Carnot Efficiency of a heat engine

In summary: The efficiency is 75% because the engine extracts energy between the input and output reservoirs of the engine, this it converts into work. Look in the section on the 2nd law of Thermodynamics how to convert the transferred heat to temperatures.
  • #1
AlaskanPow
13
0
My problem only gives me joules to work with. Is it possible to convert from joules of energy to temperature (Kelvin)?? If so how?
 
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  • #2
Best to state the problem. Maybe we can see a way around it.
 
  • #3
An engine transfers 2.00x10^3 Joules of energy from a hot reservoir during a cycle and transfers 1.50x10^3 Joules as exhaust to a cold reservoir. Find the actual efficiency of the engine and then compare it to the carnot efficiency.

The actual efficiency is 75% I calculated. For carnot efficiency i need temperature, but I don't know how to get it.
 
  • #4
Your calculation of the efficiency is wrong. Also, if you don't have the temperature of the reservoirs, you can't get the Carnot efficiency.
 
  • #5
The actual efficiency of the engine

[itex]\epsilon=\frac{work \; done \; by \; the \; engine}{total \; energy \; used \; by \; it}[/itex]
 
  • #6
My book says (efficiency=energy output/energy input)
Which would give me 75% I believe.
So there is no way to get the carnot efficiency?
 
  • #7
The engine extracts energy between the input and output reservoirs of the engine, this it converts into work. Look in the section on the 2nd law of Thermodynamics how to convert the transferred heat to temperatures.
 
  • #8
The 75% is the Carnot engine's efficiency.
 
  • #9
Hmmm interesting. My book does not go into depth very much, because I am in a survey class, so I don't understand how you could calculate it without having your temperatrure. The only equation I got in my book for carnot efficiency is
carnot efficiency=(Thot-Tcold)/ Thot
 
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  • #10
For a Carnot engine it is assumed that all of the extracted heat, QH - QL (high, low), is converted into work by the engine, so that its efficiency is given by

[itex]\epsilon=\frac{Q_{H}-Q_{L}}{Q_{H}}[/itex]
 
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  • #11
Basic_Physics said:
For a Carnot engine it is assumed that all of the extracted heat, QH - QL (high, low), is converted into work by the engine, so that its efficiency is given by

[itex]\epsilon=\frac{Q_{H}-Q_{L}}{Q_{H}}[/itex]
W = Qh-Ql for any heat engine. So this is the definition of efficiency for any heat engine. To calculate the Carnot efficiency, the maximum efficiency of any possible heat engine operating between these two reservoirs, you would need to know the temperatures, Th and Tc.

AM
 
  • #12
AlaskanPow said:
My book says (efficiency=energy output/energy input)
Which would give me 75% I believe.
So there is no way to get the carnot efficiency?
The heat exhausted to the cold reservoir is not the energy output of the heat engine.
 

What is Carnot Efficiency?

Carnot Efficiency is a measure of the maximum possible efficiency of a heat engine, which is the ratio of the work output to the heat input. It was first described by French physicist Sadi Carnot in 1824.

How is Carnot Efficiency calculated?

Carnot Efficiency is calculated by dividing the temperature difference between the hot and cold reservoirs by the temperature of the hot reservoir. This can be represented by the formula:
Efficiency = (Th - Tc) / Th

What is a heat engine?

A heat engine is a device that converts thermal energy into mechanical work. It operates by taking in heat from a hot source, converting some of it into work, and then releasing the remaining heat to a cold reservoir.

Why is Carnot Efficiency important?

Carnot Efficiency is important because it provides a theoretical limit for the efficiency of any heat engine. It serves as a benchmark for comparing the performance of real-life heat engines and helps in identifying areas for improvement.

What factors affect the Carnot Efficiency of a heat engine?

The Carnot Efficiency of a heat engine is affected by the temperature difference between the hot and cold reservoirs, as well as the temperature of the hot reservoir. It also depends on the type of working fluid and the efficiency of the engine's components such as the piston and valves.

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