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Maintaining water temperature


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#1 charlie10

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Posted 7 January 2011 - 05:46 PM

Hi

I'm just wondering if it would be possible to keep water hotter for longer by using something like a silicone heat pad placed in the water? Would this work? If not what materials should I be looking at to achieve this?


Thanks

Charlie
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#2 cypress

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Posted 7 January 2011 - 11:13 PM

Sodium acetate heating pads have very high heat capacity due to the trihydrate phase change that takes place at about 58 degrees C. The same principle as ice only in opposite. You can use these or other similar material that solidifies at the desired temperature.
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#3 CaptainPanic

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Posted 10 January 2011 - 09:07 AM

Hi

I'm just wondering if it would be possible to keep water hotter for longer by using something like a silicone heat pad placed in the water? Would this work? If not what materials should I be looking at to achieve this?


Thanks

Charlie

You only need to add as much energy to the water as you will lose from it to keep the temperature constant.

I continue the post below assuming that you want to have a hot water bottle that stays hot longer (for heating your cold feet in the bed for example).
If you want to increase the specific heat of water, there is nothing practical that can do that. Water has an incredibly high heat capacity already... so if you want to pack as much heat into a liter as possible: go for water - just plain ordinary water.

However, cypress made a good point saying that there are safe materials that will actually undergo a phase change (like freezing) or a reaction (crystallization in cypress' example)... and those will have more joules per kg of material than water (or at least I believe so - can't find the numbers so soon).

Your question however was a little unclear.
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#4 charlie10

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Posted 10 January 2011 - 12:18 PM

thanks for the reply, so would the sodium acetate heat pads warm the heat the water, giving the water more energy, resulting in the water staying hotter for longer? The question was looking at keeping a hot water bottle warmer for longer, i'm not looking at increasing the temperature, just maintaining it for longer

thanks
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#5 CaptainPanic

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Posted 10 January 2011 - 04:10 PM

thanks for the reply, so would the sodium acetate heat pads warm the heat the water, giving the water more energy, resulting in the water staying hotter for longer? The question was looking at keeping a hot water bottle warmer for longer, i'm not looking at increasing the temperature, just maintaining it for longer

thanks

If you just want to keep something warm for as long as possible, while also getting warmth from it (for your cold feet), then I'm afraid that there are hardly any alternatives for water. Water is already quite awesome... it's just so common that we forget.

The sodium acetate pads won't do anything while the water is still warm... as sodium acetate just doesn't crystallize then...
And when the water is cooling down, you want to be asleep already... but the sodium acetate pads need activation (there's often a little metal click-thingy in it which will start the crystallization process).

I'm afraid that in your case, the simple and boring solution is: use a regular hot water bottle, and bigger is better. Twice the volume of water holds twice the heat. If you use a regular bottle now, and you upgrade to a bottle twice the volume, it will stay hot for a longer period. That's because the surface area increases (relatively) less than the volume as you take a larger bottle.

Alternatively, you can take two similar bottles, and insulate them a bit. Then you also increase the heat by two, and the added insulation (a cloth) will reduce the heat you get from it. The net effect is that you get the same heat as before from one bottle (but now from two), and it takes longer to cool down.

I'm just being pragmatic here... if you prefer to discuss the reactions and chemically interesting options, just say so.
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#6 michel123456

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Posted 10 January 2011 - 04:23 PM

Glauber's Salt
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