변온유입 성층축열조의 충전과정에 대한 해석적 접근

유호선,Yoo, Hoseon 대한설비공학회 1997 설비공학 논문집 Vol.9 No.1

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.

열전도가 주도적인 삼차원 접촉융해에 대한 비정상 해석

유호선,Yoo, Hoseon 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.8

This work reports a set of approximate analytical solutions describing the initial transient process of close-contact melting between a rectangular parallelepiped solid and a flat plate on which either constant temperature or constant heat flux is imposed. Not only relative motion of the solid block tangential to the heating plate, but also the density difference between the solid and liquid phase is incorporated in the model. The thin film approximation reduces the force balance between the solid weight and liquid pressure, and the energy balance at the melting front into a simultaneous ordinary differential equation system. The normalized model equations admit compactly expressed analytical solutions which include the already approved two-dimensional solutions as a subset. In particular, the normalized liquid film thickness is independent of all pertinent parameters, thereby facilitating to define the transition period of close-contact melting. A unique behavior of the solid descending velocity due to the density difference is also resolved by the present solution. A new geometric function which alone represents the three-dimensional effect is introduced, and its properties are clarified. One of the representative results is that heat transfer is at least enhanced at the expense of the increase in friction as the cross-sectional shape deviates from the square under the same contact area.

등열유속에 의한 평판위 비정상 접촉융해에 대한 근사적 해석해

유호선,Yoo, Hoseon 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.12

This paper focuses on the unsteady close-contact melting phenomenon occurring between a phase change material kept at its melting temperature and a flat surface on which constant heat flux is imposed. Based on the same simplifications and framework of analysis as the case of constant surface temperature, an approximate analytical solution which depends only on the liquid-to-solid density ratio is successfully derived. In order to keep consistency with the known solution procedure, both the dimensionless wall heat flux and the Stefan number are properly redefined. The obtained solution proves to agree quite well with the published numerical data and to be capable of resolving the fundamental features of unsteady close-contact melting, especially in the presence of the solid-liquid density difference. The density ratio directly affects the film growth rate and the initial value of solid descending velocity, thereby controlling the duration of unsteady process. The effects of other parameters can be evaluated readily from the steady solution which is implied in the normalized result. Since the dimensionless surface temperature for the present boundary condition increases from zero to unity along the evolution path of the liquid film thickness, the unsteady process lasts longer than that for the case of isothermal heating.

지역냉방용 직접순환식 아이스슬러리 시스템의 현장적용 사례

유호선(Hoseon Yoo),이상훈(Sang Hoon Lee),이윤표(Yoon Pyo Lee) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.9

In order to investigate the feasibility of a direct ice slurry transporting system for the purpose of district cooling, a case study of field application is performed. The research aims include the field measurement of ice packing factor, the performance of coldness delivery, and the branching characteristics of ice slurry. Two representative types of pipe branch are dealt with in this work. For the slurry flow with ice volume fraction of 0.16 or less, the pipe blocking due to aggregation is not observed. Based on the time-wise variation of temperature in the storage tank, a calculating method of ice packing factor is newly developed, which seems to be useful when the brine concentration is unknown. It is confirmed that the mass flow rate of ice slurry per unit cooling load is markedly reduced with increasing the ice content. The pumping power also decreases, but remains unchanged for high ice fractions. The distribution of ice particle before and after branching shows a good uniformity within the range of 5% difference, but yields a unique trend depending on the flow rate.

과도 접촉융해과정에 대한 근사적 해석해

유호선(Hoseon Yoo) 대한설비공학회 1997 대한설비공학회 학술발표대회논문집 Vol.1997 No.6-1

변온유입에 대한 성층축열조의 과도 열응답

유호선(Hoseon Yoo),박이동(Ee-Tong Pak) 대한설비공학회 1994 대한설비공학회 학술발표대회논문집 Vol.1994 No.11

성층축열조의 충전과정 및 축열효율에 대한 입구경계조건의 영향

유호선(Hoseon Yoo) 한국태양에너지학회 1994 한국태양에너지학회 논문집 Vol.14 No.3

출구경계선조건이 엄밀히 공식화된 성층축열조의 1차원모델에 대하여 개선된 해석적인 해를 제시하였다. 2종류의 입구조건 각각에 대한 본 연구의 해는 분명히 정의된 함수의 항으로 표시될 뿐아니라 대응하는 Cabelli의 해를 포괄하는 형태이다. 이 해에 근거하여 입구조건이 충전과정 동안의 열적 거동에 미치는 영향을 규명하였다. Pe수가 클 때 입구조건은 온도분포 및 축열효율에 영향을 미치지 않지만, Pe수가 작을 때 표면온도가 정온 및 변온인 경우사이에는 현저한 차이가 있었다. 축열효율의 극한적인 거동이 물리적으로 타당한 점에서, 변온인 경우가 정온인 경우에 비하여 보다 일반화된 입구조건인 것으로 보인다. 결론적으로, 성층축열시스템의 성능예측시에는 표면온도가 변온인 경우에 대한 해가 적용되어야 한다. A set of improved analytical solutions to one-dimensional model for stratified thermal storage tanks is presented, for which the exit condition is rigorously formulated. The present solutions for two types of the inlet conditions are not only expressed in terms of well-defined functions, but also include the corresponding Cabelli's as a Subset. Based on these solutions, effects of the inlet conditions on the thermal behaviors during the charging process are investigated. For large values of Pe the inlet condition does not affect the temperature profile as well as the storage efficiency, whereas for small values of Pe there exists a significant difference between the cases of constnat and variable surface temperatures. The latter appears to be a more generalized inlet condition than the former in that the latter shows a physically realistic limiting behavior in the storage efficiency. In consequence, it is deduced that the solution to the latter case should be used for predicting the performance of the stratified thermal storage systems.

입구온도가 변화하는 성층축열조의 충전과정 해석

유호선(Hoseon Yoo) 한국태양에너지학회 1995 한국태양에너지학회 논문집 Vol.15 No.2

유입관성에 의한 유체혼합뿐 아니라 입구온도의 변화까지 고려된 성층축열조의 충전과정 모델에 대하여 해석적 근사해를 제시하였다. 해석모델은 깊이가 일정한 완전혼합 및 압출유동영역으로 구성되며, 입구온도의 변화는 중첩의 원리에 근거하여 계단함수로 근사화하였다. 완전혼합영역의 과도온도를 구한 후 함수형태에 따라 구분하고, 각각을 경계조건으로 하는 압출유동영역에 대한 최종해이다. 근사해의 타당성 및 결과의 유용성은 입구온도가 선형적으로 증가하는 경우에 대한 엄밀해와의 비교를 통하여 검증하였다. 계산수의 증가에 따라 근사해는 엄밀해로 급속히 접근하며, 유한한 수의 계단에 의한 근사해도 광범위한 혼합깊이에 대하여 엄밀해와 잘 일치한다. 또한, 혼합깊이가 클수록 소수의 계단에 의한 근사해로도 의미있는 예측결과를 얻을 수 있었다. This paper presents an approximate analytical solution to one-dimensional model of the charging process for stratified thermal storage tanks, in which variation of the inlet temperature as well as the momemtum-induced mixing is taken into accout. The mixing is incorporated into the model as a constant-depth perfectly mixed layer above the plug flow region. Based on the superposition principle, the variable inlet temperature is approximated by a number of step functions. Temperature distributions for the thermocline corresponding to three types of interfacial condition are successfully derived in terms of well-defined functions, so that a linear combination of them constitutes the final solution. Validity and utility of this work is examined through the comparison of the approximate solution with an exact solution available for the case of linearly increasing inlet temperature. With increasing the number of steps, the present solution asymptotically approaches to the exact one. Even with a limited number of steps, the present results favorably agree with those by the exact solution for a wide range of the mixing depth. Also, it is revealed that fewer steps are needed for meaningful predictions as the mixing depth becomes larger.

해외 발전플랜트 EPC 사업의 리스크 분석 및 관리방안

박의승,유호선,이재헌,Park, Euiseung,Yoo, Hoseon,Lee, Jae-Heon 한국플랜트학회 2011 플랜트 저널 Vol.7 No.3

In this work, risks in EPC project for overseas power plant projects are analyzed and risk management methods are suggested to reduce cost and to shorten time. 79% of risks occurred in the engineering phase for S project located in South-East Asia. The impact scales of risks on major project objectives which are cost, time, scope, and quality are analyzed as 3.5, 3.8, 2.7, and 3.7, respectively. The level of impact scales is very similar to each other except the impact scale of scope. The risk management methods suggested in this study have to be applied at the appropriate time to manage risks effectively. After that, risks are managed continuously by monitoring.

운전기록 모니터링에 의한 발전보일러용 고압 급수가열기 내부 튜브의 파손예측

김경섭,유호선,Kim, Kyeong-seob,Yoo, Hoseon 한국플랜트학회 2019 플랜트 저널 Vol.15 No.2

본 연구에서는 500 MW급 초임계압 석탄 화력발전소의 발전보일러용 고압 급수가열기에서 발생한 내부 튜브의 파손 사례 분석을 통해 운전 기록 모니터링에 의한 발전보일러용 고압 급수가열기 내부 튜브의 파손 예측 방안을 모색하고자 하였다. 이 연구를 통해 고압 급수가열기 내부 튜브 파손 시 쉘 측 수위 조절 밸브 개도와 보일러 급수펌프 흡입 유량의 변화로 내부 튜브 파손을 진단할 수 있는 예측 모형을 제안하였고, 제안된 예측 모형은 급수 계통의 불균형이 일어난 추가 사례를 통해 실증하였다. 이에 따라 본 연구와 유사한 특성의 발전보일러용 고압 급수가열기의 경우에도 쉘 측 수위 조절 밸브 개도와 보일러 급수펌프의 흡입 유량의 정상 운전 상태 값 대비 현재 운전 값 비교는 고압 급수가열기 내부 튜브의 파손에 대한 유력한 예측 진단 방안이 될 수 있다고 판단된다. In this study, the failure analysis of the internal tube occurred in the high pressure feedwater heater for power generation boiler of 500 MW supercritical pressure coal fired power plant was investigated. I suggested a prediction model that can diagnose internal tube failure by changing the position of level control valve on the shell side and the suction flow rate of the boiler feedwater pump. The suggested prediction model is demonstrated through additional cases of feedwater system unbalance. The simultaneous comparison of the shell side level control valve position and the suction flow rate of the boiler feedwater pump compared to the normal operating state value, even in the case of the high pressure feedwater heater for the power boiler, It can be a powerful prediction diagnosis.