low stage refrigerant alternatives: anyone ever heard if acetylene can be used?

[sphere478]

I've been trying to research possible canidates for a low stage on a cascade refrigeration build hopefully something easy to get a hold of. i thought i had found something with nitrus oxide but then i found a rather convinsing thread over at xtreme systems forums about how it will react with oil explosively :-( Bummer. I did a google search trying to find a refrigerant number for acetylene but there doesn't appear to be one. http://en.wikipedia.org/wiki/List_of_refrigerants

i found a mention on one site that acetylene reacts with strong bases to form salts or something? i guess oil is a base right? so that sounds like a non starter. kinda a bummer the pressure temp chart i found for it looks like it would be usefull if it was able to be used. it certantly wouldn't be hard to get a hold of! without more information i think i don't want to find out the hard way that it is incompatable. i would think maybe the fact that it doesn't have a refrigerant number is probably a sign that there are issues. just wish there was more info out there..

it seems the budget low stage refrigerant of choice for most builds is R-1150 Ethylene. it has proved dificult to find locally though. as a bonus question has anyone heard of a good online source for ordering it? (and the regulator/piping to charge with it)

[BradC]

I've been trying to research possible canidates for a low stage on a cascade refrigeration build hopefully something easy to get a hold of. i thought i had found something with nitrus oxide but then i found a rather convinsing thread over at xtreme systems forums about how it will react with oil explosively :-( Bummer. I did a google search trying to find a refrigerant number for acetylene but there doesn't appear to be one. http://en.wikipedia.org/wiki/List_of_refrigerants

This reply is a bit late, but hopefully might help you decide against it. There are two factors as to why Acetylene would be bad in a refrigeration system. 1) Acetylene reacts with copper to produce unstable and explosive copper acetylides. Now, you could use a copper-free system or low copper alloys, but given the next point it's rather moot. 2) Acetylene under about more than 15psi of pressure has a nasty habit of detonating. Under 15psi it will defelgrate (sp?), in that the flame front moves slower than the speed of sound. It can be quenched by large surface areas which is why flashback preventers work well. Also Acetylene regulators and manifolds have tiny passageways to maximise the surface area and minimise the gas volume. Over 15psi it has a tendency to detonate and nasty things happen. Plenty of evidence on line about the damage caused by acetylene detonation. My favorite was a muppet who thought he's save on bottle rental and decant his acetylene into a spare scuba cylinder. No filler, no acetone. I looked at making it a while ago, but when I read up on just the measures needed to compress it and fill a bottle and all the hardware they have that has no other purpose than stopping the acetylene plant turning into a crater I decided to stick with Propane.