How Much Work Can a Reversible Heat Engine Generate?

In summary, the maximum work output of a reversible engine working from a finite heat source with a thermal capacity, C=1000J/K, and initial temperature of 373K, discharging to a bath of virtually infinite heat capacity at 273K, is 268.5J. This assumes that the engine is a Carnot engine and the units of C are J/K.
  • #1
Ayame17
44
0
[/B]

Homework Statement



What is the maximum amount of mechanical work that can be got by a reversible engine working from a finite heat source of thermal capacity, C=1000J/K, if it is initially at 373K and the engine discharges to a bath of virtually infinite heat capacity at 273K?
[You may take C as a constant over the temperature range, 273K - 373K]


Homework Equations



Good question...!

The Attempt at a Solution



Well, I know that W=Q1-Q2, which is also =Q(T1-T2)/T1. I also know that W=(integral of)Pdv, and that Q=mc(deltaT). However, I can't see how to get the values for P or Q. To begin with, I'm not sure whether I should treat it as a Carnot engine, since most reversible ones are, but not all of them. And if so, should I treat the entropy (S) as 0, which might help? I worked out deltaS = Cln(T2/T1) = -312.1066, which I don't know if it is right and if it will help anyway!
Any help at all will be appreciated!
 
Physics news on Phys.org
  • #2


I would like to clarify a few things before attempting to solve this problem. Firstly, I would like to confirm if the engine in question is indeed a Carnot engine, as this will affect the approach to finding the maximum work output. Additionally, I would like to confirm the units of the thermal capacity, C, as it is typically measured in J/K, not just J.

Assuming the engine is a Carnot engine and the units of C are J/K, we can proceed with the solution. The maximum work output of a Carnot engine is given by the Carnot efficiency, which is equal to (T1-T2)/T1, where T1 and T2 are the temperatures of the hot and cold reservoirs, respectively. In this case, T1=373K and T2=273K.

Using the formula for work, W=Q1-Q2, we can rewrite the Carnot efficiency as W/Q1. Substituting Q=mc(deltaT) and rearranging, we get W=C(T1-T2)/T1.

Plugging in the given values, we get W=C(373K-273K)/373K=1000J/K(100K)/373K=268.5J. Therefore, the maximum amount of work that can be obtained from this reversible engine is 268.5J.

I hope this helps in solving the problem. If there are any further clarifications needed, please let me know.
 

1. What is a reversible heat engine?

A reversible heat engine is a theoretical device that can convert heat energy into mechanical work with 100% efficiency. It operates in a cycle, taking in heat from a high temperature source, converting some of it into work, and expelling the remaining heat to a low temperature sink.

2. How is the efficiency of a reversible heat engine calculated?

The efficiency of a reversible heat engine is calculated by dividing the work output by the heat input. This ratio is known as the Carnot efficiency and is given by the equation: efficiency = (Thot - Tcold) / Thot, where Thot is the temperature of the high temperature source and Tcold is the temperature of the low temperature sink.

3. Can a reversible heat engine actually exist?

No, a reversible heat engine is a theoretical concept that cannot be achieved in reality. This is because it would require an infinitely slow and perfectly reversible process, which is not possible due to the laws of thermodynamics.

4. What is the significance of reversible heat engines?

Reversible heat engines serve as a theoretical benchmark for the maximum efficiency that can be achieved by any heat engine. They also help in understanding the limitations of real-world heat engines and in the development of more efficient technologies.

5. How do reversible heat engines differ from irreversible heat engines?

Reversible heat engines operate in a cycle and have 100% efficiency, while irreversible heat engines do not operate in a cycle and have lower efficiencies. Additionally, irreversible heat engines produce more waste heat and are subject to the limitations of the second law of thermodynamics.

Similar threads

Replies
3
Views
560
  • Advanced Physics Homework Help
Replies
5
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
6
Views
2K
  • Advanced Physics Homework Help
Replies
8
Views
3K
  • Introductory Physics Homework Help
Replies
2
Views
825
  • Advanced Physics Homework Help
Replies
3
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
8
Views
2K
Replies
1
Views
510
Back
Top