Experimental investigation on heat transfer characteristics of tungsten microwires

The thermal conductivity($\lambda$) and Lorenz number (L) of tungsten (W) microwires at varying temperatures were investigated using the 3ω method. The results show that the electrical conductivity of W microwires decreases significantly with rising temperature. However, an anomalous phenomenon was observed: $\lambda$ exhibits a slight increase as temperature rises. X-ray Diffraction(XRD) analysis reveals that reduced lattice constants diminish phonon scattering mechanisms while enhancing phonon group velocity, leading to higher thermal conductivity. Grain refinement increases grain boundary scattering, which suppresses phonon thermal transport, thereby weakening the contribution of phonon thermal conductivity(${\lambda }_{\mathrm{ph}}$). Calculated phonon spectra demonstrate that smaller lattice constants result in higher phonon group velocities, positively contributing to phonon heat conduction. In microwires dominated by electronic heat capacity, electronic thermal conductivity(${\lambda }_e$) displays a weak upward trend with temperature. Consequently, under the combined effects of these factors, the $\lambda$ of the microwires slightly increases with temperature. Additionally, the L of metallic W is approximately 30 % higher than the Sommerfeld value, exhibiting unique thermal properties, and it shows a minor increase with temperature, gradually converging to 3.29 V²/K².