• 한국화재소방학회논문지
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• 제30권1호
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• pp.49-56
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• 2016

본 논문에서는 동절기 소방배관의 동파방지를 위한 열선의 직선 시공과 감기 시공의 효과를 수치해석을 통하여 분석하였다. 두 시공법들의 효과 분석을 위하여 3차원 에너지방정식과 비정상 비압축성 Navier-Stokes 방적식의 비정상 해를 구하였다. 수치해석에서 물의 자연대류와 소방 배관의 열전도 방정식이 상호작용을 하므로 복합열전달 해석을 상용코드 ANSYS-FLUENT에서 제공하는 압력-속도 연성기법들 중의 하나인 SIMPLE 알고리즘을 이용하여 수행하였다. 수치해석을 통하여 시간에 따른 배관 내의 유동장 및 온도분포와 배관 내 물의 최대 및 최소온도 변화를 고찰하였다. 수치해석 결과 배관 단위 길이 당 투입열량이 동일한 경우에 감기 시공과 직선 시공의 동파방지 효과는 거의 동일함을 확인하였다. 따라서, 열선 손상과 단락 등을 고려하면 직선 시공이 더 나은 시공법이라 판단된다.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1860-1873
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• 2022

Nuclear thermal-hydraulic system analysis codes have been developed to comprehensively model nuclear reactor systems to evaluate the safety of a nuclear reactor system. For analyzing complex systems with finite computational resources, system codes usually solve simplified fluid equations for coarsely discretized control volumes with one-dimensional assumptions and replace source terms in the governing equations with constitutive relations. Wall boiling heat transfer models are regarded as essential models in nuclear safety evaluation among many constitutive relations. The wall boiling heat transfer models of two widely used nuclear system codes, RELAP5 and TRACE, are analyzed in this study. It is first described how wall heat transfer models are composed in the two codes. By utilizing the same method described in Part 1 paper, heat fluxes from the two codes are compared under the same thermal-hydraulic conditions. The significant factors for the differences are identified as well as at which conditions the non-negligible difference occurs. Steady-state simulations with both codes are also conducted to confirm how the difference in wall heat transfer models impacts the simulation results.

• Journal of applied mathematics & informatics
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• 제35권5_6호
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• pp.439-447
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• 2017

This paper investigates the inverse problem of determining an unknown heat radiative coefficient, which is only time-dependent. This is an ill-posed problem, that is, small errors in data may cause huge deviations in determining solution. In this paper, the existence and uniqueness of the problem is established by the second Volterra integral equation theory, and the method of trace-type functional formulation combined with finite difference scheme is studied. One typical numerical example using the proposed method is illustrated and discussed.

• Journal of Welding and Joining
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• 제17권1호
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• pp.133-144
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• 1999

To fine seam annealer capacity of through thickness seam annealing in terms of through thickness microstructure change with increased toughness and elongation leaving heat trace on it, high strength steel pipes of ERW with different thickness were tested in different seam annealing temperature measured on the outer surface of pipes. Annealing temperature and microstructure of the weld seam were changed through applied seam annealing condition. Toughness and tensile test with hardness and microstructure analysis were done on the annealed weld seam to fine its characteristics as a primary step and annealing characteristics according to different seam annealing condition. Through a study of annealed ERW weld seam characteristics and seam annealing technology, amount of electric power should apply in decreased manner to arranged inductors of annealer in the order of 1st, 2nd, 3rd, so on for proper seam annealing. For example of 15.4mm thick and 610mm outside diameter pipe, applied power for proper seam annealing is 600 -650kw at 1st inductor, 450 - 500kw at 2nd inductor, 200-250 kw at 3rd inductor of annealer during 10 - 12M/minute moving speed of pipe. Also, the penetration depth of heat trace along the thickness direction of weld during seam annealing can be estimated through the equation 17mm/kv$\times$voltage(kv) with the microstructure and hardness analysis of thick weld seam as well as study of seam annealing and comparison of cooling condition to CCT diagram of low carbon high strength steel. From this result, the difference between the technological applicability of full annealing condition based on phase diagram and full penetration of heat trace based on CCT diagram along the thickness of weld seam is discussed.

• 한국화재소방학회논문지
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• 제28권1호
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• pp.52-57
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• 2014

본 논문에서는 에너지방정식과 비정상 비압축성 Navier-Stokes 방적식을 사용하여 동절기 소방배관의 동파방지를 위한 최적의 열선위치를 확인하였다. 물의 자연대류와 소방 배관의 전도 열방정식이 결합된 복합열전달을 해석하였다. 혼합 열전달 배관 내 물의 비정상적인 유동과 온도분포를 확인하기 위하여 SIMPLE 형태의 알고리즘을 기반으로 한 상용코드(ANSYS-FLUENT)가 사용되었다. 수치해석을 수행하여 등온선과 벡터장을 살펴보았다. 물의 열팽창계수를 일정하다고 가정할 때 소방 배관 단면의 하부에 열선을 설치하는 것이 다른 위치에 설치하는 것보다 시간에 따른 물의 최저온도가 가장 높아서 동파방지에 가장 효과적인 것을 확인할 수 있었다.

• Nuclear Engineering and Technology
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• 제50권3호
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• pp.356-367
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• 2018

A series of tests dedicated to station blackout (SBO) accident scenarios have been recently performed at the $Prim{\ddot{a}}rkreislauf-Versuchsanlage$ (primary coolant loop test facility; PKL) facility in the framework of the OECD/NEA PKL-3 project. These investigations address current safety issues related to beyond design basis accident transients with significant core heat up. This work presents a detailed analysis using the best estimate thermal-hydraulic code TRACE (v5.0 Patch4) of different SBO scenarios conducted at the PKL facility; failures of high- and low-pressure safety injection systems together with steam generator (SG) feedwater supply are considered, thus calling for adequate accident management actions and timely implementation of alternative emergency cooling procedures to prevent core meltdown. The presented analysis evaluates the capability of the applied TRACE model of the PKL facility to correctly capture the sequences of events in the different SBO scenarios, namely the SBO tests H2.1, H2.2 run 1 and H2.2 run 2, including symmetric or asymmetric secondary side depressurization, primary side depressurization, accumulator (ACC) injection in the cold legs and secondary side feeding with mobile pump and/or primary side emergency core coolant injection from the fuel pool cooling pump. This study is focused specifically on the prediction of the core exit temperature, which drives the execution of the most relevant accident management actions. This work presents, in particular, the key improvements made to the TRACE model that helped to improve the code predictions, including the modeling of dynamical heat losses, the nodalization of SGs' heat exchanger tubes and the ACCs. Another relevant aspect of this work is to evaluate how well the model simulations of the three different scenarios qualitatively and quantitatively capture the trends and results exhibited by the actual experiments. For instance, how the number of SGs considered for secondary side depressurization affects the heat transfer from primary side; how the discharge capacity of the pressurizer relief valve affects the dynamics of the transient; how ACC initial pressure and nitrogen release affect the grace time between ACC injection and subsequent core heat up; and how well the alternative feeding modes of the secondary and/or primary side with mobile injection pumps affect core quenching and ensure stable long-term core cooling under controlled boiling conditions.

• Journal of Animal Science and Technology
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• 제65권1호
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• pp.132-148
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• 2023

Ruminants are the main contributors to methane (CH₄), a greenhouse gas emitted by livestock, which leads to global warming. In addition, animals experience heat stress (HS) when exposed to high ambient temperatures. Organic trace minerals are commonly used to prevent the adverse effects of HS in ruminants; however, little is known about the role of these minerals in reducing enteric methane emissions. Hence, this study aimed to investigate the influence of dietary organic trace minerals on rumen fermentation characteristics, enteric methane emissions, and the composition of rumen bacteria and methanogens in heat-stressed dairy steers. Holstein (n=3) and Jersey (n=3) steers were kept separately within a 3×3 Latin square design, and the animals were exposed to HS conditions (Temperature-Humidity Index [THI], 82.79 ± 1.10). For each experiment, the treatments included a Control (Con) consisting of only basal total mixed rations (TMR), National Research Council (NRC) recommended mineral supplementation group (NM; TMR + [Se 0.1 ppm + Zn 30 ppm + Cu 10 ppm]/kg dry matter), and higher concentration of mineral supplementation group (HM; basal TMR + [Se 3.5 ppm + Zn 350 ppm + Cu 28 ppm]/kg dry matter). Higher concentrations of trace mineral supplementation had no influence on methane emissions and rumen bacterial and methanogen communities regardless of breed (p > 0.05). Holstein steers had higher ruminal pH and lower total volatile fatty acid (VFA) concentrations than Jersey steers (p < 0.05). Methane production (g/d) and yield (g/kg dry matter intake) were higher in Jersey steers than in Holstein steers (p < 0.05). The relative abundances of Methanosarcina and Methanobrevibacter olleyae were significantly higher in Holstein steers than in Jersey steers (p < 0.05). Overall, dietary organic trace minerals have no influence on enteric methane emissions in heat-stressed dairy steers; however, breed can influence it through selective alteration of the rumen methanogen community.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.587-590
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• 2005

This study investigates the efficient construction scheme of the immersed tunnel focusing on the hydration heat. In this respect, some alternatives in curing, temperature condition and removing of the forms are compared together to meet the required criteria. It is addressed that the strict construction stage analysis considering the placing scheme of concrete is one of the key factors to trace the realistic structural behavior for the hydration heat.

• 한국화재소방학회논문지
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• 제29권6호
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• pp.33-39
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• 2015

본 논문에서는 동절기 소방용 CPVC 배관의 동파방지를 위하여 최적의 열선위치를 에너지방정식과 비정상 비압축성 Navier-stokes 방정식을 사용하여 수치해석을 수행하였다. CPVC 배관은 탄소강관과 열용량 등 주요 물성에 큰 차이가 있어 배관 내 물의 유동에 큰 차이를 보이는 것을 확인할 수 있었다. 물의 자연대류와 CPVC 배관의 열전도가 결합된 복합열전달을 해석하였다. 상용코드(Fluent)를 사용하여 혼합 열전달 배관 내 물의 비정상적인 유동과 온도분포를 확인하였다. 소방용 CPVC 배관 단면의 하부에 열선을 설치하는 것이 다른 위치에 설치하는 것보다 시간에 따른 물의 최저 온도가 가장 높아서 동파방지에 보다 효과적인 것을 확인하였다.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3526-3539
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• 2022

Nuclear thermal-hydraulic system analysis codes have been developed to simulate nuclear reactor systems, which solve simplified governing equations by replacing source terms with constitutive relations for simulating entire reactor systems with low computational resources. For half a century, many efforts have been made for wider versatility and higher accuracy of system codes, but various factors can affect the code analysis results, and it was difficult to isolate these factors and interpret them individually. In this study, two system codes, RELAP5 and TRACE, which have many users and are highly reliable, are selected to analyze only the effects of constitutive relations. The influence of constitutive relations is analyzed using in-house platforms that replicate constitute relations of RELAP5 and TRACE equally to exclude factors that may affect analysis results, such as governing equation solvers and user effects. Among the various constitutive relations, the analysis is performed on the wall variables expected to have the most influence on the analysis results. Part 1 paper presents the methodology and wall friction model comparison, while Part 2 paper shows wall heat transfer comparison of the two selected codes.