Finding the efficiency of an engine given energy input, energy wasted.

In summary: Since the engine is operating between two heat reservoirs, the net entropy change must be positive according to the Second Law of Thermodynamics. But in this case, the net entropy change is negative, which is impossible. Therefore, the inventor's claims are not valid and it is not advisable to invest in this project.
  • #1
Dez1
2
0

Homework Statement


An inventor claims to have developed an engine which takes in 1.1x108J of heat energy at 400K, and rejects 5.0x107J of heat energy at 200K. Would you advise investing in this project? Explain your answer.


Homework Equations


W = Q1 – Q2
η = W/Q1 = 1 – Q2/Q1


The Attempt at a Solution


η=1-(Q2/Q1)
=1-(5*10^7/1.1*108)
=0.54

Which means the inventor is claiming 54% efficiency. In reality such an engine would be in the region of 30% efficiency or less.Therefore I would not suggest investing in this project."

I think my answer seems too short, which means I'm probably doing it wrong. Also, the temperatures probably have some relevance to the solution so I'm probably using the wrong equation(s).
 
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  • #3
Dez1 said:

Homework Statement


An inventor claims to have developed an engine which takes in 1.1x108J of heat energy at 400K, and rejects 5.0x107J of heat energy at 200K. Would you advise investing in this project? Explain your answer.


Homework Equations


W = Q1 – Q2
η = W/Q1 = 1 – Q2/Q1


The Attempt at a Solution


η=1-(Q2/Q1)
=1-(5*10^7/1.1*108)
=0.54

Which means the inventor is claiming 54% efficiency. In reality such an engine would be in the region of 30% efficiency or less.Therefore I would not suggest investing in this project."

I think my answer seems too short, which means I'm probably doing it wrong. Also, the temperatures probably have some relevance to the solution so I'm probably using the wrong equation(s).

Or simply consider the net entropy change of the system.
 

1. What is the efficiency of an engine?

The efficiency of an engine is a measure of how well it converts energy input into useful work. It represents the ratio of the energy output (useful work) to the energy input.

2. How do you calculate the efficiency of an engine?

The efficiency of an engine can be calculated by dividing the energy output (useful work) by the energy input and multiplying by 100 to get a percentage.

3. What is energy input?

Energy input is the amount of energy that is supplied to the engine, usually in the form of fuel or electricity.

4. What is energy wasted?

Energy wasted is the amount of energy that is not converted into useful work by the engine. This can be in the form of heat, sound, or other forms of energy that are not needed for the engine to function.

5. How can the efficiency of an engine be improved?

The efficiency of an engine can be improved by reducing the amount of energy wasted. This can be achieved through regular maintenance, using high-quality fuel, and implementing design changes that optimize the conversion of energy into useful work.

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