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A Heat Transfer and Air Flow

  1. Jul 1, 2016 #1

    I have here a complex question. My background is Chemistry and Optoelectronics. I wasn't the best when we were studying Thermodynamics at uni so I have some knowledge-gaps. Anyways, here is my problem.
    Can somebody explain me the whole process of the convection in the coffee roaster. So here is the process (I present it very simply here leaving the space for the extensive explanations):
    - the heat is produced by the gas burners (natural gas),
    - incoming cold air passes through the burners and gets hot,
    - hot air moves into the roasting chamber (rotating metal drum)
    - then it enters roasting drum with coffee,
    - the coffee absorbs the heat.
    - the rest is clear to me : ]
    I need to understand the process in to great depth. I understand complex equations so feel free to drop some more sophisticated explanations.
    My questions:
    What is exactly the process of the heat absorption of the incoming cold air? How does it happen?
    What does happen to the air moving into the roasting chamber (rotating metal drum)?
    What does happen to the beans in the drum? I know they absorb heat by the convective heat transfer. But what is exactly happening? What happens to the air that released the energy and gave up to the beans?
    What does happen with the air when I increase the air flow in the drum?
    What does happen with the beans when I increase the air flow in the drum?
    I know that increased air flow means the air moves faster, higher turbulence, and that leads to a higher heat transfer. What is the explanation? I guess there should be also a moment until when the heat transfer is efficient, right? What's beyond? High airflow decreases heat transfer and it cools down the beans or what? Is there a speed, air amount limit?

    I've already read about Heat transfer, Convective heat transfer, Turbulence, Nusselt, Biot, Reynolds numbers and the list goes on... So please try to show your solicitude by giving some ideas rather than giving links to Wiki or so.

    Thanks in advance.
  2. jcsd
  3. Jul 1, 2016 #2


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