• Macromolecular Research
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• 제17권4호
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• pp.221-226
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• 2009

The present study firstly describes the synthesis of novel, thermo-latent initiators based on xanthenyl phosphonium salts with different counter anions and phosphine moieties and secondly examines their efficiency in the bulk polymerization of glycidyl phenyl ether(GPE). The polymerization was performed with phosphonium salt initiators($I_{SbF6}$, $I_{PF6}$, $I_{AsF6}$ and $I_{BF4}$) at ambient temperature to $200^{\circ}C$ for 1 h. The order of initiator activity was $I_{SbF6}>I_{PF6}>I_{AsF6}>I_{BF4}$. To examine the effect of the phosphine moiety on the initiator activity, polymerization was carried out with $I_{SbF6}(Ph_{3}P)$ and $II_{SbF6}(Bu_{3}P)$ at ambient temperature to $170^{\circ}C$ for 1 h. The order of reactivity was $I_{SbF6}>II_{SbF6}$. In general, the conversion percentage increased with increasing polymerization temperature. The thermal stability of these salts was measured by thermo gravimetric analysis(TGA). The solubility of phosphonium salts in various organic solvents and epoxy monomers was also investigated.

• Journal of Advanced Marine Engineering and Technology
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• 제28권6호
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• pp.962-971
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• 2004

This paper has dealt with thermo-physical properties of microencapsulated phase change material slurry as a latent heat storage material having a low melting point. The measured results of the thermo-physical properties of the test microencapsulated phase change material slurry, those are, density, specific heat, thermal conductivity and viscosity, were discussed for the temperature region of solid and liquid phases of the dispersion material (paraffin). The measurements of these properties of microencapsulated phase change material slurry have been carried out by using a specific-gravity meter, a water calorimeter, a differential scanning calorimeter(DSC), a transient hot wire method and rotating type viscometer, respectively. It was clarified that the additional properties law could be applied to the estimation of the density and specific heat of microencapsulated phase change material slurry and also the Euckens equation could be applied to the estimation of the thermal conductivity of this slurry.

• 한국지반공학회논문집
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• 제37권12호
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• pp.25-31
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• 2021

지반의 열-수리 현상에 대한 수치해석에서 경계조건은 해석결과의 정확도에 중요한 역할을 한다. 본 연구에서는 지반과 대기의 상호작용을 고려한 열-수리 경계조건을 제시하였다. 지면의 에너지 평형은 태양복사, 지구복사, 바람에 의한 대류, 수분 증발에 대한 잠열 그리고 지중으로의 열전도로 구성된다. 각각의 열흐름에 대한 방정식을 제시하고, 불포화 지반의 열-수리 현상에 대한 해석프로그램과 연계하여 수치해석을 수행하였다. 울산기상대에서 관측된 기상데이터를 이용한 수리-열적 해석에서 실측된 지표면 온도와 수치해석 결과가 매우 유사하였다. 낮시간의 수분 증발에 의한 잠재열은 비포장 지면의 온도를 낮추며, 야간시간에는 지면조건의 영향이 감소한 열적평형 상태에 도달하였다. 지면의 온도변화는 지중으로 깊어질수록 열확산으로 감소하였다. 지표면의 온도가 주요 관심사인 수치해석에서는 지반과 대기의 열-수리적 상호작용을 고려한 수치해석을 수행해야 한다.

• 한국생산제조학회지
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• 제9권3호
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• pp.69-75
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• 2000

The object of the research is to estimate for pearlite structure of quenched carbon steels. The effects of temperature on physical properties metallic structures and the latent heat by phase transformation were considered. In this study a set of constitutive equations relevant to the analysis of thermo-elasto plastic materials with pearlite phase transformation during quenching process way presented on the basis of continuum thermo-dynamics. The iso-thermal transformation curve of the SM50C was formlated by cubic spline curve. The formulated equations of evolution in pearlite transformation was used for structure analysis. The volume fraction of pearlite was obtained from the results of calculated metallic structure by Finite element equation.

• 한국정밀공학회지
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• 제18권10호
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• pp.134-147
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• 2001

Laser cladding process accompanies phase transformations from melting (on heating) through solidifying (on cooling) at the same time within a small material volume and to final solid phase. The phase transformations are not reversible, but an irreversible thermodynamic process; they accompany either absorption or release of thermal energy (referred to latent heat) during transformation. Yet, most analyses on materials processed by laser as a heat source have been performed on models of neglecting the latent heat in the process and those did not Justify the simplification. With literatures on the laser material process, we have not place an answer to how little the assumption affects on analyses. This led us to our current study: the effects of latent heat on thermo-mechanical analysis. To this end, we developed a fairly accurate program accommodating an algorithm for enforcing the latent heat whenever necessary and ran it combining with ABAQUS$^{TM}$. The simulation techniques we used in this study were verified by directly comparing our prediction with experimental publications elsewhere; our numerical results agreed accurately with the experiments. On the effects of the latent heat, we performed two alternatives about considering the latent heat in analysis, and compared each other. As a result, we found that more accurate conclusions might come out when considering the latent heat in process analyses.s.

• Journal of Advanced Marine Engineering and Technology
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• 제38권5호
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• pp.533-540
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• 2014

Recently, latent heat thermal energy storage system (LHTES) has gained attention in order to utilize middle temperature (373~573 K) waste heat from biomass gasification. This paper has investigated thermo-physical properties of erythritol [$CH_2OHCHOH$ $CHOHCH_2OH$], mannitol [$CH_2OH$ $(CHOH)_4CH_2OH$] and their compounds as phase change materials (PCMs). The differential scanning calorimetry (DSC) was applied to measure the melting point and latent heat of these PCMs. Also the melting and solidification characteristics of these PCMs were observed in a glass tube with a digital camera. In the DSC measurement, when the amount of mannitol content was more than 40 mass%, the melting point of these compounds show two melting points. The experimental results showed that the velocity of melting and solidification were different for every mixture ratio of compounds. These compounds had the super-cooling phenomenon during the solidification process.

• 한국레이저가공학회지
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• 제4권1호
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• pp.21-28
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• 2001

Simulation on the electron beam welding of Al 2219 alloy was carried out by using commercial FEM code MARC, which encounters moving heat sources. Due to axisymmetry of geometry, a half of the cylinder was simulated. A coupled thermo-mechanical analysis was carried out and subroutine for heat flux was substituted in the program. The material properties such as specific heat, heat transfer coefficient and thermal expansion coefficient were given as a function of temperature and the latent heat associated with a given temperature range is considered. As a result, the proper beam power is 60㎸${\times}$60㎃ and welding speed is 1∼1.5 m/min. The residual stress in the heat-affected zone as well as the fusion zone does not increase. It is necessary to use jigs for preventing distortion of cylinder and improving weld quality.

• Korean Chemical Engineering Research
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• 제48권1호
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• pp.93-97
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• 2010

본 연구에서는 수정된 T-history 법을 사용하여 백신 또는 의약품들의 수송 시 냉매로 사용될 수 있는 $0{\sim}15^{\circ}C$의 상전이 온도를 갖는 유기 상전이 소재들과 이중 두 물질의 혼합물들의 열용량, 잠열, 비열과 같은 열 물성을 측정하였다. 순수한 파라핀들을 측정한 결과, 각 물질들의 상전이 온도를 고려하여 최적의 냉각 속도를 유지하며 측정을 하는 것이 열물성의 신뢰성을 향상시킬 수 있음을 알 수 있었고, 특히 혼합물의 열 물성 측정에 적용할 경우, 수정된 T-history 법의 사용은 기존의 DSC 분석에 사용하는 시료의 양이 소량이므로 유발될 수 있는 결과의 부정확성 등의 문제점을 해결하는데 기여할 수 있음을 알 수 있었다.

• 한국지반공학회논문집
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• 제36권8호
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• pp.49-60
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• 2020

동상민감성 시료의 동상 거동을 평가하기 위해 완전히 결합된 열-수리-역학 연계해석을 수행하였다. 이를 위한 구성모델은 질량보존방정식, 에너지보존방정식, 힘평형방정식을 기반으로 유도되었다. 구성모델을 통해 간극수의 상변화, 간극수 유동 및 수반되는 기계적 변형 등 1차원 동결에 대한 다양한 물리적 현상을 정량적으로 고려할 수 있었다. 한편, 시료의 동상발생량 및 동상속도에 미치는 영향 인자들을 조사하기 위해 민감도 분석 연구가 수행되었다. 민감도 분석 결과에 따르면, 시료의 초기 간극비는 종속변수인 동상발생량과 동상속도에 독립적으로 큰 영향을 미치는 반면 흙 입자 열전도도 및 온도구배는 독립적으로 미치는 영향보다 두 변수 간 상호 작용을 통해 더 큰 영향을 미침을 확인하였다. 본 연구에서 고려된 인자들은 모두 동상발생량과 동상속도에 영향을 미치는 주요 인자이며, 표본시료의 동상민감성 여부를 결정하는 데에 활용될 수 있을 것이다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.159-164
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• 1997

The optimal conditions were investigated in order to manufacture the light automotive body parts using the semi-solid forging process by the finite element nalysis. Considering about macro-segregation cause to difference of relative velocity between solid phase and liquid phase, solidificational phenomenon cause to heat transfer from die and export of the latent heat, so solid fraction updating algorithm can be proposed. The rigid thermo-viscoplastic finite element analysis was carried out according to die temperature with proposed algorithm, so availability of forming part were understood. The finite element program can be used to the analysis of semi solid forging process.