Thermomagnetic Mechanism for Self-Cooling Cables

Abstract

A solid state mechanism for cooling high-current cables is proposed based on the Ettingshausen effect, i.e. the transverse thermoelectric cooling generated in magnetic fields. The intense current running in the cable generates a strong magnetic field around it, that can be exploited by a small current running in a coating layer made out of a strong "thermomagnetic" material to induce a temperature difference between the cable core and the environment. Both analytical calculations and realistic numerical simulations for Bismuth coatings in typical magnetic fields are presented. The latter yield temperature drops 60K and >100K for a single-and double-layer coating respectively. These encouraging results should stimulate the search for better thermomagnetic materials, in view of applications such as self-cooled superconducting cables working at room temperature.Transmission of intense electric currents through conducting cables is of obvious importance for energy supply. However the present distribution through high-voltage power-lines suffers considerable losses due to Joule effect caused by the resistance of the metallic cables. A promising alternative is represented by superconducting cables, where the resistance is zero. However present-day materials reach the superconducting state below very low temperatures (T c 18K for a widespread "conventional" superconductor, Nb 3 Sn, while T c 90K for one of the new "high-temperature" superconductors, YBCO), making their technological use viable only in specific conditions in which cooling to cryogenic temperatures is possible. Both these types of cables are also used in the coils of high-field magnets used in medical applications like magnetic resonance imaging, in levitating train technology, energy storage and for scientific purposes.In all these situations a solid-state method for cooling the cables can potentially improve the performances by lowering the resistance in resistive cables and helping or even replacing the existing cryogenic methods to lower the environmental temperature of superconducting cables. I propose such a potentially useful method here.In the proposed setup the cable transporting the main current is coated with -but electrically insulated from -a layer of another material with strong thermomagnetic properties. A "thermomagnetic material", like elemental Bismuth, is one that manifests strong Nernst-Ettingshausen effect, which is the transverse counterpart of thermoelectric (Seebeck-Peltier) effects induced by a strong magnetic field. In particular the Ettingshausen effect (see the upper panel of Fig. 1), is the generation of a temperature gradient in the direction orthogonal to both the electric current flowing in a material and the applied perpendicular magnetic field. The technological use of thermoelectricity (for coolers, waste heat recoverers, nuclear generators in space missions, etc.), utterly boosted by the recent improvement in materials performances due to a strong research effort, is already a reality, and growing [1]. Thermomagnetic ef...

Effects of temperature dependence of electrical and thermal conductivities on the Joule heating of a one dimensional conductor

“…Joule heating limits the operation of most current carrying components and devices, ranging from large high power systems to nanoscale wires and devices. The coupled thermal-electrical conduction problem is important for wirearray Z-pinches, 1 power transmission lines, 2 high power microwave devices, 3,4 and electrical contacts. [5][6][7][8][9] In a Zpinch, in particular, coupled thermal-electrical conduction is responsible for an electrothermal instability.…”