Backyard Aquaponics
A place to discuss aquaponics

hi
anyone had any experience storing heat in Glauber's salt A salt, sodium sulfate decahydrate, that melts at 90°F; a component of eutectic salts that can be used for storing heat.


blodger

Nope, but now we are entering really interesting waters

When we melt things a HUGE amount of heat is required. The substance will stay at its melting temperature until it is all melted, absorbing a huge amount of Latent heat. when the temperature goes below it "freezing" point the heat is released again.

Exactly the pricipal behind refrigeration except we use gas/liquid phases.

FYI normal parrafin wax melts at around the 50C mark. Trick is to find a compound with a useable phase change temperature.

90F is 32C, and seem like reasonable temperature.

For those of you that are not fammiliar with specific and latent heats i'll give an example that pretty much sums it up, and you can try it at home too

put a pot of water on the stove, with a thermometer in it.

You will notice the temperature going up steadily until around the 100C mark. This is specific heat, the heat absorbed effects a rise in temperature

At 100C (depending on impurities) it will just sit there, obviously absorbing heat from the flame but with no rise in temperature. This latent (hidden) heat. The water needs to absorb enough energy to effect a pahse change to steam. Therein lies huge heat storage capability at a substances phase change temperature.

This is why being burnt with steam at a temp of 100C will give you far worse burns than water at 100C. The steam holds much more energy at the same temperature as the water
(2260Kj energy per Kg more than water at the same temp)

I love physics!
http://www.physchem.co.za/Heat/Latent.htm

B.u.k,

Is the salt readily obtainable and reasonably priced??

i will chech and get back to you

SODIUM SULFATE, ANHYDROUS is commonly availabe over here . £34.40 for 2.5 kg. my chemistry is crap. would this need adding to water to create sodium sulfate decahydrate . 10 mole of water (Na2SO4 10H2O)
did read on one site that it 'wears out' so might need replacing regularly.

blodger

You're losing me a bit my chemistry is non-existant really.

But this idea is a real good one. And I grasp it.

Are there a range of low boiling point substances?