Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 A Compact Nanostructure Enhanced Heat Sink with Flow in a rectangular channel Muhsincan Sesen 1 ,Berkay Arda Kosar 1 , Berk Ahmet Ahishalioglu 1 , Wisam Khudhayer 2 , Tansel Karabacak 2 and Ali Kosar 1,* 1 Sabanci University, Tuzla 34956, Turkey 2 University of Arkansas at Little Rock, Little Rock, AR, 72204, USA Abstract— This paper reports a compact nanostructure based heat sink. The system has an inlet and an outlet valve similar to a conventional heat sink. From the inlet valve, pressurized deionized-water is propelled into a rectangular channel (of dimensions 24mmx59mmx8mm) which houses a flat plate, on which ~600 nm long copper nanorods with an average diameter of 150 nm are integrated to copper thin film coated on silicon wafer surface. Forced convective heat transfer characteristics of the nanostructured plate are investigated using the experimental setup and compared to the results from a flat plate of copper thin film deposited on Silicon substrate. The nanorods integrated on the flat plate act as fins over the plate which enhances the heat transfer from the plate. In the design processes of many mechanical and chemical devices one of the key issues of saving energies and achieving compact designs is the enhancement of heat transfer [1]. As heat transfer is enhanced, the cooling process becomes more efficient. In designing of heat exchangers for spacecrafts, automobiles, MEMS devices and micro-processors it is really important that the heat exchanger is kept compact and lightweight [2]. For the purpose of making compact and efficient heat exchangers, heat transfer enhacement with nanostructures could be considered as a futuristic candidate. Recently, many studies have been going on for enhancing the convective heat transfer by enlarging the transfer surface using extended surfaces like fins and ribs [1,3-5]. These modifications enlarge the heat transfer surface area and provide high heat transfer rates but their drawback is increased friction factor and unwanted pressure drops. Using pin-fin structures causes pressure losses which is a significant problem in many thermo-fluid applications and designs [1]. These pressure losses occur because of the friction force formed due to the increased flow resistance imposed by pinfins. copper thin film deposited on Silicon substrate, to enhance heat transfer via single-phase flow in a rectangular channel. Heat transfer coefficients of the system were reduced for a constant heat flux scenario up to 6.5W/cm 2 and it has been shown that the nanostructured plate enhances heat transfer significantly because the surface area is greatly enhanced and thus heat removal takes place more effectively. The advantage of such a system is that it does not cause any significant extra pressure drop and thus does not raise friction factor. Pin-fin geometry imposed by nanorods on the plate (integrated to the channel wall) is on the nanoscale order so that the friction forces induce minor pressure losses. Figure 1. Cross-section views of glancing angle deposited (GLAD) Cu To achieve positive effects on heat transfer coefficients with diminishing length scale and high heat transfer performance due to enhanced heat transfer area, nanostructured surfaces have been used in more recent studies. Nanostructured surfaces have been most widely employed in pool boiling [6,7]. Different from the state of the art, this paper utilizes nanostructures in a forced convective heat transfer scheme so that their potential could be exploited from a different perspective. For this purpose, this article proposes a nanostructured flat plate, on which vertical copper nanorods of length ~600nm and average diameter ~150nm are integrated to Figure 21.5PSI and 2.5PSI *Corresponding author: kosara@sabanciuniv.edu [1] Kunugi, T., Muko, K., Shibahara, M., Superlattices and Microstructures, 35, pp. 531-542, 2004. [2] Stone, K.M., ACRC TR-105, 1996. [3] Zamfirescu, C., and Feidt, M., Heat Transfer Engineering, 28(5), pp. 451- 459, 2007. [4] Zamfirescu, C., and Bejan, A., Int. J. of Heat and Mass Transfer, 46, pp. 2785–2797, 2003. [5] Qu, W., and Siu-Ho, A., J. Heat Transfer, 130(12), pp. 124501-124504, 2008. [6] Sesen, M., Khudhayer, W., Karabacak, T., Kosar, A., Micro&Nano Letters, (in press), 2010. [7] Li, C., Wang Z., Wang P.-I., Peles Y., Koratkar N., and Peterson G., Small, 4(8), pp. 1084–1088, 2008. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 248
Poster Session, Tuesday, June 15 Theme A1 - B702 Synthesis and Structural Characterization of LiZn 0.5 Mn 1.5 O 4 Cathode Materials Burçak Ebin*, Sebahttin Gürmen, Cüneyt Arslan Metallurgical and Materials Eng. Dept., Istanbul Technical University, Istanbul 34469, Turkey Abstract – LiZn 0.5 Mn 1.5 O 4 nanoparticles were synthesized by ultrasonic spray pyrolysis method as a cathode material in lithium ion batteries. Stoichiometrically dissolved lithium, manganese and zinc nitrates in distilled water were used as precursor solution. The product characteristics, such as particle size and morphology, chemical composition, crystal structure and crystalline sizes were investigated by X-ray diffraction (XRD), scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). Developments in electronically industry have increased the demand of portable energy storage devices with low cost, environment friendly and high energy density. Lithium ion batteries have satisfied this demand to a greater degree than other battery systems. Although, the commercial cathode material for lithium ion batteries is layer structured LiCoO 2 , it has some drawbacks such as high cost, toxicity and instability at high potential [1-3]. Therefore, many researchers have been extensively studying alternative materials that have high energy density and cycling performance [2-5]. Among the promising candidates for the cathode materials, the spinel LiMn 2 O 4 has economical and environmental advantages as compared to the layered compounds [6-7]. However, there is problem of capacity fading during charge/discharge cycling of the LiMn 2 O 4 cathode material due to fracture of the structure [1,3,6-8]. Different studies realized to increase the performance of this material by partial substitution of monovalent and multivalent cations for manganese ions [1,7]. It is reported that zinc doping to the LiFePO 4 cathode structure enlarge the lattice volume without any damage to structure and deintercalation and intercalation of the lithium ions, the doped zinc atoms protect the crystal [8]. In this study, zinc doped spinel LiMn 2 O 4 structure to increase the stability of the structure and spinel structured LiZn 0.5 Mn 1.5 O 4 nanoparticles formed by ultrasonic spray pyrolysis method. Spinel LiZn 0.5 Mn 1.5 O 4 cathode particles were fabricated by ultrasonic spray pyrolysis method from mixer of lithium nitrate, zinc nitrate and manganese nitrate. Metal nitrates with atomic ratio Li:Zn:Mn=1:1/2:2 dissolved in a distilled water to prepare precursor solution and the total concentration of the total metal nitrates was 0.35 mol/dm 3 . Aerosol droplets of the precursor solution was generated by ultrasonic atomizer with 1.3 MHz frequency, and then aerosol droplets was introduced into the furnace at 800°C by air carrier gas with the 500 ml/min flow rate. The pyrolyzed particles were calcinated at 600°C for 2 h under air atmosphere. The crystalline phase and size of the samples were investigated by X-ray diffraction. Scanning electron microscope was used to determine particle size and morphology. Also, energy dispersive spectroscopy (EDS) was used to determine the chemical composition of the samples. Figure 1. SEM image of LiZn 0.5 Mn 1.5 O 4 nanoparticles Figure 1 shows that spherical LiZn 0.5 Mn 1.5 O 4 nanoparticles, nearly 50 nm particles size, were synthesized by ultrasonic spray pyrolysis method. X- ray diffraction patterns indicate that particles have spinel structure with simultaneous 1:1 tetrahedral and 1:3 octahedral cation ordering. Zn 2+ and half of the Li + cations occupy tetrahedral sites and Mn 4+ and other half of the Li + cations occupy octahedral sites in the structure. This study has been supported by ITU-BAP with a grant number 33242. *Corresponding author: ebinb@itu.edu.tr [1] C.H. Lu, et al., Mater. Chem. Phys., 112:, 115-119 (2008). [2] S.H. Park, S.W. Oh, Y.K. Sun, J. Power Sources, 146, 622-625 (2005). [3] S.H. Park, et al., Electrochimica Acta, 49, 557-563 (2004). [4] X. Cao, et al., Mater. Res. Bull., 44, 472-477 (2009). [5] X. Sihi, et al., Mater. Chem. Phys., 113, 780-783 (2009). [6] I. Taniguchi, D. Song, M. Wakihara, J. Power Sources, 109, 333-339 (2002). [7] I. Taniguchi, Mater. Chem. Phys., 92, 172-179 (2005). [8] K. Matsuda, I. Taniguchi, J. Power Sources, 132, 156-160 (2004). [9] H. Liu, et al., Electrochem. Commun., 8, 1553-1557 (2006). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 249
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