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15 pages, 2858 KiB

Open AccessArticle

Ceramic-Based Piezoelectric Material for Energy Harvesting Using Hybrid Excitation

by Bartłomiej Ambrożkiewicz, Zbigniew Czyż, Paweł Karpiński, Paweł Stączek, Grzegorz Litak and Łukasz Grabowski

Materials 2021, 14(19), 5816; https://doi.org/10.3390/ma14195816 - 5 Oct 2021

Cited by 22 | Viewed by 3005

Abstract

This paper analyzes the energy efficiency of a Micro Fiber Composite (MFC) piezoelectric system. It is based on a smart Lead Zirconate Titanate material that consists of a monolithic PZT (piezoelectric ceramic) wafer, which is a ceramic-based piezoelectric material. An experimental test rig consisting of a wind tunnel and a developed measurement system was used to conduct the experiment. The developed test rig allowed changing the air velocity around the tested bluff body and the frequency of forced vibrations as well as recording the output voltage signal and linear acceleration of the tested object. The mechanical vibrations and the air flow were used to find the optimal performance of the piezoelectric energy harvesting system. The performance of the proposed piezoelectric wind energy harvester was tested for the same design, but of different masses. The geometry of the hybrid bluff body is a combination of cuboid and cylindrical shapes. The results of testing five bluff bodies for a range of wind tunnel air flow velocities from 4 to 15 m/s with additional vibration excitation frequencies from 0 to 10 Hz are presented. The conducted tests revealed the areas of the highest voltage output under specific excitation conditions that enable supplying low-power sensors with harvested energy. Full article

(This article belongs to the Special Issue Dynamics and Application of Modern, Smart and Active Elements or Structures)

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16 pages, 5341 KiB

Open AccessArticle

On the Formation and Accumulation of Solid Carbon Particles in High-Enthalpy Flows Mimicking Re-Entry in the Titan Atmosphere

by Antonio Esposito, Marcello Lappa, Gennaro Zuppardi, Christophe Allouis, Barbara Apicella, Mario Commodo, Patrizia Minutolo and Carmela Russo

Fluids 2020, 5(2), 93; https://doi.org/10.3390/fluids5020093 - 12 Jun 2020

Cited by 7 | Viewed by 2787

Abstract

The problem relating to the formation of solid particles enabled by hypersonic re-entry in methane-containing atmospheres (such as that of Titan) has been tackled in the framework of a combined experimental–numerical approach implemented via a three-level analysis hierarchy. First experimental tests have been conducted using a wind tunnel driven by an industrial arc-heated facility operating with nitrogen as working gas (the SPES, i.e., the Small Planetary Entry Simulator). The formation of solid phases as a result of the complex chemical reactions established in such conditions has been detected and quantitatively measured with high accuracy. In a second stage of the study, insights into the related formation process have been obtained by using multispecies models relying on the NASA CEA code and the Direct Simulation Monte Carlo (DSMC) method. Through this approach the range of flow enthalpies in which carbonaceous deposits can be formed has been identified, obtaining good agreement with the experimental findings. Finally, the deposited substance has been analyzed by means of a set of complementary diagnostic techniques, i.e., SEM, spectroscopy (Raman, FTIR, UV–visible absorption and fluorescence), GC–MS and TGA. It has been found that carbon produced by the interaction of the simulated Titan atmosphere with a solid probe at very high temperatures can be separated into two chemically different fractions, which also include “tholins”. Full article

(This article belongs to the Special Issue Classical and Modern Topics in Fluid Dynamics and Transport Phenomena)

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14 pages, 1353 KiB

Open AccessArticle

The Critical Role of the Boundary Layer Thickness for the Initiation of Aeolian Sediment Transport

by Thomas Pähtz, Manousos Valyrakis, Xiao-Hu Zhao and Zhen-Shan Li

Geosciences 2018, 8(9), 314; https://doi.org/10.3390/geosciences8090314 - 23 Aug 2018

Cited by 30 | Viewed by 5618

Abstract

Here, we propose a conceptual framework of Aeolian sediment transport initiation that includes the role of turbulence. Upon increasing the wind shear stress

τ

above a threshold value

τ_{t}^{'}

, particles resting at the bed surface begin to rock in their [...] Read more.

Here, we propose a conceptual framework of Aeolian sediment transport initiation that includes the role of turbulence. Upon increasing the wind shear stress

τ

above a threshold value

τ_{t}^{'}

, particles resting at the bed surface begin to rock in their pockets because the largest turbulent fluctuations of the instantaneous wind velocity above its mean value

\bar{u}

induce fluid torques that exceed resisting torques. Upon a slight further increase of

τ

, rocking turns into a rolling regime (i.e., rolling threshold

τ_{t} ≃ τ_{t}^{'}

) provided that the ratio between the integral time scale

T_{i} \propto δ / \bar{u}

(where

δ

is the boundary layer thickness) and the time

T_{e} \propto \sqrt{d / [(1 - 1 / s) g]}

required for entrainment (where d is the particle diameter and s the particle–air–density ratio) is sufficiently large. Rolling then evolves into mean-wind-sustained saltation transport provided that the mean wind is able to compensate energy losses from particle-bed rebounds. However, when

T_{i} / T_{e}

is too small, the threshold ratio scales as

τ_{t} / τ_{t}^{'} \propto T_{e} / T_{i} \propto s d^{2} / δ^{2}

, consistent with experiments. Because

δ / d

controls

T_{i} / T_{e}

and the relative amplitude of turbulent wind velocity fluctuations, we qualitatively predict that Aeolian sediment transport in natural atmospheres can be initiated under weaker (potentially much weaker) winds than in wind tunnels, consistent with indirect observational evidence on Earth and Mars. Full article

(This article belongs to the Special Issue Aeolian Processes and Geomorphology)

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