열 하중 기반의 리츠벡터와 순차적 센서위치 선택방법을 이용한 강건하고 효율적인 열 오차 모델링

현재엽(Jaeyub Hyun),유동윤(Dongyoon Yoo),이선규(Sun-Kyu Lee),왕세명(Semyung Wang) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Thermal deformations are among the most significant factors to errors generation of machine tool, this degrades the performance and accuracy of the machine tool. There are many methods to reduce the thermal deformation, such as structural designs to minimize thermal deformation, approaches to block and/or suppress thermal source, and thermal error compensation techniques to estimate and control thermal deformation. Among these, thermal error compensation techniques have been realized as the most successful method and actively studied. Securing of robustness and effectiveness of the thermal error modeling is directly correlated to the better compensation results. Most of the current thermal error modeling methods is highly dependent on measured data, and cannot consider mechanisms of the thermal deformation due to the thermal-structural interaction effect. In this paper, therefore, a novel and innovative strategy that can select the optimized thermal sensor placement and thermal error modeling method are proposed based on thermal load dependent ritz vectors. Operation state of the actual machine tool and thermal source variation are continuously changing according to the time. Thus, the various boundary conditions are applied to properly deal with these variations. The Wilson’s Ritz algorithm is used for generating the thermal load dependent Ritz vectors. Finally, for various 2D and 3D systems such as heat pipe and spindle, both existing thermal errors modeling method to use the eigenvectors and proposed method to use thermal load dependent ritz vectors are compared and investigated. Through this, the robustness and effectiveness are verified.

열전도도 향상을 위한 직물섬유 복합재의 최적구조 설계

김명수 ( Myungsoo Kim ),성대한 ( Dae Han Sung ),박영빈 ( Young Bin Park ),박기원 ( Kiwon Park ) 한국복합재료학회 2017 Composites research Vol.30 No.1

본 연구에서는 직물섬유 복합재의 열전도를 구하는데 있어 기존의 연구보다 개선된 방법을 제시하고, 직물섬유의 기하학적 구조가 복합재의 열전도도 향상에 미치는 영향, 그리고 유전 알고리즘(Genetic algorithm)을 이용하여 복합재의 열전도도 향상을 위한 최적구조 설계에 관한 연구를 하였다. 직물섬유의 구조를 토우의 물결무늬와 너비 및 두께를 이용하여 구현하였고, 열전도도는 열전기유사법(Thermal-electrical analogy)을 이용하여 구하였다. 유전 알고리즘에서 염색체 문자열은 fill과 warp tow의 두께와 너비로 하였고 복합재의 열전도도를 향상 시키는 방향으로 목적함수를 정하였다. 연구결과 직물섬유 복합재의 열전도도를 예측을 위한 향상된 방법이 제시되었고, 섬유토우 사이의 간격(inter-tow gap)이 넓어 질수록 복합재의 열전도도가 감소하는 것으로 나타났다. 직물섬유 복합재의 구조 최적화에서는 이론적 수치해석 결과가 제시되었는데, 전체적으로 섬유토우(tow)의 축의 수직 방향보다는 축 방향의 열전도도 성분이 복합재의 전체 열전도도 향상에 크게 기여를 하는 것으로 나타났다. This research presents studies on an improved method to predict the thermal conductivity of woven fabric composites, the effects of geometric structures of woven fabric composites on thermal conductivity, and structural optimization to improve the thermal conductivity using a genetic algorithm. The geometric structures of woven fabric composites were constructed numerically using the information generated on waviness, thickness, and width of fill and warp tows. Thermal conductivities of the composites were obtained using a thermal-electrical analogy. In the genetic algorithm, the chromosome string consisted of thickness and width of the fill and warp tows, and the objective function was the maximum thermal conductivity of woven fabric composites. The results confirmed that an improved method to predict the thermal conductivity was built successfully, and the inter-tow gap effect on the composite`s thermal conductivity was analyzed suggesting that thermal conductivity of woven fabric composites was reduced as the gap between tows increased. For structural design, optimized structures for improving the thermal conductivity were analyzed and proposed. Generally, axial thermal conductivity of the fiber tow contributed more to thermal conductivity of woven fabric composites than transverse thermal conductivity of the tows.

Steady- and transient-state analyses of fully ceramic microencapsulated fuel loaded reactor core via two-temperature homogenized thermal-conductivity model

Lee, Yoonhee,Cho, Nam Zin Elsevier 2015 Annals of nuclear energy Vol.76 No.-

<P><B>Abstract</B></P> <P>Fully ceramic microencapsulated (FCM) fuel, a type of accident-tolerant fuel (ATF), consists of TRISO particles randomly dispersed in a SiC matrix. In this study, for a thermal analysis of the FCM fuel with such a high heterogeneity, a two-temperature homogenized thermal-conductivity model was applied by the authors. This model provides separate temperatures for the fuel-kernels and the SiC matrix. It also provides more realistic temperature profiles than those of harmonic- and volumetric-average thermal conductivity models, which are used for thermal analysis of a fuel element in VHTRs having a composition similar to the FCM fuel, because such models are unable to provide the fuel-kernel and graphite matrix temperatures separately.</P> <P>In this study, coupled with a neutron diffusion model, a FCM fuel-loaded reactor core is analyzed via a two-temperature homogenized thermal-conductivity model at steady- and transient-states. The results are compared to those from harmonic- and volumetric-average thermal conductivity models, i.e., we compare <I>k<SUB>eff</SUB> </I> eigenvalues, power distributions, and temperature profiles in the hottest single-channel at steady-state. At transient-state, we compare total powers, reactivity, and maximum temperatures in the hottest single-channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized thermal-conductivity model for Doppler temperature feedback cause significant differences as revealed by comparisons.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fully ceramic microencapsulated fuel-loaded core is analyzed via a two-temperature homogenized thermal-conductivity model. </LI> <LI> The model is compared to harmonic- and volumetric-average thermal conductivity models. </LI> <LI> The three thermal analysis models show ∼100pcm differences in the <I>k<SUB>eff</SUB> </I> eigenvalue. </LI> <LI> The three thermal analysis models show more than 70K differences in the maximum temperature. </LI> <LI> There occur more than 3 times differences in the maximum power for a control rod ejection accident. </LI> </UL> </P>

316 스테인레스강의 열충격 특성

이상필(Sang-Pill Lee),김영만(Young-Man Kim),민병현(Byung-Hyun Min),김창호(Chang-Ho Kim),손인수(In-Soo Son),이진경(Jin-Kyung Lee) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.5

The present work dealt with the high temperature thermal shock properties of 316 stainless steels, in conjunction with a detailed analysis of their microstructures. In particular, the effects of the thermal shock temperature difference and thermal shock cycle number on the properties of 316 stainless steels were investigated. A thermal shock test for 316 stainless steel was carried out at thermal shock temperature differences from 300℃ to 1000℃. The cyclic thermal shock test for the 316 stainless steel was performed at a thermal shock temperature difference of 700℃ up to 100 cycles. The characterization of 316 stainless steels was evaluated using an optical microscope and a three point bending test. Both the microstructure and flexural strength of 316 stainless steels were affected by the high-temperature thermal shock. The flexural strength of 316 stainless steels gradually increased with an increase in the thermal shock temperature difference, accompanied by a growth in the grain size of the microstructure. However, a thermal shock temperature difference of 800℃ produced a decrease in the flexural strength of the 316 stainless steel because of damage to the material surface. The properties of 316 stainless steels greatly depended on the thermal shock cycle number. In other words, the flexural strength of 316 stainless steels decreased with an increase in the thermal shock cycle number, accompanied by a linear growth in the grain size of the microstructure. In particular, the 316 stainless steel had a flexural strength of about 500 MPa at 100 thermal-shock cycles, which corresponded to about 80% of the strength of the as-received materials.

태양열 에너지에 의한 아스팔트 포장의 열전달 특성

이관호,김성겸 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.1

In general, the factors affecting the heat transfer of asphalt pavement are divided into weather factors and pavement materials. Among them, material factors include the thermophysical and surface properties. An experiment was conducted on the thermal-physical factors of asphalt, which are the basis for the pavement failure model. The thermal conductivity, specific heat capacity, thermal diffusivity, and thermal emissivity were evaluated as the thermo-physical properties of asphalt. The specimens (WC-2 & PA-13) used in the experiment were compacted with a Gyratory Compactor. The experimental results of WC-2 and PA-13 showed a thermal conductivity of 1.18W/m·K and 0.9W/m·K, specific heat capacity of 970.8J/kg·K and 960.1J/kg·K, thermal emissivity of 0.9 and 0.91, and thermal diffusivity of 5.15㎡/s and 4.66㎡/s, respectively. Experiments on the heat transfer characteristics (thermo-physical properties) of asphalt pavement that can be used for thermal failure modeling of asphalt were conducted. 일반적으로 아스팔트 포장체의 열전달에 영향을 미치는 인자는 크게 날씨와 포장체의 재료로 나뉘며, 그 중 포장체의 재료 요인으로는 열-물리적 인자(Thermophysical properties)과 포장체 표면의 인자(Surface property)으로 나뉜다. 본 연구에서는 포장체 전반적인 파손 모형에 기본이 되는 아스팔트의 열-물리적 인자에 대한 실험을 진행하였으며, 평가한 아스팔트의 열전달 특성 인자로는 열전도도(Thermal Conductivity), 비열용량(Specific Heat Capacity), 열확산특성(Thermal Diffusivity), 열방사률(Thermal Emissivity)를 평가하였다. 샘플로 사용한 표층용 혼합물 입도는 밀입도 포장 WC-2와 배수성 포장 PA-13으로 선회다짐기를 이용하여 제작하였다. WC-2와 PA-13의 실험결과로 열전도도는 1.18W/m·K과 0.9W/m·K로 나타났고, 비열용량은 970.8J/kg·K과 960.1J/kg·K으로 공극률이 더 낮은 혼합물인 WC-2가 혼합된 재료의 량이 많아 비열용량이 더 높은 나타나는 것을 알 수 있었다. 또한 열방사률은 0.9와 0.91, 열확산률은 5.15㎡/s와 4.66㎡/s으로 WC-2가 PA-13 대비 약 10% 더 빠른 열 확산을 보이는 것을 알 수 있다. 이러한 결과는 향후 아스팔트 포장의 열에너지 활용 및 열에너지에 의한 아스팔트 포장의 파손평가 및 모형개발 등에 연구 및 활용에 가장 근간이 되는 자료가 될 것이라 판단되다.

Cost-effective and dynamic carbon dioxide conversion into methane using a CaTiO₃@Ni-Pt catalyst in a photo-thermal hybrid system

Lee, Jae Hyung,Do, Jeong Yeon,Park, No-Kuk,Seo, Myung Won,Ryu, Ho-Jung,Hong, Jin-Pyo,Kim, Yang Soo,Kim, Seog. K.,Kang, Misook Elsevier 2018 Journal of photochemistry and photobiology Chemist Vol.364 No.-

<P><B>Abstract</B></P> <P>This research focuses on the synergy of converting carbon dioxide (CO<SUB>2</SUB>) into methane (CH<SUB>4</SUB>) by simultaneously introducing light and heat as dynamic sources to activate the catalyst. A CaTiO<SUB>3</SUB>@Ni-Pt catalyst, loaded with 30.0 wt.% Ni and 1.0 wt.% Pt on a perovskite CaTiO<SUB>3</SUB> support was introduced. The photo-thermal catalytic hybrid system has two features that distinguish it from other photo- or thermal-catalytic systems. First, unlike the CO<SUB>2</SUB> thermal-methanation reaction where CO<SUB>2</SUB> and H<SUB>2</SUB> react at a molar ratio of 1:4, 2.0 mol of H<SUB>2</SUB> was replaced with 2.0 mol H<SUB>2</SUB>O in the photo-thermal catalytic hybrid system compared to the thermal-methanation reaction requiring 4.0 mol of H<SUB>2</SUB>. Second, by loading Ni and Pt, which are catalytic active species with excellent CO<SUB>2</SUB> and H<SUB>2</SUB> adsorption abilities, the CO<SUB>2</SUB> reduction (46.48%) was promoted and the CH<SUB>4</SUB> selectivity (99.46%) in the product was increased compared to the photo-methanation reaction. The CaTiO<SUB>3</SUB>@Ni-Pt not only inhibited the recombination of the photo-generated charges, but also facilitated the adsorption of the reactants in the photo-thermal hybrid system. The quantum efficiency of the CaTiO<SUB>3</SUB>@Ni-Pt catalyst measured for the photo-thermal hybrid system steadily increased to 180 °C. Nevertheless, this study implies that a photo-thermal hybrid system can be useful to photo-reducing CO<SUB>2</SUB> by adding a small amount of heat. From a thermal reaction standpoint, a photo-thermal hybrid system can be used to reduce the reaction temperature during CO<SUB>2</SUB> thermal-methanation and to reduce the consumption of H<SUB>2</SUB> in half.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A CaTiO<SUB>3</SUB>@Ni-Pt catalyst was applied to the photo-thermo catalytic hybrid system. </LI> <LI> Both of CO<SUB>2</SUB> reduction and CH<SUB>4</SUB> selectivity were increased on CaTiO<SUB>3</SUB>@Ni-Pt. </LI> <LI> The photo-reducing CO<SUB>2</SUB> easily occurred by adding a small amount of heat. </LI> <LI> The photo-thermal system reduced the reaction temperature and the consumption of H<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Code development on steady-state thermal-hydraulic for small modular natural circulation lead-based fast reactor

Zhao, Pengcheng,Liu, Zijing,Yu, Tao,Xie, Jinsen,Chen, Zhenping,Shen, Chong Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.12

Small Modular Reactors (SMRs) are attracting wide attention due to their outstanding performance, extensive studies have been carried out for lead-based fast reactors (LFRs) that cooled with Lead or Lead-bismuth (LBE), and small modular natural circulation LFR is one of the promising candidates for SMRs and LFRs development. One of the challenges for the design small modular natural circulation LFR is to master the natural circulation thermal-hydraulic performance in the reactor primary circuit, while the natural circulation characteristics is a coupled thermal-hydraulic problem of the core thermal power, the primary loop layout and the operating state of secondary cooling system etc. Thus, accurate predicting the natural circulation LFRs thermal-hydraulic features are highly required for conducting reactor operating condition evaluate and Thermal hydraulic design optimization. In this study, a thermal-hydraulic analysis code is developed for small modular natural circulation LFRs, which is based on several mathematical models for natural circulation originally. A small modular natural circulation LBE cooled fast reactor named URANUS developed by Korea is chosen to assess the code's capability. Comparisons are performed to demonstrate the accuracy of the code by the calculation results of MARS, and the key thermal-hydraulic parameters agree fairly well with the MARS ones. As a typical application case, steady-state analyses were conducted to have an assessment of thermal-hydraulic behavior under nominal condition, and several parameters affecting natural circulation were evaluated. What's more, two characteristics parameters that used to analyze natural circulation LFRs natural circulation capacity were established. The analyses show that the core thermal power, thermal center difference and flow resistance is the main factors affecting the reactor natural circulation. Improving the core thermal power, increasing the thermal center difference and decreasing the flow resistance can significantly increase the reactor mass flow rate. Characteristics parameters can be used to quickly evaluate the natural circulation capacity of natural circulation LFR under normal operating conditions.

현장 열응답 시험을 통한 수직 밀폐형 지중열교환기용 그라우트와 열교환 파이프 단면의 성능 평가

최항석,박문서,민선홍,손병후,이철호 한국지반공학회 2010 한국지반공학회논문집 Vol.26 No.7

In performing a series of in-situ thermal response tests, the effective thermal conductivities of six vertical closed-loop ground heat exchangers were experimentally evaluated and compared one another, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than bentonite grouting, and the efficiency of graphite better performs than silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance. Based on the results from the in-situ thermal response tests, a series of economic analyses have been made to show the applicability of the new addictives and 3 pipe-type heat exchanger.

Sample holder design for effective thermal conductivity measurement of pebble-bed using laser flash method

Lee, Youngmin,Ku, Duck Young,Park, Yi-Hyun,Ahn, Mu-Young,Cho, Seungyon Elsevier 2017 Fusion engineering and design Vol.124 No.-

<P><B>Abstract</B></P> <P>Since the stress due to the thermal load on breeding blanket structure is one of the main design driver, the thermal conductivity is necessary input data for thermal-structural and thermo-hydraulic analyses performed in order to understand the heat transfer phenomena and estimate the thermal stress. Since for the functional materials of solid type breeding blanket a pebble-bed form is mainly adopted instead of a bulk form such as a block or a disk, it should be needed to measure the thermal conductivity of pebble-bed. In this study, the effective thermal conductivity of pebble-bed is measured by laser flash method, which is one of the various thermal conductivity measurement methods, because this method has several advantages such as a wide thermal conductivity range of the measurement and a small amount of pebbles. A sample holder considering the heat transfer mechanism from the laser source to pebble-bed has been specially designed in order to apply the laser flash technique to the pebble-bed sample and it has been validated by the experiments. This paper introduces preliminary results of the effective thermal conductivity on the pebble-bed using this sample holder.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effective thermal conductivity of a graphite pebble-bed was successfully measured by Laser Flash Method. </LI> <LI> For the measurement on pebble-bed form, the new sample holder was specially designed. </LI> <LI> The 3-layers measurement technique was designed in order to make the laser flash method successful. </LI> <LI> The effective thermal conductivity of a graphite pebble-bed was converged around 3.2W/mK. </LI> <LI> The effect of the temperature (RT∼200°C) in a graphite pebble-bed was negligible. </LI> </UL> </P>

상변화 물질을 이용한 위성 탑재체 열제어기구 개발 및 환경시험

서정기,이상윤,김택영,현범석 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.11

상변화 물질을 이용한 열제어 장치는 상변화 물질이 갖는 잠열특성, 특정온도 상변화 성질을 활용한 온도제어 장치이다. 이는 첨단 열제어기술로 달탐사선, 화성탐사선 등에 사용되어 달과 화성의 극단적인 열환경에서도 시스템 정상임무 수행에 중요한 역할을 담당하였다. 본 연구에서는 기존 실용급 위성에 적용된 바 있는 위성 탑재체 열제어 장치를 상변화 물질 열제어 장치로 대체하여 경량화 및 열전달성능 개선을 목표로 하였다. 이를 위해 상변화 물질과 히트파이프(Heat Pipe)을 병렬로 연결한 새로운 열제어 시스템에 대한 개념 설계를 수행하였고, 핵심 부품인 상변화 물질 용기의 설계/해석/우주인증시험을 수행하여 개발된 장치의 신뢰성을 확인하였다. 본 연구결과로 제작된 열제어장치는 향후 개발 예정인 달탐사선 열제어에 적용될 수 있을 것으로 예상된다. TCDPCM(Thermal Control Device with Phase Change Material) is a thermal control device designed for spacecraft thermal control using phase change material. TCDPCM’s have been used in thermal control of several lunar rovers, Mars rovers and proved their thermal performance in spite of extreme thermal condition in Moon or Mars. In this study, a new thermal control device using phase change material and heat pipe is proposed and validated. Also, structural analysis and space qualification tests were performed for a PCM Container which is the most important component of the device. TCDPCM shows a good thermal/structural performance and can be used in thermal control device of real spacecraft.