Water Expansion After Frozen ```Name: Dennis T. Status: other Age: 50s Location: N/A Country: N/A Date: 12/20/2004 ``` Question: At sea level, water begins to freeze at 32 degrees F. Is there a point below 32 degrees F. that the ice reaches a maximum expansion? I work for a public drinking water utility company. The question came up regarding damage to water pipes resulting from temps below 32 degrees. Note: Although the temperature gets below the 32 degrees and will freeze, it usually seems that our pipes begin to burst when the temp gets down to around 20 degrees F. Replies: My guess is real life is different than experiments. When my furnace went out , I think it was 20 outside air but inside it was 40. the reason latent heat, objects retain heat and gradually lose it. So, it your case, the air inside, the pipes, actually the diameter of the pipes is also in the mix. Water in a free state freezes at 32 ( even then the factors are depth, surface area etc). So my point what conditions effect the water are your key. I do not know the molecular behavior , but it does not seem logical to me that a maximum occurs before a stage change. The solution to your pipes is wrapping with wire, the intermittent current warming the pipes and keeping the temperature inside above freezing. James Przewoznik No, ice does not expand as it gets colder. When water freezes, it increases in volume about 9%. The ice then shrinks as the temperature decreases. The shrinkage is tiny, about 0.4% going from 30F to -50F. As a side note, liquid water is densest at a temperature of 39.2F. The density differences at higher and lower temperatures are very tiny. Cooling 39.2F water to 0F expands it only 0.01%. Another note, there are at least 12 forms of ice. Most can be obtained only in the laboratory under high pressure. It is likely that the bursting at 20F is due to parts of the water system that are not yet frozen at 32F finally freezing at the colder temperature. Bob Erck It is possible to supercooled water, but it is not likely that this would happen in the environment of a water pipe. There are too many sites for ice crystals to form. The critical temperature of ~ 20F probably has to do with how cold it must get in order to freeze enough water in the pipe that the pipe plugs and having no where to go, the pressure build up is extreme. There are many excellent web sites on the properties of water and ice if you do a Google search on the topics "properties of ice" or "properties of water". Vince Calder It usually seems that our pipes begin to burst when the temp gets down to around 20 degrees F ---That is interesting. No, water in the solid phase has normal expansion characteristics (unlike the liquid phase: expanding with cold just before freezing). Ice's temperature coefficient of expansion is about 50 ppm/degC (http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm, at the bottom). This is a positive number, meaning that ice expands with heat and contracts with cold just like almost all other materials. Great reference by the U.S. Coast-Guard at http://www.chrismanual.com/Intro/prop.htm. Density of ice vs. temperature at http://www.engineeringtoolbox.com/24_576.html. First, if your pipes are in the ground, be sure you are measuring the temperature of the pipes, not of the air above. Ground stores a significant amount of heat and is likely to be warmer than your latest cold-snap. How much warmer depends on depth. And any ongoing flow of water through the pipes will probably carry in higher temperatures 32F or higher. Suppose ice builds up slowly on the pipe walls, in competition with the flow of slightly warmer water running through the center. It is possible that no complete plug of ice forms anywhere along your pipe until significantly colder than 32F. When the first complete plug forms (likely to be at some point above the ground), then there is trapped water, gradually freezing and building up pressure in the pipe. If you had a thermometer directly on or in the pipe and this happened, the thermometer would never show less than 32F until the hours _after_ the pipes had burst. At http://www.lsbu.ac.uk/water/explan.html#dens, look at the blue line. You can see there that ice's density (the blue line) is slightly decreasing with increasing temperature, so it seems that stable ice does not expand as it gets colder. But the green line at the same place may offer an explanation for your bursting: Perhaps the water in the pipe is pure and still, so it supercools (fails to solidify) for about 6 degrees C. This is not a difficult degree of supercooling to find. Then at 20F it finally freezes, more rapidly than usual. This would raise the pressure quickly and burst the pipes promptly. If you had a thermometer directly on or in the pipe and this happened, the temperature would gradually go down to 20F, all water, then when freezing started it would jump up to 32F until freezing was complete, and then slowly decline to 20F again, this time all ice. Somewhere during the 32F period the pipe-bursting would occur. It comes to mind that pressure reduces the melting point of ice. (ice skating...) Supposing the water in the pipe was trapped by frozen plugs in both directions, Could freezing at one place would raise the pressure enough that another place would remain liquid until 20F? That way a percentage of the expansion-upon-freezing would be delayed. It turns out that too much pressure is required. 13 MPa, about 130 atmospheres or 2000 psi, only reduce the melting point by 1 degree C or about 2 degrees F. (http://www.lsbu.ac.uk/water/explan2.html, "11") Your pipes would burst by 1000 psi or less, so I think you could only get down to 31 degrees F that way. Some places mention that ice has "unusual compressibility", but I do not think it is high enough to matter at the low pressures of pipes bursting. The Young's modulus is 8 GPa (http://www.doitpoms.ac.uk/tlplib/BD1/printall.php, 6x lower than salts or aluminum, but still too high to matter here. (1/compressibility) = Bulk Modulus = 8.8 (?GPa) at http://www.aist.go.jp/GSJ/dMG/dMGold/hydrate/hydrate.ice.property.html), and 7.8e10 dyne/cm2 (=7.8 GPa) at http://www.du.edu/~jcalvert/phys/ice.htm Ice can be compressed only 0.1% at the pressure where your pipes burst, but pipes probably stretch more like 1% before breaking, so I do not think there is any strange compressibility of ice is delaying the bursting. http://www.newton.dep.anl.gov/askasci/chem00/chem00985.htm deals with the density of ice too. Good luck figuring it out. Jim Swenson Click here to return to the Engineering Archives

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