|MadSci Network: Engineering|
Hello Karim Get a thin-wall copper tubeof say 1/8" inch diameter and wind it into s spiral of pitch 1/4" and diameter 3/4". Get a Dewar vacuum flask 1" neck diameter and deep enough to contain your spiral helical copper tube. Crinp or solder a very fine nozzle to the lower end of the spiral helix so that the CO2 exhausts VERY fast (say a hole 1/100th inch diameter: experiment woth different sizes). At the top of the copper helix put a runbber or other seal so the CO2 cartridge can be attached without leaks. Now the cartridges I am familiar with have weak necks which you break to release the gas. If yours work that way you will have to work out a cunning way to break the neck WITHOUT losing the gas. It must pressurise the copper helix with the ONLY leak beive via the jet at the lower end of the helix! Now due to the Joule-Thompson effect (see Wikipedia: this is how they make liquid air) the expanded gas is very cold. While exiting the vacuum flask the cold gas PRE-cools the tube and the gas within. So we have POSITIVE FEEDBACK - the cooling, by expansion, of precooled gas! As liqid CO2 is not stable at atmospheric pr3essure, soon dry ice will coat the copper helix. It may take LOTS of cartridges! Then when you have enough dry ice you can remove the helix and do what you like with the dry ice. A LOOSE-fitting foam polystyrene lid on the Dewar flask will help. Watch that you do not get so much dry ice you cannot get it past the neck of the flask! Good luck Karim and above all HAVE FUN! John
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