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Homeroasters.org » BUILDING A ROASTER » Fluidbed Roaster
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Heat gun CFM (compact fluid bed)
rbata
Hi, i'm planning on building a small fluid bed roaster, something around 200-300g per batch.

Is it possible to use only the heat gun blower without any auxiliary blower?

I found a heat gun that is capable of 20cfm and maximum of 1100F (maybe not both at same time). 20CFM is enough for a small batch?

And how many minutes is expected or ideal for this batch size? 8-12 minutes?
 
oldgearhead
Did you check this:
forum.homeroaster...ad_id=1876
No oil on my beans...
 
rbata
Yes, actually went trough the whole topic, found a bit confusing at sometimes, and soon the blower was upgraded for something more powerfull. My english is a little bit rusty, it's hard to understand some parts (i'm brazilian).

I think I read something like 4oz up to 3/4lb at that topic would be feasible with a stock heat gun.

I'm thinking on using this model: http://mlb-s1-p.m...2014-O.jpg

http://www.tektoy...d=571&

This gun have a LCD with temperature control (10 degrees increments) and blower control trough the LCD from 4 to 20CFM.

So I thought this would be cheaper than buying separate parts like heater, blower, electronics for temperature/blower control.

I was thinking in disassembling it and insert it inside a pipe or some case/housing and have the LCD at a more ergonomic position. Build a chamber for the beans and a chaff filter at the top.
Edited by JackH on 02/15/2016 14:54
 
oldgearhead
It has been done. I recall a mention of the Michael Sivetz sample roaster.
Try this:
forum.homeroaster...post_49243

My 500 gram roaster uses a 1550 watt heat gun element for heat. However, it requires 40 - 60 CFM to loft the 500 grams. However, I pull reclaimed hot air from the roast chamber and you may need higher pressure. I use a vacuum cleaner blower (100 CFM flow/100 Inch H2O prrssure).I can put 300 grams into my roast chamber and measure the flow rate, if you like.
Edited by oldgearhead on 02/15/2016 17:49
No oil on my beans...
 
oldgearhead
Most major heat gun manufacturers and dealers have spare elements (heat coils) available. I'm afraid your unit will probably max out at 100 grams, depending on the ambient temperature. But with a larger blower, 300 grams should be possible...
No oil on my beans...
 
scotthal
rbata wrote:

Hi, i'm planning on building a small fluid bed roaster, something around 200-300g per batch.

Is it possible to use only the heat gun blower without any auxiliary blower?

I found a heat gun that is capable of 20cfm and maximum of 1100F (maybe not both at same time). 20CFM is enough for a small batch?

And how many minutes is expected or ideal for this batch size? 8-12 minutes?


The heat gun fan most probably lacks sufficient 'oomphf' to loft 300gm in a true fluid bed implementation. Problem is static pressure - the heat gun fan is designed to move air w/o significant obstruction.

That said ... a shift towards 'spouting bed' might serve yr needs. Tilt the column - idea is to take advantage of the induced bean circulation. Hot air stream grabs the top beans & kicks 'em away. Gravity (& funnel geometry) brings the cold(er) beans back to the throat.
Food for thought; coffee for concentration
 
allenb
I agree with Scott on the lack of oomphf. The heatgun Sivetz sold in his sample roaster package was a little wimpy in the static pressure department but at least the model he used incorporated a squirrel cage blower as in one of the master appliance models. The heatgun rbata has linked to is a radial fan style heatgun which will most likely create little to no static pressure.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
rbata
Oldgearhead, it would be nice if you could measure that for me.

I think I get the concept, the spec CFM is at free flow. As soon as I restrict the heat gun blower, it will not react with enough pressure to lift the beans.

Scotthal, I didn't knew the spouting bed. I'll research a little further. Is that similar to what happens inside a popper? The beans don't actually lift, they just roll around.

For comparison purposes, a hair dryer blower would be powerful than a heat gun blower? I never used a heat gun before, have no idea what 20cfm looks like.

Thanks everyone!
 
scotthal
rbata wrote:

Scotthal, I didn't knew the spouting bed. I'll research a little further. Is that similar to what happens inside a popper? The beans don't actually lift, they just roll around.



Fluid bed :: spouting bed may be an artificial distinction (figment of my obsessions ...). Fluid bed lifts the majority of the bean mass in the air stream. Spouting bed 'fountains' over a restricted air feed, and relies on gravity & geometry to circulate the beans.

The Hearthware Precision was a spouting bed roaster - base of the chamber was ~6" diameter shallow funnel; air feed was restricted to the 0.5" radius around the central deflector stalk. Wimpy fan, but it was only lifting a small column :: subset of the bean load.

My old Poppery1 can easily handle 150gm, whilst sitting on my stove top. Can't push beyond that unless I tilt it ... beans shift, thins the obstruction at the top, & you get a blow out. Top beans go ballistic down tube (?up throat); gravity feeds the bottom :: cooler beans back into the vortex.

Flat on the stove top, I'd call it a fluid bed rig. Tilted, it's definitely spouting.
Food for thought; coffee for concentration
 
oldgearhead
I would say any roaster that uses only heated air to circulate the beans is a fluid-bed roaster. There are many roasters using heated air for heat but mechanical means for circulation. For instance my roaster uses part of a cocktail shaker to induce bean movement. During the drying phase it produces a single spout. But in the 'ramp up to first crack phase' the beans are moving very slowly with no visible spout. During 'cooling' all the beans are suspended in cool air..

forum.homeroaster...ad_id=2207
Edited by oldgearhead on 02/17/2016 06:43
No oil on my beans...
 
oldgearhead
rbata wrote:

Oldgearhead, it would be nice if you could measure that for me.

I think I get the concept, the spec CFM is at free flow. As soon as I restrict the heat gun blower, it will not react with enough pressure to lift the beans.

snip>


rbata,
I just took a liters per second measurement of 300 grams of green coffee beans in my roast chamber.
The reading was 19.1 L/sec.(40 CFM). So next I calculated the pressure of my blower at that flow rate and it came out to be 1500 millimeters H2O water column. Two things I need to explain:
1) My blower is ported to atmosphere, so that, it runs at a higher RPM for better motor cooling.
2) The blower feeds into a perforated plate located at the bottom of the roast chamber. This plate has seventeen 0.45 millimeter holes.
Good luck with your project!
oldgearhead attached the following image:
dsc_5397_8.jpg

Edited by JackH on 02/18/2016 15:21
No oil on my beans...
 
scotthal
oldgearhead wrote:

I would say any roaster that uses only heated air to circulate the beans is a fluid-bed roaster. There are many roasters using heated air for heat but mechanical means for circulation. For instance my roaster uses part of a cocktail shaker to induce bean movement. During the drying phase it produces a single spout. But in the 'ramp up to first crack phase' the beans are moving very slowly with no visible spout. During 'cooling' all the beans are suspended in cool air..

forum.homeroaster...ad_id=2207


Yaah. Appears to be a difference in definition - I'd go with fluid bed being any methodology which 'liquefies' the majority of the bean mass. Common case is using a hot air stream - provides uniform heating, at the expense of CFM :: static pressure requirements. Spouting bed only has a fraction suspended.

Gedanken experiment - use a tactile transducer :: shaker :: butt kicker to liquefy the bean mass, & a heat gun for the thermal input. Is it a fluid bed roaster?
Food for thought; coffee for concentration
 
rbata
Thanks oldgear!

At first I was confused about my calculations, with air speeds so elevated.... I think you meant 4,5mm instead of 0,45mm for the 17 holes, right?

At this flow rate you have a air speed of around 70m/s at the perforated plate.

My heat gun is arriving this week, I'll try to start some tests... at the worst case scenario, if it doesn't have enough cfm at least for a spouting bed roaster, I'll shift the project to a bread maker.

Thanks all for the inputs.
 
oldgearhead
All my air speed reading are taken at the roast chamber exit port with beans in the chamber. All flow rate calculations are a factor of the diameter of this opening.
You are correct the 17 holes are 4.5mm not .45.
Starting with heat gun calculations simply check the manufactures temperature/ flow rate and multiply the flow rate by 2, and divide the temperature by 2. In other words if your heat gun is like mine it's specs are 540C at 11 l/s. But in realty it takes a lot more than 11 l/s to loft 300 grams of beans. In fact it takes close to twice (22 l/s) to loft the beans. In other words the temperatures are inversely proportional to the flow. Therefore, increasing the flow decreases the temperature and decreasing the flow increases the temperature.
With my roaster I do not control the heating element during a roast, Instead I use the blower controls to control the roast profile...This works because bean drying occurs in moving air above 100C and as the beans lose moisture they become lighter and it takes less air to support the fluid motion, so the temperature increases for roasting..
No oil on my beans...
 
rbata
Thanks for the additional information!

The specs are:
- temperature 630C (1.160F)
- flow rate 9,1l/s (19cfm)

A fluidized bed seens impossible with this specs... I'll be happy with a spouting bed.

Will begin with 4 or 5 holes with 3 or 4mm in the middle, and test the green beans capacity. Then will play with batch size, holes diameter and quantity.
 
oldgearhead

>snip<
The specs are:
- temperature 630C (1.160F)
- flow rate 9,1l/s (19cfm)

A fluidized bed seens impossible with this specs... I'll be happy with a spouting bed.
>snip<


I don't understand the difference between a 'fluid-bed' and a 'spouting' bed??? All the beans must be in motion or they will burn. Also you will need more air pressure for 300 gram loads,,,
more like 20 l/s..
No oil on my beans...
 
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