28 May 06 15:03
Thanks to all. The link (Brines.pdf) provided by 25362 was especially helpful. Although, when I approximate the values for Cp from the graphs, it again shows that PG has a higher Cp than EG. I still don't see the evidence to support the statement that EG has better heat transfer capabilities than PG. What am I missing? I believe that the second formula in the above link may take into account the other variables needed to support the original premise, but I don't have sufficient background to apply the formula.
The other issue is the high temperature stability of the corrosion inhibitors. The inhibitor degradation when the system is operating close to the maximum temperature is a potential problem. The collectors are already 23 years old and I am refurbishing the rest of the system. It has also been widely stated that PG has to be replaced more frequently than EG due to inhibitor breakdown.
I know that the fluid should be checked for pH and inhibitors annually. But, how often does PG and EG have to be replaced based on oprating experience.
I am inclined to use EG, but the data doesn't seem to justify the use of the less available EG.
I have included a table of the various fluids on which I have gathered data. I would like to use the most thermodynamic fluid with the highest maximum temperature and the longest potential useful life.
Mix Cs Cs Temp Viscocity Boil/Max Freeze
Hercules Cryo-tek Original PG Undiluted 0.908 160 220 -22
Hercules Cryo-tek 100 PG Undiluted 0.843 160 230 -70
Hercules Cryo-tek 100 PG 75% -17
Hercules Cryo-tek Artic Grade PG 40% -8
DowTherm SR-1 EG EG 50% 0.842 180 0.94 250 -34
DowTherm 4000 EG EG 50% 0.835 180 0.94 350 -34
DowCal 10 EG EG 50% 0.835 180 0.94 350 -34
DowFrost PG 50% 0.902 180 1.10 250 -28
DowCal N PG 50% 0.902 180 1.10 250 -34
ThermalSafe PG 50% 0.901 180 1.07 220 -27
ThermalCool EG EG 50% 0.842 180 0.95 226 -34
Mathamatical Model EG (apprx) EG 50% 0.86 158 1.30 -35
Mathamatical Model PG (apprx) PG 50% 0.88 158 1.10 -32