Critical heat flux (CHF) in pool boiling under static and rolling conditions

Tanjung, Elvira F.,Albdour, Samah A.,Jeong, Yeon Uk,Jo, Daeseong Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.3

Experimental investigations were attempted to simultaneously observe the vapor behaviors and critical heat flux under static and rolling conditions. From visualization results, vapor initiated, grew, and detached individually in a vertical direction from the static heated surfaces (at 10, 20, and 30°). While under rolling motion, initiated vapor grew, and interacted with each other, resulting in forming a wider dry spot on the heated surface. Also, it was observed that the vapor drifted upward and stayed on the heated surface longer compared to under static condition. The faster the platform rolls, the longer the vapor stay on the heated surface, significantly decreasing the CHF. On the other hand, as the platform rolls slower (at high rolling period), CHF increases. CHF was decreased with increasing maximum rolling amplitude and inclination angle under both conditions (static and rolling). CHF under rolling conditions was noticed to be lower than under static condition except at maximum rolling amplitude of 10°. The bubble departure frequency at a maximum rolling amplitude of 10° was the highest among all of rolling amplitudes, thereby enhancing the CHF. These results indicate that rolling motion significantly affects vapor behaviors and CHF.

Effect of the Axial Heat Flux on the Critical Heat Flux in Low Flow Conditions with Vertical Annuli

MOON, Sang-Ki,CHUN, Se-Young,PARK, Jong-Kuk,BAEK, Won-Pil Atomic Energy Society of Japan 2006 Journal of nuclear science and technology Vol.43 No.11

<P>An experimental study on the critical heat flux (CHF) has been performed for a water flow in vertical annuli with uniform and chopped cosine axial heat flux distributions under low flow and a wide range of pressure conditions. The effect of an axial heat flux distribution on the critical power is large at low-pressure conditions, but the effect decreases rapidly as the pressure increases. The ‘overall power’ hypothesis becomes more accurate as the pressure and critical quality increase, and the ‘local conditions’ hypothesis is not valid at high quality conditions. For a fixed mass flux and pressure, the relationship between the critical quality and the boiling length is represented by a single curve for the whole range of the present experimental conditions, regardless of the axial heat flux distributions. Smolin <I>et al.</I>’s <I>F</I>-factor and Bowring’s <I>Y</I> parameter show good prediction results for the present CHF data.</P>

한국 무용비평계 연구 - 등단과정과 활동을 중심으로 -

이지선 한국무용예술학회 2007 무용예술학연구 Vol.21 No.-

By concentrating on the debut process and activities of the dance critics, one of the primary purpose of this study is understanding the dance criticism in Korea. The other is defining the problems which dance criticism in Korea has and suggesting the improvement devices.In early days, by appearing in the press at the editor?s requests, the writers, artists and dancers could be easily carry out as a dance critic without the specific debut process. From 1970s to 1990s, many dance critics could debut through the dance magazines. And recently, the most critics are coming out through the specific system like ?critic award? presented by dance magazines. The debuts of dance critic regardless of way of process are not objective and has no definite criterion. Either the debut through the magazine or through the specific system, editor?s choice is the most influential. If this social factor keep effect on the critic?s debut, their status and public trust will hardly be acquired.Also the activities of dance critics were too diversified and uneconomical to concentrate on their critiques. The main problem of the dance criticism in Korea which existing researches have insisted on was that there are insufficiency of dance critics. But at the result of this study, major causes are laid on not their number but their inactivity. Through the above discussion, I suggest follows,1. necessity of the academical criticism2. necessity of the economical support to the critic?s activities3. necessity of the training system for the dance criticDance criticism make the dance be popular and it discover the values and meanings of dance. In conclusion, this research can be a contribution to identify the way to expand the dance audience base and to improve in future-oriented by understanding the structure of the dance criticism in Korea and suggesting the expansive dance criticism culture which is under the opening culture markets.

Practical deployment of pipelines for the CCS network in critical conditions using MINLP modelling and optimization: A case study of South Korea

Kim, Changsoo,Kim, Kyeongsu,Kim, Jeongnam,Ahmed, Usama,Han, Chonghun Elsevier 2018 INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL Vol.73 No.-

<P><B>Abstract</B></P> <P>In applying Carbon Capture and Storage (CCS) technology, pipelines are an economic choice for transporting CO<SUB>2</SUB>. However, it is difficult to plan the pipeline network in detail since various factors, such as mountain regions and high population density increase the cost of pipeline installation. Also, uncertainty of the reservoir capacity and national policies is important factors in practical pipeline deployment, especially in critical conditions mentioned above.</P> <P>In this study, the development of an optimal CCS pipeline network in critical conditions, and the effect of practical design conditions on the network, are studied using mixed-integer nonlinear programming (MINLP) modeling and optimization. South Korea is selected as a case study and optimal CCS networks are obtained according to four scenarios developed with regard to reservoir capacity and policy options. A rigorous cost model was developed, and subdivided penalty factors were applied to consider the drastic change in geographical conditions. The four scenarios were evaluated and the effect of the considered factors on the timely development of the CCS network was analyzed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Framework for CCS network design in critical conditions is proposed. </LI> <LI> Effect of reservoir uncertainty and CCS policy options is analyzed. </LI> <LI> Policy options affect the network design more than reservoir uncertainty. </LI> </UL> </P>

Improvement of TASS/SMR code using a simple correlation for subcooled boiling flow prediction

Chung, Y.J.,Kim, H.,Bae, K.H. Pergamon Press ; Elsevier Science Ltd 2017 Annals of nuclear energy Vol.99 No.-

SMART, which was an advanced integral type small modular PWR, was developed by KAERI (Kim et al., 2014). To analyze the thermal hydraulic phenomena including behaviors at the SMART specific components, the TASS/SMR code which can predict a heat transfer for various thermal hydraulic conditions, has been developed. Information of the void distribution in a subcooled boiling flow is important in predicting the inception of a two-phase flow and an onset of the critical heat flux condition. The TASS/SMR code adopts an energy partitioning method and a critical enthalpy correlation determining a point of net vapor generation for subcooling conditions. A range of the subcooling degree investigated is 1.5-50.6K to validate the method for a subcooled boiling flow prediction. The TASS/SMR code predicts well the void distribution along the height for the subcooled boiling flow conditions compared with the experimental data. The predicted location of the onset of void generation is simulated well at most investigated conditions and delayed slightly at the very high subcooling condition.

MULTIPLICITY RESULTS AND THE M-PAIRS OF TORUS-SPHERE VARIATIONAL LINKS OF THE STRONGLY INDEFINITE FUNCTIONAL

TACKSUN JUNG,Q-HEUNG CHOI 한국산업응용수학회 2008 Journal of the Korean Society for Industrial and A Vol.12 No.4

Let I ∈ C<SUP>1,1</SUP> be a strongly indefinite functional defined on a Hilbert space H. We investigate the number of the critical points of I when I satisfies two pairs of Torus-Sphere variational linking inequalities and when I satisfies m (m≥2) pairs of Torus-Sphere variational linking inequalities. We show that I has at least four critical points when I satisfies two pairs of Torus-Sphere variational linking inequality with (P.S.)<SUP>*</SUP>c condition. Moreover we show that I has at least 2m critical points when I satisfies m (m≥2) pairs of Torus-Sphere variational linking inequalities with (P.S.)<SUP>*</SUP>c condition. We prove these results by Theorem 2.2 (Theorem 1.1 in [1]) and the critical point theory on the manifold with boundary.

Multiplicity Results and the M-Pairs of Torus-Sphere Variational Links of the Strongly Indefinite Functional

Tack Sun Jung,Q Heung Choi 한국산업응용수학회(구 한국산업정보응용수학회) 2008 한국산업정보응용수학회 Vol.12 No.4

Let I ∈ C(1,1) be a strongly indefinite functional defined on a Hilbert space H. We investigate the number of the critical points of I when I satisfies two pairs of Torus-Sphere variational linking inequalities and when I satisfies m (m≥2) pairs of Torus-Sphere vari-ational linking inequalities. We show that I has at least four critical points when I satisfies two pairs of Torus-Sphere variational linking inequality with (P.S.)*c condition. Moreover we show that I has at least 2m critical points when I satisfies m (m≥2) pairs of Torus-Sphere variational linking inequalities with (P.S.)*c condition. We prove these results by Theorem 2.2 (Theorem 1.1 in [1]) and the critical point theory on the manifold with boundary.

자동차용 CO₂ 에어컨 시스템의 성능 특성에 관한 실험적 연구

이대웅(Daewoong Lee) 한국자동차공학회 2015 한국 자동차공학회논문집 Vol.23 No.1

In this study, a CO₂ air-conditioning system was investigated with different types of electrically driven compressors, parallel flow type gas cooler, four-pass type evaporator, internal heat exchanger integrated with accumulator, and electric expansion valve. The experimental study was conducted under various operating conditions (ie., different rotational compressor speeds, air inlet temperatures and air velocity coming into heat exchangers). The experimental results showed the cooling capacity was 3.5kW at 35°C ambient temperature when the vehicle was idle (ie., the worst condition for cooling off the gas cooler). In terms of performance effect of the compressor, the e-RP model had a slightly better cooling capacity and coefficient of performance than the e-GR model under the same test conditions. An experimental equation for optimum cooling-performance control was also suggested based on the results. A high-pressure control algorithm for the super critical cycle was determined to achieve both maximum cooling performance and efficient energy consumption. The results from the experimental equation coincided with those of previous experimental studies.

PALAIS-SMALE CONDITION FOR THE STRONGLY DEFINITE FUNCTIONAL

Jung, Tacksun,Choi, Q-Heung The Kangwon-Kyungki Mathematical Society 2009 한국수학논문집 Vol.17 No.4

Let ${\Omega}$ be a bounded subset of $R^n$ with smooth boundary and H be a Sobolev space $W_0^{1,2}({\Omega})$. Let $I{\in}C^{1,1}$ be a strongly definite functional defined on a Hilbert space H. We investigate the conditions on which the functional I satisfies the Palais-Smale condition. Palais-Smale condition is important for determining the critical points for I by applying the critical point theory.

한계 상태 기반 수정 Modified Cam Clay 파괴면

우상인,Woo, Sang Inn 한국지반공학회 2020 한국지반공학회논문집 Vol.36 No.4

본 논문은 점성토의 응력-변형률 관계를 모사하기 위해 한계 상태 이론을 기반으로 하여 수정한 Modified Cam-Clay 파괴면을 제안한다. 평균유효응력과 von Mises 응력의 공간에서 타원형상의 파괴면을 가지는 Modified Cam-Clay 모델의 경우, 강성 및 발달법칙 미적용시, 비배수 전단조건하에 한계상태 평균유효응력은 선행압밀 평균유효응력의 절반이 되며, 이는 실제 점성토의 거동과 차이가 있다. 본 연구에서는 선행압밀 평균유효응력은 점성토의 압밀이력으로 정량화되고, 한계상태 평균유효응력은 점성토의 현재 간극비로 산정되어, 이 둘간의 비율이 고정되지 않는 찌그러진 형태의 파괴면을 제안한다. 제안된 파괴면을 항복평면으로 가정하고, 비배수 삼축압축 거동을 모사한 결과, 실내 실험 결과와 유사한 결과를 얻을 수 있었다 This paper proposes a revised Modified Cam Clay type failure surface based on the critical state theory. In the plane of the mean effective and von Mises stresses, the original Modified Cam Clay model has an elliptic failure surface which leads the critical-state mean effective stress to be always half of the pre-consolidation mean effective stress without hardening and evolution rules. This feature does not agree with the real mechanical response of clay. In this study, the preconsolidation mean effective stress only reflects the consolidation history of the clay whereas the critical state mean effective stress only relies on the currenct void ratio of clay. Therefore, the proposed failure surface has a distorted elliptic shape without any fixed ratio between the preconsolidation and critical state mean effective stresses. Numerical simulations for various clays using failure surfaces as yield surface provide mechanical responses similar to the experimental data.