A Compact Electrohydrodynamic Pump Using Copper And TPU

Electrohydrodynamics (EHD) involves the dynamics of electrically charged fluids, which effectively means making fluids move using nothing but electric fields, making it an attractive idea for creating a pump out of. This is the topic of a 2023 paper by [Michael Smith] and colleagues in Science, titled “Fiber pumps for wearable fluidic systems”. The ‘fiber pumps’ as they call the EHD pumps in this study are manufactured by twisting two helical, 80 µm thick copper electrodes around a central mandrel, along with TPU (thermoplastic polyurethane) before applying heat. This creates a tube where the two continuous electrodes are in contact with any fluids inside the tube.

For the fluid a dielectric fluid is required to create the ions, which was 3M Novec 7100, a methoxy-fluorocarbon. Because of the used voltage of 8 kV, a high electrical breakdown of the fluid is required. After ionization the required current is relatively low, with power usage reported as 0.9 W/m, with one meter of this pump generating a pressure of up to 100 kilopascals and a flowrate of 55 mL/minute. One major limitation is still that after 6 days of continuous pumping, the copper electrodes are rendered inert due to deposits, requiring the entire system to be rinsed. Among the applications the researchers see artificial muscles and flexible tubing in clothing to cool, heat and provide sensory feedback in VR applications.

While the lack of moving parts as with traditional pumps is nice, the limitations are still pretty severe. What is however interesting about this manufacturing method is that it is available to just about any hobbyist who happens to have some copper wiring, TPU filament and something that could serve as a mandrel lying around.

Thanks to [Aaron Eiche] for the tip.

21 thoughts on “A Compact Electrohydrodynamic Pump Using Copper And TPU

  1. Smith et al. are taking some confusing liberties with language here.

    di·​elec·​tric ˌdī-ə-ˈlek-trik
    : a nonconductor of direct electric current

    “When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean – neither more nor less.”

    1. Pretty snarky comment.
      Im not sure where your definition comes from, but the dielectric constant of a material has much more to do with it’s ability to become polarised while still non conducting.
      Think about capacitors. They most certainly have a Dielectric layer, and are also most certainly are used in AC circuits as often as DC

      1. It’s straight from Merriam-Webster, in case that makes a difference. I mean, you’re right to take offense at many of the spelling abuses old Noah did to the language when he penned his dictionary, but it’s at least accurate.

        The quote is from a children’s book. Were you so distracted by it that you skipped reading the paper entirely and rushed right into posting an orthogonal comment? What you stated has nothing to do with the contents of the paper, or my comment.

        If you ionize a dielectric and conduct DC current through it, like the paper authors say they do, it’s by definition not a dielectric any more. But the authors define the word the way they choose anyway, like Alice’s acquaintance did in the children’s story.

  2. The researchers did an amazing amount of work here. Impressive.

    “current” of 0.9 W/m notwithstanding, the measured peak efficiency is between 0.73 to 2.1 percent (and zero at maximum pressure). It also requires a very specific fluid. Neat niche trick, but not going to replace general purpose pumps or actuators any time soon.

    With alternating positive and negative electrodes, I don’t get their argument of why this device has a preferred direction of flow. The say the spacing is asymmetric, causing the electric field strength to be greater in one direction than the other, but this also means there is more fluid to act on between electrodes in the opposite direction, which (naively) should cancel out forces, giving no preferred direction. Clearly their work shows it works, however.

    With all that ionization of the “dielectric” I wonder how long the fluid lasts. They uses fresh fluid for each test, and the electrodes degrade, so there’s obviously some breakdown happening.

    1. I think it’s pretty obvious this wouldn’t be meant to replace general purpose pumps, it’s definitely for some niche medical thing when even a peristaltic pump is too much. Idk what that purpose is, though

  3. This pump’s best application is making a peristaltic pump look like an awesome and highly practical choice. Its 2nd-best application is probably some niche application where moving parts absolutely must be eliminated at all costs.

    1. I agree that this pump is not practical at the moment. But this fails the simple sniff test of the desire to remove moving parts at all costs as well. Removing moving parts is a decision based on reducing wear consequences. This pump is using sacrificial copper wires to move a fluid. It will probably wear out faster than a similar spec mechanical pump.

      1. There’s also the matter of TPU hardening over time, and being well known for leeching its plasticizers.

        Then there’s electrical interference, shock hazard, and so on.

  4. Does anyone know what ‘deposits’ you would be seeing with this choice of conductor and working fluid?

    Is it the sort of thing that could be resolved with more fiddly attention to impurities in the system; or is it inherent to ionizing a fluorocarbon and turning something that’s normally pretty chemically stable into a certain amount of fluorine looking to make new friends with almost anything in its vicinity?

    If it’s just a purity problem that seems like the sort of thing that clever process optimization will likely sort out, or at least massively improve, over time; there are absolutely loads of things that don’t or barely work if you are winging it on the benchtop that have been coaxed into working with sufficient effort; but if it’s a more fundamental problem of ionization being a necessary part of the mechanism of action and ions ripped free from their preferred locations being chemically fighty that seems likely to be a much more stubborn problem. Even if you went expensive with something like platinum electrodes you can still get platinum halides.

    1. “On December 20, 2022, 3M announced plans to exit per- and polyfluoroalkyl substance (PFAS) manufacturing, effectively discontinuing all Novec and Fluorinert products by the end of 2025.”

      PFA’s are called “forever chemicals”, so at a guess 3M are stopping before they are asked to pay for any global cleanup costs.

  5. I would be curious what kind of efficiency and throughput you could get with graphene or other wire. but here is a simple solution, perhaps?

    PTFE, PEI , or HDPE bag liners, and a fluid that is also permeable by electric and magnetic fields neutral perhaps running on outside of bag to keep melting ( just a little sloshing around if bag tends to melt) , check for toxicity though depending on your objectives. PTFE around 327°C is likely best bet , choosing wire that doesn’t heat up easily is a good choice

    also gold wire helps a lot, usually easier to avoid a problem that seems impossible to fix

    Duty cycle switching sets of wires eliminates heating and corrosion issues (at least I think so)

    jeep this project going and let me know if this is helpful

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