ENTROPY-BASED DESIGN OF LIQUID-REPELLENT NANOCHANNELS DESTINED TO ENERGY ABSORPTION SYSTEMS (EAS)

摘要

Entropy production is a key parameter to evaluate the maximal efficiency of engineering systems. Recently, liquid penetration/exudation in/from non-wetted nanoporous solids was employed to develop ecological energy absorption systems (EAS). Dissipation is based on the well-known fact that external work must be done to spread a liquid on a lyophobic surface. Minimization of the entropy production is usually required to obtain high-efficiency engineering systems. However, enhancement of the EAS nano-damping ability requires oppositely maximization of the entropy generated through interfacial, frictional and thermal instabilities. A model of the entropy production during water flow inside of a liquid-repellent silica nanopore is proposed. A mixture of hydrophobized nanoporous silica and water is introduced inside of a compression-decompression chamber. Using a thermo-camera, the temperature distribution on the external surface of the test chamber is recorded versus the working time and the positions of main heat sources are identified. Such experiments allow determination of the overall dissipation, generated heat, and the heat flux at the wall of silica nanochannel. Then, the test rig is introduced inside of an incubator that allows temperature adjustment in the range 0～50 °C and the thermal effects on the hysteresis and damping performances are evaluated. From such tests one determines the variation of the solid surface tension on the nanochannel wall versus temperature. Entropy (heat) production in the nanochannel is estimated and compared with experimental data to validate the proposed model.