Carbon Nanotube Interfaces for Magneto Thermoelectric Actuation

Magneto thermoelectric generator cell technology uses the ferromagnetic phase transition of gadolinium to drive the movement of a diaphragm ‘shuttle’ whose mechanical energy can be converted to electrical form and which enhances heat transfer through both conduction and convection. This paper describes the thermal behavior of gadolinium foils used in magneto thermoelectric generator cells that, in conjunction with a planar array of similar devices, would form a thermal backplane to a solar photovoltaic panel. In this scenario, the backplane operates as a self-powered cooling device that can simultaneously convert thermal energy to electrical energy as well as improve photovoltaic efficiency through active cooling. This form of energy harvesting and enhancement shows the potential of increasing the energy density of silicon photovoltaic panels. The synthesis and characterization of thermal interfaces applied to the gadolinium shuttles and hot/cold substrates are described. Carbon nanotube arrays are implemented as the thermal interfaces, and their performance under static conditions is assessed. Optimization of the carbon nanotube interfaces on the gadolinium shuttles is achieved using photoacoustic experiments for measuring the thermal interface resistances above and below the gadolinium foil. Carbon nanotube growth studies on gadolinium demonstrated a reduction in thermal interface resistances from 28.8 ± 2.1 mm²K/W to as low as 17.9 ± 0.8 mm²K/W. Initial design, fabrication, and experimental techniques and results are presented in this paper.