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Krypton roasting? (not Superman's)
dBndbit
I've been running through some free-thinking blue-sky ideas on roaster theory before I start my next project. For all roasters that aren't primarily IR-based, one of the natural limitations is the density of air. The density of the heat transfer medium limits how fast we can transfer heat inside the bean.

Air is mainly nitrogen and oxygen, both with similar densities. Most other safe and available industrial gases also have about the same or lower density. But krypton is somewhat unique because it's a safe, inert gas available from industrial and lab suppliers, but it has 3x the density of air.

Has anybody heard anything about pre-charging a recirculating roaster with krypton? Theoretically it should increase the batch size, cut the roast time or raise the oven efficiency by a factor of 3.

From what I see in my roaster, little or no venting is required up until first crack. At that point most of the energy has been added to the beans and the rest of the roast is mainly exothermic (pyrolysis). After that normal air-fed venting could begin to remove smoke and combustion gases. It seems like a krypton fill with no venting could make a big difference.

Sanity check?
Edited by dBndbit on 01/26/2008 10:10 AM
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
Kaffee Bitte
As a purely thought experiment I have some thoughts about this idea. One thing you will have to really focus on is sealing the roaster very well. Seems that using krypton might be expensive after a while so look for a way to pull into another container as well. The expense of it though might keep you from doing this.

For the heat transfer part, how fast are you wanting to bring the beans to 1st? Too fast and you will not get the most from the coffee. Then there is the concern that once you are up to 1st you will not be able to control the roast enough to extend the time before 2nd, even with an influx of normal air. Infact the air added in might drop the temperature too low, thus stalling the roast.

Another thing to consider is flavor. Krypton is an inert gas, but it may very well effect the coffee flavor wise.
Lynn

"Some days it's spice, other days it's bitter dirt."
seedlings
I'm not qualified to hazard any comments...

...but that won't stop me. My very first thought is there will be enough small leaks the gas will be displaced with regular air so fast it won't make a difference. If we're just talking theory, why not throw in zero gravity so the beans will need only an eensy-weensy bit of krypton flow to get the beans circulating? I'm probably amusing no one but myself with the zero gravity comment. Sorry.

I always say let's never be limited by convention! Keep it up, Jim!

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Alchemist
And while theory is being discussed - density is not heat capacity. Just because it is more dense doesn't mean it will hold three times the heat.

And there is no reason it should increase efficiency by 3x either even if it was heat capacity being discussed.

Finally quite a bit of venting is needed before 1st crack - all that moisture has to go somewhere, and in a mixing environment, there is no way the krypton and water vapor are not going to mix and be separably. When you vent one, you vent the other.

Sanity check - unknown, but the theory has some holes. I love thought experiments though....
Kaffee Bitte
Alchemist has a good point about the heat transfer. Maybe do some searches online to find out what the heat carrying capacity of krypton is. It has to be out there somewhere.
Lynn

"Some days it's spice, other days it's bitter dirt."
dBndbit
Thanks for the sanity check. Though of course in a forum of dedicated home roasters, we can't hope for much of that! And who wants sanity anyway? It just spoils a lot of fun.

But seriously, folks...
As an inert gas, I would not expect it to have any effect on coffee flavor. And the free oxygen/nitrogen in normal air that would be displaced by the krypton aren't big players in roasting chemistry. It's all going on inside the bean.

Keeping the gas in the roaster is a concern. You can't seal any oven tightly (except a pressure cooker) because as things heat up, the gases expand hugely. But that means the flow is going to be all outward! I should be able to inject a small charge, 2-3 cubic feet at room temp to fill the oven. Then start the heating process. The main rise in temperature, where most of the heating power is required, is the initial period up to 1st crack. Even with a few small leaks, the heavier krypton should just continuously expand and the roaster should not exchange much air outside to inside. At any rate, I thought a considerable percentage of krypton should persist for the few minutes till 1st crack. After that we wouldn't need it.

There's about 1.5 oz of water in a pound of beans, most of which would escape out of the oven with the hugely expanding gas. And I think what's left will only help the heating process. The heat capacity of krypton is only about 30% less than nitrogen/oxygen which would still leave me with a 2x heating improvement from the 3x higher density. It could result in faster roasts or (my favorite) bigger batches. After 1st crack, when the bulk of the heating is done and the krypton isn't needed, I would turn on the fan for venting the more serious combustion products that start to appear. In my home roasters, venting before 1st crack doesn't seem to be of much use.

Am I crazy? Well, let me re-phrase that. Does this still sound like a crazy way to get bigger batches?
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
seedlings
Hey, Jim... are we still in "theory" or is this a baby you can actually conceive? I'd personally love to see it, but probably wouldn't buy any stock in the IPO.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
dBndbit
Hey CHAD, I'm still in theory mode, maybe moving toward feasibility mode.

My real purpose in this is to design a roaster big enough that a homeroaster could make a decent living from it as a full-time day job. I figure that means a 20# roaster minimum. I haven't yet decided which kind of machine fits the need best. But it's got to be relatively cheap and easy to put together with little or no machine shop requirements. And it's got to run on the limited power available in most homes. Hence the benefit of a krypton jolt. Either a faster roast cycle or bigger batches would offer more pounds for sale in an 8-hour day. All it would take is a few standard gas fittings, a regulator and valve, and a rented refillable tank.

I think I'm liking the mechanical simplicity and efficiency of a recirculating electric-heat air spout machine with a simple propane afterburner. I'm trying to work through the numbers now for building a simple all-metal recirculator fan. All of the stock centrifugal metal fans I've found are designed for volume, not pressure. And the few that are true pressure fans are too expensive. I know that several of you guys here have done real well with the leaf blowers and heat guns, but I really want quiet operation. I think I can do a deep-blade, simple, cheap, low-RPM, quiet blower.

Wish me luck, eh?
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
seedlings

Quote

dBndbit wrote:
I think I'm liking the mechanical simplicity and efficiency of a recirculating electric-heat air spout machine with a simple propane afterburner. I'm trying to work through the numbers now for building a simple all-metal recirculator fan. All of the stock centrifugal metal fans I've found are designed for volume, not pressure. And the few that are true pressure fans are too expensive. I know that several of you guys here have done real well with the leaf blowers and heat guns, but I really want quiet operation. I think I can do a deep-blade, simple, cheap, low-RPM, quiet blower.

Wish me luck, eh?


Check out the 2/2/08 post at http://forum.home...#post_7392. I haven't quite given up on the turbocharger. Almost, though.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
dBndbit
Yep. Definitely a cool possibility. Let me check on the density and heat capacity of nitromethane!

I just thought I'd try a larger diameter, slower speed thing cut from sheet aluminum. I'm hoping it would be easy to scale up for a large batch roaster.
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
Alchemist

Quote

dBndbit wrote:
There's about 1.5 oz of water in a pound of beans, most of which would escape out of the oven with the hugely expanding gas. And I think what's left will only help the heating process. The heat capacity of krypton is only about 30% less than nitrogen/oxygen which would still leave me with a 2x heating improvement from the 3x higher density. It could result in faster roasts or (my favorite) bigger batches.

Am I crazy? Well, let me re-phrase that. Does this still sound like a crazy way to get bigger batches?


Hey, I think you are missing a basic concept here. Density has no relation at all to heat capacity in this gas phase, but you are still acting like it does.

The specific heat capacity you are using is in units of J/mol/K, not J/g/K where mass would make a difference. You need to use the first one since you are in the gas phase where all "ideal" gases are at 22.4 mol/L. What this translates to is that if you have a set volume in the roaster, the one filled with Krypton will weight 3 times as much (as contributed by the gas) as the air filled one, but both will contain the same moles of gas. Since the moles are the same, the krypton filled one will actually be LESS efficient, not more. It's only going to weigh more.

BTW, that 1.5 oz of water is going to displace nearly 2 cubic feet of gas once it goes gaseous, if it were at room temperature. A bit more once it is hot.

I am pretty sure you are running into a dead end here.
dBndbit
Sorry, Alchemist. I definitely did not overlook your comment. I've been doing more homework... I hate homework. And as an electronicker I freely admit to being out of my element with gases.

You're right, of course. I've been mostly working out of Sivetz's book, Coffee Technology. And my dyslexic memory inserted density in the part about heat transfer, when actually he had only use it to calculate air velocity for bean lifting. And also I think I just intuitively associate mass with heat in a direct relationship. As you point out, that's a bad assumption.

When I dug out the specific heat values based on mass, there's about a 4:1 difference between air and krypton, in favor of air. I should have done that in the beginning since the roasting will take place at a constant pressure rather than a constant volume.

Apparently, the backwards logic of this has to do with the complexity of the molecules, not the atoms themselves. Multiple energy storage vectors at work.

Good sanity check. I am crazy. Thank you very much! s:2s:2s:2

But I still don't view the water vapor as a serious issue since it will be expanding out of the roaster with the expanding gas.
Edited by dBndbit on 02/05/2008 7:13 AM
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
Alchemist
No problem - any time I can shoot a project down based on the laws of physics, just you let me know.

Oh, and unless your would be roaster was going to expand :@ it would be constant volume too. It's just not constant temperature nor is it a sealed system.
dBndbit
I assumed it would be a constant pressure system since the inside of the roaster stays at an average of 1atm absolute except for the small fan action, even in a recirculating oven. Constant pressure being the case where energy can freely expand the gas. The descriptions I read about constant volume experiments required a sealed chamber to ensure a constant number of molecules, but at a varying pressure. Which should allow more of the energy to be expressed in temperature. Did I read that wrong?
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
dBndbit
Also... I was just interrupted by a call from my daughter. Her comment was that I should definitely abandon the crazy idea of krypton loaded roasting, in favor of methane!

Her logic was that then I could roast ordinary beans and sell it for huge bucks because I could create the same flavor profile as Kopi Luwak coffee!!!

I blame this kind of thing on her mother.
Edited by dBndbit on 02/05/2008 8:22 AM
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
seedlings
I have another hunch... that if you use Sivetz book and the formulas he uses for his application, you'll end up at the same conclusions he did, building a roaster just like his. Admittedly, that'd be KILLER sweeeeet though!

CHAD

P.S. I'm open to breaking the laws of physics at every opportunity. I still have a bad taste in my mouth from the MU physics professor that failed me.
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Alchemist

Quote

dBndbit wrote:
I assumed it would be a constant pressure system since the inside of the roaster stays at an average of 1atm absolute except for the small fan action, even in a recirculating oven. Constant pressure being the case where energy can freely expand the gas. The descriptions I read about constant volume experiments required a sealed chamber to ensure a constant number of molecules, but at a varying pressure. Which should allow more of the energy to be expressed in temperature. Did I read that wrong?


It is constant pressure.

For volume you are kind of in a mixed "real life" situation. It isn't constant volume in one sense because it isn't sealed, but it is constant volume in another in that you are only concerned about the fixed volume of gas inside the roaster. Most constant volume experiments are also constant moles, so the experiments limits are contained, but expandable (balloon like). Modeling real world situations is notoriously difficult Shock. I find the best solution is to start with theory, attempt to factor in worst case, build it, find out worst case was not worst case and fix it. ;)
Kaffee Bitte

Quote

dBndbit wrote:
Also... I was just interrupted by a call from my daughter. Her comment was that I should definitely abandon the crazy idea of krypton loaded roasting, in favor of methane!

Her logic was that then I could roast ordinary beans and sell it for huge bucks because I could create the same flavor profile as Kopi Luwak coffee!!!

I blame this kind of thing on her mother.


Um, I would definitely not build the roaster to roast in Methane gas! Two things come to mind. The stench of Methane infusing your coffee. BLECH! And the VERY real danger of explosions! Methane is VERY combustible. Even if your roaster were completely air tight with no oxygen at all (which would be very difficult to pull off), It would still be a tremendous concern! Methane is used as a fuel for good reason. It burns hot and reacts readily with oxygen.
Edited by Kaffee Bitte on 02/07/2008 12:27 AM
Lynn

"Some days it's spice, other days it's bitter dirt."
dBndbit
Lynn, thanks for precautionary comments on methane. I hadn't thought about it when I posted, but there might certainly be people reading the threads that wouldn't recognize that roasting with methane in the oven was supposed to be a joke.
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
seedlings

Quote

dBndbit wrote:
Lynn, thanks for precautionary comments on methane. I hadn't thought about it when I posted, but there might certainly be people reading the threads that wouldn't recognize that roasting with methane in the oven was supposed to be a joke.


Joke!!!! {erase, erase, erase} Aw dang it!

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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