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Convection, Conduction, Radiation - Heat Transfer Ratios!
seedlings
Smaller version of what HVAC uses? Like when you look up at the ductwork at Lowe's?

Click on the picture to enlarge a little.

CHAD
seedlings attached the following image:
13heatgunductwork.jpg

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
dBndbit
I like the idea of experiments and shoot-outs! Though we may run into problems trying to isolate the heat modes (contact, air, IR).

As I understand IR, all objects above the temperature of absolute zero are always radiating heat at some wavelength. So everything hot in the roaster is also radiating heat energy. It doesn't matter how things get hot, just that they are hot. The hotter they are the more they radiate, but the radiated energy also includes shorter and shorter wavelengths. At very high temperatures, objects start to radiate at wavelengths so short we can see it as a dull red glow. IR and visible light are the same thing, just different wavelength ranges.

Point being that isolating an 80+% any-one-mode of roaster may be difficult. I suspect a high-speed air spout roaster might be the only true high-percentage "convection" roaster, though convection is really the wrong word for this. And even so, the hot metal surfaces of the roast chamber get hot and become an IR source for the beans in addition to whatever they may catch from the air or conduct by contact.

Same would be true in any drum with or without perforations. Once heated to 450-500F, a solid drum becomes a source of IR for the beans. Even a hot air gun is radiating a huge amount of IR anywhere you can see the heat elements. (line-of-sight) That's one of the reasons their heating effect diminishes so quickly when you back off. IR effects drop at a strict inverse square of distance unless reflected or focused.

I guess what I'm saying is that I think IR can play a bigger role in pumping up the efficiency of most any roaster if it's given the chance by using reflective metals. And it might be a mistake to over-simplify our thinking about how heat energy is working at any given point in a roaster.

I really like Marshall's (endlesscycle) view of:

Quote

analyzing your roaster design in the shoes of a coffee bean with an engineering degree

Be the bean.

Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
stuartgrant
Hey Chad - just a quick one.

Can you provide a link to the ducted-HG roaster you mention? I've done a fairly comprehensive search of this forum but couldn't find anything... what can you tell me? It sounds great!

Cheers
Stu.
stuartgrant
Hey Jim - great (very insightful) comment - thanks!

Your explanation of how ALL hot objects emit IR was really useful for getting a mental picture of what's going on - especially in a traditional drum roaster.

Based on that, do you reckon the ~2% figure for "most modern drum roasters" (Ambex Roasters link - first post) is likely to be accurate? Intuitively, I'd guess it to be higher, but perhaps the magnitude of IR emitted by hot metal is fairly low? Any thoughts? (As you said in you first post, these questions might be unanswerable with any degree of certainty, but I'll settle for educated anecdotes from guys like you who I'd trust on these matters!)

Cheers
Stu.
endlesscycles
Here's some required reading:

http://www.sweetm...ept-03.pdf
http://www.ambexr...icles.html
-Marshall Hance
Asheville, NC
dBndbit
Stuart,
Don't trust me! I'm just an amateur who reads a lot. I have zero experience with professional roasting machines. My background is electronics.

Why do people assume that IR absorption depends on color or darkness in visible light? Visible light is a tiny band of frequencies covering just a 2:1 range of wavelength. IR covers more than a 100:1 range. The coffee bean may look completely different across that wide spectrum.

I gotta say that when somebody from Ambex says:
"You can neither measure [IR] nor control it..." and
"The rate and ratio of radiation in a roaster is an unknown",
I have to suspect the person just doesn't know the answers and is trying to make me concentrate on something else: using his machines rather than understanding them. In fairness I'm sure that engineering details were beyond the purpose of the document. I have no doubt that Ambex roasters are fine machines, but those comments are very unsatisfying.

IR can certainly be measured and controlled by design, if not by the knobs and levers on an Ambex. In the past I once purchased and use some very fine lab equipment for measuring IR. But for some reason when I retired they wouldn't let me keep any of them.

I wonder why I couldn't make my own sensor from a set of filtered IR photodiodes from Digikey. Sensitivity could be crude and I could probably work up my own calibrator with a piece of metal of known emissivity and a temperature probe. I need to think about this more.

You are asking the right questions. Don't stop just because the answers (or people who already know the answers) are hard to find.
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
seedlings

Quote

stuartgrant wrote:
Hey Chad - just a quick one.

Can you provide a link to the ducted-HG roaster you mention? I've done a fairly comprehensive search of this forum but couldn't find anything... what can you tell me? It sounds great!

Cheers
Stu.


Sorry, Stu, but it's imaginary. I can imagine pictures of glorius wonders, but get bogged down in reality. You should be able to make something like that. Bigger tube, smaller tubes...?

Oh, and great links, Marshall ThumbsUp

CHAD
Edited by seedlings on 09/06/2009 8:26 PM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
stuartgrant
Hi all,

#Marshall - thanks for those links. The Ambex roasters article (The Heat is On) was one of the main triggers in getting me thinking about these issues. Great read. The other link was also a good read.

#Jim - you're humble, too?? ;) Thanks for the opinion on the article's failure to address IR heat transfer. If I were to hypothesise why that's the case, I guess it would be one or both of: 1) total radiated heat transfer is too hard to measure (for the reasons you stated), and/or, 2) they consider it too low a proportion of the total heat transfer to bother measuring properly... Not sure which!

#Chad - aah, imaginary. Oh well; you're right about the general principle being fairly easy to replicate. What about a stirring paddle with jets of hot air streaming out of it as it spins?? Ok, that would be a nightmare to pull off!


Someone posted today on Coffeesnobs about an experiment they tried with their Corretto where they managed to get to FC in 5-6 minutes by starting the roast with just the BM element (to 50C/122F), then with the HG on low (for another minute), before proceeding as normal (HG on high etc...). They managed to avoid any tipping by doing this. There's no way our HG-only Corretto could do that without tipping.

In any case, I'd prefer to reach FC around 10-12min, but the principle is very useful! I think it (anecdotally) suggests that using a non-convective heat source (or by limiting air flow) at the beginning of the roast, the beans have a chance to dry out more evenly and are less prone to tipping later on. I think this is what happens in a drum roaster; most of the conductive heat transfer happens fairly quickly at the beginning of the roast - and the convective heating takes over from the point of equilibrium onwards.

Hot air (especially early in the roast) would tend to dry out the tips, leaving them prone to tipping. That's my theory.

How does that sound?
Cheers
Stuart.
Edited by stuartgrant on 09/07/2009 7:05 AM
Koffee Kosmo
I have found that everything works at its peak on a sweet spot
With a car its a certain RPM

Its my belief that roasters work the same way as our bodies do
Lungs to fan and stoke the fire
Stomach to roast and change a chemical state
Intestines to remove the chaff

So
The sum of all working parts must work in harmony for best results

Did I just come up with a quotable quote B)

KK
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
stuartgrant
Hey KK,

Yeah, I'd say that was quotable. ;)

There are so many factors involved:
- amount of heat
- type of heat
- directionality of heat
- air flow
- thermal mass of roaster itself
- volume of roasting chamber

So you're right - it's always going to be a matter of balancing these things in a design.

---

Another tangent, then. What did you say the volume of the roasting chamber is in your TO roaster KK? And what volumes did the previous (perhaps less successful) iterations have?

Anyone else... what roasting chamber volumes do you use and what % of it is filled with green beans?

Cheers
Stuart.
stuartgrant
Just another FYI:

Been looking at air flow of heat guns. Most are:
250 l/min on low setting (if applicable) - 8.8 cu.ft/min
500 l/min on high setting - 17.7 cu.ft/min

I was surprised to discover that the HG we use (Ryobi 2000W LED) can be used on the lower fan speed at up to the 550C setting (ie. 90% of full heat). Might have to try that. Carefully... as Chad pointed out above.

I'd love to know how this compares to turbo ovens, but this info isn't easy to find. Does it say on the box anyone? I might email someone at Tiffany!

Cheers
Stuart.
Koffee Kosmo

Quote


Another tangent, then. What did you say the volume of the roasting chamber is in your TO roaster KK?


I have calculated my current roaster volume with false floor
it is * 11 litres
Go to this site and find out what is your roasters volume
http://www.online...volume.php

Quote

And what volumes did the previous (perhaps less successful) iterations have?


15 litres in volume at the start of the modifications

Don't forget that insulation has been a contributing factor as well as the speed of agitation as noted below

Just today I roasted a 900gr batch just as an experiment
As I have been testing different power supplies for the new Kit Roaster
The original roaster that everyone knows with the window winder motor is not fused and the more amps you give it the faster is spins
I used a 12 Volt 5 Amp lap top power supply
70RPM was the agitator speed

Single batch 900gr of PNG Kinjibi AA
First snaps 10.30 min
Rolling FC 12.10 min
Second snaps 18 min but slow
Building to good SC at 20 min

Did it without a hiccup

Quote

I'd love to know how this compares to turbo ovens, but this info isn't easy to find. Does it say on the box anyone? I might email someone at Tiffany!


The Tiffany TO fan is very gentle It is softer than a regular fan forced oven
If I was to guess at the RPM of the chaff spinning at the bottom it would be approx 50 rpm so not fast or forceful at all but it is a closed system so the heat penetrates the beans with a little help of pressure

Here is a photo of that 900gr batch
KK
Koffee Kosmo attached the following image:
png_kinjibiaancu.jpg

Edited by Koffee Kosmo on 09/11/2009 8:29 PM
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
farmroast
Agitation is to heat transfer as the grinder is to espresso. Well designed aggressive agitation greatly improves heat transfer. Mechanical agitation is the easiest to keep consistent but the design needs to be complex. Fluid bed are tough to get the bean action just right. Higher bean agitation makes more noise and harder to watch and for off the shelf roasters I think are common complaints and why many are too tame. Hearing first crack tells little to me anyway. Bean temp and roast chamber temp ET will tell you more about how the beans are reacting to the heat being applied. The Loring roaster uses a fixed drum with moving paddles. I went the convection oven top for it's direct heat application. Spread out evenly over a decent sized area. I supplement a lower plate heater to balance the heat application top to bottom. Then added high speed bean bats to get the beans airborne. The heat gun is direct application but the application is small in area.
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills http://coffee-roa...gspot.com/
Koffee Kosmo
Thanks for that input & nice to hear from you again Ed

I had a gut feeling that if the agitator speed was increased it was possible to roast a larger batch

Just goes to show the tweak-ability of this TO design. It's one of my favourite things about it
However apart from the great roast results, another one of my favourite parts is the chaff separation

I love to tinker

KK
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
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