Body Heat Energy Generation

BuzzSkyline writes "Researchers in Belgium have developed devices to harvest the waste heat our bodies throw off in order to convert it to electricity to run devices such as a wristband blood oxygen sensor and an electrocardiogram shirt. As a side benefit, the power sources help cool you down and keep you looking cool, all while running sundry micropower devices. In fact, the researchers mention that the energy harvesting head band works so well that it can get uncomfortably cold. In that case, they say, 'This problem is solved in exactly the same way as someone solves it on the body level in cold weather: a headgear should be worn on top of the system to limit the heat flow and make it comfortable.' But it would be such a shame to cover up the golden heat-harvesting headband with a hat."

not usually how it works

[v1]

As a side benefit, the power sources help cool you down

Typically if you take something that's trying to dump waste heat, and install something that recovers power from that heat, it creates an insulating effect, reducing the cooling the object was receiving. Heat can't be turned directly into energy, only difference in heat. Adding a heat reclamation system doesn't help cool something down because the power it's getting is from the temperature difference, not the heat itself. Instead it takes power from the temperature gradient, and as such reduces the temperature gradient, thus reducing cooling efficiency.

Re:Cold?

[Anonymous Coward]

Compared to your body temp, ambient temperature is cold. Try putting a piece of ambient steel against your skin and tell me if it's cold.

Re:Cold?

[confused one]

It's better at conducting heat away from your skin than air; and, because it's extracting energy and using a small radiator as a heat sink, it remains colder than the skin. It only feels cold. It would never actually reach ambient because your body is keeping it above ambient, with the asumption that "ambient" is well below body temperature. From the article:

"At 22C, it produces about 30W/cm2, i.e., close to the theoretical limit of power generation on people at this temperature in a compact device. There is, however, a drawback of such high power generation: at lower ambient temperatures, the heat flow rapidly exceeds the sensation of discomfort and the device turns into uncomfortably cold object. For example, at 19C, the TEG already produces 3.7 mW, but the sensation of cold becomes too annoying. "

Re:Bullshit

[jdunn14]

I was going to just mod you down, but the summary at least never said anything about lowering any part of the device below ambient. It said that the headband will "feel cold". Touch a piece of wood at room temperature. It will sometimes "feel" warm. Do the same thing with a piece of steel. It will "feel" cold. This is true even if both are at the exact same temperature. Heat conduction [wikipedia.org]

The kids section of my local science museum even has hand-shaped pieces of different materials to demonstrate the effect.

Re:not usually how it works

[maxwell demon]

Well, unless they built a perpetual motion machine of the second kind. :-)

But actually, it may be due to the fact that normally you don't really feel the real temperature, but when it's cold, the temperature of the air directly at your skin is still higher than the surrounding air (unless there is wind, which is why you feel cold faster when there's wind). If this device has better heat transport to the surrounding air (e.g. because the surface to air is larger than the surface to you skin), you may feel colder that normally.

Re:Cold?

[Issarlk]

The headband is at ambiant temperature, but your body is much warmer. Heat flow from your body to the headband and leaves a cold sensation on your skin. The material of the headband applied to the body is probably a good conductor of heat ; it's like with a piece of metal that feels cold to the touch and a piece of wood that doesn't while both are at room temperature.

Re:not usually how it works

[JerryLove]

Yes. Power is generated when heat is moved from an area of high concentration (your head) to an area of low concentration (the air).

If the device facilitates that transfer in order to get more energy from it; then it would indeed cool you down. It requires only tha the headband be more effective at radiating heat than your skin is.

Blue Smarties. . .

[Fantastic Lad]

Though perhaps they won't need massive amounts of force to subdue humanity; from what I've seen, most people would choose the blue pill.

I've long believed that the physical reality we live in, being entirely a product of energy and thus little more than an illusion, the idea of matter and as such is inherently linked to consciousness. . , that all things in our reality can be observed as and understood to be metaphors for systems and conflicts we are experiencing in our conscious awareness.

-You have to plug humans into the Matrix at the start of their lives when kids are most inquisitive. Red Smarties are the most popular color, and the battle over Blue Smarties rages on. . !

In 2006 it was announced that Nestlé [wikipedia.org] were removing all artificial colourings from Smarties in the UK, owing to consumer concerns over the effect of chemical dyes on children's health. Nestlé decided to replace all synthetic dyes with natural ones, but as they were unable to source a natural blue dye, the blue Smarties were removed from circulation, and white Smarties were introduced in their place. White Smarties were later removed from the range, and blue Smarties were re-introduced in the UK in February 2008, using a natural blue dye derived from the cyanobacteria spirulina.

Dieticians [...] said that the blue coloring was the one which was most likely to cause intolerance in kids. [medindia.net] "The thing about blue is there are no natural equivalents. All the others can be obtained from natural sources," said Linda Hodge, a dietitian. "I believe the Brilliant Blue causes the worst symptoms of chemical intolerances."

She added that when consumers are being tested for intolerances, the first color tried out is yellow. "When we are trying to determine if a person is sensitive to food coloring, we test them first on yellow. If there is no reaction we then use red, then blue. We don't start off with blue because it is a the strongest color and gives the worst reactions," she observed.

Humans naturally try to reject the Matrix. "Entire crops were lost."

Neat, huh?

-FL

Re:Wristband blood oxygen sensor?

[quercus.aeternam]

If you need continuous monitoring, you probably need more accuracy than non-invasive means will get you.

As of 2003 (when I spent a summer internship at Sensys Medical), the best non-invasive method (near-infrared spectroscopy) would get you within 20% of the actual value - and that's with an initial blood sample for calibration. IIRC, most consumer devices are accurate to 10-15%, with cheaper clinical devices being accurate to 5%.

Knowing the hardware necessary for even that degree of accuracy as well as the difficulties we had getting a clean signal while trying to shrink stuff down to shoebox size, there's no way that this would work - not with IR, anyway.

The accuracy should have improved since then, and these numbers are purely from memory. That said, you are right. That would be something - but given accuracy and demand, don't plan on it in your lifetime.

Re:Screw that

[Thelasko]

Unfortunately, the summary and the Physics Buzz article grossly misrepresent the research being done here. The device only becomes "uncomfortably cold" when ambient temperatures are below what are considered comfortable by most people. The AIP article also notes that it is unlikely that this device will ever be able to harvest enough energy to power current portable devices. They instead suggest that future devices be designed around the power output of this device.

Re:Screw that

[Wardish]

Sorry to say, since it's a heat engine, it moves heat from warmest to coolest. In hot weather YOU are the coolest. The device would warm you up.