3 ms·

Glycol has a much lower heat capacity than water, I don't get why adding that to water would increase the capacity to store energy? It's usually added as an ant

Glycol has a much lower heat capacity than water, I don't get why adding that to water would increase the capacity to store energy? It's usually added as an anti-freezing agent to protect the pipes or to prevent fouling

Spivak 3y ago
That's a good point I hadn't even thought about it. It seems the property they want is the higher boiling point but I don't know enough about heat storage to know why they consider that a win compared to pure water.
- 15457345234 3y ago
  A glycol/water mix is almost always chosen primarily because of the anticorrosion purposes and freezing point alteration. If you have a racing car you run pure water with a bit of 'wetter' (a surfactant) in the cooling system as it gives you the highest thermal capacity / cm^3 ratio. If you want to increase the boiling point (to run a smaller heat exchanger) that's most trivially achieved through pressurisation.
m463 3y ago
Hmm I wonder too. Most energy storage systems store a lot of energy when a phase change is involved. for instance ice at 32F -> water 32F is 80 calories.
01HNNWZ0MV43FF 3y ago
They probably run it very hot since the computer controller can prevent scalding. If the glycol elevates the boiling point, you could store energy above 100 C. The human-safe temperatures on a normal water heater must be closer to 50 or 60 C. Room temperature is about 20? I imagine if you more than double your temperature difference, you might more than quadruple your energy storage, that might offset the lower heat capacity of the glycol. Sort of like high-voltage power lines being able to use thinner wires but requiring thicker insulation (meters of air) so they don't kill anyone. User 15457345234 pointed out that you could just pressurize the water. But building a steam pressure vessel requires a weight-safety tradeoff. Maybe a mixture that boils hotter is cheaper overall than safely containing steam pressure.

Spivak 3y ago

That's a good point I hadn't even thought about it. It seems the property they want is the higher boiling point but I don't know enough about heat storage to know why they consider that a win compared to pure water.

15457345234 3y ago
A glycol/water mix is almost always chosen primarily because of the anticorrosion purposes and freezing point alteration. If you have a racing car you run pure water with a bit of 'wetter' (a surfactant) in the cooling system as it gives you the highest thermal capacity / cm^3 ratio. If you want to increase the boiling point (to run a smaller heat exchanger) that's most trivially achieved through pressurisation.

m463 3y ago

Hmm I wonder too. Most energy storage systems store a lot of energy when a phase change is involved. for instance ice at 32F -> water 32F is 80 calories.

01HNNWZ0MV43FF 3y ago

They probably run it very hot since the computer controller can prevent scalding. If the glycol elevates the boiling point, you could store energy above 100 C. The human-safe temperatures on a normal water heater must be closer to 50 or 60 C. Room temperature is about 20? I imagine if you more than double your temperature difference, you might more than quadruple your energy storage, that might offset the lower heat capacity of the glycol. Sort of like high-voltage power lines being able to use thinner wires but requiring thicker insulation (meters of air) so they don't kill anyone. User 15457345234 pointed out that you could just pressurize the water. But building a steam pressure vessel requires a weight-safety tradeoff. Maybe a mixture that boils hotter is cheaper overall than safely containing steam pressure.