Not that I needed to, but I did a small mod to input hot air to the roaster

I bought 10' of copper tube. I used an iron pipe with wrapped around masking tape and a vise to obtain the shape I needed. It works as a heat exchanger.



Then I bended the end so that it makes it to the air intake hole



and wrapped the copper with insulation



This is the result. The difference is in the mid phase to 1C from dry phase to finish phase. The temperature of the mass of the beans climbs now much faster to 1C by using convection. That's the only difference from before. Compare the slopes of BT and MET in the pic bellow



compare that with my performance before



With the new mod, my delta BT is very high up to the 400Fs where I need to bring down the power. I think I can do now much heavier loads and keep good times.

The air input is from a vacuum cleaner in reverse mod. It blows air instead. I use this vacuum cleaner:

http://www.shopvac.com/vacs/detail.asp?...x&StoreID=

but a less powerfull vacuum would be needed for best performance. I brought down the output of the vacuum cleaner with a router speed control. There is an accessory that brings down the hole size and fits the hose perfect.

PS: next weekend I'll plug the input hole so that the roaster will only use heated air.

Cheers

Rafael,
Amazing, I think that Quest had better employ you as a development engineer.
All the Best
Eric

Thanks Eric. But the ideas (input hot air) are from Jim!

The vacuum cleaner with the variable router speed control sounds just like a jet engine. My neighbors may call the police! jeje

Cheers

I upgraded the vacuum cleaner for an air blower (quieter). The air blower also responds better (smoother) to the router speed controller.

This video shows the power of the blower. Since the internal diameter of the copper lines is small, some power is needed but as much as the capacity of the blower. The router speed controller selects the best power to obtain the highest delta BT.



the blower was ~$70 and it is advertised with an 64 db noise level (low)

This is a link to the blower:

http://www.amerimerc.com/air-blower~max-air.htm

Max Air 1 HP 120V 4.5 amp Portable Spa Blower


Cheers

To provide warmed air to the input wouldn't a small hair dryer and some tubing be a simple solution?

How does the shorter roast time affect the flavor?

Is it more useful on some beans (and/or some roast profiles) than others?

I don't know the answer.

The current draw from the blower (as it would be used) is only ~ 1.85A. It runs very cool and it is very quiet. It does get warm in the connection to the hose after ~20 mins use. . With a heat gun, the danger would go up and so it would the current draw. Another thing. The heat gun would mess up the control of the PID (uncontrollable). An air dryer may be OK but I haven't tested it. I haven't tested if it is OK to plug the hole and use only force air either.

Lets do some math. The max current from the roaster is 10A. lets say the current from the blower could go up to 2.5. So my total current is 12.5A, which meets my 15A max (but I am plugged to a 20A jeje).

The blower lets me get the extra boost I need in the mid phase. I need only a little, no a whole lot.

I haven't done any taste comparisons yet so I cannot comment on that. The blower would also increment the batch size of the roaster.

PS: the blower doesn't run that cool. I check the temp output to be 115F without any restrictions (room at 78F). I thought that the warmth at the hose at the connection was caused by the pressure but it is caused by the heat of the electric motor. The blower already works as an air dryer jeje

Cheers

This is another pic once the blower is installed



The blower is not that small so I had to put it on the side jeje. The roaster is taking over! The blower turns off by itself if it gets too hot (it has a resettable thermal switch) and it did turned off after about maybe 30 mins of testing (maybe more). This tells me that I can only use for the ramp to 1C and then turn it off.

I did changed the thermocouple to the other side of the chimney so that it does not get bathe with the extra incoming air. And did a new autotune for the PID.

Cheers

I've tried a bigger load (300 grams) and the effects were not noticeable. Meaning, the air trick did not shorten the roast time. It seems that the mass of the beans blocks the air. Or, that the air does not get through the larger mass of beans.

This would indicate to me that in a normal drum roaster, the larger the drum surface the more the heat transfer capabilities as it would have more surface (conduction), and more opportunity for air to move through the beans (convection). I guess that a perforated drum may have more air advantage but don't know as I never had one.

Cheers