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.

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.

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.

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.

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.

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.

과도 접촉융해과정에 대한 근사적 해석해

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

석탄화력발전소 이산화탄소 배출량 산정을 위한 연료분석법과 연속측정법의 특성

최현호,유호선,Choi, Hyun-Ho,Yoo, HoSeon 한국플랜트학회 2017 플랜트 저널 Vol.13 No.1

500 MW급 석탄화력발전소를 대상으로 연료분석법 및 연속측정법을 사용하여 이산화탄소 배출량을 산정하고 특성을 알아보았다. 연료분석법은 산정방법 중 배출량이 가장 낮게 산정되는 것을 확인하였다. 이는 순발열량이 낮게 분석되기 때문으로 저열량탄을 사용하는 경우 연료분석법을 활용하는 것이 유리하다. 또한 입하탄 보다 소비탄을 시료로 사용하였을 때 배출량이 낮게 산정되는 특성을 보인다. 하지만 차이는 2% 미만으로 미미하여, 분석 인력 및 장비가 한정된 현 여건에서는 입하탄을 연료분석에 사용하여도 적정하다고 판단된다. 연속측정법은 연료분석법 대비 배출량이 다소 높게 산정되지만 국내외 제시된 배출계수를 사용한 산정량보다 낮게 산정된다. 따라서 석탄 탄종 변화로 연료분석법에 의한 산정량이 증가할 경우, 유량 측정방법을 보완하여 사용한다면 배출량 산정 시 유리할 것이다. This study calculates carbon dioxide emissions using the fuel analysis and the continuous measurement from 500 MW-class coal-fired power plants and evaluates the characteristics of each method. The emissions calculation using fuel analysis was the lowest calculation among the emissions calculation methods. This is because of low net calorific value analysis. When using the low calorific coals, it is beneficial to utilize the fuel analysis. Also it showed the characteristics of the lower calculation emissions when used the as fired coals than the as received coals. However, the difference is negligible to less than 2%. As sample analysis personnel and equipment are limited in the present circumstances, it is also deemed appropriate to use the as received coals to fuel analysis. Continuous measurement showed somewhat higher emissions than the fuel analysis, and lower emissions than calculation method using domestic emission factors. Thus, if the calculated emission using fuel analysis increases with the coal type changes, it is beneficial to using modified flow rate measurement method.

수평형 HRSG의 탈질설비에서 암모니아 분사위치 변동에 따른 암모니아 유량비교

박재현,유호선,Park, Jae-Hyun,Yoo, Hoseon 한국플랜트학회 2018 플랜트 저널 Vol.14 No.4

발전설비에서의 질소산화물 배출 규제치가 강화됨에 따라 1990년대에 설치된 HRSG도 탈질설비를 추가로 설치해야 하는 상황이 되었다. 그러나 HRSG 내부에 촉매와 암모니아 분사장치 모두를 설치할 수 있는 공간이 없기 때문에 그 대안으로써 HRSG 내부에는 촉매만 설치하고 암모니아 분사장치는 가스터빈 배기덕트로 변동하여 설치하는 것을 검토하였다. 본 연구에서는 인천복합발전소를 대상으로, 암모니아 분사장치를 HRSG 중압 과열기 후단과 가스터빈 배기덕트에 설치하여 암모니아를 분사였을 때 대기 배출기준 8.5 ppm을 만족하는 암모니아 소비량을 각각 측정하였다. 연구결과 가스터빈 배기덕트 암모니아 분사방식이 HRSG 중압 과열기 후단 분사방식에 비해 소비량이 1.2배 정도 증가한 것으로 나타났다. 따라서 HRSG 수명 30년 운영을 고려한다면 HRSG 내부에 암모니아 분사장치를 설치할 수 없는 경우 가스터빈 배기덕트에 암모니아 분사장치를 설치하는 것이 추천된다. As the emission limits for NOx in power generation facilities were strengthened, HRSGs installed in the 1990s became necessary to install additional DeNOx system. However, since there is no space in the HRSG for installing the entire the catalyst and ammonia injection grid, as an alternative, the catalyst was installed inside of the HRSG and the ammonia injection device was installed in the exhaust duct of the gas turbine. Experiments were conducted in horizontal HRSG of Incheon combined cycle power plant. Experimental results show that the ammonia injection method in the gas turbine exhaust duct is 1.2 times higher than the HRSG internal ammonia injection method. However when operating a HRSG for 30 years as its life span, ammonia injection method in the gas turbine exhaust duct is more economical than the cost of new HRSG construction.