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Turbulent power

Nature Materials volume 14, page 1188 (2015)Cite this article

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The kinetic energy of an electrically conducting fluid can be converted into electricity by means of the Lorentz force. This process, called magnetohydrodynamic generation, was first envisioned by Michael Faraday. He discovered that moving an electric conductor through a fixed magnetic field can be used as a voltage source — he even tried, although unsuccessfully, to measure the voltage generated by the salty estuarine water flowing through London's Waterloo Bridge due to the Earth's magnetic field. This conversion mechanism, schematically shown in the left panel of the figure, has been explored in recent times to improve the efficiency of steam power plants. Now, Ryo Takahashi and collaborators show that a potential difference can be generated in a conductive fluid in the absence of a magnetic field, as the result of the spin-current produced by the vortices formed in the fluid1.

In their experiment, Ryo Takahashi and collaborators make a fluid metal (Hg or Ga62In25Sn13) flow through a cylindrical insulating pipe in the turbulent regime1. Due to its viscosity, vortices are formed in the fluid close to the pipe walls and, as depicted in the right panel of the figure using pink curled arrows with different radii, a gradient of mechanical rotation is formed in the liquid transverse to its flow. The spin–rotation coupling converts this mechanical gradient into a spin voltage across the liquid. Spin voltages in metals are typically detected electrically through the inverse spin Hall effect which converts a spin current into an electric field due to the spin–orbit coupling. In the case of the metallic fluid, this electric field is parallel to the liquid flow causing an electric voltage difference, or inverse spin Hall voltage, between any two points along the pipeline. The generation of spin-current and electric voltage without applying magnetic fields is thus demonstrated.

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References

  1. Takahashi, R. Nature Phys. http://doi.org/8xp (2015).

  2. Matsuo, M., Ieda, J., Saitoh, E. & Maekawa, S. Phys. Rev. Lett. 106, 076601 (2011).

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  4. Matsuo, M., Ieda, J., Harii, K., Saitoh, E. & Maekawa, S. Phys. Rev. B 87, 180402(R) (2013).

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  1. David Ciudad
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Ciudad, D. Turbulent power. Nature Mater 14, 1188 (2015). https://doi.org/10.1038/nmat4499

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