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#1 | |
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Join Date: May 2009
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![]() This thread will be about phase change materials - parafin wax for higher temperature applications (solar, automotive), water/ice for lower temps, and anything else. I'll start with olive oil.
I found this page about using phase change thermal mass in the refrigerator to extend its off time. In this case it is olive oil, which has a freezing temperature only a few degrees higher than water, allowing it store more thermal energy at refrigerator temps than water. OK, this got me excited, so I read up on freezing olive oil. According to this, olive oil doesn't really freeze because it doesn't have a regular crystal structure. Instead it just becomes more and more viscous. This page explains it even further. So, if olive oil doesn't technically "freeze", but only "slows down", then does it really change phase and store more energy than just changing temperature? On the other hand, the author of the this page cites some numbers for olive oil's heat of fusion, so maybe it is a phase change? Here's a quote: Quote:
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#2 |
Less usage=Cheaper bills
Join Date: Nov 2010
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![]() Olive oil turns solid at a temperature a bit higher than the refrigerator is kept at. How do I know? My olive oil is solid in the cupboard downstairs.
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#3 |
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![]() As I understand it, it takes a calorie to raise the temp of a gram of water one degree but it takes three calories to raise frozen water that one degree to make it liquid, not 100 calories...
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#4 |
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![]() Here are some statistics I found online. I think the calculations are correct:
For water at its normal freezing point of 0 ºC, the specific heat of Fusion is 334 J g-1. This means that to convert 1 g of ice at 0 ºC to 1 g of* water at 0 ºC, 334 J of heat must be absorbed by the water. Conversely, when 1 g of water at 0 ºC freezes to give 1 g of ice* at 0 ºC, 334 J of heat will be released to the surroundings. One joule is 0.239 calories. 0.239 calories x 334 J g-1 = 79.826 calories removed to form ice per gram or cubic centimeter of water 1 US gallon = 3,785.41178 cm3 3,785.41178 cm3 x 79.826 calories = 302174.28 calories to melt I gallon of ice 1 BTU=0.252164401 kilocalories or 252 calories so 1 gallon releases 302174/252 or about 1200 BTU when it melts but there is no temperature change |
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