• Title/Summary/Keyword: Mixed convection

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Evaluation of Thermal Behavior of Oil-based Nanofluids using Ceramic Nanoparticles (세라믹 분말을 이용한 오일 기지 나노유체의 열적거동 평가)

  • Choi, Cheol;Yoo, Hyun-Sung;Oh, Je-Myung
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.20 no.7
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    • pp.587-593
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    • 2007
  • Oil-based nanofluids were prepared by dispersing spherical and fiber shaped $Al_2O_3$ and AlN nanoparticles in transformer oil. Two hydrophobic surface modification processes using oleic acid (OA) and polyoxyethylene alkyl acid ester (PAAE) were compared in this study. The dispersion stability, viscosity and breakdown voltage of the nanofluids were also characterized. $(Al_2O_3+AlN)$ mixed nanofluid was prepared to take an advantage of the excellent thermal conductivity of AlN and a good convective heat transfer property of fiber shaped $Al_2O_3$. For $(Al_2O_3+AlN)$ particles with 1 % volume fraction in oil, the enhancement of thermal conductivity and convective heat transfer coefficient was nearly 11 % and 30 %, respectively, compared to pure transformer oil. The nanofluid, containing $Al_2O_3+AlN$, successfully lowered the temperature of the heating element and oil itself during a natural convection test using a prototype transformer.

Prismatic-core advanced high temperature reactor and thermal energy storage coupled system - A preliminary design

  • Alameri, Saeed A.;King, Jeffrey C.;Alkaabi, Ahmed K.;Addad, Yacine
    • Nuclear Engineering and Technology
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    • v.52 no.2
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    • pp.248-257
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    • 2020
  • This study presents an initial design for a novel system consisting in a coupled nuclear reactor and a phase change material-based thermal energy storage (TES) component, which acts as a buffer and regulator of heat transfer between the primary and secondary loops. The goal of this concept is to enhance the capacity factor of nuclear power plants (NPPs) in the case of high integration of renewable energy sources into the electric grid. Hence, this system could support in elevating the economics of NPPs in current competitive markets, especially with subsidized solar and wind energy sources, and relatively low oil and gas prices. Furthermore, utilizing a prismatic-core advanced high temperature reactor (PAHTR) cooled by a molten salt with a high melting point, have the potential in increasing the system efficiency due to its high operating temperature, and providing the baseline requirements for coupling other process heat applications. The present research studies the neutronics and thermal hydraulics (TH) of the PAHTR as well as TH calculations for the TES which consists of 300 blocks with a total heat storage capacity of 150 MWd. SERPENT Monte Carlo and MCNP5 codes carried out the neutronics analysis of the PAHTR which is sized to have a 5-year refueling cycle and rated power of 300 MWth. The PAHTR has 10 metric tons of heavy metal with 19.75 wt% enriched UO2 TRISO fuel, a hot clean excess reactivity and shutdown margin of $33.70 and -$115.68; respectively, negative temperature feedback coefficients, and an axial flux peaking factor of 1.68. Star-CCM + code predicted the correct convective heat transfer coefficient variations for both the reactor and the storage. TH analysis results show that the flow in the primary loop (in the reactor and TES) remains in the developing mixed convection regime while it reaches a fully developed flow in the secondary loop.

Partial premixed combustion modeling of diffusion flame burner for SiO2 deposition as optical fiber cladding (광섬유 클래딩용 SiO2 증착을 위한 확산 화염 버너의 부분 예혼합 연소 모델링)

  • Park, Hyung-Bin;Han, Yoonsoo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.29 no.6
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    • pp.365-371
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    • 2019
  • In this study, the flame temperature distribution of the diffusion flame burner for SiO2 deposition was analyzed by the computational fluid analysis. This corresponds to the previous step for simulating the SiO2 preform deposition process for manufacturing optical fibers using environmentally friendly raw materials. In order to model premixed combustion, heat flow, convection, and chemical reactions were considered, and Reynolds-averaged Navier-Stokes equations and k-ω models were used. As a result, the temperature distribution of the flame showed a tendency to increase the distance from the nozzle surface to the maximum temperature when the flow rate of the auxiliary oxygen increased. In addition, it was confirmed that the temperature distribution due to incomplete combustion was large in the combustion reaction with a large equivalence ratio of the mixed gas.

Prediction of Heat-treatment Time of Black Pine Log Damaged by Pine Wilt Disease (소나무재선충병 피해를 받은 곰솔 원목의 열처리 소요시간 예측)

  • Han, Yeonjung;Seo, Yeon-Ok;Jung, Sung-Cheol;Eom, Chang-Deuk
    • Journal of the Korean Wood Science and Technology
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    • v.44 no.3
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    • pp.370-380
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    • 2016
  • The black pine logs damaged by pine wilt disease in Jeju-do were heat-treated to extend the utilization of domestic trees damaged by pine wilt disease. The heat-treatment of wood requires wood to be heated to $56^{\circ}C$ for 30 min at the core. The average moisture content and top-diameter of the black pine logs were ranged from 46% to 141% and from 180 mm to 500 mm, respectively. And the basic specific gravity and oven-dry specific gravity of the black pine logs were 0.47 and 0.52, respectively. The time required for heat-treatment at $105^{\circ}C$ temperature was ranged from 7.7 h to 44.2 h, depending on moisture content and top-diameter. The temperature distribution was used to predict the time required for heat-treatment of black pine log with various moisture contents and top-diameters using finite difference method. The thermal properties of wood including the thermal conductivity and specific heat in accordance with moisture content were calculated. Heat transfer coefficient for mixed convection in form of adding natural convection and forced convection was used for heat transfer analysis. The error between the measured and predicted values ranged from 3% to 45%. The predicted times required for heat-treatment of black pine log with 50% moisture content and 200 mm, 300 mm, and 400 mm top-diameter were 10.9 h, 18.3 h, and 27.0 h, respectively. If the initial moisture content of black pine log is 75%, heat treatment times of 13.6 h, 22.5 h, and 32.8 h were predicted in accordance with top-diameter. And if the initial moisture content of black pine log is 100%, heat treatment times of 16.2 h, 26.5 h, and 38.2 h were predicted in accordance with top-diameter. When the physical properties of logs damaged by pine wilt disease are presented, these results can be applicable to the heat-treatment of red pine and Korean pine logs as well.

Seasonal Variability of Thermal Structure and Heat Flux in the Juam Reservoir (주암호의 계절별 수온 구조와 열수지 변화)

  • Sun, Youn-Jong;Cho, Cheol;Kim, Byong-Chun;Huh, In-Aa;Yoon, Jun-Heon;Chang, Nam-Ik;Cha, Sung-Sik;Cho, Yang-Ki
    • Korean Journal of Ecology and Environment
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    • v.36 no.3 s.104
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    • pp.277-285
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    • 2003
  • Temperature profiles were observed to understand seasonal variation of thermal structures in the Juam reservoir from March 2000 to May 2001. Heat flux which affects thermal structures was calculated by observed water temperature and meteorological data. Temperature became homogeneous vertically by convection due to the surface cooling in winter. Maximum heat loss through the surface (109.45W/$m^2$) occurred in December. There was a horizontal gradient of water temperature in winter. The temperature was $3^{\circ}C$ at upstream and $5^{\circ}C$ near the dam. The surface temperature increased by the increase of solar radiation in spring and summer. Maximum heat gained through the surface was 101.95 W/$m^2$ in July. Maximum surface temperature was $29^{\circ}C$ in August, whereas the bottom water was $7^{\circ}C.$ Surface mixed layer became thicker and its temperature decreased by surface heat loss in fall and winter.

Heat Transfer Characteristics of CO2 at Supercritical Pressure in a Vertical Circular Tube (수직원형관에서 초임계압 CO2의 열전달 특성)

  • Yoo, Tae-Ho;Bae, Yoon-Yong;Kim, Hwan-Yeol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.1
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    • pp.23-31
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    • 2011
  • At supercritical pressure, the physical properties of fluid change substantially and the heat transfer at a temperature similar to the critical or pseudo-critical temperature improves considerably; however, the heat transfer may deteriorate due to a sudden increase in the wall temperature at a certain condition of a mass and heat flux. In this study, the heat transfer rates in $CO_2$ flowing vertically upward and downward in a circular tube with a diameter of 4.57 mm under various conditions were calculated by measuring the temperature of the outer wall of the tube. The published heat transfer correlations were analyzed by comparing their prediction values with 7,250 experimental data. By introducing a buoyancy parameter, a heat transfer correlation, which could be applied only to a normal heat transfer regime, was extended such that it can be applied to regime of heat transfer deterioration. The published criteria for heat transfer deterioration were evaluated against the conditions obtained from the experiment in this study.

Computer Simulation for the Thermal Analysis of the Energy Storage Board (에너지 축열보드 열해석을 위한 컴퓨터 수치해석)

  • 강용혁;엄태인;곽희열
    • Journal of Energy Engineering
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    • v.8 no.2
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    • pp.224-232
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    • 1999
  • Latent heat storage system using micro-encapsuled phase change material is effective method for floor heating of house and building. The temperature profile in capsule block and flow rate of hot water are important parameters for the development of heat storage system. In the present study, a mathematical model based on 3-D, non-steady state, Navier-Stokes equations, scalar conservation equations and turbulence model ($\kappa$-$\varepsilon$), is used to predict the temperature profiles in capsule and the velocity vectors in hot water pipe. The multi-block grids and fine grids embedding are used to join the circle in hot water pipe and square in capsule block. The phase change process of the capsule is quite complex not only because the size of phase change material is very small, but also because phase change material is mixed with the cement to form thermal storage block. In calculation, it's assumed that the phenomena of phase change is limited only the thermal properties of phase change material and the change of boundary is not happened in capsule. The purpose of this study is to calculate the temperature profiles in capsule block and velocity vectors in hot water pipe using the numerical calculation. Two kinds of thermal boundary condition were considered, the first (case 1) is the adiabatic condition for the both outside surfaces of the wall, the second (case 2) is the case in which one surface is natural convection with atmosphere and another surface is adaibatic. Calculation results are shown that the temperature profile in capsule block for case 1 is higher than that for case 2 due to less heat loss in adaibatic surface. Specially, in the domain of near Y=0, the difference of temperature is greater in case 1 than in case 2. The detailed experimental data of capsule block on the temperature profile and the thermal properties such as specific heat and coefficient of heat transfer with the various temperature are required to predict more exact phenomena of heat transfer.

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Preliminary Analysis of the CANDU Moderator Thermal-Hydraulics using the CUPID Code (2상 유동 해석코드 CUPID를 이용한 CANDU 원자로 감속재 열수력 예비해석)

  • Park, Sang Gi;Lee, Jae Ryong;Yoon, Han Young;Kim, Hyoung Tae;Jeong, Jae Jun
    • Journal of Energy Engineering
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    • v.21 no.4
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    • pp.419-426
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    • 2012
  • A transient, three-dimensional, two-phase flow analysis code, CUPID, has been developed in KAERI. In this work, we performed a preliminary analysis using the CUPID code to investigate the thermal-hydraulic behavior of the moderator in the Calandria vessel of a CANDU reactor. At first, we validated the CUPID code using the three experiments that were performed at Stern Laboratories Inc. To avoid the complexity to generate computational mesh around the Calandria tube bundles, a porous media approach was applied for the region. The pressure drop in the porous media zone was modeled by an empirical correlation. The results of the calculations showed that the CUPID code can predict the mixed flow pattern of forced and natural convection inside the Calandria vessel very well. Thereafter, the analysis was extended to a two-phase flow condition. Also, the local maximum temperature in the Calandria vessel was plotted as a function of the injection flow rate, which may be utilized to predict the local subcooling margin.

Trichloroethylene Treatment by Zero-Valent Iron and Ferrous Iron with Iron-Reducing Bacteria - Model Development (영가철 및 철환원균을 이용한 2가 산화철 매질에 의한 TCE 제거 연구 - 모델수립)

  • Bae, Yeun-Ook;Kim, Doo-Il;Park, Jae-Woo
    • Journal of Korean Society of Environmental Engineers
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    • v.30 no.11
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    • pp.1146-1153
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    • 2008
  • Numerical simulation was carried out to study the trichloroethylene (TCE) degradation by permeable reactive barrier (PRB), and revealed the effect of concentration of TCE, iron medium mass, and concentration of iron-reducing bacteria (IRB). Newly developed model was based on axial dispersion reactor model with chemical and biological reaction terms and was implemented using MATLAB ver R2006A for the numerical solutions of dispersion, convection, and reactions over column length and elapsed time. The reaction terms include reactions of TCE degradation by zero-valent iron (ZVI, Fe$^0$) and ferrous iron (Fe$^{2+}$). TCE concentration in the column inlet was maintained as 10 mg/L. Equation for Fe$^0$ degradation includes only TCE reaction term, while one for Fe$^{2+}$ has chemical and biological reaction terms with TCE and IRB, respectively. Two coupled equations eventually modeled the change of TCE concentration in a column. At Fe$^0$ column, TCE degradation rate was found to be more than 99% from 60 hours to 235 hours, and declined to less than 1% in 1,365 hours. At the Fe$^{2+}$ and IRB mixed column, TCE degradation rate was equilibrated at 85.3% after 210 hours and kept it constant. These results imply that the ferrous iron produced by IRB has lowered the TCE degradation efficiency than ZVI but it can have higher longevity.http://kci.go.kr/kciportal/ci/contents/ciConnReprerSearchPopup.kci#

Physicochemical Characteristics of Fermented Pig Manure Compost and Cow Manure Compost by Pelletizing (펠렛 가공처리에 따른 돈분 발효퇴비와 우분 발효퇴비의 물리화학적 특성)

  • Jeong, Kwang Hwa;Park, Chi Ho;Choi, Dong Yun;Kwak, Jung Hoon;Yang, Chang Bum;Kang, Ho
    • Journal of the Korea Organic Resources Recycling Association
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    • v.13 no.4
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    • pp.118-127
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    • 2005
  • The best way to treat livestock manure is a recycling the manure to arable land as an organic fertilizer. In this study, fermented cow manure compost and pig manure compost were used as a raw materials for pelletizing. The changes of physicochemical properties of each composts and pellets were investigated. The aim of this research was to improve availability of livestock manure compost. In pelletizing process of fermented livestock manure compost, the optimal water content to make pellet was around 40%. When clay was mixed by volume more than 15% as a bonding agent, the condition of pelletizing process was beginning to improve. On a dry matter basis, the contents of N, P and K of fermented pig manure compost were 2.05%, 1.89% and 1.31%, respectively. After pelletizing, the contents of compost pelleted with the pig manure compost were 1.96% 1.73% and 0.89%, respectively. The same parameters of cow manure compost were 2.52%, 1.01% and 2.98%, respectively. After processing, the contents of compost pelleted with the cow manure compost were 2.45%, 1.10% and 2.93%, respectively. After pelletizing, there were little change in the content of heavy metals such as Pb, Cd, As and Hg. When pelleted compost dried naturally was submerged in water, it was completely dissolved in 30 minutes. On the other hand, Pelleted compost dried with the mechanical convection oven set $70^{\circ}C$ for 24 hours was completely dissolved in 960 minutes. The volume and weight of pelleted compost were decreased with time. After 30 days of storing, the weight of pelleted compost was decreased by 15% compared with its original weight. The volume of it was decreased by 17~25% in the same time.

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