I am doing some more brain storming on the cooling side of my little $\ce{CO2}$ engine project.

I have decided to use ice to cool the 550 degree gaseous $\ce{CO2}$ returning it to liquid by having the ice surround the coiled $\ce{CO2}$ exhaust that is outside the cylinder. As the gas descends down the coil it will cool returning to liquid.

The liquid will be stored in the 6 coils on the outside of the 6 cylinders until it is needed. At which point until the pressure drops to a predetermined level then the liquid $\ce{CO2}$ will be injected into the 550 degree heated chamber via a pump maintaining the pressure .

After a good amount of looking at bulky freezer designs that would require large condensers and large run times to keep cool with results in the mid $\mathrm{-12^oF}$ to $\mathrm{-18^oF}$ range. I have looked at portable ice makers. My entire system is powered/controlled by electricity. That electricity is maintained by a small gas motor. The portable ice makers are quick and can be maintained cheaply while being compact.

The ice will drop down filling inside and around the coils as a level indicator dictates. As the ice melts the liquid will run down to the bottom where it will be picked up by a pump and returned to the ice maker saving fluid.

The issue that I am running into is that most of these only produce ice that is -10F/-23.33C.

I am hoping for something closer to double or even triple that to reduce the pressure that will leak into the cylinder and cause compression.

Because it is not going to be eaten and the tray is based upon weight, what kind of chemicals can I use or can I mix with distilled water to lower the freezing point?

Right now sodium seems like a good choice to get down to -20F/-28.99C. But I am wondering if I can go lower using another type of chemical. As far as corrosion is considered most of the parts are plastic or can be changed over to plastic or forms of chemical resistant materials used. That being said the parts that touch the liquid is easily replaced. The only part that would be somewhat complicated to reproduce would be the copper probes themselves. With that in mind chemicals that are compatible with copper would be strongly advised.

If I can lower the temperature of the ice to around -30F/-34.44C that would be more then ideal while producing the pressures I am after. Chemicals that would be somewhat easy replenished that could provide that temperature drop is outside of my understanding and any help would be much appreciated.

  • $\begingroup$ Your question is too long :P $\endgroup$ – Red Floyd Feb 5 '17 at 18:26
  • $\begingroup$ A picture is worth a lot of words. I find myself so caught up in trying to picture your device that I loose track of the chemistry issues, which is all we can really help you with here. I would suggest that you either loose any unnecessary descriptions, or draw a clearly labeled diagram. Also, are all of your temperature units in degrees F? It would be great if you could include units for all values so we don't have to assume. If you wanted to convert them to degrees C, that would be fine too ;) . But they need to be consistently labeled regardless. $\endgroup$ – airhuff Feb 6 '17 at 4:22
  • $\begingroup$ I need to keep the cooling side as cold as possible. I am using a ice maker that uses the weight of the ice to determine the time to stop cooling them and "drop" them. I am looking for a somewhat safe and readly available chemical that will allow me to get close to -30F/-34.44C without causing copper probes to corrode at a increased rate. $\endgroup$ – cerial Feb 6 '17 at 4:54
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    $\begingroup$ Shortened initial question $\endgroup$ – cerial Feb 6 '17 at 5:06
  • $\begingroup$ OK, it is much more readable. One comment right off is that when you say "sodium" I assume you mean a sodium salt of some kind. That would almost certainly be nasty toward the copper pipes. Also, lowering the temperature of water ice doesn't really buy you much as most of the cooling from ice comes from the latent heat associated with melting it. In other words, it's good for holding a temperature of 0C for however long it takes to melt. I think you're on the right track with using a water mixture or some other liquid altogether. I'm still thinking about that ;) $\endgroup$ – airhuff Feb 6 '17 at 9:41

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