• Nuclear Engineering and Technology
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• 제56권2호
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• pp.624-635
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• 2024

In two-fluid simulations of flow boiling, the modeling of the mean bubble diameter is a key parameter in the closure relations governing the intefacial transfer of mass, momentum, and energy. Monodispersed approach proved to be insufficient to describe the significant variation in bubble size during flow boiling in a heated pipe. A population balance model (PBM) has been employed to address these shortcomings. During nucleate boiling, vapor bubbles of a certain size are formed on the heated wall, detach and migrate into the bulk flow. These bubbles then grow, shrink or disintegrate by evaporation, condensation, breakage and aggregation. In this study, a parametric analysis of the PBM aggregation and breakage models has been performed to investigate their effect on the radial distribution of the mean bubble diameter and vapor volume fraction. The simulation results are compared with the DEBORA experiments (Garnier et al., 2001). In addition, the influence of PBM parameters on the local distribution of individual bubble size groups was also studied. The results have shown that the modeling of aggregation process has the largest influence on the results and is mainly dictated by the collisions due to flow turbulence.

• Preventive Nutrition and Food Science
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• 제6권4호
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• pp.224-229
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• 2001

We investigated the effects of bean sprouts (Glycine max), dropwort (Oenanthe javanica), and radish (Raphanus sativus var. hortensis for. acanthiformis) extracts on alcohol dehydrogenase (ADH). The extracts from three kinds of vegetables were prepared by extracting with boiling water, distilling water, and ethyl alcohol. Among extracts, boiling water extract showed the highest activating effect on ADH, respectively and distilled water extract had a greater effect on ADH activation than that of alcohol extract. The ADH facilitating effect of bean sprout extract by distilled water was significantly higher than dropwort or radish, hut the effect of the bean sprout extract by ethyl alcohol was lower than others. The facilitating effect on ADH of mixture extracts of bean sprout and dropwort were mixed at 1 : 1 mixture of boiled-water extract showed the highest effectiveness. And bean sprout extract separated below 3000 molecular weight (MW) range of extract fraction had greater ADH activity than large MW parts.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1189-1196
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• 2001

The objective of this paper is to investigate the applicability of acoustic emission(AE) technique to monitor the progress of the thermal shock damage on alumina ceramic. For this purpose, alumina ceramic specimen was heated in the furnace and then was quenched in the water tank. When the specimen was quenched in the water tank, complex AE signals due to the initiation of micro-cracks and boiling effect were generated by the progress of thermal shock damage. These mixed AE signals have to be classified for monitoring the degree of the thermal shock damage of alumina ceramics. In this paper, the mixed AE signals generated from both the boiling effect and the crack initiation under thermal shock test was analyzed. The characteristics of AE signals were also discussed by considering the variation of bending strength and Yongs modulus of specimens.

• 설비공학논문집
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• 제16권10호
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• pp.942-951
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• 2004

This paper presents the results of a theoretical study of the effect of radiation during free convective laminar film boiling for methanol/water binary mixtures on an isothermal vertical wall at atmospheric pressure. With the well-known boundary layer theory as a basis, a theoretical model has been formulated into consideration for mass diffusion at liquid phase. The equations are numerically solved by a similarity method to investigate the effects of radiation emissivity on the surface with various parameters such as wall superheat and composition of more volatile component at liquid phase far from the wall. From the results, the distributions of the physical quantifies are investigated in both phases. New correlations are proposed to predict the heat transfer coefficient of binary mixtures. It is shown that the proposed correlations are in good agreement with numerical results and with Bromley's correlation within maximum $11\%$ errors. It is also found that as the wall superheat is increased, radiation effect becomes more important.

• 한국식품영양과학회지
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• 제3권1호
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• pp.13-16
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• 1974

Chlorophyll을 함유(含有)하고 있는 녹색 식물(植物)의 조리(調理)에 의(依)한 색깔 변화(變化)는 대단히 중요(重要)하므로, 본실험(本實驗)은 각각(各各) 다른 열처리(熱處理)와 시간(時間)이 풋고추의 chlorophyll 함량(含量)에 미치는 영향을 조사하였다. 풋고추는 boiling water steam 그리고 hot air 를 사용(使用)하여, $100^{\circ}C$에서 5 10 15 분간(分間) 가열(加熱)했고, microwave oven에서는 1 2 3 분간(分間) 처리했다. 결과(結果)에 의(依)하면 chlorophyll 함량(含量)은 일반적(一般的)으로 가열시간(加熱時間)이 길어짐에 따라 감소하는 경향이었으며, 가열처리중(加熱處理中) steam이 가장 큰 영향을 주었고, boiling water 가 그 다음이었다. Hot air와 microwave 처리한 풋고추는 아주 적은 양의 chlorophyll이 변화(變化)하였다. 일반적으로 pheophytin 생성(生成) chlorophyll 함량(含量)이 감소함에 따라 증가(增加)하였다.

• Nuclear Engineering and Technology
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• 제43권3호
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• pp.257-270
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• 2011

A set of reflood tests has been performed using ATLAS, which is a thermal-hydraulic integral effect test facility for the pressurized water reactors of APR1400 and OPR1000. Several important phenomena were observed during the ATLAS LBLOCA reflood tests, including core quenching, down-comer boiling, ECC bypass, and steam binding. The present paper discusses those four topics based on the LB-CL-11 test, which is a best-estimate simulation of the LBLOCA reflood phase for APR1400 using ATLAS. Both homogeneous bottom quenching and inhomogeneous top quenching were observed for a uniform radial power profile during the LB-CL-11 test. From the observation of the down-comer boiling phenomena during the LB-CL-11 test, it was found that the measured void fraction in the lower down-comer region was relatively smaller than that estimated from the RELAP5 code, which predicted an unrealistically higher void generation and magnified the downcomer boiling effect for APR1400. The direct ECC bypass was the dominant ECC bypass mechanism throughout the test even though sweep-out occurred during the earlier period. The ECC bypass fractions were between 0.2 and 0.6 during the later test period. The steam binding phenomena was observed, and its effect on the collapsed water levels of the core and down-comer was discussed.

• 대한화학회지
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• 제63권2호
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• pp.123-133
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• 2019

이 연구에서는 H대학교 화학교육과 예비교사들을 대상으로 반응적 교수법의 효과를 알아보고자 하였다. 이를 위하여 토론을 학습자 생각의 본질 존중하기, 학습자 생각에서 학문적 연결 관계 인식하기, 학습자 생각의 본질 확장하기의 3단계로 구성하였다. 학습자 생각의 본질 존중하기 단계에서는 예비교사 20명을 대상으로 실시한 설문지를 분석하여 증발과 끓음에 관련된 예비교사들의 생각의 본질을 파악하였다. 이 중에서 5명의 예비교사를 선발하여 자신의 생각과 학문적 연결 관계를 인식하도록 하였다. 이러한 단계를 통해 예비교사들은 증발과 끓음에 대한 자신들의 생각의 본질을 파악하였으며, 이러한 생각의 본질을 학문적으로 연결하여 사고의 프레임을 수정하거나 확장하는 과정을 경험하였다. 또한 예비교사 스스로 자신의 개념이 역동적인 변화하는 과정을 직접 체험함으로써 반응적 교수법의 효과를 인식하였다.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.1939-1944
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• 2020

Pool boiling heat transfer of a copper microporous coating was experimentally studied in borated water with a concentration of boric acid from 0.0 to 5.0 vol percent (vol%) to determine the effect of boric acid on boiling heat transfer in water. A high-temperature, thermally conductive microporous coating (HTCMC) was created by sintering copper powder with an average particle size of 67 ㎛ onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 ㎛ within a furnace in a vacuum environment. The tests showed that the nucleate boiling heat transfer coefficient (NBHT) of HTCMC became slightly less enhanced as the concentration of boric acid increased but the NBHT coefficient values were still significantly higher than those of the plain surface. The critical heat flux (CHF) values from 0 to 1.0 vol% were maintained at ~2,000 kW/㎡, and then, they gradually decreased down to ~1,700 kW/㎡ as the concentration increased further to 5.0 vol%. It is believed that the micro-scale pores of the HTCMC were partially blocked by the high boric acid concentration during the nucleate boiling such that the small bubbles were not effectively created using the HTCMC reentrant cavities as the boric acid concentration increased.

• 대한기계학회논문집B
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• 제40권7호
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• pp.457-470
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• 2016

벽면비등 모델로 열분배모델을 채택하는 CFD 스케일의 전산해석코드는 저압 조건에서 미포화비등 발생 시 2상유동 변수의 해석 정확도가 낮은 것으로 알려진다. 본 연구에서는 열분배모델을 기반으로 벽면비등 현상을 예측하는 열수력 기기해석코드인 CUPID 코드를 이용하여 수직상향류 미포화비등 실험을 해석하였다. 10 bar 이상의 고압 조건에서는 CUPID 코드의 기포율 예측 정확도가 높았으나, 대기압 주변의 저압 조건에서는 기포율 분포에 대한 해석결과가 실험결과와 큰 차이를 보였다. 따라서 열분배모델 내 주요 인자에 사용되는 부모델에 대한 민감도 분석을 수행하였으며, 저압 조건 미포화비등 예측에 적합한 최적 부모델 조합을 선정하였다. 또한, 열분배모델 내 주요 인자 중 하나인 K-인자가 기포율에 미치는 영향을 평가하였다.

• 수산해양기술연구
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• 제30권1호
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• pp.33-44
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• 1994

This work studies for boiling and condensation heat transfer performance of trapezoidally shaped integral-fin tubes having fin densities from 748fpm to 1654fpm. For comparison, tests are made using a plain tube having the same inside and outside diameter as that of the root of fins of finned tubes. Hahne's theoretical model and Webb's theoretical model are used to predict the R-11 boiling heat transfer coefficient and condensing heat transfer coefficient respectively for plain tube and all integral-fin tubes. Experiments are carried out using R-11 as working fluid. This work is limited to film-wise condensation and pool boiling on the outside surface of plain tube and 4 low integral-fin tubes. In case of condensation, the refrigerant condenses at saturation state of 32$^{\circ}C$ on the outside tube surface cooled by coolant and in case of boiling. the refrigerant evaporates at saturation state of 1bar on the outside tube surface. The amount of non-con-densable gases in the test loop is reduced to a negligible value by repeated purging. The actual boiling and condensing processes occur on the outside tube surfaces. Hence the nature of this surface geometry affects the heat transfer performances of condenser and evaporator in refrigerating system. The condensation heat transfer coefficient of integral-fin tube is enhanced by both extended tube surface area and surface tension. The ratio of the condensation heat transfer coefficients of finned to plain tubes is greater than that of surface area of finned to plain tubes, while ratio of the boiling heat transfer coefficient of finned to plain tubes shows reverse result. As a result, low integral-fin tube can be used in condenser more effectively than used in evaporator.