Energy Interaction: Work Transfer in a Heated Oven

[AirForceOne]

- 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 well-insulated 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!

 

[Mapes]

1) Would the flow of electrons be considered mass flow, making it an open system?

A flow of electrons is strictly mass flow, but the electron mass flux in a problem like this is absolutely negligible compared to the mass of the system. Most physicists would assume that the system is essentially closed in terms of mass. The much more important consideration is that the power source is doing work on the system in the form of moving electrical charge.

2) If the answer to question #2 is "yes", would mass flow be considered work?

No, mass flow is not generally equated with work. But in this case, the electrons represent a negligible amount of mass transfer and a considerable amount of electrical charge transfer.

1) In an open system, can energy transferred be both in the form of heat AND work?

Sure; energy can enter/leave in the form of heat, work, and/or mass simultaneously.

 

[K^2]

For simplest example of open system loosing energy to work, consider a gas-filled 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.

 

[AirForceOne]

Thanks guys! I think I understand now.

 

[PJC01]

I would like to provide a response to your questions and concerns regarding energy interaction and work transfer in a heated oven.

Firstly, let's clarify the difference between heat and work. Heat is the transfer of thermal energy between two objects due to a temperature difference, while work is the transfer of energy due to a force acting over a distance.

In the case of a heated oven, the energy transfer between the heating element and the air inside the oven can be considered as work, as the heating element is using electrical energy to generate heat, which is then transferred to the air molecules by the process of conduction. This transfer of energy is considered as work because it involves a force (electrons flowing in the heating element) acting over a distance (the distance between the heating element and the air molecules).

Now, to address your questions:

1) The flow of electrons can be considered as mass flow only if there is a net movement of electrons from one location to another. In the case of a closed system, the electrons are continually circulating within the heating element, and there is no net movement of electrons in or out of the system. Therefore, the flow of electrons in this scenario would not be considered as mass flow.

2) As explained above, the flow of electrons in a closed system would not be considered as work. However, in an open system, where there is a net movement of electrons in or out of the system, the flow of electrons can be considered as mass flow and work. This is because the movement of electrons involves both a force (electrical potential) and a distance (movement of electrons).

Now, to address your final question:

In an open system, energy transfer can indeed occur in the form of both heat and work. For example, in a steam turbine, the steam (mass flow) is heated (heat transfer) and then used to drive the turbine blades (work transfer) to generate electricity.

I hope this response has helped to clarify your understanding of energy interaction and work transfer in a heated oven.