Heat Rejection process of Carnot Refrigeration

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Discussion Overview

The discussion revolves around the energy dynamics in a Carnot Refrigeration Cycle, specifically focusing on the classification of energy during the heat addition process when using refrigerant-134a. Participants explore the concepts of enthalpy and internal energy, their definitions, and their roles in thermodynamic systems.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether the energy involved in the heat addition process should be classified as enthalpy or internal energy, seeking clarification on the distinction between these two terms.
  • There is a mention that enthalpy and internal energy are functions of the thermodynamic state of a system and differ from the heat that passes through system boundaries.
  • One participant provides a description of internal energy for ideal and real gases, noting that internal energy includes kinetic energy and molecular interactions, while enthalpy is defined as H = U + PV.

Areas of Agreement / Disagreement

The discussion reflects uncertainty regarding the classification of energy in the heat addition process, with participants expressing different levels of understanding about enthalpy and internal energy. No consensus is reached on the correct classification.

Contextual Notes

Participants express confusion over the definitions and implications of enthalpy and internal energy, indicating potential limitations in their understanding of thermodynamic concepts.

ChildLikEsper
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Hi there, I just sign up today. I'm curious to know about the energy added/released in a Carnot Refrigeration Cycle. Let's say the problem is like this:

A Carnot Refrigerator used refrigerant-134a as the working fluid. During the heat addition process, a percentage of mass of the refrigerant vaporise.
So the question is how do we classify the energy in heat addition process? Is it enthalpy or internal energy? And why?
 
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ChildLikEsper said:
Hi there, I just sign up today. I'm curious to know about the energy added/released in a Carnot Refrigeration Cycle. Let's say the problem is like this:

A Carnot Refrigerator used refrigerant-134a as the working fluid. During the heat addition process, a percentage of mass of the refrigerant vaporise.
So the question is how do we classify the energy in heat addition process? Is it enthalpy or internal energy? And why?
You are aware that enthalpy and internal energy are functions of the thermodynamic state of a system, and are inherently different from heat passing through the boundaries of a system, correct?
 
Chestermiller said:
You are aware that enthalpy and internal energy are functions of the thermodynamic state of a system, and are inherently different from heat passing through the boundaries of a system, correct?

Can you elaborate on these, I may get these 2 terms confused.
 
ChildLikEsper said:
Can you elaborate on these, I may get these 2 terms confused.
For an ideal gas, the internal energy is just the sum of the kinetic energies of all the molecules. For a real gas, the internal energy also includes attractive and repulsive energetic interactions between the molecules. The enthalpy is just a convenient parameter to work with in many kinds of problems, and has no fundamental significance. It is defined as H = U + PV.

chet
 

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