SoylentNews is people
SoylentNews
from the getting-a-charge-out-of-painting dept.
NewAtlas has a story about a new thermoelectric paint which can turn any surface into an electricity generator.
Thermoelectric generators convert heat or cold to electricity (and vice-versa). Normally solid-state devices, they can be used in such things as power plants to convert waste heat into additional electrical power, or in small cooling systems that do not need compressors or liquid coolant. However the rigid construction of these devices generally limits their use to flat, even surfaces. In an effort to apply thermal generation capabilities to almost any shape, scientists at the Ulsan National Institute of Science and Technology (UNIST) in Korea claim to have created a thermoelectric coating that can be directly painted onto most surfaces.
Variously known as the Peltier, Seebeck, or Thomson effect, the thermoelectric effect is seen in semiconductor devices that create a voltage when a different temperature is present on each side or, when a voltage is applied to the device, it creates a temperature difference between the two sides. In this instance, the new paint created by the UNIST researchers is used specifically to heat a surface when a voltage is applied.
The specially-formulated inorganic thermoelectric paint was created using Bi2Te3 (bismuth telluride) and Sb2Te3 (antimony telluride) particles to create two types of semiconducting material. To test the resultant mixture, the researchers applied alternate p-type (positive) and n-type (negative) layers of the thermoelectric semiconductor paint on a metal dome with electrodes at the top and the base of the dome.
Applying a voltage across the electrodes, the researchers were able to measure a temperature gradient from the hot top of the dome to the cooler bottom. According to the researchers, the entire device generated an average power output of 4 mW per square centimeter.
Original Paper (Complete text)
(Score: 1, Interesting) by Anonymous Coward on Monday December 12 2016, @06:53PM
In any thermoelectric device, you have two ends. In operation, either can be the cold end, and the other the hot end, depending on electrical polarity. A conventional TE device is a thin plate, with one end on each face; you sandwich the device between a hot object on one side, and a heatsink & fan (or watercooling block, or whatever) on the other side, and it works (either generating power by slowing down heat transfer, or increasing heat transfer at the expense of power).
In this painted-on TE device, however, the hot end is one region on the surface it's painted onto, and the cold end is another region on the same surface. So it won't work well at all on a surface with decent thermal conductivity (the experimenters used glass substrates), as most of the heat flux would go through the underlying surface rather than the TE layer. In fact, it's hard to think of a situation where it's likely to work well for generating electricity -- the paper depicts a hemisphere with a hot pole and a cold equator, but I can't think where one would see a heat distribution like that on an existing surface.
And if you have to add a glass substrate connecting, say, a hot metal cylinder head to a cooling block, and paint TE stripes on that substrate, the ability to shape that glass arbitrarily and paint over the resulting curves doesn't seem so great -- why not just shove a planar TE device between the head and the cooling block? Even if you have to add an aluminum spacer to adapt a curved surface on the head to a flat surface for the TE device, that doesn't seem worse than having to add a glass substrate connecting them.
And the worst part is, the extended length from the hot end to the cold end increases resistance, which is largely responsible for the very poor performance. Conventional planar configurations have many short elements because it works better that way.
If I try to think where this could make sense, the big potential of their hemispherical demonstration unit seems to not be conforming to arbitrary surfaces, but the fact that the hot and cold ends are not the same size. In fact, with the hot end at the center of a circular disc, and the cold end at the outside, you significantly increase the surface area -- this could benefit convection. Consider the back of your refrigerator -- it has a long, serpentine metal tube to cool and condense the refrigerant. We'd like to keep this cooled by natural convection, as it already is, but also generator electric power from it. Take a series of plastic discs with a hole sized to push onto that tubing, and paint/print TE elements on both sides -- push dozens (hundreds?) of these on each horizontal run of tubing, with insulating spacers between. The idea is that increase in surface area from the discs balances out the increased thermal resistance and the partial or complete insulation of the tubing between fins -- same heat flow as before, but now it (mostly) flows through the TE elements. (However, I haven't run any numbers on this, and even if it works, it's not clear this sinterable paint is actually better than stacking discrete semiconductor blocks around the tube, with an aluminum or copper heatsink fin, since we're disregarding the purported benefit of conforming to arbitrariy curved surfaces. In either case, I expect it will prove ludicrously expensive.)
In fact, it seems like the most interesting part in the paper may be the one not being talked about -- using this sinterable semiconductor "paint" to fill molds, and producing round discs (or arbitrary shapes) of p-type and n-type material to be used in building more conventional planar TE devices. I'm not sure how the semiconductor blocks in conventional devices are produced commercially -- it's not clear to me that molding to arbitrary shapes is (or is not) actually an interesting step forward for commercial devices, but it's interesting (even if not commercially, it could be good for hobbyists, though Te is toxic), and actually produces devices with reasonable performance.