Hydrodynamic heat transfer in solids

In solids, hydrodynamics have been observed in both amorphous and crystalline materials under a wide range of conditions. However, its fundamental physics is still unclear. Recent advancements in nanotechnology, biomedicine and electronics have reinvigorated interest in research on hydrodynamic solids. Here, we established the hydrodynamic transport in solids from solid mechanics. We showed that isentropically, a solid becomes superfluid locally in space and time when subjected to periodic motions, and at resonance, the first and second sound are generated. We validated the speed of the second sound against the velocity of S waves, and the agreement is satisfactory. From the concept of the boundary of the second law, we established the boundary conditions for the governing equations of the supersolid and obtained the transient and steady-state solutions of the supersolid. The theory agrees well with the measured flash temperature of the bulk metallic glass (BMG), which elucidates the physics why thermocouples do not measure flash temperature accurately. The finding shall lead to the review of the adequacy of instrumentation where temperature measurement is critical. The validation of the steady-state solution was carried out by comparison to the interfacial thermal conductance (ITC) on solid-solid interfaces. The first dataset has metal-metal interfaces with variable pressures, and the second dataset has metaldielectric interfaces with variable temperatures, whose ITC differs by 4 orders of magnitude. We discuss the physics of this difference. We believe that the theory of hydrodynamics in solids provides insights for a vast number of disciplines and that the methods and solutions can help practitioners. & COPY; 2023 Elsevier Ltd. All rights reserved.