Aluminum nitride–filled elastic silicone rubber composites for drag reduction

Abstract

This study presents aluminum nitride/silicone rubber composite as a drag reduction material, inspired by the boundary heating drag reduction mechanism of dolphin skin. Aluminum nitride was added as a thermal conductive filler at weight fractions of 16.67, 21.05, and 28.57 wt% to pristine silicone rubber. Tests of the thermal conductivity and tensile properties showed that the thermal conductivity of all three aluminum nitride/silicone rubber composites were increased 27.9%, 41.4%, and 43.7% than that of the pristine silicone rubber, and the elastic modulus of the composites was increased with the aluminum nitride content. Droplet velocity testing, which can reflect the drag reduction mechanism of the heating boundary controlled by the aluminum nitride/silicone rubber composites, was performed between all three aluminum nitride/silicone rubber composites and pristine silicone rubber. The results showed that the droplet velocity of all three aluminum nitride/silicone rubber composites were higher than pristine silicone rubber, implying that the composites had a drag-reducing function. In terms of the drag-reducing mechanism, the heat conductivity performance of the aluminum nitride/silicone rubber accelerates the heat transfer between the aluminum nitride/silicone rubber composite surface and droplet. The forces between the molecules and droplet dynamic viscosity are reduced, which result in drag reduction. The application of aluminum nitride/silicone rubber composite to control fluid medium will have important value for fluid machinery.

The Effects of Aluminum-Nitride Nano-Fillers on the Mechanical, Electrical, and Thermal Properties of High Temperature Vulcanized Silicon Rubber for High-Voltage Outdoor Insulator Applications

“…Moreover, at measurement temperatures of 45 °C and 55 °C, the enhancement of the thermal conductivity was more than 100%, i.e., 105% and 107%, respectively, as shown in Figure 10a. Our results are comparable to the published results related to the AlN-filled polymer composites, such as AlN-epoxy and AlN-silicone rubber [7,8,10,15,16], but with a much lower volume ratio of the AlN filler in our study. Such differences may come from the smaller dimensions of the AlN particles in current case, i.e., nano versus micro.…”

“…Large-size fillers (>1 μm) are usually better for thermal conductivity improvement because of their lower interfacial area, which usually behaves as a resistant barrier for thermal conduction [9]. However, large particles will deteriorate the mechanical properties of the composites and tend to introduce more voids in the composite [10,11]. On the other hand, nanofillers will enhance the thermal conductivity considerably at a much lower volume ratio due to the easily formed thermal conduction path, i.e., percolation behavior [12].…”

“…They also found that with increasing the micron AlN content (from 5 wt% to 30 wt%), the high-voltage electrical tracking behavior was exacerbated [17]. Tian et al modified the surface of micron AlN particles with KH550 coupling agent and obtained a thermal conductivity of 1.3 W/m·K at a filling level of 28.5 wt% in silicon rubber [10].…”