I am trying to simulate a vapor compression cycle in ASPEN plus to turn Carbon Dioxide into dry ice. Using Joule Thompson Flashing , I managed to bring down the gas temperature to -88 C at 1 atm. But only 2% of gas turns to liquid Carbon Dioxide.
What am I doing wrong?
Hi Captain Jack, Captain Roy here from his REDSTAR vessel.
Don't believe our colleague Thaer Roomi here above. He is right though about CO2 having no liquid phase under atmospheric pressure conditions. But, my friend, carbon dioxide has a liquid phase above its triple point in the pressure-temperature phase space (see also Gibbs theory on this).
In thermodynamics (and high school) you can learn that, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. It is that pressure and temperature at which the sublimation curve, fusion curve and the vaporization curve meet.
The graph (Triple point.jpg) explains this even better.
Compare the triple point of water and CO2:
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Pressure (kPa) / Temp (K)
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Water .611 / 273.16
Carbon dioxide 517 / 216.40
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It explains it all. It also explains why the boiling point of water drops when you climb into the death zone in the Himalayan mountains. Likewise, it's hard to boil an egg on top of the Mount Everest, let alone on the surface of Mars!
Cheers,
Roy
Carbon Dioxide is converted into dry ice by pumping liquid carbon dioxide into holding tanks, which reduces the temperature to -109° F and pressurizes the substance into solid blocks.
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