CoffeeAir - 1kg Indoor Electric Roaster Trial

[liteglobe]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Hi Chad
Posted Photos of my version 22 Nov POLL What Do You Use To Home Roast page 11

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Hi Chad  
may be off topic I have recently finished a fluid bed roaster copying yours with the two heat guns.
some modifications but works great thanks for a great idea. you are correct you  will not get sufficient heat from
one 120v circuit
Will post photos next time i roast
Cheers

Fantastic to hear your success on a new roaster!

Meanwhile, Im still struggling with this one. Ive left the electronic heat element and currently have roasted a couple of test batches with a propane torch... but... this latest torch is too powerful. 1 pound roasted to french in 2 minutes! Ouch!

Rather than going on and on, if you have interest, please read the drama and failures over at http://www.homeroasters.org/php/foru...4&rowstart=160

Ive abandoned re-circulation and electric heat elements. Ill install a vent to outdoors once this thing actually works.

From page 9 on might be interesting reading about propane torches.

Thanks, and sorry for linking another site. Its just too much to keep up both sites.

CHAD

[liteglobe]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Hi Chad
may be off topic I have recently finished a fluid bed roaster copying yours with the two heat guns.
some modifications but works great thanks for a great idea. you are correct you will not get sufficient heat from
one 120v circuit
Will post photos next time i roast
Cheers

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Gday mate....

Yeah, I thought you might run into a bit of trouble . The Gas Torch idea really does work though and if you grab a couple of different sized burners to go with it, itll make it easier to arrive at an optimum setup. What I did with my rig, was to position the burner (a cyclonic one I think it was, rated at around 2.5KW) about 40-50mm behind a coarse brass mesh (platinum would be even better ) so that the flame would heat this up and increase the efficiency of the heat transfer.... Worked like a charm but I guess any burner with a decent output would do the job.

All the best Chad, very interested to hear how you get on mate,

Cheers,
Mal.

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

It turns out that 1800W just isnt enough, even if the air is recirculated. I was able to take about .5Kg to about 170C in 15 minutes. Its just not enough.


So, I picked up a propane torch, and plan to honor RoasterRob by using his brilliant torch idea. But, trust me, I have no metal working abilities, so this will be nothing like Robs artwork! Ill put some sort of vent in so that the smoke/chaff is directed outdoors.

In the US, we use 120V AC, and I considered running a 220V outlet, but the cost was out of the budget for now. 220V would allow me to double the power from 1800W up close to 4000W. But, I would have to re-build everything. Ive already roasted enough money.

Thanks all! Ill still keep you posted.

CHAD

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Mal, Ive been looking for mica board, but its quite hard to find. On-line manufacturers want you to order 1000 widgets worth of the stuff. Im tempted to go to the thrift store and pick up a couple of used toasters and salvage the mica boards from them.

Hi again mate,

Do you have any motor rewind shops, industrial heater manufacturers or air-conditioning manufacturers within driving distance of you? Most of these types of businesses will use Micaboard of one form or another and may be quite happy to sell or even give you some off-cuts from the manufacturing/repair process. Might be worth a look.

Sounds like youre making good progress though Chad, using the cement board. I spose the only thing you need to be careful of when using this sort of design is that all of the element coils are in the air-stream; mainly to ensure efficient heat transfer and the avoidance of hot-spots on the elements. Anyway, it seems like its all starting to work out 8-)... Cant wait to see the finished result. All the best mate,

Mal.

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

I sure wish I could accurately calculate airflow.  All I know is Im using 1/3 of the 6 amps this vacuum motors rating.  I dont know if thats a linear relationship, though... I searched for modern vacuum motors and 120 cubic feet per minute is pretty normal.  So, maybe Im only using half of that?  Hard to say for sure.

Mal, Ive been looking for mica board, but its quite hard to find.  On-line manufacturers want you to order 1000 widgets worth of the stuff.  Im tempted to go to the thrift store and pick up a couple of used toasters and salvage the mica boards from them.

But, Im trying a solution with an item on hand... cement board.  I fashioned a frame from the cement board and wound the new 24ga nichrome around that.  I think Im trying to run the nichrome too hot (12 amps!), though as the first 2 attemts burnt up after about a minute.  Air was HOT though, which is promising.  Im about to start on another element with two 6-amp nichrome wires in parallel.  Im gaining some confidence, though!

CHAD

**edit: Heres the next attempt. 2 coils in parallel for 11.2 ohms. Each coil should see about 5 amps which corresponds to 1300F, well below the max operating temp of 1600F.

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Yep,

Kanthal is good.... I think the main problem though is more related to overall thermodynamics of the application itself. Probably need to establish the air flow required for creating the optimum "fluid bed" and once that info is on board, it should be possible to do the sums for heat transfer and transport through to the fluid bed. Location of the "element" will be critical, will need to be quite close to the bottom of the fluid bed and interlocked with air flow so as to avoid over-heating in the event that air flow is reduced excessively or stopped altogether.

A very interesting project indeed...

Mal.

[beanflying]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Also for heating elements look up Kanthal as an alternate. As it gets hotter the resistance actully decreases slightly (less voltage drop) so the element get hotter when in use rather than cooling slightly like nichrome does.

http://www.kanthal.com/

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

UPDATE: Im having trouble with the heat coils. Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked. In test runs there just wasnt enough heat as it is now.

Have you given any consideration to making an element fashioned into a spiral, supported on a simple framework made from"Micaboard" (a high temperature insulation panel usually used in industrial heating applications - link here). If you can locate a manufacturer near where you live, it is quite inexpensive and would be relatively simple to knock-up a frame that would support the element and allow you to mount it across the direction of air-flow to maximise the transfer of heat within a pipe like structure.

Might give you some ideas mate,

All the best,
Mal.

[mobbarley]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

UPDATE: Im having trouble with the heat coils. Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked. In test runs there just wasnt enough heat as it is now.

It will probably be hard to heat such a volume of air... you would probably need a very long thin coil or possibly some kind of metal heat-exchanging core which you can heat with the coil :-?

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Why do something the easy way when, after significantly more time, work, and money, I could fail doing it the hard way? My wife REALLY wants to start working on framing the basement....

Fair enough mate... ;D

Nothing like trying stuff out for yourself, Im the same :. Its all well and good that someone else has tried a design that produced results that they werent particularly happy with, doesnt mean that YOUR design wont perform admirably. Go for it Chad and well look forward to reading about your results.... [smiley=thumbsup.gif]

Cheers mate,
Mal.

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Mal, Java, your points quite valid, and I cant argue any of them. If this wont work out the way Id like, the backup plan is a standard air roaster vented to the outdoors. That method is much easier, just too cliche`.

Why do something the easy way when, after significantly more time, work, and money, I could fail doing it the hard way? My wife REALLY wants to start working on framing the basement....

If this project ever progresses past where I am now, Ill be sure to post the results!

Thanks again all,
CHAD

[JavaB]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Also, I shied away from using an electric element with this sort of setup as using a simple gas torch with various types of burners and gas flow, I was able to achieve a very useful arrangement, very easily. Chad has hit on the problems you experience with heating elements and air flow, very difficult to arrive at a satisfactory equilibrium that marries heat transfer/transport, an ideal fluid bed action and robustness of the element. The use of LPG gas heating simplifies the establishment of an empirical design in my opinion.

Mal.

Agreed Mal, the amount of heat you can get from electric elements is very limited..... thats why you wont see many electrically heated roasters above about 300gms...... recirculating the air would, in theory at least, provide greater efficiency (just as long as the heat input was greater than the loss of heat from the roaster)..... Gas I would regard as the ideal heat source..... but wont work in a closed system.

The other problem would be controlling the heat. As the heaters have low thermal mass..... and ON/OFF type arrangement wont work very well (As I proved when I tried to PID a corretto). Analogue control would be the go - either a variac, a powerful triac "light dimmer" (for manual control) or ideally a PID with an analogue output (if an automated profile is desired).

Also the HT produces very little smoke (thanks to its rear filter)...... but the moment the beans are dumped for cooling - huge clouds of smoke from the beans once they exit the drum! So that will also be an issue for indoor roasting..... the inbuilt fan could be used (without the heater on)...... but that would take way too long to cool the beans.....

And once you open the chamber - smoke city

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

The resulting roast could be very nice (depending on your taste preference)..... but Im certain will be nothing like from an air bed roaster..... and will be even more "drum roasted" than you would get from a drum roaster.... if you get what I mean.

Yep, this is what I discovered with only a partial recirculation of the gasses/hot air... It has to be said though, I love a good roast, what ever method is employed but I do prefer the cleaner and clearer flavour spectrum of an air roast system....

Also, I shied away from using an electric element with this sort of setup as using a simple gas torch with various types of burners and gas flow, I was able to achieve a very useful arrangement, very easily. Chad has hit on the problems you experience with heating elements and air flow, very difficult to arrive at a satisfactory equilibrium that marries heat transfer/transport, an ideal fluid bed action and robustness of the element. The use of LPG gas heating simplifies the establishment of an empirical design in my opinion.

Mal.