am thinking that I might need to funnel it around the heating element. Possibly through a double wall pipe sort of arrangement. |
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| seedlings |
Posted on 02/11/2008 9:16 PM
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1 1/2 Pounder Posts: 4226 Joined: June 27, 2007 |
I've always wondered if one of those dryer elements was bendable. What do you think, Zena13, could you bend it to a different shape without breaking? I'm not saying to go try it, but feel it out and give us your thoughts about how brittle it is. Keep experimenting and don't give up! I'm stuck at the moment in my design and theory... but sometimes ideas come from the strangest places. This is a strange place B) CHAD Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| zena13 |
Posted on 02/11/2008 10:03 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
Chad, The element that I am using is a coil element suspended by ceramic insulators inside a 6" duct pipe so the element itself is very flexible. I would love to know how Sivetz manages the air flow on their 5, 8 and 12 lb roasters. I love to tinker so I won't be giving up the fight anytime soon. |
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| Dan |
Posted on 02/12/2008 4:50 AM
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1 1/2 Pounder Posts: 1662 Joined: October 24, 2005 |
Chad, if you want to increase the temperature, start shortening that heating coil. But first, you'll have to figure out what that airflow really is. |
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| seedlings |
Posted on 02/12/2008 8:32 AM
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1 1/2 Pounder Posts: 4226 Joined: June 27, 2007 |
Quote zena13 wrote: Chad, The element that I am using is a coil element suspended by ceramic insulators inside a 6" duct pipe so the element itself is very flexible. I would love to know how Sivetz manages the air flow on their 5, 8 and 12 lb roasters. I love to tinker so I won't be giving up the fight anytime soon. Wellll, you learn something every day. I thought a dryer would have a heat element more like the electric oven in my kitchen. Woops. Regarding air flow, I'm not sure about the Sivetz, but in the -->Sonofresco<-- you must use a specific amount of green coffee, one "tin can" scoop. I believe there is no airflow adjustment, and the amount of coffee IS how airflow is controlled. CHAD Edited by seedlings on 02/12/2008 8:33 AM Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| dBndbit |
Posted on 02/12/2008 8:46 AM
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1/2 Pounder Posts: 268 Joined: January 13, 2007 |
Not sure how much help it will be, but on my website I just put up some of the math for calculating air flow and also some of the reference links. Since I haven't done anything physical yet, as Zena13 is doing, I'm really interested in how you end up setting the air flow and all the physical dimensions, etc. Don't give up! The air flow stuff is on the page for my 10K Roaster Project. Don't expect much since I'm just getting started. Any feedback is greatly appreciated, PM or public. |
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| seedlings |
Posted on 02/12/2008 9:59 AM
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1 1/2 Pounder Posts: 4226 Joined: June 27, 2007 |
Quote dBndbit wrote: Not sure how much help it will be, but on my website I just put up some of the math for calculating air flow and also some of the reference links. Since I haven't done anything physical yet, as Zena13 is doing, I'm really interested in how you end up setting the air flow and all the physical dimensions, etc. Don't give up! The air flow stuff is on the page for my 10K Roaster Project. Don't expect much since I'm just getting started. Any feedback is greatly appreciated, PM or public. Good stuff, dBndbit! All I have to add is this resource: http://heatersplu...at-sel.pdf On page I-16 talks about requirements to heat moving air. CHAD Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover |
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| zena13 |
Posted on 02/12/2008 8:45 PM
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Newbie Posts: 18 Joined: February 06, 2008 |
I have now restricted the flow down to about 1-1/2" into my makeshift 6" roast chamber and am seeing temperatures upwards of 380 degrees and the element does not appear to be overworking itself. If nothing else it makes a great space heater !!! Just out of curiosity i checked the temperature of my air popcorn popper and it was only 308 degrees. It roasts fine so it makes me wonder if my thermometer is accurate. I did pick up one of the 9.99 router speed controls at our local Harbor Freight and it works great. I guess I am making some progress |
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| Justin Marquez |
Posted on 02/12/2008 9:32 PM
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Newbie Posts: 31 Joined: December 31, 2007 |
dBndbit said (on your website): "As an aside, air temp is important because as it heats up it becomes less dense and therefor exerts less force on objects. The effect is that very hot air at 550?F needs a speed of 78 ft/s to lift beans, but room-temp air at 68?F would lift the beans at only 56 ft/s. Using a one-speed fan, the beans will spout differently as the roaster heats up. " Which I do agree with. In addition, as the beans roast, they become less dense (both lighter and larger) and will fluidize at lower air speeds. Edited by Justin Marquez on 02/12/2008 9:34 PM Safe Journeys and Sweet Music!
----------------------------------- Coffee gear: HG/DB and RK Drum, Solis Maestro Plus, Cuisinart 975 Drip, Presspot, Aeropress and "cowboy coffee" |
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| Dan |
Posted on 02/13/2008 8:43 AM
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1 1/2 Pounder Posts: 1662 Joined: October 24, 2005 |
My experience with spouting is the opposite of yours, Justin. When I turn on the heat (adds energy) the beans spout more, not less. To me, its like the effect of a small afterburner kicking in. Variable speed on your blower is a must have, to me. Dan |
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| Justin Marquez |
Posted on 02/13/2008 11:45 AM
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Newbie Posts: 31 Joined: December 31, 2007 |
Quote Dan wrote: My experience with spouting is the opposite of yours, Justin. When I turn on the heat (adds energy) the beans spout more, not less. To me, its like the effect of a small afterburner kicking in. Variable speed on your blower is a must have, to me. Dan A variable speed fan would be a great place to start! Probably what you see is that the blower suction is on the cool air side (at a relatively constant rate) and then when the air heats up, it's velocity increases due to the lower density. This would explain the kick you are seeing. Now, as moisture is removed from the beans, they get less dense and more easily "fluffed". As they hit first crack and expand, that "fluffing" is accentuated even more. Edited by Justin Marquez on 02/13/2008 11:47 AM Safe Journeys and Sweet Music!
----------------------------------- Coffee gear: HG/DB and RK Drum, Solis Maestro Plus, Cuisinart 975 Drip, Presspot, Aeropress and "cowboy coffee" |
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