day wrote:If we preheat to 300 degrees, turn off the gas and just leave it off, then at some point the bean temperature and environmental temp will stabilize and be equal, at first the beans will heat up very quickly But as they get closer to the et the ror will slow down. Thus, let's call that initial ror 60f/min. As the bt reaches 150degrees the drum is still much hotter than the beans but is losing heat and the two are much closer in temp, so now the ror will be lower, let's call it 40f/min
Well said, Brian.
But may I ask a follow-up question, how you reconcile charging different bean mass in this case? Set aside the non-equal contributions of radiation, conduction and convection, is it theoretically possible to achieve similar heating (RoR) patterns when you load 0.5X, 1X and 2X of bean in the case?
Some people use capacitor as the analogy of the drum mass, but I'm no expert. Assuming (drum temperature equals to et) in your above example, and you preheat to 300F and charge 1X of bean. The temperature difference between the drum and the bean reduces overtime.
If you charge 2X of bean at the same 300F, the temperature difference would reduce faster and drop to a lower temperature. If we want to best maintain the BT/RoR pattern and to compensate the effect of greater charge mass, we need to increase the charge temperature and supply additional heat during the process (hence leave the gas on).
If you charge 0.5X of bean at the same temperature as you charge 1X of bean, the rising temperature may go out of control. Gas-off is a method to tame the heat in this low-charge-mass situation.