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Sökning: WFRF:(Liu Johan 1960)

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  • Liu, Ya, 1991, et al. (författare)
  • Effect of Boron Nitride Particle Geometry on the Thermal Conductivity of a Boron Nitride Enhanced Polymer Composite Film
  • 2019
  • Ingår i: THERMINIC 2019 - 2019 25th International Workshop Thermal Investigations of ICs and Systems.
  • Konferensbidrag (refereegranskat)abstract
    • Hexagonal Boron Nitride (h-BN) has been considered as a promising enhancement filler for thermal management due to its high thermal conductivity, structural stability, and super electrical resistivity. Numerus studies have reported using BN as an enhancement filler to achieve high thermally conductive polymer based thermal management materials. However, there are limited data regarding the influence of the flake size of BN sheets to the thermal management property of BN filled composites. In this work, three h-BN size geometries, including microscale h-BN powder, h-BN nanosheets, and a mixture of micro and nanoscale h-BN, were studied regarding its thermal transfer performance. The results show that h-BN nanosheets are able to achieve the highest in-plane thermal conductivity with loading from 0 - 5 wt% while for the through-plane thermal conductivity, all three geometries show similar thermal property when the filler loading less than 5 wt%. Through-plane thermal conductivity exhibits a sudden increase to 5.69 W m-1 K-1 at a loading of 5 wt%..
  • Liu, Ya, 1991, et al. (författare)
  • Egg albumen templated graphene foams for high-performance supercapacitor electrodes and electrochemical sensors
  • 2018
  • Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 6:37, s. 18267-18275
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate a simple and scalable strategy to obtain N, S and Si co-doped biocompatible graphene foams (GFs) with different shapes using egg albumen as the template. The unique porous structure and element doping endow the GFs with a high charge-discharge rate and good wettability, which largely improve the electrochemical performance of the electrodes, including ultrahigh specific capacitance (534 F g-1at 1 A g-1), and excellent rate capability (308 F g-1at 100 A g-1) and cycling performance (96.1% retention of the initial capacitance after 10000 cycles at a high current density of 10 A g-1). Besides, when used as an electrochemical sensor for dopamine, the GF exhibits a detection limit as low as 1.2 μM with a linear response up to 70 μM, due to the low equivalent series resistance. These reveal great potential for promoting the application of 3D graphene in energy storage and electrochemical sensors.
  • Liu, Ya, 1991, et al. (författare)
  • Graphene based thermal management system for battery cooling in electric vehicles
  • 2020
  • Ingår i: 2020 IEEE 8th Electronics System-Integration Technology Conference (ESTC). - 9781728162928
  • Konferensbidrag (refereegranskat)abstract
    • In this work, a graphene assembled film integrated heat sink and water cooling technology was used to build an experimental set-up of a thermal management system to demonstrate the possibility to achieve efficient cooling of the propulsion battery in electric vehicles. The experimental results showed that the temperature decrease of a Li-ion battery module can reach 11°C and 9 °C under discharge rates as of 2C and 1C, respectively. The calculated thermal resistance of the graphene based cooling system is about 76% of a similar copper based cooling system. Surface modification was carried out on the graphene sheet to achieve a reliable bonding between the graphene sheet and the battery cell surface. This work provides a proof of concept of a new highly efficient approach for electric vehicle battery thermal management using the light-weight material graphene.
  • Liu, Yangming, et al. (författare)
  • Numerical investigation on the thermal properties of the micro-cooler
  • 2010
  • Ingår i: Proceedings - 2010 11th International Conference on Electronic Packaging Technology and High Density Packaging, ICEPT-HDP 2010; Xi'an; 16 August 2010 through 19 August 2010. ; :Article number 5583917, s. 634-638
  • Konferensbidrag (refereegranskat)abstract
    • The micro-pin-fins prepared on the back side of the power chip enable heat removal on the level of modern microsystem demands. Carbon nanotube (CNT) has been proven to be a potential material for micro-cooler because of its superior advantages including high thermal conductivity, good mechanical property and so forth. And there emerges various applications of CNT in the micro-cooler system. In the present paper, micro-pin-fin heat sink with gas impinging jet as the cooling medium is analyzed. The heat dissipation of forced air convection cooling with micro-pin-fin structures made of aligned carbon nanotube arrays has been taken into consideration. The three-dimensional computational fluid dynamics (CFD) simulation was carried out. The temperature distribution and the pressure drop are studied in the cases of various geometrical parameters of the micro-pin-fin heat sinks at the same heating power prescribed. The fluid flow and the heat transfer phenomena in the micro-pin-fins heat sinks are investigated. The heat removal efficiency of the air microcooler is evaluated. An array of 8×8 fins with the optimized fin-to-base length ratio achieves the best cooling effect © 2010 IEEE.
  • Liu, Ya, 1991, et al. (författare)
  • Surface modification of graphene for use as a structural Fortifier in water-borne epoxy coatings
  • 2019
  • Ingår i: Coatings. - 2079-6412. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Graphene, the typical two-dimensional sp2 hybridized carbon allotrope, is widely used as a filler for improving the mechanical performance of polymers. However, its superhydrophobic surface makes it a big challenge to obtain stable graphene dispersions, especially in water-borne systems. On the contrary, graphene oxide (GO) shows excellent dispersibility in water, but strong oxidants and acids destroy its structure and degrade its mechanical properties. This largely limits its application in water-borne coatings. In this work, graphene from mechanical exfoliation was surface modified by p-aminophenol derived diazonium salt to achieve a homogenous dispersion. Moreover, the hydroxyl groups in p-aminophenol are able to combine with epoxy resins during the curing process to improve mechanical performance of the final coatings. The result shows that functionalized graphene shows a lower coefficient of friction and better abrasion resistance compared to GO.
  • Liu, Ya, 1991, et al. (författare)
  • Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
  • 2019
  • Ingår i: Proceedings - 2019 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2019. ; , s. 1-5
  • Konferensbidrag (refereegranskat)abstract
    • Thermally conductive materials with electrically insulating properties have been extensively investigated for thermal management of electronic devices. The combined properties of high thermal conductivity, structural stability, corrosion resistance and electric resistivity make hexagonal boron nitride (h-BN) a promising candidate for this purpose. Theoretical studies have revealed that h-BN has a high in-plane thermal conductivity up to 400-800 W m-1 K-1 at room temperature. However, it is still a big challenge to achieve high thermally conductive h-BN thick films that are commercially feasible due to its poor mechanical properties. On the other hand, many polymers exhibit advantages for flexibility. Thus, combining the merits of polymer and the high thermal conductivity of h-BN particles is considered as a promising solution for this issue. In this work, orientated PVP/h-BN films were prepared by electrospinning and a subsequent mechanical pressing process. With the optimized h-BN loading, a PVP/h-BN composite film with up to 22 W m-1 K-1 and 0.485 W m-1 K-1 for in-plane and through-plane thermal conductivity can be achieved, respectively. We believe this work can help accelerate the development of h-BN for thermal management applications.
  • Manchili, Swathi Kiranmayee, 1987, et al. (författare)
  • Effect of Nanopowder Addition on the Sintering of Water-Atomized Iron Powder
  • 2020
  • Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - 1073-5623. ; 51:9, s. 4890-4901
  • Tidskriftsartikel (refereegranskat)abstract
    • A promising method of improving the densification of powder metallurgical steel components is to blend nanopowder with the otherwise typically used micrometre-sized powder. The higher surface-to-volume ratio of nanopowder is hypothesized to accelerate the sintering process and increase the inter-particle contact area between the powder particles. This is supposed to enhance the material transport and improve the densification. In the present investigation, water-atomized iron powder (− 45 μm) was mixed separately with pure iron and low-carbon steel nanopowder, each at a ratio of 95 to 5 pct. These powder mixes were compacted at different pressures (400, 600 and 800 MPa) and then sintered at 1350 °C in a pure hydrogen atmosphere. The sintering behavior of the powder blend compacts was compared to that of the compact with micrometre-sized powder only. Densification commenced at much lower temperatures in the presence of nanopowder. To understand this, sintering at intermittent temperatures such as 500 °C and 700 °C was conducted. The fracture surface revealed that the nanopowder was sintered at between 500 °C and 700 °C, which in turn contributed to the densification of the powder mix at the lower temperature range. Based on the sintering experiments, an attempt was made to calculate the activation energy and identify the associated sinter mechanism using two different approaches. It was shown that the first approach yielded values in agreement with the grain-boundary diffusion mechanism. As the nanopowder content increased, there was an increase in linear shrinkage during sintering.
  • Mo, Zhimin, et al. (författare)
  • Integrating nano carbon tubes with microchannel cooler
  • 2004
  • Ingår i: Proceedings of The 6th IEEE CPMT International Symposium on High Density Packaging and Component Failure Anlaysis (HDP'4). ; 04:EX905, s. pp 373-376
  • Konferensbidrag (refereegranskat)
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