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Hot Water Bottles
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I seem to spend most of my day with either a microwaveable wheat pack or hot water on my back. Neither of these things stay hot for very long.
I decided to heat the wheat heat pad for longer and the result was that it was hotter but didn't last noticeably longer. After using it a couple of times it went on fire.
So I am back to using a hot water bottle and my question is - does the amount of water poured into the bottle affect/effect (?) the length of time it stays hot?I
I decided to heat the wheat heat pad for longer and the result was that it was hotter but didn't last noticeably longer. After using it a couple of times it went on fire.
So I am back to using a hot water bottle and my question is - does the amount of water poured into the bottle affect/effect (?) the length of time it stays hot?I
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Yup.
The amount of heat in the water depends upon its volume but the rate at which heat is lost depends upon its surface area. If, say, you increase the volume by 8 (equals 2 cubed), you only increase the surface area by 4 (equals 2 squared). So you've got 8 times as much heat but only 4 times the area for it to dissipate through, so it's retained for longer.
That's why the contents of a small Thermos flask, holding just a single cup of coffee for one person, cool down very quickly but the contents of a big Thermos flask, holding enough coffee for an entire football team at half-time, remain hot for far longer.
The same will apply to your hot water bottle.
The amount of heat in the water depends upon its volume but the rate at which heat is lost depends upon its surface area. If, say, you increase the volume by 8 (equals 2 cubed), you only increase the surface area by 4 (equals 2 squared). So you've got 8 times as much heat but only 4 times the area for it to dissipate through, so it's retained for longer.
That's why the contents of a small Thermos flask, holding just a single cup of coffee for one person, cool down very quickly but the contents of a big Thermos flask, holding enough coffee for an entire football team at half-time, remain hot for far longer.
The same will apply to your hot water bottle.
I'd recommend a heating pad also. I've considered putting it on the sofa soon before I use central heating...and hope Toby doesn't think it's for him.
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