Body heat as a power source

Discussion in 'General Science & Technology' started by Plazma Inferno!, Sep 1, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

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    Our muscle activity and metabolism cause our bodies to produce constant heat, some of which is released through the skin into the environment. Because of the relatively small temperature difference between skin (approximately 32°C) and the temperature of our surroundings, it is not so easy to make use of body heat.
    Previous thermoelectric generators, such as those based on semiconductors, produce too little energy, are costly, or are too brittle for use in wearable systems. Thermocells with electrolyte solutions are difficult to integrate into extensive wearable systems.
    A team led by Jun Zhou at Huazhong University of Science and Technology (Wuhan, China) has now found a solution to this problem: thermocells with gel-based electrolytes.
    The researchers are making use of the thermogalvanic effect: if two electrodes in contact with an electrolyte solution—or an electrolyte gel—are kept at different temperatures, a potential difference is generated. The ions of a redox pair in the electrolyte can rapidly switch between two different charge states, accepting or releasing electrons at electrodes with different temperature.
    In order to use this to produce a current, the scientists combined two types of cells containing two different redox pairs. Each cell consists of two tiny metal plates that act as electrodes, with an electrolyte gel in between. The first cell type contains the Fe2+/Fe3+ redox pair. The second type of cell contains the complex ions [Fe(CN)6]3-/[Fe(CN)6]4-.
    In an environment at 5 °C, it was possible to produce 0.7 volts and about 0.3 µW. By optimizing this system, it should be possible to improve the power, even with smaller temperature gradients.
    This flexible, wearable thermocell based on two different gel electrolytes is described in the journal Angewandte Chemie ("Wearable Thermocells Based on Gel Electrolytes for the Utilization of Body Heat").

    http://www.nanowerk.com/nanotechnology-news/newsid=44358.php

    Paper: http://onlinelibrary.wiley.com/doi/...ionid=F06B1A768E9829ADEF48B8C975A7903B.f03t02
     
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  3. Baldeee Valued Senior Member

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    Is anyone convinced of any economical or even practical benefit for this?
    Will it not cost more in energy terms than will actually be produced by the device?
    And in what situations will body heat ever be worth turning into power before using mechanical exchangers?
    Okay, Arctic explorers caught without other power sources needing to power a satellite phone... maybe.

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    Wearable tech that generates through motion, I get that, although small wind-up generators (spring or dynamo based) are still surely the easiest and cheapest means of converting human to electrical power on demand?
     
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  5. Russ_Watters Not a Trump supporter... Valued Senior Member

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    The Matrix was a science fiction movie (trilogy).
     
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  7. exchemist Valued Senior Member

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    Arctic explorers won't want this. It will cool them down, the last thing they need!

    The reason it is so useless is given in the second line - the lack of significant temperature difference between the skin and the environment, unless you are in a situation (e.g. the Arctic) in which it is imperative to maintain a temperature that is as large as possible, thus precluding the use of the device at all.
     
  8. billvon Valued Senior Member

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    You would need over a million people to generate enough energy with this system to power a cellphone. (And at that point, the guy you want to call is probably going to be right there anyway.)
     
  9. Russ_Watters Not a Trump supporter... Valued Senior Member

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    That isn't quite right, but pointed in the right direction: the mechanism of any thermodynamic power source is to get in the way of a gradient (in this case a temperature gradient), and thereby harness it. So adding this to an existing temperature gradient will provide insulation. The problem is that to work the best the gradient needs to be as steep as possible: so they need to be naked except for the thermoelectric suit!
     
  10. exchemist Valued Senior Member

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    What I meant was that to get power out you need a heat flow, whereas the object of insulation is to stop heat from flowing.

    Whatever energy is harnessed by this device must come from body heat, so the more power it extracts, the more heat must flow out of the body to power it.
     
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