건물의 벽체 열관류율 현장 측정법의 비교

박소민(So Min Park),송두삼(Doo Sam Song) 대한설비공학회 2021 대한설비공학회 학술발표대회논문집 Vol.2021 No.6

리츠 법을 이용한 열방어 시스템 패널의 열 좌굴 특성 연구

이희수,김용하,박정선 항공우주시스템공학회 2019 항공우주시스템공학회지 Vol.13 No.1

초고속 비행체는 발사 및 재진입 시 공력 가열에 의해 높은 열 하중을 받는다. 초고속 비행체의 외피 구조물인 열방어 시스템 패널은 기계적으로 구속되어 있기 때문에 고온 가열 시 열 좌굴이 발생할 수도 있다. 이는 초고속 비행체의 유동장에 변화를 주어 공력특성을 불안정하게 한다. 따라서 열방어 시스템 패널은 초고속 비행에 의한 공력가열 시 비행안정성을 유지하기 위해 열 좌굴을 방지하도록 설계되어야 한다. 본 논문에서는 운용 시 안팎에 큰 온도차가 존재하는 열방어 시스템 패널에 대해 유한차분법을 사용하여 열전달 특성을 분석하였으며, 리츠 법을 사용하여 열 좌굴 특성에 대한 근사적 모델을 제안하였다. 또한 정의된 근사적 모델의 정확도를 검증하기 위해 유한요소 해석결과와 비교하였다. 마지막으로, 수립된 근사 기법을 바탕으로 열방어 시스템 패널의 좌굴 발생 온도에 대한 매개변수 분석을 수행하였다. High speed vehicles are subjected to high thermal loadings due to aerodynamic heating during ascent and reentry. Since a thermal protection system panel is mechanically constrained, it may cause thermal buckling under excessive thermal loadings. The thermal buckling could disturb the field of flow and make aerodynamic characteristics unstable. It is thus necessary to design the thermal protection system panel to prevent thermal buckling. This study defines the analytical model of temperature distribution using the finite difference method for the thermal protection system panel with large temperature differences inside and outside. This paper proposes the approximate model of the thermal buckling characteristics for the thermal protection system panel through the use of the Ritz method. The validity of the present method was verified by comparing the results of the finite element analysis. Furthermore, this research performs the parametric analysis of the thermal buckling characteristics for the thermal protection system panel by using the approximate model.

A comparison of temperature distribution in PEMFC with single-phase water cooling and two-phase HFE-7100 cooling methods by numerical study

Choi, Eun Jung,Park, Jin Young,Kim, Min Soo Elsevier 2018 International journal of hydrogen energy Vol.43 No.29

<P><B>Abstract</B></P> <P>Thermal management has been considered as one of the critical issues in proton exchange membrane fuel cell (PEMFC). Key roles of thermal management system are maintaining optimal operating temperature of PEMFC and diminishing temperature difference over a single fuel cell and stack. Severe temperature difference causes degradation of performance and deterioration of durability, so understanding temperature distribution inside a single fuel cell and stack is crucial. In this paper, two-phase HFE-7100 cooling method is suggested for PEMFC thermal management and investigated regarding temperature change inside a fuel cell. Also, the results are compared to single-phase water cooling method. Numerical study of temperature distribution inside a single PEMFC is conducted under various conditions for the two different cooling methods. Fuel cell model considering mass transfer, electrochemical reaction and heat transfer is developed.</P> <P>The result indicates that two-phase HFE-7100 cooling method has an advantage in temperature maintenance and temperature uniformity than single-phase water cooling method, especially in high current density region. It is also revealed that the cell temperature is less dependent on system load change with two-phase cooling method. It indicates that the fuel cell system with two-phase cooling method has high thermal stability. In addition, the effect of coolant flow rate and coolant inlet pressure in two-phase HFE-7100 cooling method are discussed. As a result, two-phase cooling method showed reliable cooling performance even with low coolant flow rate and the system temperature increased as coolant pressure rose.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two-phase HFE-7100 cooling method is suggested for PEMFC thermal management. </LI> <LI> Numerical study investigating temperature distribution inside PEMFC is conducted. </LI> <LI> Single-phase water cooling and two-phase HFE-7100 cooling methods are compared. </LI> <LI> Two-phase cooling shows better thermal performance than single-phase cooling. </LI> </UL> </P>

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>

열교저감방식에 따른 진공단열패널이 적용된 벽체의 열교특성분석

민다혜,김상명,김진희,김준태 한국생태환경건축학회 2019 한국생태환경건축학회 논문집 Vol.19 No.2

Purpose: The insulation requirements for buildings are being strengthened to make zero energy mandatory. Vacuum insulation panel (VIP) has about 8~10 times better insulation performance than existing insulation and also maintains high insulation performance with a slimmer thickness. However, when VIP is installed on a building wall, thermal bridge occurs. Thermal bridges of VIP itself, thermal bridges due to air gaps between adjacent vacuum insulation panels, and thermal bridges with other building materials that make up the walls. Thermal bridges deteriorate the insulation performance of the building envelope. The purpose of this study is to compare and analyze the insulation performance by designing a wall with vacuum insulation panels and applying a method to improve the insulation performance degradation due to heat bridges. Method: In this paper, thermal bridge phenomenon of the wall was analyzed using Physibel TRISCO simulation program. The walls were designed for VIP encapsulated EPS insulation application walls. The parameters of thermal bridges reduction were set to air gsp seals between VIPs, application of thermal bridge fastener and both. A total of 4 cases were designed. Result: Based on the simulation results thermal bridge effect for wall with encapsulated VIP reduced by 5.2% for Case 1, 7.2% for Case 2, and 13.6% for Case 3. As a result, it was confirmed that the airtight seal between VIPS and the type of connection material affect the thermal bridge of the wall. From the findings in this paper, it is recommended that necessary techniques are adopted to prevent deterioration of insulation performance primarily due to thermal bridges.

인공위성 내부 전장박스 열해석을 위한 유한요소 제약조건 구현 기법 연구

김민기 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11

본 논문은 인공위성 내부의 집중화된 온도로 모델링된 전장박스의 열해석을 위한 유한요소 열해석의 제약조건의 구현 기법에 대한 연구에 대해 논의한다. 일반적으로 인공위성 내부 전장박스의 열해석 시 박스 자체의 온도를 단일화하여 집중화된 상태로 위성체 전체의 열해석 수행 후, 박스 내부는 상기의 해석 결과를 바탕으로 별도의 상세 해석을 수행한다. 이를 유한요소 열해석으로 구현하기 위하여 본 연구에서는 제약조건을 구현하는 세 가지 방법론인 라그랑지 승수법, 직접 대입법, 벌칙법에 대해 언급하고 해당 방법들의 장, 단점을 비교, 대조 후 직접 대입법을 적용하여 그 결과를 벌칙법과 비교하였다. 우주복사 환경 하의 평판 전장박스 문제의 결과 비교 결과 해당 방법의 결과의 유효성을 확인할 수 있으며 벌칙법에 비하여 해의 수렴성 문제에서도 자유로울 수 있다는 것을 확인할 수 있다. This paper presents the implementation methods of thermal constraints in finite element thermal analysis for a satellite with dummy boxes including electric devices. Generally, for the case of the thermal analysis of a satellite, temperatures of a dummy box lumped into a single unknown is solved to analyze fine temperature distribution of internal devices in the dummy box. To implement the thermal constraint in finite element thermal analysis, Lagrange multiplier method, direct substitution method, penalty method and the comparison of their characteristics are described. In this study, direct substitution method is applied and the result is compared with that of penalty method. The comparison of the results of a plate with a dummy box in the space radiation problem proves direct substitution method is the best way to implement the thermal constraints.

레이저 섬광법을 이용한 열확산계수 측정시 오차요인별 분석연구

이원식,박상흡 대한용접접합학회 2002 대한용접·접합학회지 Vol.20 No.6

Laser flash method have been widely used for practical measuring method of thermal diffusivity. And it can be used for measurement of non-conductive materials as well as conductive materials and also for measuring thermal multi-properties. We have analyzed effects of error occurring during measurement of thermal properties in order to enhance measuring accuracy. Also we have studied delay time between measurement starting time with synchronizing signal and laser oscillating time, because it is important that measuring a time to rise temperature of specimen from room temperature to a half of measuring temperature at measuring a thermal diffusivity by laser flash method. We could reduce non-uniform heating error from non-uniform energy distribution by developing 3D uniformizer to eliminate non-uniform heating error. We have measured thermal diffusivities of POCO AXM-5Q1 and Glassy-Carbon which are standard specimen of NIST(USA) and candidate standard specimen of NRLM(japan) respectively for laser flash method. Maximum error fell within 2% for POCO AXM-5Ql gaphite and 2% for Glassy-Carbon. Those results showed error decreasing methods were effective.

Thermal performance evaluation of low-income buildings based on indoor temperature performance

Lee, Junghun,Kim, Seohoon,Kim, Jonghun,Song, Doosam,Jeong, Hakgeun Elsevier 2018 APPLIED ENERGY Vol.221 No.-

<P><B>Abstract</B></P> <P>In South Korea, about 40,000 buildings of low-income households have been diagnosed and remodeled annually by the Energy Welfare Program, using the normative method. The normative method is based on the heat gain elements of a building. In contrast, the performance-based method is based on the output derived from the thermal performance of each building part. In the normative method, there is no other building in which the input conditions of a building are perfectly matched. Further, cost-effective energy remodeling strategies vary according to the capacity of the diagnosis engineer. In this paper, we analyze the thermal performance of buildings by the performance-based method using indoor temperature, and examine the possibility of a database for the optimal remodeling method. For this, we analyzed more than 2500 simulation cases by combining thermal performance of each building part. The indoor temperature pattern can be similar even when the thermal performance of each building part is different. In buildings with similar indoor temperature patterns, the coefficient of variation of the root mean squared error of energy demand falls within the acceptable error range. Furthermore, changes in energy demand and predicted mean vote are similar when window thermal performance is changed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Indoor temperature pattern can be similar even building conditions are different. </LI> <LI> If similar indoor temperature patterns occur, energy demand is also similar. </LI> <LI> Changes in energy demand are similar when window thermal performance is changed. </LI> <LI> Overall thermal performance of low-income buildings can be diagnosed. </LI> <LI> Databases can store remodeling plans using indoor temperature for future use. </LI> </UL> </P>

연속 강합성거더교의 온도프리스트레싱 효과 해석을 위한 간략해석법의 개발

김준환(Kim Jun-Hwan),안진희(Ahn Jin Hee),최규태(Choi Kyu Tae),김상효(Kim Sang-Hyo) 대한토목학회 2007 대한토목학회논문집 A Vol.27 No.6A

온도프리스트레싱 공법을 이용한 연속 강합성거더교의 시공은 연속지점부의 콘크리트 바닥판에 프리스트레스를 도입함으로써 교축직각방향으로 발생하는 인장균열을 억제하는데 그 목적이 있다. 교량의 시공시 일시적으로 인위적인 온도경사를 강거더에 발생시켜 발생하는 거더의 휨변형이 프리스트레싱을 위한 외력으로 작용하므로 별도의 긴장재가 필요 없으며 교축방향 보강철근 사용량 및 강거더 단면을 감소시킬 수 있는 장점이 있다. 온도프리스트레싱 효과의 해석에 있어서는 인위적인 가열로 인한 비선형의 온도분포를 고려하여야 하므로 이전까지의 연구에서는 3차원 입체요소를 사용한 유한요소해석에 의존해왔다. 또한 이전의 해석기법에서는 3차원 열전달해석과 열탄성해석을 연계하는 방법을 적용하여 모형화가 어렵고 해석시간이 많이 소요되며 비전문가는 사용이 어렵다는 단점이 있었다. 본 연구에서는 연속 강합성거더교의 온도프리스트레싱 효과를 해석함에 있어 수치해석 모형화와 해석에 소요되는 해석비용을 획기적으로 감축하고 설계 실무자들이 쉽게 접근할 수 있도록 온도프리스트레싱 효과의 간략 해석법을 개발하였다. 이전의 연구에서 제안된 기존 해석법을 활용한 2경간 연속 강합성 거더교의 해석결과와 비교ㆍ분석한 결과, 간략 해석법은 기존 해석법 대비 5% 이내의 오차를 보여 온도프리스트레싱을 적용한 설계 실무에 충분히 적용이 가능한 것으로 판단되었다. The purpose of thermally-prestressed continuous composite girder bridges lies in mitigation of transverse cracks in the concrete deck. Instead of using tendons for prestressing, the thermal prestressing method utilizes the deflection of steel girders induced by a temporary heating process without mechanical prestressing. While the transverse cracks can be effectively controlled, decrease in the amount of rebar and the steel girder's section area is also possible. Although the computation method of thermal prestressing effect proposed in previous studies can give accurate results, the computation cost is high and may be difficult for inexperienced engineers. In this study, a simplified method is proposed for computing the thermal prestressing effect, which neglects the heat transfer analysis procedure and utilizes simple 2-D beam element FE models. Comparison of the computation results using existing and simplified methods was performed where the error between the two methods was less then 5%. Therefore, it is concluded that the simplified method can be used with acceptable accuracy for computation of the thermal prestressing effect.

A 3D Thermal Field Restructuring Method for Concrete Dams Based on Real-Time Temperature Monitoring

Peng Lin,Haoyang Peng,Qixiang Fan,Yunfei Xiang,Zongli Yang,Ning Yang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.4

Temperature monitoring and control is of great significance to ensure concrete quality during the construction of dam concrete. In this study, a 3D thermal field restructuring method is developed for the complex evolution process of thermal field in dam concrete during construction, based on real-time temperature monitoring. The proposed method is related to the ordinary Kriging interpolation and the distributed optical fiber temperature sensing (DTS) technology. Based on the temperature monitoring of the Wudongde (WDD) super-high arch dam, the 3D thermal field can be acquired effectively and fast by the proposed restructuring method. The results indicate the temperature difference between the temperature measured by thermometers and the restructured temperature is within 1°C. The evolution process of the restructured 3D thermal field for the WDD arch dam is in good agreement with the site situation. In addition, the uncertainty, cons and pros of the proposed method and the optimal layout of temperature sensors are further discussed. Although the proposed thermal field restructuring method has some limitations, it is believed to be a valuable tool for acquiring the 3D thermal field and thermal gradient of dam concrete.