Heat injection and work during Rankine cycle

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Discussion Overview

The discussion centers on the Rankine cycle, specifically addressing the role of work during the isobaric processes and the implications of heat injection and removal at constant pressure. Participants explore the physical interpretations of work in the context of thermodynamic processes within the cycle.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why work done during isobaric processes is often ignored in analyses of the Rankine cycle, suggesting it may relate to the steam's expansion.
  • Another participant asserts that during isobaric processes, heat is added or removed at constant pressure, leading to a lack of physical activity that would result in work being done.
  • A further contribution reiterates that while heat is added at constant pressure, the volume increases, which typically results in work. However, it is suggested that most heat is used for vaporization or condensation, potentially explaining the assertion that no work is done during these processes.
  • A participant introduces the concept of the open system (control volume) version of the first law of thermodynamics, implying a need for consideration of this framework in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the nature of work during isobaric processes, indicating that the discussion remains unresolved with multiple competing interpretations present.

Contextual Notes

There are limitations regarding assumptions about the physical processes involved in work during isobaric conditions, and the discussion does not resolve the implications of the first law of thermodynamics in this context.

GwtBc
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I have been researching the Rankine cycle. I know that it consists of two adiabatic and two isobaric processes. However, I'm not entirely sure why we ignore the work done during the isobaric processes (this seems to be the case in the analysis I'm looking at). Is that because the work done there is simply the work that the steam does to make room for itself? (and vice versa)
 
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In these processes heat is just being added or removed at constant pressure . Where is there any physical activity that results in work being done ?
 
Nidum said:
In these processes heat is just being added or removed at constant pressure . Where is there any physical activity that results in work being done ?
You add heat and pressure is kept constant, i.e. volume increases. That is usually the physical process that results in work being done. But here most of the heat goes into vaporization/condensation. Is this why we say that there is no work done during these processes?
 
Are you familiar with the open system (control volume) version of the 1st law of thermodynamics?
 

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