Adiabatic cooling in this process involving liquid ammonia

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    Ammonia Thermodynamics
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Discussion Overview

The discussion revolves around the thermodynamic process involving liquid ammonia, specifically focusing on adiabatic cooling during expansion and the implications of heat transfer and pressure changes. Participants explore the conditions and outcomes of this process, including temperature changes and the configuration of a pressure-enthalpy (p-H) diagram.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question whether the exit temperature of ammonia will always be higher than the entry temperature due to the irreversibility and inefficiency of the process.
  • There is a proposal that using an expander with a load could potentially allow for an exit temperature lower than the entry temperature by extracting more internal energy from the gas.
  • Multiple requests for clarification on the process details, including the need for a p-H diagram to illustrate the end points of each step.
  • A participant corrects an earlier claim about the state of ammonia at point B, asserting it represents a saturated liquid rather than gas.
  • There is a discussion about the correct location of point B on the p-H diagram, with emphasis on its position relative to the saturation envelope.

Areas of Agreement / Disagreement

Participants express differing views on the temperature outcomes of the process and the correct representation of states on the p-H diagram. The discussion remains unresolved regarding the exact implications of the process and the configuration of the diagram.

Contextual Notes

Participants indicate errors in initial conditions and seek to reevaluate them, highlighting potential limitations in assumptions made during the discussion. There is also a focus on the dependence of outcomes on the definitions used in the context of the thermodynamic process.

aladinlamp
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TL;DR
Adiabatic cooling
Entry conditions: liquid ammonia , 1 bar , temp -34 celsius,
i supply heat Q to heat it to 4.5 celsius, 10 bar,
than i release it into empty vessel until inside reaches also 1 bar,
expansion,adiabatic cooling, uses internal energy of ammonia to expand and cool itself

1. can we assume, after this cycle finishes, exit temperature of ammonia will be always higher than entry temperature, since this process is not fully reversible, not 100% efficient ?
2. can we achieve exit temperature lower than entry temp, if we use expander with load, to extract even more internal energy from gas?
 
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Please provide more details of the process. For example, show end points of each step in p-H diagram, and describe better what is the process for each step.
 
Chestermiller said:
Please provide more details of the process. For example, show end points of each step in p-H diagram, and describe better what is the process for each step.
Hi, I made some errors in setting up my initial conditions, so let's reevaluate them step by step. In the diagram, there are two points, A and B:

  • Point A represents a 1-liter container filled with liquid ammonia at a pressure of 1 Bar and a temperature of 240 Kelvin. Heat, denoted as Q1, is added to the ammonia to increase its temperature.
  • Point B represents a 1-liter container filled only with gaseous ammonia at a pressure of 20 Bar and a temperature of 323 Kelvin.
I'm trying to determine a new point C on the chart under these assumptions:

  • The heat exchange occurs only within the ammonia itself.
  • The ammonia from the 1-liter container is released through a valve into another container until the pressure in both containers equalizes at 1 Bar. Eventually, there will be ammonia at 1 Bar pressure in a both volumes.
My question is: What will be the average temperature of ammonia in both containers at the end of this process, where is next point C ?
ab.png
 
Last edited:
aladinlamp said:
Hi, I made some errors in setting up my initial conditions, so let's reevaluate them step by step. In the diagram, there are two points, A and B:

  • Point A represents a 1-liter container filled with liquid ammonia at a pressure of 1 Bar and a temperature of 240 Kelvin. Heat, denoted as Q1, is added to the ammonia to increase its temperature.
aladinlamp said:
  • Point B represents a 1-liter container filled only with gaseous ammonia at a pressure of 20 Bar and a temperature of 323 Kelvin.
Point B on the p-H diagram represents saturated liquid, not gas.
 
ok, where is correct location of point B ?
 
aladinlamp said:
ok, where is correct location of point B ?
On the right hand side of the saturation envelope, not the left hand side. But, of course, for the same mass of ammonia at points A and B, the volume at B will be much larger than 1 liter.
 

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