Entropy Generation of an Electric Motor: Analyzing du/dt & dS/dt

In summary, the solution manual sets the change of internal energy and total entropy to zero for the given question. This is because energy is conserved, but there is still expected to be some entropy generation. The total rate of entropy generation, Sg, and its origin are also requested in the question.
  • #1
wynnl
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For the following question, the solution manual sets du/dt (change of internal energy) = 0. Moreover, it also set the change of total entropy to zero. Why is that?

An electric motor under steady load draws 9.7 amperes at 110 volts; it delivers 0.93 kW of mechanical energy. The temperature of the surroundings is 300 K. What is the total rate of entropy generation Sg ? What is its origin ?
 
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  • #2
wynnl said:
For the following question, the solution manual sets du/dt (change of internal energy) = 0. Moreover, it also set the change of total entropy to zero. Why is that?

An electric motor under steady load draws 9.7 amperes at 110 volts; it delivers 0.93 kW of mechanical energy. The temperature of the surroundings is 300 K. What is the total rate of entropy generation Sg ? What is its origin ?
Energy is conserved. I would expect some entropy generation (the problem statement even asks for its amount!), however.
 

Related to Entropy Generation of an Electric Motor: Analyzing du/dt & dS/dt

What is entropy generation and why is it important in electric motors?

Entropy generation is a measure of the amount of disorder or randomness in a system. In the context of electric motors, entropy generation refers to the amount of wasted energy and heat generated during the motor's operation. It is an important concept because it can affect the efficiency and performance of the motor.

How do du/dt and dS/dt affect entropy generation in an electric motor?

Du/dt and dS/dt are mathematical representations of the rate of change of internal energy and entropy, respectively. In an electric motor, these values can help us understand how much energy is being converted into work and how much is being dissipated as heat. A higher du/dt and dS/dt can indicate higher levels of entropy generation.

What factors can contribute to high entropy generation in an electric motor?

There are several factors that can contribute to high entropy generation in an electric motor. These include friction between moving parts, electrical resistance, and inefficiencies in the energy conversion process. Poor maintenance and overloading of the motor can also lead to increased entropy generation.

How can entropy generation be reduced in an electric motor?

To reduce entropy generation in an electric motor, it is important to minimize the factors that contribute to it. This can include using high-quality materials, regular maintenance, and proper sizing and installation of the motor. Additionally, using advanced technologies such as regenerative braking can help capture and reuse some of the energy that would otherwise be lost as heat.

Can entropy generation be completely eliminated in an electric motor?

No, it is not possible to completely eliminate entropy generation in an electric motor. The second law of thermodynamics states that entropy will always increase in a closed system, and an electric motor can be considered a closed system. However, by optimizing the design and operation of the motor, we can reduce the amount of entropy generation and improve its overall efficiency.

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