Browsing by Author "Xiong, Xiaoman"
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- ItemAerogel Embedded High-performance Fibrous Materials(2018-2-5) Xiong, Xiaoman; ; Mishra Rajesh, doc. Ph.D. Skolitel : 60165Vlákenné materiály jsou široce používány jako tepelné izolátory v různých aplikacích pro úsporu energie. Jejich tepelně izolační vlastnosti jsou omezeny, pokud je tloušťka materiálu omezena na několik milimetrů. V dnešní době je stále častěji kladen důraz na vývoj vysoce výkonných tepelně izolačních materiálů pro úsporu energie, zvýšení pohodlí, snížení nákladů a složitosti těchto systémů. Aerogel, který vykazuje vynikající tepelnou izolaci s extrémně nízkou tepelnou vodivostí, byl shledán jedním z nejatraktivnějších tepelně izolačních materiálů. Cílem této práce bylo vyvinout vysoce výkonný aerogel spojený s vlákennými materiály pro tepelnou izolaci a prověřit jeho výkon.Vrstvená nanovlákenná síťovina /aerogel /netkané materiály byly připraveny použitím laminovací metody s práškem s nízkým bodem tání jako tepelně spojujícím materiálem. Byl zkoumán účinek aerogelu a tepelného lepidla na tepelnou izolaci a propustnost vzduchu. V úvahu byl vzat sériový model pro tepelný odpor, byly porovnány a analyzovány teoretické předpoklady a naměřené výsledky. Bylo navrženo, že by měly být vzaty v úvahu nové techniky kombinující aerogel s vysoce porézními textiliemi s menším využitím pojivových materiálů.Nový aerogel obalený vlákenným materiálem bez použití jakéhokoliv pojivového materiálu, který spojuje částice aerogelu, byl vyvinut pomocí techniky laserového gravírování a laminovací metody. Pro měření tepelného výkonu byly použity termální kamera, zařízení Alambeta a KES-FT-II Thermolab. Byla provedena tlaková zkouška ke zkoumání kompresního zotavení, které určuje udržitelnost tepelné izolace. Dále bylo použito laboratorně vyráběné dynamické zařízení pro přenos tepla pro zjištění konvektivního tepelného chování těchto vícevrstvých materiálů, jakož i netkaných textilií obalených aerogelem, při různých rychlostech proudění vzduchu a zahřívání. Byly porovnány teplotní křivky v reálném čase z měření předehřátých podmínek. Byly vypočteny a posouzeny hodnoty teplotních rozdílů a konvektivního součinitele přestupu tepla za podmínek kontinuálního ohřevu. Zjištění by mohla přispět k novému vývoji pružných vysoce výkonných textilních materiálů se zabudovaným aerogelem pro průmyslové i oděvní aplikace.Pružné polyuretanové a polyvinylidenfluoridové nanoporézní membrány kombinované s aerogelem na bázi oxidu křemičitého byly připraveny elektrostatickým zvlákňováním. Tepelné vlastnosti a propustnost vzduchu byly hodnoceny a porovnávány. Byl učiněn závěr, že nanovlákna s aerogelem jsou vhodná pro tepelnou izolaci za chladného počasí. Tepelně izolační nosiče obsahující nanovlákna by mohly případně snížit hmotnost a objem tepelně ochranného oblečení.Pro provedení a vyhodnocování všech statistických výsledků byl v této práci použit statistický a analytický software Matlab_R2017a. Dosažené výsledky jsou významné a mohou být použity pro další studium v oblasti tepelných vlastností vysoko pevnostních vlákenných materiálů s aerogelem, které mohou být využity například pro tepelnou izolaci budov či ochranné oděvy.
- ItemAn experimental evaluation of convective heat transfer in multi-layered fibrous materials composed by different middle layer structures(SAGE PUBLICATIONS INC, 2455 TELLER RD, THOUSAND OAKS, CA 91320 USA, 2019-10-01) Xiong, Xiaoman; Venkataraman, Mohanapriya; Jašíková, Darina; Yang, Tao; Mishra, Rajesh; Militký, Jiří; Petrů, MichalIn this work, three types of multi-layered fibrous materials with different middle layer structures, including Struto nonwoven, Struto nonwoven with air pockets and Struto nonwoven with air pockets filled by aerogel particles, were prepared based on laser engraving technique and laminating method. A custom-built new device was fabricated to evaluate convective thermal behaviour of the multi-layered materials in cross flow. It was found that in cross flow the heat transfer coefficient of the multi-layered material with encapsulated aerogels is directly proportional to Reynolds number. There are considerable variances in heat transfer rates of the three structures at low airflow velocity (less than 10 m/s), but the values are very close at high airflow velocity. It is concluded that the air pockets and aerogels present in the multi-layered fibrous material have significant effect on convective thermal behaviour of the overall structure in cross flow. The finding is a new contribution to the field of aerogel-based fibrous materials as thermal insulators in building and industrial facilities.
- ItemEffect of silanization on copper coated milife fabric with improved EMI shielding effectiveness(Elsevier Ltd, 2020-01-01) Periyasamy, Aravin Prince; Yang, Kai; Xiong, Xiaoman; Venkataraman, Mohanapriya; Militký, Jiří; Mishra, Rajesh; Křemenáková, DanaElectromagnetic interference takes place due to the increase in complexity of electronic devices/systems in the form of higher packing density for quick response. To overcome its adverse effects, the effective shielding of components is needed abundantly. This leads to an increase of undesirable influence of electromagnetic signals and troublesome charges against which protection of human beings is required. Textile based structure with electromagnetic shielding ability has promising replacement of conventional materials due to its flexibility, air permeability and comfort properties. In this work, a copper coated fabric was silanized with different types of silane to stabilize the copper deposition on the fabric. Three different silanes were used for the silanization treatment to stabilize the copper deposition. The results showed excellent electromagnetic shielding properties. In addition to that, electrical and physical properties of the fabrics were evaluated before and after silanization treatment.
- ItemInfluence of EMI Shielding on Silane-coated Conductive Fabric(TEXTILE BIOENGINEERING & INFORMATICS SOCIETY LTD, TBIS 2010 SECRETARIAT MN104, HONG KONG POLYTECHNIC UNIV, HONG KONG SAR, 0000, PEOPLES R CHINA, 2019-01-01) Periyasamy, Aravin Prince; Yang, Kai; Xiong, Xiaoman; Venkatraman, Mohanapriya; Militký, Jiří; Mishra, Rajesh; Křemenáková, DanaElectromagnetic interference (EMI) takes place due to an increase in the complexity of electronic devices/systems in the form of higher packing density for a quick response. To overcome its adverse effects, the effective shielding of components is abundantly needed. This leads to an increase in the undesirable influence of electromagnetic signals and troublesome charges against which the protection of human beings is required. A textile-based structure with electromagnetic shielding ability is a promising replacement for conventional materials due to its flexibility, air permeability and comfort properties. In this work, a Cu-coated fabric was silanized with different types of silane to stabilize the Cu deposition fabric. Three different silanes were used in the silanization treatment in order to stabilize the Cu deposition. The results showed improved electromagnetic shielding properties.
- ItemInvestigation on sound absorption properties of aerogel/polymer nonwovens(2019-02-01) Yang, Tao; Xiong, Xiaoman; Venkataraman, Mohanapriya; Mishra, Rajesh; Novák, Jan; Militký, JiříThis paper presents an investigation on sound absorption performance of aerogel/polymer nonwoven fabrics. Polyester/polyethylene nonwovens embedded with hydrophobic amorphous silica aerogel were chosen for sound absorption measurements. The sound absorption coefficient (SAC) of single and laminated layers of aerogel nonwovens blankets was tested by Bruel and Kj AE r impedance tube, the noise reduction coefficient (NRC) was used for numerical analysis. A sound absorption index was developed to analyze the effect of aerogel content on sound absorption ability. The effect of air-back cavities on SAC of single-layer aerogel/polymer nonwoven fabrics was investigated. The results show that there is a decrease in SAC with the increase of aerogel content. It is observed that the NRC linearly increased with the increase of layers for all the samples. It was also found that the air-back cavities result in resonance phenomenon, as the increase in thickness of air-back cavities the peak values of SAC shift toward lower frequencies.
- ItemPreparation of Electrosprayed, Microporous Particle Filled Layers(MDPI, 2020-06-15) Venkataraman, Mohanapriya; Yang, Kai; Xiong, Xiaoman; Militký, Jiří; Křemenáková, Dana; Zhu, Guocheng; Yao, Juming; Wang, Yan; Zhang, GuoqingPolytetrafluoroethylene (PTFE) is a synthetic fluoropolymer known for its excellent hydrophobic properties. In this work, samples from PTFE dispersions with different combinations of water and carbon microparticles were prepared using an electrospraying method. The morphologies and sizes of carbon particles were investigated and the properties of layers including roughness, hydrophobicity and electrical resistivity were investigated. The non-conductive carbon microparticles were selected as a model particle to check the compatibility and electrospraying ability, and it had no effect on the hydrophobic and electrical properties. Carbon microparticles in polymer solution increased the degree of ionization and was found to be beneficial for the shape control of materials. The results showed that PTFE dispersion with the composition of water and carbon microparticles produced fine sphere particles and the layer fabricated with increased roughness. It was also found that the electrical resistivity and hydrophobicity of all the layers comparatively increased. The fabricated microporous layers can be used in various applications like interlining layer in multilayer textile sandwiches.
- ItemSound absorption and compression properties of perpendicular-laid nonwovens(SAGE PUBLICATIONS LTD, 1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2019-02-01) Yang, Tao; Xiong, Xiaoman; Mishra, Rajesh; Novák, Jan; Militký, JiříThis study presents an investigation into the sound absorption behavior and compression properties of perpendicular-laid nonwovens. Seven types of perpendicular-laid nonwovens produced by vibrating and rotating perpendicular lappers were selected. Nonwovens with varying thickness and areal density were prepared by the heat-pressing method to investigate the effect of structural parameters such as thickness and areal density on sound absorption ability. Measurements of sound absorption properties were carried out with a Bruel and Kj AE r measuring instrument. The effect of manufacturing techniques on sound absorption performance and compression properties was investigated. The effect of porosity on sound absorption ability was studied. The influence of density and fiber orientation angle on compression properties was analyzed. The results show that samples prepared by vibrating perpendicular lapper exhibit better compression properties, whereas there is no significant influence of two manufacturing techniques on sound absorption performance. The increase of areal density results in improvement in the sound absorption ability. The increase of thickness can improve the sound absorption coefficient in the low-frequency range, but decrease of the coefficient occurred in the high-frequency range. A quadratic relationship between porosity and sound absorption ability has been found. The results also show that compressional resistance has a strong relation with density - the correlation coefficient is 0.95, indicating that the compressional resistance is directly proportional to the density of perpendicular-laid nonwovens. The results indicate that the perpendicular-laid nonwovens with higher initial fiber orientation angle have better compression properties.
- ItemSound Absorption Properties of Natural Fibers: A Review(MDPI, 2020-01-01) Yang, Tao; Hu, Lizhu; Xiong, Xiaoman; Petrů, Michal; Noman, Muhammad Tayyab; Mishra, Rajesh; Militký, JiříIn recent years, in an attempt to substitute the conventional synthetic sound absorption material, natural fibers and their sound absorption properties have been increasingly studied. This is due to the fact that conventional synthetic fiber has potential health risks for human beings and significant environmental impact. In this review, existing and newly emerging natural fiber sound absorbers are summarized and highlighted in three categories: raw material, fiber assembly and composite. The sound absorption mechanism, several widely used prediction models and the popular acoustic characterization methods are presented. The comparison of sound absorption properties between some natural sound absorbers and glass fiber is conducted in two groups, i.e., thin material and thick material. It is found that many natural fibers have comparable sound absorption performance, some of them can be the ideal alternatives to glass fiber, such as kapok fiber, pineapple-leaf fiber and hemp fiber. Last, the conclusion part of this review gives an outlook regarding the promotion of the commercial use of natural fiber by means of theoretical study, efficient and environmentally friendly pretreatment and Life Cycle Assessment.
- ItemStudy on the sound absorption behavior of multi-component polyester nonwovens: experimental and numerical methods(2019-08-01) Yang, Tao; Saati, Ferina; Horoshenkov, Kirill V.; Xiong, Xiaoman; Yang, Kai; Mishra, Rajesh; Marburg, Steffen; Militký, JiříThis study presents an investigation of the acoustical properties of multi-component polyester nonwovens with experimental and numerical methods. Fifteen types of nonwoven samples made with staple, hollow and bi-component polyester fibers were chosen to carry out this study. The AFD300 AcoustiFlow device was employed to measure airflow resistivity. Several models were grouped in theoretical and empirical model categories and used to predict the airflow resistivity. A simple empirical model based on fiber diameter and fabric bulk density was obtained through the power-fitting method. The difference between measured and predicted airflow resistivity was analyzed. The surface impedance and sound absorption coefficient were determined by using a 45 mm Materiacustica impedance tube. Some widely used impedance models were used to predict the acoustical properties. A comparison between measured and predicted values was carried out to determine the most accurate model for multi-component polyester nonwovens. The results show that one of the Tarnow model provides the closest prediction to the measured value, with an error of 12%. The proposed power-fitted empirical model exhibits a very small error of 6.8%. It is shown that the Delany-Bazley and Miki models can accurately predict surface impedance of multi-component polyester nonwovens, but the Komatsu model is less accurate, especially at the low-frequency range. The results indicate that the Miki model is the most accurate method to predict the sound absorption coefficient, with a mean error of 8.39%.
- ItemTheoretical and Experimental Studies on Thermal Properties of Polyester Nonwoven Fibrous Material(MDPI, 2020-06-26) Yang, Tao; Xiong, Xiaoman; Petrů, Michal; Tan, Xiaodong; Kaneko, Hiroki; Militký, Jiří; Sakuma, AtsushiPolyester nonwoven fibrous material is widely used in construction and automobile industries for thermal insulation purposes. It is worthy and meaningful to understand the effect of structural parameters on the thermal property. Fiber orientation, as one of the most vital parameters, has a significant effect on thermal property. However, there has been little quantitative analysis focusing on this aspect. This paper theoretically and experimentally analyzes the thermal conductivity of samples with varying fiber orientation. Existing models were selected to predict the thermal conductivity of polyester nonwoven samples. Two different apparatus were applied to carry out the experimental measurements. The relative differences between the predicted and measured results were compared. One commonly used model was modified for accurate prediction. It was shown that some existing models under- or overestimate the thermal conductivity compared to the measured values. The results indicate that the modified model can accurately predict the thermal conductivity of polyester nonwoven materials within a 0.2% relative difference.
- ItemTransport Properties of Electro-Sprayed Polytetrafluoroethylene Fibrous Layer Filled with Aerogels/Phase Change Materials(MDPI, 2020-01-01) Xiong, Xiaoman; Venkataraman, Mohanapriya; Yang, Tao; Kučerová, Klára; Militký, Jiří; Yang, Kai; Zhu, Guocheng; Yao, JumingThis work is the first attempt to prepare microporous polytetrafluoroethylene (PTFE) fibrous layers embedded with aerogels/phase change materials. For preparation of this layer, the needle-less electrospray technology of water dispersion of individual components is used. Microstructure characteristics, including surface morphology and particle size distribution, and various properties of the prepared materials were investigated and explained. Transport performance of the fibrous layers embedded with aerogels/phase change materials, such as the transmission of heat, air, and water vapor was evaluated and discussed in details. It was found that the electro-sprayed materials composed by spherical particles with rough surface had compact disordered stacking structure. Aerogels and phase change materials (PCMs) play different roles in determining structural parameters and transport properties of the materials. Those parameters and properties could be flexibly adjusted by optimizing the spinning parameters, changing the content or proportion of the fillers to meet specific requirements.