Naked Science Forum
General Science => General Science => Topic started by: Camerart on 02/06/2022 08:21:01
-
Hi,
I'm thinking about different ideas around solar energy, in particular heat storage.
Years ago, I heard that if a chemical is mixed with water, it can then store more heat that simple water, due to some conversion, that needs heat. I can remember much more than that.
This got me to think about alternatives. I know that copper can hold a lot of heat, but is expensive compared to water. Then there's storage heater bricks, I think they're not pricey.
Is there a chart of materials, that show their heat retaining quaities?
Cheers, Camerart.
-
https://en.wikipedia.org/wiki/Table_of_specific_heat_capacities
-
The heat capacity reflects how much heat a material will hold without changing state (state=solid/liquid/gas).
- And water has one of the best price/performance ratios!
However, when a material changes from solid to liquid, it can absorb a considerable amount of heat, without the temperature changing very much at all (the same for changing from liquid to gas).
- This parallel thread gets a bit technical in places, but looks at whether you can regulate temperature in a home using materials which change state at a convenient temperature like 25C (water is not ideal for this, as its melting point is too low, and its boiling point is too high).
https://www.thenakedscientists.com/forum/index.php?topic=84812.0
-
Storage heater bricks are essentially just concrete. It's the most abundant man-made product ever, ridiculously cheap, and very good for building. And it was invented in Britain!
Architect friends in Maine use a very thick (at last 60 cm) floor slab, well insulated from the subsoil, and illuminated by a south-facing triple-glazed window. Together with plenty of insulation on the other walls and roof, this produces a completely passive 4-bedroom family house that stays at a sensible indoor temperature (15 - 25 deg C) year-round whilst the outdoors varies between -20 and +40. Been there, loved it.
-
And it was invented in Britain!
A more orthodox view doesn't require time travel as an explanation for concrete in ancient Greece.
-
Pre-19th century "concrete" used lime cement. Practically all modern concrete uses Portland cement, for all sorts of good reasons. The etymology of "concretion" may appeal to pedants, but the compressive strength and water resistance of Portland cement appeals to engineers. Earlier materials are better classed as mortared ballast.
-
Hi,
Concrete is a bit permanent for a test! Is there a comparison between sand, concrete, water, that is understandable to the laymen? e,g, top ten.
When I look at the chart, I noticed that wood seemed to be able to hold heat well, is this true?
C
-
Any table of specific heat capacities will do. Just multiply by the relative densities to get the heat capacity per unit volume.
Concrete has about 20% of the specific heat capacity of water, and about 2.5 times the density. In practice it would be comparable with oak which has about half the specific heat capacity and 0.8 times the density of water. Either is a lot easier to play with than sand or water, which need containment!
-
Any table of specific heat capacities will do. Just multiply by the relative densities to get the heat capacity per unit volume.
Concrete has about 20% of the specific heat capacity of water, and about 2.5 times the density. In practice it would be comparable with oak which has about half the specific heat capacity and 0.8 times the density of water. Either is a lot easier to play with than sand or water, which need containment!
Hi A,
I'm trying to zone in on the most practical test, I can do, taking lots of things into consideration.
My ideas around:
PV: would be to have a central core where the heater is, surrounded by a block of whatever, then insulation.
Thermal: would be probably water, contained in some kind of heat exchanger, trying to stem the mixing of hot and cold, where the central core would be almost boiling, and controlled by perhaps a pump.
A possible idea is to sink down below the house (I undertsand the dangers etc) and make perhaps a tank, or depending on cost piping. I've had previous dealings with heat exchangers and building, although this needs quite some consideration.
Thanks all,
C.
-
Hi,
I haven't had any suggestions to my question, what chemical when mixed with water makes it hold more heat?
C
-
If you are going to sink a bore below the house, use the soil as a heat store. Search for reversible ground-source heat pumps and save yourself a lot of hard work!
Preferably, put the bore some way outside the dwelling boundary so you don't disturb the foundations when you alter the subsoil temperature.
-
Hi,
I haven't had any suggestions to my question, what chemical when mixed with water makes it hold more heat?
C
As a liquid, probably nothing of any use.The specific heat capacity of water is anomalously high. You really need a change of state to make a big difference. The latent heat of crystallisation of sodium metabisulphite or ammonium chloride from solution seems to ring a cracked bell in my memory but BC has a better grasp of such things.
-
I'm trying to zone in on the most practical test, I can do, taking lots of things into consideration.
Mixing a bag of concrete with a bucket of water is very easy, and you can make the resulting solid any shape you like.
-
If you are going to sink a bore below the house, use the soil as a heat store. Search for reversible ground-source heat pumps and save yourself a lot of hard work!
Preferably, put the bore some way outside the dwelling boundary so you don't disturb the foundations when you alter the subsoil temperature.
Hi A,
A different subject I think.
C
-
I'm trying to zone in on the most practical test, I can do, taking lots of things into consideration.
Mixing a bag of concrete with a bucket of water is very easy, and you can make the resulting solid any shape you like.
Hi A,
As mentioned a ton of concrete is a bit too permanent compared to a ton of water, so I'll stick to water for now.
For any PV tests though, I would need a none circualting section.
C
-
Hi,
I haven't had any suggestions to my question, what chemical when mixed with water makes it hold more heat?
C
It isn't obvious that there is an answer.
Do you mean something like this
Salt hydrate technology
Here
https://en.wikipedia.org/wiki/Thermal_energy_storage#Thermo-chemical_Heat_Storage
-
Hi,
I haven't had any suggestions to my question, what chemical when mixed with water makes it hold more heat?
C
It isn't obvious that there is an answer.
Do you mean something like this
Salt hydrate technology
Here
https://en.wikipedia.org/wiki/Thermal_energy_storage#Thermo-chemical_Heat_Storage
Hi B,
Your link is a bit of an eyful, for a dyslexic, but the answer is probaly in there somewhere :)
I searched and found this which sounds like what I remember, but I don't think it was common salt, so maybe different chemicals have different properties?
[ Paint each bottle with flat black enamel on one side and with white enamel on the other, using a paintbrush. Black paint absorbs sunlight, so the black side faces the sun. White inhibits heat transmission, so the white side faces the greenhouse wall.
Fill the bottles with a saturated solution of salt and water. A saturated solution is one in which no more salt will dissolve. Salt raises the boiling point of water, thereby increasing the amount of heat each bottle can retain. ]
C