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.
Highlights
As a bionic prototype of a drag-reducing surface, dolphin skin has generated considerable attention during the past 80 years
An aluminum nitride (ALN)/silicone rubber (SR) composite material was designed and prepared inspired by the fluid control mechanism of the elastic and boundary heating abilities of dolphin skin
The thermal conductivity of aluminum nitride/silicone rubber (ALN/SR) composites relies on electronic heat transfer and mutual interaction of lattice vibrations between the pristine silicone rubber (PSR) matrix and the ALN fillers
Summary
As a bionic prototype of a drag-reducing surface, dolphin skin has generated considerable attention during the past 80 years. Some research indicates that boundary heating mechanism by the dolphin’s skin reduces the viscosity of the fluid, which leads to drag reduction, because there is a 9°C difference in temperature between the dolphin’s skin and the boundary layer fluid when a dolphin is swimming at high speed.[7,8,9,10] It is well known that the frictional resistance between the surface and the fluid is positively correlated with the dynamic viscosity of liquid; the latter decreases as the temperature increases,[11,12] so the drag reduction occurs when the liquid dynamic viscosity decreases. When using highly elastic polymer materials to control the fluid medium, the heat produced by the large elastic deformation is not dissipated, resulting in accelerated aging and failures. This decreases the effect of drag reduction, limiting the material’s application in engineering. A material with both elastic characteristics and thermal conductivity properties should be considered for applications in fluid control engineering
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