Adiabatic cooling in this process involving liquid ammonia

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    Ammonia Thermodynamics
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SUMMARY

This discussion focuses on the adiabatic cooling process involving liquid ammonia, specifically under conditions of 1 bar and -34 degrees Celsius. The process involves heating liquid ammonia to 4.5 degrees Celsius at 10 bar, followed by expansion into an empty vessel until the pressure equalizes at 1 bar. Key questions include the exit temperature of ammonia post-cycle and the potential for achieving an exit temperature lower than the entry temperature through the use of an expander to extract additional internal energy. The p-H diagram is utilized to illustrate the process, with points A and B representing specific states of ammonia.

PREREQUISITES
  • Understanding of thermodynamic principles, particularly adiabatic processes.
  • Familiarity with ammonia properties and phase changes.
  • Knowledge of p-H diagrams and their interpretation.
  • Experience with heat transfer concepts in thermodynamic systems.
NEXT STEPS
  • Study the principles of adiabatic expansion and its effects on temperature and pressure.
  • Learn to construct and interpret p-H diagrams for refrigerants like ammonia.
  • Research the design and operation of expanders in thermodynamic cycles.
  • Examine the efficiency of non-reversible processes in thermodynamic systems.
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Thermodynamic engineers, HVAC professionals, and researchers in refrigeration technology will benefit from this discussion, particularly those focused on ammonia as a refrigerant and its cooling processes.

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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