Role of electron–phonon coupling in thermal conductivity of metallic nanofluids

The main heat carriers in metal particles are free electrons. In the heat conduction of metallic nanofluids, electrons in metal nanoparticles (MNPs) usually exchange energy with phonons in MNPs first, then the energy can be conducted to liquid. An additional thermal resistance due to the electron–phonon coupling could occur in the process, which has rarely explored. In the present study, a two-temperature model is developed to estimate the thermal conductance of electron–phonon coupling in five metallic nanofluids, including Ag, Cu, Au, Al and Fe. The results show that the electron–phonon coupling conductances (0.52–1.3 GW m⁻² K⁻¹) are comparable with the interfacial conductances from the diffuse mismatch model (DMM) (0.33–0.97 GW m⁻² K⁻¹), which indicates the effect of electron–phonon coupling cannot be ignored. Then, the predictions of thermal conductivity in metallic nanofluids represent that ignoring the electron–phonon coupling resistances can lead to an overestimation to nanofluid thermal conductivities, and the effect is stronger for smaller particle size. When antioxidative coating on metallics nanoparticles is used, the interfacial thermal conductance and thermal conductivity in metallic nanofluids are also discussed. (paper)