Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 26/09/2015 01:50:02
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Karl asked the Naked Scientists:
Today I would like to ask two related science questions:
What substances other than water are there that have a maximum density at a temperature not far from ordinary ambient temperatures?
And have people tried to harvest energy from temperature changes around such maximum densities, possibly utilizing some mechanical advantage to turn the density changes into macroscopic movements?
I'm a regular listener to your podcast (http://www.thenakedscientists.com/HTML/podcasts/), and I really like the way you interview experts, asking them the right questions instead of just "dumbing down" what they say, as so many other "popular science" shows do.
What do you think?
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Premise: water [has] a maximum density at a temperature not far from ordinary ambient temperatures
Bear in mind that when you talk of density and temperature, you should also consider that pressure also has a major impact on density.
At high pressures, different phases (crystal structures) of water ice appear; some of them have a higher density than liquid water. For example, Ice X (http://www1.lsbu.ac.uk/water/ice_phases.html) (Roman Numerals 10) has a density around 2.5 times greater than liquid water.
Going the other way, at low pressures (approaching a vacuum), the density of water is extremely low, because water becomes a vapor at "room temperature" (http://www1.lsbu.ac.uk/water/water_phase_diagram.html) (273K).
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Both atomic count per volume and mass per volume data can be found searching on Google...
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Both atomic count per volume and mass per volume data can be found searching on Google...
So can videos of Rick Astley.
They won't tell you about variation of density with temperature.
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At standard atmospheric pressure, water has a local maximum in density at around 4°C which is ambient temperature in a large part of the world at one point or another per year...
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Both atomic count per volume and mass per volume data can be found searching on Google...
So can videos of Rick Astley.
They won't tell you about variation of density with temperature.
Google returned 103 000 000 results on the subject of "Atomic density vs temperature"...
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Both atomic count per volume and mass per volume data can be found searching on Google...
So can videos of Rick Astley.
They won't tell you about variation of density with temperature.
Google returned 103 000 000 results on the subject of "Atomic density vs temperature"...
Good; did any of them actually answer the OP's question?
If so, please share that wisdom.
Otherwise please explain why you think it's a useful result to cite.
Oh, BTW, what if the best candidate for the OP's purpose is a compound?
It won't have a meaningful atomic density.
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Karl asked the Naked Scientists:
And have people tried to harvest energy from temperature changes around such maximum densities, possibly utilizing some mechanical advantage to turn the density changes into macroscopic movements?
What do you think?
Highest density does not necessary provide the highest heat conductivity...
If you are trying to construct the most efficient thermo-electric cell then you should check the current state of the art...
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And have people tried to harvest energy from temperature changes around such maximum densities?
There have been proposals around Ocean Thermal Energy Conversion (http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion) (OTEC). This utilizes the fact that colder water is denser, and lies at greater depth than warmer water.
Use this temperature difference to generate electricity.
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Density only states at a given temperature how much volume does a certain mass of material take up.
Now since you cannot create nor destroy mass (as long as you stay away from nuclear reactors).. You are left with 2 variables to play with.. Temperature and volume.. all heat engines use the combination of these to produce macroscopic work.
You need a hot source (energy input) and a cold source (energy sink) to create the cycle.. the greater the difference the greater the efficiency.
The main issue that we face is that density and temperature typically have a linear relationship other than at change in states.. and we operate around the change in states to generate maximum density difference to generate our work. (plus its much harder to get the energy from solids than it is from liquids or gasses)
As for other substances that have maximum densities at ambient, you need to look at materials that form a certain crystalliune structure when they turn to solids, meaning that the solid is less dense than the liquid.. (gallium, bismuth, Antimony, Germanium, Silicon and Acetic Acid also exhibit this behaviour) most materials are at maximum density when they are solid and get more dense as temperature decreases.
I think gallium has a melting point within an extended ambient (roughly 30degc) range.. and can be used with soft metals to create an alloy that has a lower melting point..
Acetic Acid is quite similar to water but since it is an acid probably less useful.
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This article is rather technical, but tries to predict Negative Thermal Expansion in a variety of materials at a variety of pressures. It does mention the causes of it in water, as localized phase changes.
http://www.nature.com/articles/srep07043
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Karl asked the Naked Scientists:
And have people tried to harvest energy from temperature changes around such maximum densities, possibly utilizing some mechanical advantage to turn the density changes into macroscopic movements?
What do you think?
Highest density does not necessary provide the highest heat conductivity...
If you are trying to construct the most efficient thermo-electric cell then you should check the current state of the art...
Why would you think this has anything to do with thermoelectric effects or heat conductivity?