In a recent post I speculated on what impact salt and other TDS components might have on the freezing point of pool water. Does anyone here have a formula or explanation as to how much a given quantity of salt reduces the freezing point?
polyvue said:The presence of chlorine, calcium and other constituents in pool water should lower the freezing point to below 32Â°F, the commonly accepted point at which water freezes at sea level (0' elevation.) Those who add salt to their pools (whether or not they have a SWG) or have high levels of TDS have even less to worry about regarding freezing pool water. My [very modest] understanding of this process is that the salts interfere with the conjoining of hydrogen and oxygen; I believe the extended quote (see below) also states this. What I don't know is how much these salts affect the freezing point.
The following explanation, from a grad student writing in 1998, is expressed very clearly. (Admittedly, Ms Benison has dropped a zero from the stated salinity of ocean water--which I understand to be roughly 35,000 ppm, but I think her points are still valid.)
If anyone here has a firmer, or different, understanding of this I hope they will post it.Kathy Counter Benison said:Salt lowers the temperature at which water freezes and melts. Pure water, H2O, freezes (and melts) at 0Â°C (32Â°F). But the more "salt" (any elements or compounds carried by the water in solution, such as Na (sodium), Ca (calcium), Cl (chloride), and SO4 (sulfate)) in water, the lower its freezing point. For example, seawater, which has approximately 3500 parts per million "salt" (including Na, Ca, Cl, SO4, Mg, K, and CO3), will freeze (and melt) at -2.2Â°C. A water with extreme salinity such as very salty lake waters at Death Valley, California (approximately 300,000 parts per million "salt") may freeze and melt at temperatures as low as -20 - -30Â°C! Because salt lowers the freezing point depression, it is added to icy roads in order to melt the ice.