• Composites Research
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• 제25권1호
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• pp.26-30
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• 2012

본 연구에서는 스트레인게이지 회로를 이용하여 GRP 복합관의 열팽창계수를 측정하고자 하였다. 이를 위해 다양한 스트레인게이지 회로를 적용하여 알루미늄 보의 열팽창계수를 측정함으로써 측정방법의 타당성을 검증하였다. 또한 스트레인게이지의 부착위치와 반복횟수를 달리하며 또한 열팽창계수가 다른 스트레인게이지를 적용한 경우에 대해 GRP 복합관의 길이방향 및 원주방향 열팽창계수를 측정함으로써 열변형률 결과와 측정결과의 재현성에 미치는 영향을 조사하였다. 연구결과에 따르면 GRP 복합관의 경우 보강된 유리섬유에 의해 원주방향의 열변형률이 제한되어 원주방향 열팽창계수가 길이방향의 열팽창계수에 비해 낮게 나타났다. 또한 GRP 복합관의 후경화로 인해 측정횟수가 증가할수록 측정된 열팽창계수는 다소 증가하지만 증가폭은 점차 감소하였다. 아울러 열팽창계수가 다른 스트레인게이지를 적용하더라도 기준보상시편을 통해 스트레인게이지의 열변형률을 보상하면 동일한 열팽창계수가 얻어짐을 알 수 있었다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
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• pp.179-193
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• 2000

Aluminium titanate (Al₂TiO5) with an excellent thermal shock resistant and a low the expansion coefficient was obtained by solid solution with MgO, SiO₂, and ZrO₂ in the Al₂TiO5 lattice or in the grain boundary solution through electrofusion in an arc furnace. However, these materials have low mechanical strength due to the presence of microcracks developed by a large difference in thermal expansion coefficients along crystallographic axes. Pure Al₂TiO5 tends to decompose into α-Al₂O₃ and TiO₂-rutile in the temperature range of 750-1300℃ that rendered it apparently useless for industrial applications. Several thermal shock tests were performed: Long therm thermal annealing test at 1100℃ for 100h; and water quenching from 950 to room temperature (RT). Cyclic thermal expansion coefficients up to 1500℃ before and after decomposition tests was also measured using a dilatometer, changes in the microstructure, thermal expansion coefficients, Young's modulus and strengths were determined. The role of microcracks in relation to thermal shock resistance and thermal expansion coefficient is discussed.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.820-827
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• 2006

The convection heat transfer coefficients on the top surface of a large liquid petroleum liquid injection(LPLi) engine piston are analyzed by solving an inverse thermal conduction problem. The heat transfer coefficients are numerically found so that the difference between analyzed temperatures from the finite element method and measured temperatures is minimized. Using the resulting heat transfer coefficients as the boundary condition, temperature of a large LPLi engine piston is analyzed.

• 한국항공우주학회지
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• 제35권9호
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• pp.771-777
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• 2007

본 논문에서는 직접 수치 모사 기법을 이용해 섬유 강화 복합재료의 열팽창계수를 예측하였다. 직접 수치 모사 기법을 통해 구한 열팽창계수 예측치와 실험치의 비교를 통해 본 논문에서 제안한 직접 수치 모사 기법을 이용하면 인위적인 가정을 최소화하면서 기존의 방법과 유사하게 복합재료 열팽창계수를 예측할 수 있음을 확인하였다. 또한 섬유 체적비 변화에 따른 열팽창계수의 변화를 예측하고 그 경향성을 고찰하였다.

• 열처리공학회지
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• 제26권6호
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• pp.300-305
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• 2013

The effects of solute carbon atoms on the thermal expansion coefficients of ferrite and austenite as well as austenitization behavior were investigated by comparing carbon-free ferrite and carbon-containing ferrite. The thermal expansion coefficients and austenitization start and finish temperatures were measured using a dilatometer. Solute carbon atoms at elevated temperatures above the cementite dissolution temperature (650 K) decreased the thermal expansion coefficients of both ferrite and austenite. In addition, minute amount of carbon atoms dissolved in ferrite stimulated austenite nucleation during continuous heating, resulting in the lower starting temperature of austenitization.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4685-4694
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• 2023

The ability to calculate the material density sensitivity coefficients of power with respect to the material density has broad application prospects for accelerating Monte Carlo-Thermal Hydraulics iterations. The second-order material density sensitivity coefficients for the general Monte Carlo score have been derived based on the differential operator sampling method in this paper, and the calculation of the sensitivity coefficients of cell power scores with respect to the material density has been realized in continuous-energy Monte Carlo code RMC. Based on the power-density sensitivity coefficients, the sensitivity coefficients of power scores to some other physical quantities, such as power-boron concentration coefficients and power-temperature coefficients considering only the thermal expansion, were subsequently calculated. The effectiveness of the proposed method is demonstrated in the power-density coefficients problems of the pressurized water reactor (PWR) moderator and the heat pipe reactor (HPR) reflectors. The calculations were carried out using RMC and the ENDF/B-VII.1 neutron nuclear data. It is shown that the calculated sensitivity coefficients can be used to predict the power scores accurately over a wide range of boron concentration of the PWR moderator and a wide range of temperature of HPR reflectors.

• 설비공학논문집
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• 제13권11호
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• pp.1065-1071
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• 2001

To investigate hydraulic and thermal characteristics of ice slurries in a circular tube, ice slurries were tested in a flow loop with a constant heat flux test section, for ranges of flow velocity, ice fraction and heat flux. Heat transfer coefficients and friction factors of ice slurries were calculated by measuring the outer wall temperatures of the test section and the pressure drops over the test section. Heat transfer coefficients of ice slurries were 9% higher than the heat transfer coefficients expected by Petukhov. Friction factors were about 4% lower than the friction factors expected by Petukhov. The effective thermal capacity of ice slurry with 12.8% ice fraction, was found to be about 3 times higher than the thermal capacity of water.

• Bulletin of the Korean Chemical Society
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• 제12권3호
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• pp.315-322
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• 1991

In a recent $paper^1$ we reported equilibrium (EMD) and non-equilibrium (NEMD) molecular dynamics simulations of liquid argon using the Green-Kubo relations and NEMD algorithms to calculate the thermal transport coefficients-the self-diffusion coefficient, shear viscosity, and thermal conductivity. The overall agreement with experimental data is quite good. In this paper the same technique is applied to calculate the thermal transport coefficients of liquid water at 298.15 K and 1 atm using TIP4P model for the interaction between water molecules. The EMD results show difficulty to apply the Green-Kubo relations since the time-correlation functions of liquid water are oscillating and not decaying rapidly enough except the velocity auto-correlation function. The NEMD results are found to be within approximately ${\pm}$30-40% error bars, which makes it possible to apply the NEMD technique to other molecular liquids.

• 전기학회논문지
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• 제65권9호
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• pp.1504-1510
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• 2016

The aim of this study is to improve properties both glass transition temperature($T_g$) and coefficient of thermal expansion(CTE) using epoxy/micro-nano alumina composites with adding glycerol diglycidyl ether (GDE:1,2,3,5g). This paper deals with the effects of GDE addition for epoxy/micro alumina contents (40, 50, 60wt%)+surface modified nano alumina(1_phr) composites. 20 kinds specimen were prepared with containing micro, nano alumina and GDE as a micro composites(10, 20, 30, 40, 50, 60, 70wt%) or a nano/micro alumina composites(1phr/40, 50, 60wt%). Average particle size of nano and micro alumina used were 30nm and $1{\sim}2{\mu}m$, respectively. The micro alumina used were alpha phase with Heterogeneous and nano alumina were gamma phase particles of spherical shape. The glass transition temperature and coefficients of thermal expansion was evaluated by DSC and TMA. The glass transition temperature decreased and coefficients of thermal expansion become smaller with filled contents of epoxy/micro alumina composites. On the other hand, $T_g$ and CTE as GDE addition variation(1,2,3,5g) of epoxy/micro-nano alumina composites decreased and increased respectively.

• 공학논문집
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• 제6권2호
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• pp.141-151
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• 2004

금합금계 매몰재 재료의 물리적 특성은 각각 열팽창계수과 압축강도, 입도 분포에 크게 좌우된다. 일반적으로 금합금계 매몰재는 cristobalite와 quartz, plaster로 주성분을 구성하고 있다. 그리고 cristobalite와 quartz의 열팽창계수는 $2.6\times10^{-6}/^\circC$, $2.32\times10^{-6}/^\circC$, 로 이 두 재료의 혼합비가 매몰재의 열팽창 계수를 변화시키는 매우 중요한 역할을 하고 있다. 현재 국내에서는 금합금계 매몰재는 전량 수입에 의존하고 있고 그 시장 수요 또한 대단히 크다. 따라서 균일한 입도 분포를 가지는 cristobalite와 quartz의 개발과 주조금속의 열팽창과 냉각에 따른 수축력을 고려한 열팽창계수를 가지면서 매몰재의 요구강도에 적합한 압축강도를 가지는 금합금계 매몰재의 개발이 필수적이다. 따라서 본 연구에서는 먼저 균일한 입도를 갖는 cristobalite와 quartz 분체의 제조와 cristobalite와 quartz의 혼합비에 따른 열팽창계수와 압축강도를 비교 분석하였다. 본 연구의 결과로 표면이 매끄럽고 균일한 입도 분포를 갖는 cristobalite와 quartz를 제조하였으며, cristobalite와 quartz의 혼합비가 45:25가 열팽창계수와 압축강도에서 매몰재가 요구하는 조건을 만족하였다.