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Energy Interaction 
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#1
Jan1011, 07:02 PM

P: 49

 We know that for closed systems, energy transfer between the system and the environment can be in the form of heat or work.
We know that for open systems or control volumes, energy transfer between the system and the environment can in the form of heat, work, or mass flow. Let's say we have a wellinsulated oven with a heating element inside. We consider the heating element and the air inside the oven to be the system. When the oven is turned on, energy is transferred in the form of work into the system. This is because the electrons flowing in the heating element crosses into the boundary. I'm struggling to understand how the energy transferred is in the form of work instead of heat. Questions: 1) Would the flow of electrons be considered mass flow, making it an open system? 2) If the answer to question #2 is "yes", would mass flow be considered work? Questions not directly relevant to the problem: 1) In an open system, can energy transferred be both in the form of heat AND work? Thanks! 


#2
Jan1011, 07:54 PM

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#3
Jan1011, 08:53 PM

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For simplest example of open system loosing energy to work, consider a gasfilled cylinder with a piston as your system. When the gas inside moves the piston, it is the work done by the closed system against whatever is pushing from the other side.



#4
Jan1011, 11:43 PM

P: 49

Energy Interaction
Thanks guys! I think I understand now.



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