No abstract

Acoustic metamaterials, capable of both sound insulation and energy harvesting, composed of Helmholtz resonators and built-in decorated membranes are proposed. It is theoretically and experimentally proved that the proposed metamaterial can obtain two sound insulation bands where the sound energy is also efficiently harvested at the same frequency simultaneously. The peak of the output power can reach up to 244 nW when the incident sound pressure is 1 Pa, which is about 14 times larger than structures composed of single membrane reported before with the same input. Moreover, considerable energy harvesting with average output power of about 20 nW can be achieved within wider frequency ranges (with bandwidth up to 90 Hz) by choosing proper parameters. Additionally, the hybrid resonance mechanism of the proposed metamaterials is explained well with an equivalent theoretical model. These novel properties of the proposed metamaterial can be applied in many potential applications in noise control and energy harvesting.

No abstract

No abstract

In order to reveal the physical drying characteristics of various kinds of cotton fabrics and further provide theoretical guides for designing drying equipment and improving drying technologies, a finite element model is built that is able to describe coupling of the drying process between fabrics and environment. Specifically, three kinds of cotton fabrics mesoscopic structures parameters and mechanical properties are firstly measured and then these fabrics are equivalent to porous media, and the equivalent media can characterize the fabrics precisely. Then, the formulas for calculating the convection heat transfer and thermodynamic properties of fabrics are also improved and verified by corresponding experiments. The results shows that the improved formulas can calculate the properties more accurately. Next, we apply this model to analyze the regular change of surface temperature and water content with time during the drying process of three kinds of fabrics under different technologies. The results indicates that the coupled heat and mass transfer of drying processes are obviously affected by liquid phase transition. In addition, with higher wind temperature, the velocity of water evaporation inside fabrics is faster and, when water content inside fabric becomes lower in the drying process, the velocity of water evaporation decreases. The numerical values agrees well with the corresponding experimental values: The mean absolute error of water content inside fabric in the drying process is less than 1.51 g, while the average absolute error of fabric surface temperature is about 1.63℃, which means this model can precisely capture the coupling drying process of various kinds of cotton fabrics inside the oven. It is expected that the model can be applied for providing theoretical guidance for designing structures of drying equipment and improving drying technologies.

No abstract

No abstract

No abstract