Naked Science Forum
Non Life Sciences => Technology => Topic started by: scientizscht on 26/01/2019 18:35:08
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Hello!
Is there a material that can receive 0.5kW of heat or electricity in one hour and raise its temperature by 1 degree C?
I need it to be 50 qubic mm.
Thanks!
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Probably not.
It may not matter much, but do you mean a cube 50 mm on each side or do you really mean 50m cubic mm (about 3.7 mm each side)?
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Hello!
Is there a material that can receive 0.5kW of heat or electricity in one hour and raise its temperature by 1 degree C?
I need it to be 50 qubic mm.
Thanks!
0.5kWh is 1800000 J
50 cubic mm is 0.05 mL
So, if you're expecting all of that energy to be absorbed by the substance, and have only 1°C increase in temp, that would require a specific heat of 360000000 J*mL–1*°C–1. Water (which has a very high heat capacity) is only about 4.2 J*mL–1*°C–1. So this is not anywhere close to feasible...
However, there are some possible solutions, depending on how the question is interpreted. There are plenty of materials (like copper or aluminum) that would allow 0.5 kW of electrical energy to pass through them, while only retaining enough to warm them slightly (this will depend on many other factors not discussed here, like AC vs DC electricity, shape of the substance, etc.)
Another option, is to have a physical or chemical reaction driven by the thermal (or electrical) energy.
The latent heat of vaporization of water is 2260 J/mL (using that energy to convert liquid water to water vapor), which is a little bit closer to the required 360000000 than 4.2, but still very far.
Or that energy could go into splitting the water into hydrogen and oxygen, in which case this increases to 15800 J/mL...
Splitting aluminum oxide is only going to get you to 64880 J/mL (still 4 orders of magnitude too low).
And there isn't going to be much better than that (maybe some very exotic materials under very extreme conditions could get you one more order of magnitude, but not four)...
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You could try stuffing neutrons into a hydrogen nucleus, perhaps?
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You could try stuffing neutrons into a hydrogen nucleus, perhaps?
Just the sort of thing the average person does before breakfast.
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Is there a material that can receive 0.5kW of heat in one hour ?
Yes, my dog (a daschund). In winter, he sits right in front of the gas heater for ages, and I'm sure he absorbs close to 0.5kW.
His core temperature hardly changes.
I need it to be 50 qubic mm.
As mentioned above, this measure is unclear, but if we mean "small" (smaller than a daschund), you are probably looking at something like a heatsink.
The most efficient heatsinks use evaporation of a fluid and liquid transport via wicking.
The effective thermal conductivity varies with heat pipe length, and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper.
See: https://en.wikipedia.org/wiki/Heat_pipe
As noted previously, transporting electricity can be made much more efficient than transporting heat...
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I am so sorry I mean 0.5W
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do you mean a cube 50 mm on each side or do you really mean 50 cubic mm (about 3.7 mm each side)?
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do you mean a cube 50 mm on each side or do you really mean 50 cubic mm (about 3.7 mm each side)?
Yes, I mean 50qmm
The piece is 3mm x 3mm x 7mm
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OK, now what do you mean by "0.5W of heat or electricity in one hour "
Do you mean for an hour?
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OK, now what do you mean by "0.5W of heat or electricity in one hour "
Do you mean for an hour?
Basically the material will receive energy in the form of heat of 1600joules in total during one hour. So 0.5joules for every second.
What is the minimum temperature rise that this will induce after 1h? Using the right material?
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What is the minimum temperature rise that this will induce after 1h?
Well that's enough energy to melt about 5g of ice. YOu are trying to dissipate it in something like 50 mg of material
There's no way to store it in such a small object
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What is the minimum temperature rise that this will induce after 1h?
Well that's enough energy to melt about 5g of ice. YOu are trying to dissipate it in something like 50 mg of material
There's no way to store it in such a small object
1600 joules are needed to melt 5grams of ice? From 0C to 1C?
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1600 joules are needed to melt 5grams of ice? From 0C to 1C?
No
That's the energy needed to melt it without raising the temperature.
To convert it from ice at 0C to water at 0C
The latent heat of fusion of water is about 334 J/g
On a gram for gram basis, it's about as good as you get.
Why are you trying to do something impossible?
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1600 joules are needed to melt 5grams of ice? From 0C to 1C?
No
That's the energy needed to melt it without raising the temperature.
To convert it from ice at 0C to water at 0C
The latent heat of fusion of water is about 334 J/g
On a gram for gram basis, it's about as good as you get.
Why are you trying to do something impossible?
I don't know, it doesn't look so impossible to me. There are materials that you make a glove and it allows you to touch a flame or something very very hot without getting burned. There are heatshields that from one side you have 1000C and from the other side you have 100C.
Are you sure it is impossible? Aren't there materials that are very very resistant to get hot?
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Aren't there materials that are very very resistant to get hot?
Yes, Ice is one of the very best of them.
https://en.wikipedia.org/wiki/Latent_heat#Table_of_specific_latent_heats
You are looking for something that's a hundred times better than one of the best.
There are materials that you make a glove and it allows you to touch a flame or something very very hot without getting burned.
They work by making sure that very little power is actually carried to your hand. They insulate the heat rather than trying to absorb it.
(also, your hand is mainly water, which has a very high heat capacity, and it's also connected to the rest of you which is not only a big "thermal mass", but is able to deliberately shed heat by sweating.)
The thing that keeps the inside of the glove cool is as much you as it is the glove.
What are you actually trying to do?
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You need to understand the difference between heat (the total kinetic energy of all the molecules in an object) and temperature (the average kinetic energy of a molecule in an object). Some materials retain their integrity at high temperatures, some conduct heat very slowly.
The amount of heat required to raise the temperature of a substance is its specific heat capacity, expressed in joules per kilogram.degree.
The amount of heat required to change the state of a substance is the latent heat of fusion or evaporation expressed in joules per kilogram.
The rate of heat transfer across a substance depends on its thermal conductivity, expressed in watts per meter.degree
So if you can state exactly what property you are looking for, someone can direct you to the appropriate table of material properties.
A device like an oven glove needs to have a low thermal conductivity, and a melting point well above the highest temperature you are likely to encounter. A dry cotton towel is the standard tool in restaurant kitchens because it contains plenty of air, which has a very low conductivity A wet towel is useless because although its heat capacity is about 3000 times that of a dry one, water is a very good conductor of heat.
You also need to specify your starting conditions. The latent heat of melting ice is very useful as a heat shield at low ambient temperatures, but the latent heat of vaporisation of water is 7 times as large.