That ultra-white paint that helps refresh surfaces? Make your own!
It all started with [KB9ENS] looking for paints or coatings for passive or radiative cooling, and in the process he decided to tinker with his own. Not only is it perfectly accessible to a home experimenter, but its early results also look promising.
[KB9ENS] has discovered a type of ultra-white paint formulation that not only reflects heat, but is able to radiate it out into space, cooling the painted surface to a temperature below room temperature. This is intriguing because while commercial paints can insulate and reflect heat, they cannot make a surface colder than its surroundings.
Anecdotally, this painted battery section of a solar charger gets too hot to touch in direct sunlight. But when painted, it was just warm.What really got [KB9ENS] thinking is that at its core, passively cooled paint in research is basically a collection of different particle sizes of barium sulfate (BaSO₄) mixed in an acrylic binder. Both of these ingredients are remarkably accessible. Half a pound of BaSO₄ at a pottery supply store was only a few dollars, and a regular acrylic base is easily obtained from almost any paint or art supplier.
[KB9ENS] decided to mix up a raw batch of BaSO₄ paint, apply it to some things, and see how well it compared to other paints and coatings. He wetted the BaSO₄ with isopropyl alcohol to help it mix with the base, and did a few different concentrations. A concentration of 60% by volume seemed to give the best overall results.
There's no indication if cooling below room temperature is occurring, but according to a non-contact thermometer, even this homemade mix is better at preventing sunlight from heating things up than similarly applied commercial paints (although it was only marginally better than the titanium dioxide-based white paint in the initial test.)
[KB9ENS] also painted the battery section of a solar charger with their house paint and noted that under normal circumstances - i.e. direct sunlight - this section gets too hot to touch, with the paint coating it was just hot.
True passive cooling can do more than just keep something cooler than it otherwise would be. We've recently seen it used to passively and continuously generate energy thanks to its ability to create a constant temperature differential, day and night.
It all started with [KB9ENS] looking for paints or coatings for passive or radiative cooling, and in the process he decided to tinker with his own. Not only is it perfectly accessible to a home experimenter, but its early results also look promising.
[KB9ENS] has discovered a type of ultra-white paint formulation that not only reflects heat, but is able to radiate it out into space, cooling the painted surface to a temperature below room temperature. This is intriguing because while commercial paints can insulate and reflect heat, they cannot make a surface colder than its surroundings.
Anecdotally, this painted battery section of a solar charger gets too hot to touch in direct sunlight. But when painted, it was just warm.What really got [KB9ENS] thinking is that at its core, passively cooled paint in research is basically a collection of different particle sizes of barium sulfate (BaSO₄) mixed in an acrylic binder. Both of these ingredients are remarkably accessible. Half a pound of BaSO₄ at a pottery supply store was only a few dollars, and a regular acrylic base is easily obtained from almost any paint or art supplier.
[KB9ENS] decided to mix up a raw batch of BaSO₄ paint, apply it to some things, and see how well it compared to other paints and coatings. He wetted the BaSO₄ with isopropyl alcohol to help it mix with the base, and did a few different concentrations. A concentration of 60% by volume seemed to give the best overall results.
There's no indication if cooling below room temperature is occurring, but according to a non-contact thermometer, even this homemade mix is better at preventing sunlight from heating things up than similarly applied commercial paints (although it was only marginally better than the titanium dioxide-based white paint in the initial test.)
[KB9ENS] also painted the battery section of a solar charger with their house paint and noted that under normal circumstances - i.e. direct sunlight - this section gets too hot to touch, with the paint coating it was just hot.
True passive cooling can do more than just keep something cooler than it otherwise would be. We've recently seen it used to passively and continuously generate energy thanks to its ability to create a constant temperature differential, day and night.
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