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Hung T.-C.,Military Academy | Yan W.-M.,National University of Tainan | Yan W.-M.,Research Center for Energy Technology and Strategy | Wang X.-D.,North China Electrical Power University | Huang Y.-X.,National Cheng Kung University
International Journal of Heat and Mass Transfer | Year: 2012

This work uses an optimization procedure consisting of a simplified conjugate-gradient method and a three-dimensional fluid flow and heat transfer model to investigate the optimal geometric parameters of a double-layered microchannel heat sink (DL-MCHS). The overall thermal resistance R T is the objective function to be minimized, and the number of channels N, channel width ratio β, lower channel aspect ratio α l, and upper channel aspect ratio α u are the search variables. For a given bottom area (10 × 10 mm) and heat flux (100 W/cm 2), the optimal (minimum) thermal resistance of the double-layered microchannel heat sink is about R T = 0.12°C/m 2W. The corresponding optimal geometric parameters are N = 73, β = 0.50, α l = 3.52, and, α u = 7.21 under a total pumping power of 0.1 W. These parameters reduce the overall thermal resistance by 52.8% compared to that yielded by an initial guess (N = 112, β = 0.37, α l = 10.32, and α u = 10.93). Furthermore, the optimal thermal resistance decreases rapidly with the pumping power and then tends to approach an constant value. As the pumping power increases, the optimal values of N, α l, and α u increase, whereas the optimal β value decreases. However, increasing the pumping power further is not always cost-effective for practical heat sink designs. © 2012 Elsevier Ltd. All rights reserved. Source


Wang S.-H.,Research Center for Energy Technology and Strategy | Lin Y.-Y.,Research Center for Energy Technology and Strategy | Teng C.-Y.,Research Center for Energy Technology and Strategy | Chen Y.-M.,Research Center for Energy Technology and Strategy | And 5 more authors.
ACS Applied Materials and Interfaces | Year: 2016

This study reports on a high ionic-conductivity gel polymer electrolyte (GPE), which is supported by a TiO2 nanoparticle-decorated polymer framework comprising poly(acrylonitrile-co-vinyl acetate) blended with poly(methyl methacrylate), i.e., PAVM:TiO2. High conductivity GPE-PAVM:TiO2 is achieved by causing the PAVM:TiO2 polymer framework to swell in 1 M LiPF6 in carbonate solvent. Raman analysis results demonstrate that the poly(acrylonitrile) (PAN) segments and TiO2 nanoparticles strongly adsorb PF6 - anions, thereby generating 3D percolative space-charge pathways surrounding the polymer framework for Li+-ion transport. The ionic conductivity of GPE-PAVM:TiO2 is nearly 1 order of magnitude higher than that of commercial separator-supported liquid electrolyte (SLE). GPE-PAVM:TiO2 has a high Li+ transference number (0.7), indicating that most of the PF6 - anions are stationary, which suppresses PF6 - decomposition and substantially enlarges the voltage that can be applied to GPE-PAVM:TiO2 (to 6.5 V vs Li/Li+). Immobilization of PF6 - anions also leads to the formation of stable solid-electrolyte interface (SEI) layers in a full-cell graphite|electrolyte|LiFePO4 battery, which exhibits low SEI and overall resistances. The graphite|electrolyte|LiFePO4 battery delivers high capacity of 84 mAh g-1 even at 20 C and presents 90% and 71% capacity retention after 100 and 1000 charge-discharge cycles, respectively. This study demonstrates a GPE architecture comprising 3D space charge pathways for Li+ ions and suppresses anion decomposition to improve the stability and lifespan of the resulting LIBs. © 2016 American Chemical Society. Source


Huang M.R.S.,National Cheng Kung University | Erni R.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Liu C.-P.,National Cheng Kung University | Liu C.-P.,Research Center for Energy Technology and Strategy | Liu C.-P.,Advanced Optoelectronic Technology Center
Applied Physics Letters | Year: 2013

The influence of surface oxidation on the low-loss spectrum of aluminum nitride (AlN) is investigated in electron energy-loss spectroscopy with scanning transmission electron microscopy. Contrary to intrinsic bulk AlN, oxidized AlN exhibits considerable spectral broadening both in the full width at half maximum of bulk plasmon and the subsidiary features. The modification in the low-loss lineshapes due to oxidation significantly complicates the determination of the dielectric function intrinsic to AlN. Simulations based on dielectric theory qualitatively consist with the experimental results while incorporating thick overlayers, further suggesting that the surface oxide of AlN can be rough and porous in nature. © 2013 American Institute of Physics. Source


Hung T.-C.,Roc Military Academy | Yan W.-M.,National University of Tainan | Yan W.-M.,Research Center for Energy Technology and Strategy
International Journal of Heat and Mass Transfer | Year: 2012

A three-dimensional analysis aimed at enhancing the thermal performance of a double-layered microchannel heat sink by using a nanofluid and varying the geometric parameters has been conducted. A system of fully elliptic equations that govern the flow and thermal fields are solved using the finite volume method. The analysis indicates that the dominant factors determining the thermal resistance of the channel include the type of nanofluid; particle volume fraction; geometric parameters of the channel, such as the channel number, channel width ratio, channel aspect ratio; and pumping power. The results indicate that the greatest enhancement in channel cooling can be expected when an Al 2O 3-water nanofluid is used. The thermal resistance of the channel can be minimized by properly adjusting the particle volume fraction under various pumping powers; the minimum thermal resistance depends on the geometric parameters. The study also reveals that the relationship between the thermal resistance and channel number, channel width ratio, or channel aspect ratio exhibits a decrease followed by an increase. The thermal performance of the channel can usually be improved by decreasing the channel number or channel aspect ratio, or increasing the channel width ratio. Finally, increasing the pumping power reduces the overall thermal resistance. An Al 2O 3 (1%)-water nanofluid shows an average improvement in thermal performance of 26% over that of pure water for a given pumping power. However, the design's effectiveness declines significantly under high pumping power. In particular, the thermal resistance obtained by employing nanofluids was not necessarily lower than that of water under all pumping powers, but it can be reduced by properly adjusting the geometric parameters under optimal conditions. © 2012 Elsevier Ltd. All rights reserved. Source


Hung T.-C.,Roc Military Academy | Huang Y.-X.,National Chung Cheng University | Sheu T.-S.,Roc Military Academy | Yan W.-M.,Research Center for Energy Technology and Strategy
Numerical Heat Transfer; Part A: Applications | Year: 2014

The present study deals with the optimal geometric parameters design of a microchannel heat sink (MCHS) filled with sintered porous medium through an optimization procedure. This procedure integrates the simplified conjugate-gradient method (SCGM) and a three-dimensional heat sink model as an optimizer. The optimal design variables such as the number of channel N, channel-width ratio β, and channel aspect ratio α that minimize the overall thermal resistance of the microchannel heat sink are obtained under various pumping powers and porous conditions. Optimization results show that, for a given pumping power, the optimal design variables are N = 108, β = 0.90, and α = 8.15, with a corresponding minimum overall thermal resistance of 0.070 K W-1, and the overall thermal resistance is decreased by 40% over that of the initial guess (N = 56, β = 0.4, α = 4.8, and R T = 0.115 K W-1). The predicted results also reveal that the optimal thermal resistance and all the corresponding optimal values of N, β, and α decrease with the increase of porosity. Moreover, as the pumping power increases, the optimal thermal resistance decreases, both the corresponding optimal values of N and α increase, where as β reaches a maximum limitation. The proposed combined approach is effective in optimizing the geometric parameters for a porous-microchannel heat sink. © 2014 Copyright Taylor and Francis Group, LLC. Source

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