Progress To Harvest Waste Heat For Electricity

Researchers at Utrecht University, the Netherlands reveal in a new study a novel mechanism for controlling the energy transfer between electrons and the bismuth crystal lattice. Mastering this effect could, ultimately, help convert waste heat back into electricity.

At the atomic level, bismuth displays a number of quirky physical phenomena. Piotr Chudzinski from Utrecht University investigated the collective motion of electrons in bismuth, which behaves in a fluid manner with waves propagating in it, a phenomenon referred to as a low energy plasmon. Electrons moving throughout the material constantly aim to preserve the same density.

Bismuth exhibits two types of electrons – extremely light ones and heavier ones – moving at different speeds. As a result, an area of less dense electron liquid is formed. In response, electrons move back to compensate at the lower density end. Yet, some of them move faster than others. And a more sparsely dense area appears in another part of the material. And so on and so forth. . .

The study paper, published in the European Physical Journal B, available in open access, demonstrates that the low energy plasmons, when tuned to the same wavelength as the lattice vibrations of the bismuth crystal, or phonons, can very efficiently slow lattice motion. In essence, this plasmon-phonon coupling mechanism, once intensified under specific conditions, could be a new way of transferring energy between electrons and the underlying crystal lattice.

One important potential is that the plasmon-phonon coupling can help to explain a long since observed, significant effect in bismuth: the so called Nernst Effect. The Nernst Effect occurs when a sample is warmed on one side and subjected to a magnetic field, causing it to produce a significant electrical voltage in the perpendicular direction. Thus, it turns heat into useful electricity. Within the new interpretation the Nernst Effect scales up with temperature in a manner that is in line with experimental observations in bismuth, lends strong support to the theory.

The study is more important than a first impression might imply. The Nernst Effect is a particularly large effect that has until now defied mathematical support to the theory. Now that the math is in sight the engineering could soon follow.

With such an incredible amount of heat escaping the economy, an efficiently working and hopefully low cost recovery of heat directly to electricity would be a boon to energy efficiency and reducing expenses. Lets hope industry takes notice at this very early point.