Chestermiller said:
The dimensions of PVC pipes are the same as steel pipes of the same nominal diameter. But the thermal conductivity of PVC is 100 x lower than steel. This would result in significant resistance to heat transfer through the wall in PVC pipes. Based on this, I estimate that the freeze times with PVC pipe will be on the order of about 5X those of steel. Is this what is observed experimentally?
Summarily…it’s possible if 3/4” steel froze in 5-mins as for 3/4” CPVC I use 25-mins.
I’ve never frozen steel pipe in either location, but I have frozen both copper and CPVC in Colorado. Field results suggest 12-minutes for 3/4” copper with water (guessing) between 10º-16ºC and 25 minutes for 3/4” CPVC. For 1/2” copper, 8-minutes seems to work. I’ve never frozen 1/2” CPVC, so I have no observations.
For the Detroit location, we’ve only frozen 1” copper and smaller, so no observations for steel or plastic. Freeze times follow the CS table; however, the number of freezes per 20-lb bottle are fewer than indicated on CS table.
Going forward I’m going to collect quality measurements including documenting supply water temp, pipe size, type, LCO2 used, tank temp and time. Always I have run a stop watch or countdown on my phone, yet actual freeze time is a bit fuzzy.
For example, when it was super cold outside at -14ºC and I was freezing 3/4” CPVC, the water was probably closer to 4ºC in the pipe. Still I used 25-mins freeze time and actually gave it 28-mins just to be sure (basically used all but 3-4 lbs of 20-lb cylinder). This was also the first time I had to warm the tank and no idea how warm it got. So on this day did the plug freeze at or earlier than 23-mins? At 25 or 28? Who knows.
Honestly, you never really know if the plug is good until you test it. The problem is if you test it and it’s too early, you really have no choice but to start again. Another example: I’ve tried 15-minutes on 3/4“ CPVC (assuming water circa 10ºC), and 100% it’s been a bust every time. So I just use 25-mins as minimum for 3/4” CPVC and really you don’t get much more than one freeze from a 20-lb cylinder. You have some residual, so you can start a freeze next time with it, but it doesn’t last long before you’re swapping to tank #2.
