Re: Question about drum roaster design
- From: jim schulman <jim_schulman@xxxxxxxxxxxxx>
- Date: Sat, 17 Sep 2005 17:28:44 -0500
On Sat, 17 Sep 2005 13:59:46 GMT, "Dan Bollinger"
>Let's look at the modes:
>First, the slower the drum is turning, the longer (in percent) the bean is in
>contact with the drum and heat is being transferred by conductance. ...
The tenor of the chaper is that virtually all heat transfer is by
convection even in conventional drum roasters.
>Second, the faster the air is moving past individual beans the higher the heat
>transfer rate is by convection. The reason being that heat transfer is at a
>greater rate when the temperature differential is higher. Pushing cooler air
>away from the bean means the differential is maintained at a higher level.
>If the drum and air are both heated by the same heat source and their
>temperature is nearly identical -- as is the case with a perforated drum in a
>closed (non-ventilated) roaster -- increasing the drum speed will increase heat
>transfer (and speeding the roast).
This was my impression. On my PIDed airroaster, if I hold the inflow
air temperature constant, and blow faster, the roast speeds up. I
thought this was due only to increasing the available heat. Now this
convection bit comes up and I'm scratching my head. The ideal way to
tell is a completely sealed drum with constant heat input (or more
properly, held a constant temperature) -- if it's slow whirl, slow
roast, fast whirl, fast roast, tha would nail it.
>What's next, a PID'd drum speed roaster? ;)
That would be more elegant than some of the current automation
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