• Title/Summary/Keyword: 유효열전도율

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The Effect of Environmental Parameters on Frost Formation on a Horizontal Cylinder (수평 실린더에서의 서리 생성에 대한 환경 변수들의 영향)

  • Lee, Yun-Bin;Ryu, In-Sang;No, Seung-Tak
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.2
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    • pp.253-260
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    • 2002
  • It is known that frost formation on surfaces of the heat exchanger seriously affects the performance of the refrigeration system. Accordingly, defrosting should follow, and effective defrosting is possible only when both analytic tools and comprehensive experimental data on frost formation are assailable. An experimental investigation was undertaken to characterize the effect of environmental parameters on frost formation on a horizontal cylinder in cross uniform flow. Several experiments were carried out with various environmental parameters such as inlet air temperature, inlet air humidity, air velocity and cooling surface temperature. Frost thickness, mass, surface temperature and cylinder inner and outer temperature were measured at front and rear positions of the cylinder. Thickness, mass, density, and effective thermal conductivity of the frost layer were obtained from measured data and effects of environmental parameters on the frost formation were analyzed. Data from experiments were correlated using dimensionless variables.

Development of Homogenization Data-based Transfer Learning Framework to Predict Effective Mechanical Properties and Thermal Conductivity of Foam Structures (폼 구조의 유효 기계적 물성 및 열전도율 예측을 위한 균질화 데이터 기반 전이학습 프레임워크의 개발)

  • Wonjoo Lee;Suhan Kim;Hyun Jong Sim;Ju Ho Lee;Byeong Hyeok An;Yu Jung Kim;Sang Yung Jeong;Hyunseong Shin
    • Composites Research
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    • v.36 no.3
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    • pp.205-210
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    • 2023
  • In this study, we developed a transfer learning framework based on homogenization data for efficient prediction of the effective mechanical properties and thermal conductivity of cellular foam structures. Mean-field homogenization (MFH) based on the Eshelby's tensor allows for efficient prediction of properties in porous structures including ellipsoidal inclusions, but accurately predicting the properties of cellular foam structures is challenging. On the other hand, finite element homogenization (FEH) is more accurate but comes with relatively high computational cost. In this paper, we propose a data-driven transfer learning framework that combines the advantages of mean-field homogenization and finite element homogenization. Specifically, we generate a large amount of mean-field homogenization data to build a pre-trained model, and then fine-tune it using a relatively small amount of finite element homogenization data. Numerical examples were conducted to validate the proposed framework and verify the accuracy of the analysis. The results of this study are expected to be applicable to the analysis of materials with various foam structures.

An experimental study of frost forming on the horizontal cylinder under cross flow (직교유동 내에 놓인 수평 실린더에서 서리 생성에 관한 실험적 연구)

  • 이윤빈;노승탁
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.4
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    • pp.448-456
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    • 1999
  • Variations of thickness and effective thermal conductivity of frost forming on the horizontal] cylinder with respect to time were measured under cross flow. The local heat flux around the cylinder was determined by measuring the radial temperature distribution in the cylinder having small holes drilled axially in which T-type thermocouples were inserted, then by using one dimensional cylindrical heat conduction equation. The thickness and the surface temperature of the frost layer around the cylinder were measured periodically while developing the frost. Each experiment was peformed by varying the Reynolds number, the temperature, and the humidity condition. Specially the dew point temperature of the most cases was below the freezing point. Experimental data showed that the frost layers on the front and the rear surface were thicker than those on the top and the bottom one which was near the separation point. The thickness and effective thermal conductivity of the frost layer were affected by inlet air velocity, temperature, and humidity. Moreover, the effective thermal conductivity and the effective thermal resistance increase with respect to time.

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Thermal Resistance Characteristics of the Backfill Material with Bottom Ash (저회 되메움재의 열저항 특성)

  • Jung, Hyuksang;Cho, Sam-Deok;Kim, Ju-Hyong;Park, Jongsik;Kong, Jin-Young
    • Journal of the Korean GEO-environmental Society
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    • v.17 no.6
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    • pp.5-12
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    • 2016
  • This paper deals with the result of thermal resistance test with backfill materials as bottom ash by using backfill material. Bottom ash, one of coal ashes, can be reused to replace sand because of its similar engineering properties. But without considering the thermal property, the abuse of bottom ash resulted in damage for existing structures. To investigate the thermal conductivity of bottom ash, laboratory tests for thermal resistance of that were carried out in this study. Thermal properties of bottom ash was compared with those of in-situ soil, sand, backfill material which can be applied as filling material. The tests were classified by water contents defined as the major influence factor. The beneficial use method of bottom ash was suggested as backfilling material.

A Study on the Evaluation of Pressure Resistance and Effective Thermal Conductivity of Thin Heat Pipes Using Polymer Compound Sheets for Bonding Metal Thin Plates (금속박판 접합용 고분자화합물시트를 이용한 박형 히트파이프 내압성 및 유효열전도율 평가에 관한 연구)

  • Yu, Byeong-Seok;Kim, Jeong-Hun;Kim, Dong-Gyu
    • Journal of the Korean Society of Industry Convergence
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    • v.24 no.4_2
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    • pp.509-515
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    • 2021
  • In this study, a pressure vessel for a heat pipe was fabricated by bonding a metal thin film using a polymer compound sheet. In order to confirm the applicability of the experimentally manufactured copper material thin heat pipe of 0.6 mm or less, the pressure resistance and effective thermal conductivity for pressure generated according to the type of the working fluid of the heat pipe were evaluated to suggest the commercialization potential of the thin heat pipe. As a result of evaluating the pressure resistance and effective thermal conductivity performance of the thin heat pipe, the following conclusions were drawn. 1) Using a PEEK-based polymer compound sheet, it was possible to fabricate a pressure vessel for a thin heat pipe with a pressure resistance of up to 1.0 MPa by bonding a copper thin film, and the possibility of commercialization was confirmed at a temperature below 120 ℃. 2) In the case of the effective thermal conductivity performance evaluation test, the effective thermal conductivity of ethanol was higher than that of FC72 and Novec7000, and in the case of ethanol, the maximum effective thermal conductivity was 2,851 W/mK at 3.0 W of heating.

A Study on Heat Dissipation Characteristics of PMMA Composite Films with Phase Change Material (상변화물질을 이용한 PMMA 복합필름의 방열 성능 향상에 관한 연구)

  • Kwon, Junhyuk;Yoon, Bumyong;Cho, Seung-hyun;Lee, Stephanie K.;Kim, Hyung-ick;Kim, Donghyun;Park, Kyungui;Suhr, Jonghwan
    • Composites Research
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    • v.30 no.5
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    • pp.288-296
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    • 2017
  • The focus of this study is to experimentally investigate the heat dissipation characteristics of poly (methyl methacrylate) (PMMA) composite films with phase change materials (PCM) to resolve heat build-up problems encountered in various electronic devices. In this study, two different types of phase change materials were used to fabricate the composite films by compression molding method and PCM paste sealing method then compared. It was observed in this study that the heat dissipation capability of PCM/PMMA composite films was remarkably enhanced by applying graphite sheet or graphene film into the composite due to their high thermal conductivity. These PCM/ PMMA composite films were attached on the hot spot inside smart phone and tested its surface temperature change according to time. The heat dissipation capability of PCM/PMMA composite film incorporated smart phone was increased 154% and hybrid PCM/PMMA composite film incorporated smart phone was increased 286% over the reference, respectively.

A Physical Properties of Lightweight Foamed Concrete According to Lightweight Aggregate Types and Foaming agent Types (경량골재와 기포제 종류에 따른 경량기포 콘크리트의 물리적 특성)

  • Kim, Ha-Seog;Lee, Sea-Hyun;Sun, Jung-Soo;Kim, Jin-Man
    • Journal of the Korea Concrete Institute
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    • v.28 no.4
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    • pp.435-444
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    • 2016
  • In Korea, approximately 48% of all households live in apartments, which are a form of multi-unit dwellings, and this figure increases up to 58%, when row houses and multiplex houses are included. As such, majority of the population reside in multi-unit dwellings where they are exposed to the problem of floor impact noise that can cause disputes and conflicts. Accordingly, this study was conducted to manufacture a high-weight, high-stiffness foamed concrete in order to develop a technology to reduce the floor impact noise. For the purpose of deriving the optimum mixing ratio for the foamed concrete that best reduces the floor impact noise, the amounts of the foaming agent, lightweight aggregate and binder were varied accordingly. Also, the target characteristics of the concrete to be developed included density of over $0.7t/m^3$, compressive strength of over $2.0N/mm^2$ and thermal conductivity of under 0.19 W/mK. The results of the experiment showed that the fluidity was very excellent at over 190 mm, regardless of the type and input amount of foaming agent and lightweight aggregate. The density and compressive strength measurements showed that the target density and compressive strength were satisfied in the specimen with 50% foam mixing ratio for foamed concrete and in all of the mixtures for the lightweight aggregate foamed concrete. In addition, the thermal conductivity measurements showed that the target thermal conductivity was satisfied in all of the foamed concrete specimens, except for VS50, in the 25% replacement ratio case for Type A aggregate, and all of the mixtures for Type B aggregate.