• Title/Summary/Keyword: 다공성 모델

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Thermal Characteristic Analysis of Thermal Protection System with Porous Insulation (다공성 단열재를 포함한 열방어구조의 열 특성 분석)

  • Hwang, Kyungmin;Kim, Yongha;Lee, Jungjin;Park, Jungsun
    • Journal of Aerospace System Engineering
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    • v.10 no.4
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    • pp.26-34
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    • 2016
  • In a number of industries, porous insulations have been frequently used, reducing thermal insulation space through excellent performance of the thermal insulation's characteristics. This paper suggests an effective thermal conductivity prediction model. Firstly, we perform a literature review of traditional effective thermal conductivity prediction models and compare each model with experimental heat transfer results. Furthermore, this research defines the effectiveness of thermal conductivity prediction models using experimental heat transfer results and the Zehner-Schlunder model. The newly defined effective thermal conductivity prediction model has been verified to better predict performance than other models. Finally, this research performs a transient heat transfer analysis of a thermal protection system with a porous insulation in a high speed vehicle using the finite element method and confirms the validity of the effective thermal conductivity prediction model.

Prediction Modeling on Effective Thermal Conductivity of Porous Insulation in Thermal Protection System (열방어구조의 다공성 단열재 유효 열전도율 예측 모델링)

  • Hwang, Kyung-Min;Kim, Yong-Ha;Kim, Myung-Jun;Lee, Hee-Soo;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.3
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    • pp.163-172
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    • 2017
  • Porous insulation have been frequently used in a number of industries by minimizing thermal insulation space because of excellent performance of their thermal insulation. This paper devices an effective thermal conductivity prediction model. First of all, we perform literature survey on traditional effective thermal conductivity prediction models and compare each other model with heat transfer experimental results. Furthermore this research defines advanced effective thermal conductivity prediction models model based on heat transfer experimental results, the Zehner-Schlunder model. Finally we verify that the newly defined effective thermal conductivity prediction model has better performance prediction than other models. Finally, this research performs a transient heat transfer analysis of thermal protection system with a porous insulation using the finite element method and confirms validity of the effective thermal conductivity prediction model.

Basic Study on Flame-Stabilization Characteristics in a Multi-Channel Combustor via a Model of a Porous-Media Combustor (다공성 연소기 모델로서의 다중 채널 연소기 내부 화염의 안정화 특성 기초 연구)

  • Park, Seung-Il;Lee, Min-Jung;Kim, Nam-Il
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.8
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    • pp.815-823
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    • 2011
  • Combustion phenomena in porous media combustors are widely used in industrial fields for the combustion of lowgrade fuels and the regeneration of combustion heat. However, studies of combustion phenomena in porous media have been limited, because these phenomena are difficult to observe, and the configurations of porous media are complex. We propose a simple model combustor: a multi-channel combustor that consists of many layers of combustion channels made of quartz plates. We conducted an experimental observation of the flames in the multi-channel combustor and obtained experimental results for the flame stabilization limits. Flames formulated in the multi-channel combustor showed variation in the spatial distribution depending on the heat transfer between neighboring channels. A simple analytical model was developed and the variation in the flammability limits of the multi-channel combustor was discussed. This study will enhance our understanding of flame behavior in a porous-media combustor.

Design of a Perforated Panel for Transmission Noise Reduction (투과 소음 저감을 위한 다공성 패널 설계)

  • Park, Younghyo;Bae, Jaehyeok;Lee, Jin Woo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.4
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    • pp.437-445
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    • 2015
  • A design method for a perforated panel is suggested to reduce the level of incident noise without obstructing the flow of incoming fluid. The key idea was to insert an array of 1/4 wavelength tubes around the holes of the perforate panel. First, various case studies were performed for a unit model with only one hole. In order to avoid any increase in the panel thickness, the unit model was vertically divided into three layers, and only the middle layer was used as the design domain. The number and array of 1/4 wavelength tubes connected to the hole were optimized to obtain the widest effective frequency range in the transmission loss curve as possible. Then, the optimally designed unit model was converted to a periodic array in the perforated panel to achieve the design goals. Even if the target frequency and the target transmission loss were set to 1000 Hz and 10 dB, respectively, the suggested design method for the a perforated panel could achieve noise reduction for various target values.

Two-way Coupling with Absorption and Sinking (흡수와 침수를 수반하는 유체-물체 상호작용 시뮬레이션 기법)

  • Um, Ki-Won;Baek, Seung-Ho;Han, Jung-Hyun
    • Proceedings of the Korean Information Science Society Conference
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    • 2012.06c
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    • pp.377-378
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    • 2012
  • 본 논문은 다공성 물체와 유체 간의 상호작용 기법을 제안한다. 다공성 물체는 구성 물질의 특성에 따라 물에 떠있다가 점차 물을 흡수하고 결국 가라앉는다. 제안하는 시뮬레이션 기법은 Eulerian 프레임워크를 이용하며, 다공성 물체의 물리적 속성을 복셀 안에 정의하여 시간에 따라 변화하는 흡수를 시뮬레이션 한다. 본 논문에서는 확산모델의 편미분 방정식을 이용해 풀어내어 흡수를 간단하게 시뮬레이션 할 수 있는 방법을 제안한다.

Frequency- and Porosity-dependent Acoustic Characteristics of Porous Medium with Water- and Air-filled Pores (물과 공기 다공을 갖는 다공성 매질의 주파수 및 다공율 변화에 따른 음향특성)

  • Lee Kang Il;Roh Heui-Seol;Yoon Suk Wang
    • Proceedings of the Acoustical Society of Korea Conference
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    • autumn
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    • pp.209-212
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    • 2001
  • 수중에서 물과 공기 다공을 갖는 다공성 매질의 주파수 및 다공율 변화에 따른 음향특성을 고찰하였다. 다공성 매질로서 원통형 다공을 인위적으로 균일하게 배열한 판형 루사이트 (Lucite)를 사용하였다. 수중에서 음파를 다공성 매질의 원통형 다공의 축 방향과 평행하게 입사하였을 때, 빠른 파 (fast wave)는 다공 내의 매질에 영향을 받지 않으나, 느린 파 (slow wave) 및 원통형 다공을 전파하는 비평면 고차 정상 모드 파 (nonplanar higher normal mode wave)는 다공 내의 매질에 크게 영향을 받는다. 3MHz부터 4MHz까지의 주파수 영역에서 전체 파 (total wave), 빠른 파 및 느린 파의 음속 및 음압투과계수를 주파수 및 물과 공기 다공율 변화에 따라 측정하였다. 비강체 다공성 매질에서의 음파 전파특성에 대한 MBA (modified Biot-Attenborough) 모델의 이론 결과와 실험결과를 비교, 분석하였다.

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A New Structural Model for Predicting Effective Thermal Conductivity of Variably Saturated Porous Materials (포화도에 따른 다공성 매질의 유효열전도도 변화 예측 모델)

  • Cha, Jang-Hwan;Koo, Min-Ho;Keehm, Young-Seuk
    • Journal of the Korean earth science society
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    • v.32 no.6
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    • pp.629-639
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    • 2011
  • Based on Maxwell-Eucken(ME) model, which is one of structural models, a new model for predicting the effective thermal conductivity of variably saturated porous materials is proposed. The new model is a linear combination of three ME models having matrix, water, and air as a continuous phase. The coefficient of the corresponding linear equation is defined by a parameter referred to as 'the continuity coefficient', which provides a relative degree of continuity of each phase. The continuity coefficient of matrix is assumed to be linearly proportional to porosity. The model can be linear or nonlinear depending on how the continuity coefficients of water and air vary with water saturation. The feasibility of the proposed model was examined by both numerical and experimental results. Both linear and nonlinear models showed a high accuracy of prediction with $R^2$ values of 0.86-0.98 and 0.88-0.99, respectively. The numerical and experimental results also showed that the continuity coefficient of matrix was linearly proportional to porosity. Therefore, the proposed prediction model can be effectively used to estimate effective thermal conductivity of unsaturated porous materials by measuring porosity, water content and mineralogical compositions of matrix.

Thermal Phenomena of an N2O Catalyst Bed for Hybrid Rockets Using a Porous Medium Approach (다공성 매질 접근법을 적용한 하이브리드 로켓 N2O 촉매 점화기의 열적 현상)

  • 유우준;김수종;김진곤;장석필
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.9
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    • pp.89-96
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    • 2006
  • In this study, fluid flow and thermal characteristics in a catalyst bed for nitrous oxide catalytic decomposition which is introduced as a hybrid rocket ignition system for small satellites were theoretically considered. To analyze the thermal phenomena of the catalyst bed, a so-called porous medium approach has been opted for modeling the honeycomb geometry of the catalyst bed. Using a Brinkman-extended Darcy model for fluid flow and the one-equation model for heat transfer, the analytical solutions for both velocity and temperature distributions in the catalyst bed are obtained and compared with experimental data to validate the porous medium approach. Based on the analytical solutions, parameters of engineering importance are identified to be the porosity of the catalyst bed, effective volumetric ratio, the ratio of the radius of the catalyst bed to the radius of a pore, heat flux generated by a heater, and pumping power. Their effects on thermal phenomena of the catalyst bed are studied.

상 분리 메커니즘에 의한 3차원 규칙 배열 다공 구조 형성 시뮬레이션

  • Kim, Dong-Uk;Cha, Pil-Ryeong;Byeon, Ji-Yeong
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2011.05a
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    • pp.241.2-241.2
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    • 2011
  • 다공 소재는 큰 비표면적과 규칙적으로 정렬된 구조의 특성으로 인해 자성메모리 소자용 재료, 나노 와이어 제작용 템플릿, 마이크로 반응기, 메타물질용 소재 등으로 각광을 받고 있다. 자기조립 수직배열 다공구조 재료를 제작하는 방법으로 흔히 알루미늄의 양극산화 방법과 이원공정계의 상분리 방법이 등이 있다. 본 연구에서는 상변태를 비롯한 패턴형성과 계면 운동을 가장 정확하게 다루는 이론적 모델로 알려진 상장모델(Phase Field model)을 이용하여 이원공정계의 박막성장과정 동안의 자발적 상분리에 의한 수직배열 자기조립 다공구조 형성을 시뮬레이션 한다. 상장모델을 기초로 하여 상분리 메커니즘에 의해 발현된 미세조직을 해석하고 다양한 공정변수가 미세조직 발현에 미치는 영향에 대해 연구한다. 또한 상장모델을 통해 얻은 결과는 기존에 발표된 연구들의 결과와 비교를 통해 유효성을 입증한다.

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A Numerical Study on Flow in Porous Structure using Non-Hydrostatic Model (비정수압 수치모형을 이용한 다공성 구조물의 유동에 관한 수치적 연구)

  • Shin, Choong Hun;Yoon, Sung Bum
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.30 no.3
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    • pp.114-122
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    • 2018
  • This paper introduces a non-hydrostatic wave model SWASH for simulating wave interactions with porous structures. This model calculates the flow in porous media based on volume-averaged Reynolds-averaged Navier-Stokes equations (VARANS) in ${\sigma}$-coordinate. The empirical coefficients of resistance used to account for the flow in a porous media often need to be measured or calibrated. In this study, the empirical resistance coefficients used in the model are calibrated and validated using laboratory experiments, involving dam-break flow through porous media, and solitary wave interactions with a porous structure. It is shown that the agreement between experimental and numerical results is generally satisfactory. It is also confirmed that non-hydrodynamic model, SWASH, is computationally much more efficient than the three-dimensional porous flow models based on VOF approach.