Sodium Sulfate (Na2SO4) thermal battery questions
I've been reading about various ways that Sodium Sulfate (decahydrate) can be used to store heat energy for later use. What makes it good for this
process is it's heat of fusion at 252kJ/kg (vs H2O at 334kJ/kg) at 90 deg F.
I always get a little confused as to how the energy in the phase change works and want to clear this up before I continue my research.
Once the Sodium Sulfate is heated to 90 F, it will require significantly more heat to reach the 91 degree mark (well, I guess it will still be 90 F,
but liquid..?). The energy required to do this is the latent heat or heat of fusion (IDK which, I've seen both used). So if it took 10kJ to raise
each kg 1 deg F (this is not accurate, just example), it will take 252kJ/kg to go from the solid state to the liquid state, while remaining the same
temp or will it rise 1 deg F?
Let's assume this battery is for heating water for target temps of 90-210 deg F.
Now once the substance is liquid, is there any benefit to raising the temp to say 500F or would the application be better served by incorporating more
sodium sulfate to keep the material near the phase change state.
Now if 100kg of sodium sulfate were heated to 92 deg F, (through the phase change state), how hot can the harvested temps (say through liquid in
pipes) get from this 100kg @92 deg F if the temp were to drop to ~89 deg F. Can the heat pulled from the system ever get above the current temp of
the storage device or is it's main use to store large capacities of heat at this "moderate" temperature?
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