What is the mechanism of heat transfer and air flow in coffee roasters?

In summary, the conversation discusses the process of convection in a coffee roaster and how it affects the beans. The heat is produced by gas burners and is absorbed by the incoming cold air as it passes through the burners. The hot air then enters the roasting chamber and transfers heat to the coffee beans, which absorb it through convective heat transfer. Increasing the air flow in the drum results in higher turbulence and a higher heat transfer, but there is a limit to how much air flow can efficiently transfer heat. Beyond that, increased air flow can cool down the beans. The conversation also mentions other factors such as IR heating and various terms related to heat transfer and turbulence.
  • #1
Chemchampa
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Hello,

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 into 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.
 
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1. How does heat transfer occur?

Heat transfer occurs when there is a difference in temperature between two objects or substances. The heat energy will naturally flow from the warmer object to the cooler object until they reach equilibrium or the same temperature.

2. What are the three types of heat transfer?

The three types of heat transfer are conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between two objects. Convection is the transfer of heat through the movement of fluids, such as air or water. Radiation is the transfer of heat through electromagnetic waves.

3. How does air flow affect heat transfer?

Air flow can affect heat transfer by either increasing or decreasing the rate of transfer. When air is stagnant, it acts as an insulator and slows down heat transfer. However, when air is in motion, it can increase the rate of heat transfer by carrying the heat away from the source.

4. What factors affect air flow?

The three main factors that affect air flow are temperature, pressure, and density. When the temperature of air increases, it becomes less dense and rises, causing air flow. Similarly, differences in pressure between two areas can also cause air to move from high pressure to low pressure areas.

5. How can heat transfer and air flow be controlled?

Heat transfer and air flow can be controlled through various methods such as insulation, air flow regulation, and air conditioning systems. Insulation helps to reduce heat transfer by creating a barrier between two objects with different temperatures. Air flow can be regulated through the use of fans, vents, and air ducts. Air conditioning systems use a combination of insulation, air flow regulation, and refrigeration to control both heat transfer and air flow.

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