• Title/Summary/Keyword: Fluidized particles layer

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A Study on the Radiative Heat Transfer Characteristics in the Fluidized Particles Layer (유동입자층에서의 복사열전달 특성에 관한 연구)

  • 김금무;김용모;김경근
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.4
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    • pp.33-42
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    • 1994
  • The radiative heat transfer analysis in the fluidized particles layer has important application in many technological areas such as combustion chambers at high pressure and temperature, plasma generators for nuclear fusion, MHD generator using pulverized coal and the liquid droplet radiator used to reject wasted heat from a power plant operating in space. To accurately model the radiation properties of the fluidized particles layer, it is necessary to know the radiation interchange factors of particles in each layer. But the solutions are usually not possible for the equations of radiative heat transfer because it has an inherent difficulty in treating the governing intergo- differential equations, which are derived from the remote effects of radiative heat transfer. In this study, the analysis uses the Monte Carlo simulation method with optical depth model to calculate the radiation interchange factors of particles in each layer with wall and with each other.

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Characteristics of Fluid Flow and Heat Transfer in a Fluidized Bed Heat Exchanger (순환유동층 열교환기내 유동과 열전달 특성)

  • 안수환;이병창;김원철;이윤표
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.4
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    • pp.315-323
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    • 2002
  • The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the drag force coefficients of particles in the internal flow were higher than those in the external flow, in addition, the solid particle periodically hitting the tube wall broke the thermal boundary layer, and increased the rate of heat transfer. Particularly when the flow velocity was low, the effect was more pronounced.

Effect of Deposition Parameters on the Property of SiC Layer in TRISO-Coated Particles (TRISO 피복 입자에서 증착 조건이 탄화규소층의 특성에 미치는 영향)

  • Park, J.H.;Kim, W.J.;Park, J.N.;Park, K.H.;Park, J.Y.;Lee, Y.W.
    • Korean Journal of Materials Research
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    • v.17 no.3
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    • pp.160-166
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    • 2007
  • TRISO coatings on $ZrO_{2}$ surrogate kernels were conducted by a fluidized-bed chemical vapor deposition (FBCVD) method. Effects of the deposition temperature and the gas flow rate on the properties of SiC layer were investigated in the TRISO-coated particles. Deposition rate of the SiC layer decreased as the deposition temperature increased in the temperature range of $1460^{\circ}-1550^{\circ}C$. At the deposition temperature of $1550^{\circ}C$ the SiC layer contained an excess carbon, whereas the SiC layers had stoichiometric compositions at $1460^{\circ}C\;and\;1500^{\circ}C$. Hardness and elastic modulus measured by a nanoindentation method were the highest in the SiC layer deposited at $1500^{\circ}C$. The SiC layer deposited at the gas flow rate of 4000 sccm exhibited a high porosity and contained large pores more than $1{\mu}m$, being due to a violent spouting of particles. On the other hand, the SiC layer deposited at 2500 sccm revealed the lowest porosity.

Effect of Deposition Temperature on Microstructure and Hardness of ZrC Coating Layers of TRISO-Coated Particles Fabricated by the FBCVD Method (유동층 화학기상증착법으로 제조된 TRISO 피복입자의 ZrC 층 미세구조와 경도에 미치는 증착온도의 영향)

  • Ko, Myung-Jin;Kim, Daejong;Kim, Weon-Ju;Cho, Moon Sung;Yoon, Soon Gil;Park, Ji Yeon
    • Journal of the Korean Ceramic Society
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    • v.50 no.1
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    • pp.37-42
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    • 2013
  • Tristructural-isotropic (TRISO)-coated particles were fabricated by a fluidized-bed chemical vapor deposition (FBCVD) method for use in a very high temperature gas-cooled reactor (VHTR). ZrC as a constituent layer of TRISO coating layers was deposited by a chloride process using $ZrCl_4$ and $CH_4$ source gases in a temperature range of $1400^{\circ}C$ and $1550^{\circ}C$. The change in the microstructure of ZrC depending on the deposition temperature and its effect on the hardness were evaluated. As the deposition temperature increased to $1500^{\circ}C$, the grain size of the ZrC increased and the hardness of the ZrC decreased according to the Hall-Petch relationship. However, at $1550^{\circ}C$, the ZrC layer was highly non-stoichiometric and carbon-rich and did not obey the Hall-Petch relationship in spite of the decrease of the grain size. A considerable amount of pyrolytic carbon at the grain boundaries of the ZrC as well as coarse granular pyrolytic carbon were locally distributed in the ZrC layer deposited at $1550^{\circ}C$. Therefore, the hardness decreased largely due to the formation of a large amount of pyrolytic carbon in the ZrC layer.

Preparation process of functional particles: III. Preparation of composite particles by rapid expansion of supercritical fluid solutions and release behavior (기능성 미분말의 제조공정에 관한 연구 : III. 초임계 분출법에 의한 복합분체의 합성과 용출특성)

  • ;;;Eiichi Abe
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.1
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    • pp.55-59
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    • 1999
  • The Rapid Expansion of Supercritical fluid Solutions (RESS) process was applied to particles coating. Microcapsules prepared by spray drying were used as the core particles, and two kinds of paraffin were used as the coating materials. Supercritical $CO_{2}$ solutions of paraffin were expanded through the short nozzle into the bed that was fluidized by air. Extraction temperature and pressure were varied at $50~120^{\circ}C$, $150~200\;kg/\textrm{cm}^2$, respectively. The thickness of theoritical coating layer ws measured, and precipitate coating layer on surface was analyzed by using SEM, FT-IR. The release behaviors of $Mg^{2+}$ ions were inspected by atomic absorbance spectrophtometer.

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Microstructure of ZrC Coatings of TRISO Coated Particles by Codeposition of Free Carbon and Control of Stoichiometry (유리탄소의 동시증착에 의한 TRISO 피복입자의 ZrC 코팅층 미세구조와 화학양론비 제어)

  • Ko, Myung-Jin;Kim, Daejong;Park, Ji Yeon;Cho, Moon Sung;Kim, Weon-Ju
    • Journal of the Korean Ceramic Society
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    • v.50 no.6
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    • pp.446-450
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    • 2013
  • TRISO coated particles with a ZrC barrier layer were fabricated by a fluidized-bed chemical vapor deposition (FBCVD) method for a use in a very high temperature gas-cooled reactor (VHTR). The ZrC layer was deposited by the reaction between $ZrCl_4$ and $CH_4$ gases at $1500^{\circ}C$ in an $Ar+H_2$ mixture gas. The amount of free carbon codeposited with in ZrC was changed by controlling the dilution gas ratio. Near-stoichiometric ZrC phase was also deposited when an impeller was employed to a $ZrCl_4$ vaporizer which effectively inhibited the agglomeration of $ZrCl_4$ powders during the deposition process. A near-stoichiometric ZrC coating layer had smooth surface while ZrC containing the free carbon had rough surface with tumulose structure. Surface roughness of ZrC increased further as the amount of free carbon increased.

Effect of Lower Bed Height on Collapse Velocity in the Two-Stage Bubbling Fluidized-Bed with a Standpipe for Solid Transport (고체 수송관이 있는 2 단 기포 유동층에서 붕괴 속도에 대한 하단 층 높이의 영향)

  • Khurram, Muhammad Shahzad;Choi, Jeong-Hoo
    • Korean Chemical Engineering Research
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    • v.56 no.6
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    • pp.864-870
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    • 2018
  • The effect of lower bed height on the collapse velocity was investigated for a two-stage bubbling fluidizedbed (0.1 m in diameter, 1.2 m high) connected with a standpipe (0.025 m in diameter) for solid transport. Air was used as fluidizing gas and mixture of coarse (< $1000{\mu}m$ in diameter and $3625kg/m^3$ in apparent density) and fine (< $147{\mu}m$ in diameter and $4079kg/m^3$ in apparent density) particles as solid particles. Mixing ratio of fine particles, height of the lower bed and the distributor of the upper bed were considered as experimental variables. The collapse velocity increased with static height of the lower bed. However, the effect decreased as the mixing ratio of fine particles increased. The effect seemed to be attributed to the increase in height of the dense layer of coarse particles that prevented the gas from flowing into the standpipe, not in pressure drop for the standpipe, as the bed height increased. The collapse velocity decreased a little as the pressure drop of the distributor of the upper bed increased. An improved correlation was proposed for predicting the collapse velocity.

Effect of Deposition Parameters on the Property of Silicon Carbide Layer in Coated Particle Nuclear Fuels (피복입자핵연료에서 증착조건이 탄화규소층의 특성에 미치는 영향)

  • Kim, Yeon-Ku;Kim, Weon-Ju;Yeo, SungHwan;Cho, Moon Sung
    • Journal of Powder Materials
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    • v.23 no.5
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    • pp.384-390
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    • 2016
  • Tri-isotropic (TRISO) coatings on zirconia surrogate beads are deposited using a fluidized-bed vapor deposition (FB-CVD) method. The silicon carbide layer is particularly important among the coated layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO-coated particles. In this study, we obtain a nearly stoichiometric composition in the SiC layer coated at $1400^{\circ}C$, $1500^{\circ}C$, and $1400^{\circ}C$ with 20 vol.% methyltrichlorosilane (MTS), However, the composition of the SiC layer coated at $1300-1350^{\circ}C$ shows a difference from the stoichiometric ratio (1:1). The density decreases remarkably with decreasing SiC deposition temperature because of the nanosized pores. The high density of the SiC layer (${\geq}3.19g/cm^2$) easily obtained at $1500^{\circ}C$ and $1400^{\circ}C$ with 20 vol.% MTS did not change at an annealing temperature of $1900^{\circ}C$, simulating the reactor operating temperature. The evaluation of the mechanical properties is limited because of the inaccurate values of hardness and Young's modulus measured by the nano-indentation method.

Spherical UO2 Kernel and TRISO Coated Particle Fabrication by GSP Method and CVD Technique (겔침전과 화학증착법에 의한 구형 UO2 입자와 TRISO 피복입자 제조)

  • Jeong, Kyung-Chai;Kim, Yeon-Ku;Oh, Seung-Chul;Cho, Moon-Sung
    • Journal of the Korean Ceramic Society
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    • v.47 no.6
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    • pp.590-597
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    • 2010
  • HTGR using a TRISO coated particles as nuclear raw fuel material can be used to produce clean hydrogen gas and process heat for a next-generation energy source. For these purposes, a TRISO coated particle was prepared with 3 pyro-carbon (buffer, IPyC, and OPyC) layers and 1 silicone carbide (SiC) layer using a CVD technique on a spherical $UO_2$ kernel surface as a fissile material. In this study, a spherical $UO_2$ particle was prepared using a modified sol-gel method with a vibrating nozzle system, and TRISO coating fabrication was carried out using a fluidized bed reactor with coating gases, such as acetylene, propylene, and methyltrichlorosilane (MTS). As the results of this study, a spherical $UO_2$ kernel with a sphericity of 1+0.06 was obtained, and the main process parameters in the $UO_2$ kernel preparation were the well-formed nature of the spherical ADU liquid droplets and the suitable temperature control in the thermal treatment of intermediate compounds in the ADU, $UO_3$, and $UO_2$ conversions. Also, the important parameters for the TRISO coating procedure were the coating temperature and feed rate of the feeding gas in the PyC layer coating, the coating temperature, and the volume fraction of the reactant and inert gases in the SiC deposition.