Reversibility of heat transfer

Click For Summary
SUMMARY

The discussion centers on the concept of reversible heat transfer, specifically the process of raising the temperature of a cooler body from T1 to T2 through infinitesimal heat exchanges with heat reservoirs. It establishes that for reversibility, the temperature difference must be infinitesimal at each step, leading to a net increase in entropy despite the process being theoretically reversible in the limit as dT approaches zero. The conclusion emphasizes that while true reversibility is unattainable in nature due to the infinite time required, the concept serves as a valuable approximation for actual processes.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the second law of thermodynamics.
  • Familiarity with concepts of entropy and its implications in heat transfer.
  • Knowledge of heat reservoirs and their role in thermal processes.
  • Basic grasp of calculus, particularly limits and infinitesimal changes.
NEXT STEPS
  • Research the second law of thermodynamics and its implications for real-world processes.
  • Explore the concept of entropy in greater detail, focusing on its calculation and significance.
  • Study the behavior of heat reservoirs and their impact on thermal equilibrium.
  • Investigate practical applications of reversible processes in engineering and physics.
USEFUL FOR

This discussion is beneficial for thermodynamics students, physicists, and engineers interested in the principles of heat transfer and the theoretical limits of thermodynamic processes.

kelvin490
Gold Member
Messages
227
Reaction score
3
In the case of reversible heat exchange which the cooler body rises in temperature from T1 to T2, it requires that the temperature difference between the system and the heat source must be infinitesimal in every step. Usually the model is like that: Give a heat reservoir of temperature slightly higher than T1, make a small amount of heat transfer, than the temperature of cold body rise a little bit. Then use another hotter reservoir and transfer another infinitesimal amount of heat, repeat the steps until the body is T2.

The problem is: In every step the entropy decrease of hotter reservoir is smaller than the entropy increase of the cooler body. There is a net increase in entropy of the system. Although the increase is close to zero, we have done infinite number of step in order to increase the temperature to T2. How can we ensure the overall increase in entropy is zero so that it is a reversible process?
 
Science news on Phys.org
It is reversible only in the limit of dT = (T2-T1) → 0 .
There is no truly reversible process in nature, since such a process would take an infinite time.
Actual processes can at most be very close to reversible.
It is nevertheless a useful concept and it can even be useful as an approximation to actual processes.
 
  • Like
Likes   Reactions: 1 person

Similar threads

Undergrad Entropy change due to heat transfer between sources
  • · Replies 15 ·
Replies
15
Views
3K
High School Question regarding Heat Transfer in Carnot Engine
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Reversibility in thermodynamics
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Reversible compression of a gas - faulty reasoning?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Irreversible Isochoric Process in a Cycle
  • · Replies 8 ·
Replies
8
Views
4K
Graduate Why is 0 K unattainable?
  • · Replies 11 ·
Replies
11
Views
1K
Graduate Practical use of an overall heat transfer coefficient?
  • · Replies 14 ·
Replies
14
Views
3K
High School How are thermodynamic laws related to one another?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Why does Callen insist a process must be reversible here?
  • · Replies 8 ·
Replies
8
Views
2K
Graduate Understanding the Laws of Thermodynamics as described by Feynman
  • · Replies 4 ·
Replies
4
Views
2K