성층 온수 저장 중 과도 열거동과 축열효율에 관한 연구

박이동(E.T.Pak),주영진(Y.J.Chu),김영헌(Y.H.Kim) 한국태양에너지학회 1997 한국태양에너지학회 논문집 Vol.17 No.3

장기 성층 온수 저장조 내의 중간 경계면에서 전달되는 열량을 예측하기 위하여 이론식을 유도 확립하고 이론적인 축열효율을 구하였다.<br/> 그리고 이론 축열효율값과 비교 고찰하기 위하여 여러 실험 조건을 통한 실제 축열효율을 구하였고, 저장조 내의 중간 경계면에서 일어나는 혼합정도를 효과적으로 해석하기 위하여 유효 열확산 계수를 정량화하였다.<br/> 중간 경계면에서 열전도에 의한 손실이 일회 충수 시간이 짧을수록 즉, Pe 수가 증가할 수록 많이 발생함을 알았다. In this study, the theoretical equation of thermal storage efficiency was established to applied long term hot water storage system.<br/> The effective thermal diffusivity and storage efficiency were measured through the experiment to predict the degree of mixture in thermal storage tank.<br/> The effective thermal diffusivity was inversely preportional to the storage efficiency. The most effective storage efficiency was obtained under condition of low flow rate and using the perforated distributor.

에너지 절약을 위한 벽체형 열다이오드 개발에 관한 기초

박이동(E.T.Pak),장영근(Y.G.Chang),최성식(S.S.Chea) 한국태양에너지학회 1997 한국태양에너지학회 논문집 Vol.17 No.3

공기도 열전도 계수가 낮으므로 밀폐공간 내에서 적당한 형태를 형성하여 자연대류 열전달을 촉진 시킨다면 태양열 집열기로서 건물 난방에 이용할 수 있고, 또 자연대류가 일어나지 않도록 유동을 억제 시킨다면 매우 훌륭한 단열재로 사용할 수 있다. 따라서, 본 연구에서는 건물벽 구조에 따라 내·외벽 사이에 단순 사각 밀폐공간을 형성하여 외벽의 가열부와 내벽의 방열부의 위치를 변화시켜 가며 수치해석을 수행하여 최대 난방 및 단열효과를 얻을 수 있는 새로운 대체 건물벽 개발에 관한 기초 설계 자료를 제시하고자 한다.<br/> 연구 결과 부력에 의한 driving force를 얻기 위해서는 방열부가 가열부보다 항상 위쪽에 위치하고 크기는 전체 높이의 1/2 이하일 때 열전달이 촉진됨을 알았다. In order to development of a new wall structure type thermal diode for energy saving, the numererical studies have been performed for natural convection across a rectangular enclosure with the various lengthes of the heat source and sink plate.<br/> The governing equations for the two-dimensional, laminar, natural convection process in an enclosure are discretized by the control volume approach which insures the conservative characteristics to be satisfied in the calculation domain, and solved by a elliptic SIMPLE algorithm The momentum and energy equations are coupled through the buoyancy term.

응답계수(應答係數)를 이용(利用)한 건물벽에서의 열부하(熱負荷) 계산(計算)

황영규,박이동,Hwang, Y.K.,Pak, E.T. 대한설비공학회 1988 설비저널 Vol.17 No.4

An application of thermal response coefficient method for obtaining thermal load on stud-frame walls in a typical house is presented. A set of stud-frame walls is two-dimensional heat conduction transients with composite structure. The ambient temperature on the right-hand face of the stud-frame walls is a typical day-cycle input and the room temperature on the left-hand face is a constant input. The desired output is thermal load at the left-hand face. The time-dependent ambient temperature is approximated by a continuous, piecewise-linear function each having one hour interval. The conduction problem is spatially discretized as 8 computer modelings by finite elements to obtain thermal response coefficients. The discretization and round-off errors can be neglected in the range of adequate number of nodes. A 60-node discretization is recommended as the optimum model among 8 computer modelings. Several sets of response coefficients of the stud-frame walls are generated by which the rate of heat transfer through the walls or some temperature in the walls can be calculated for different input histories.

성층화된 축열조의 1차원모델에 대한 해석적인 해

유호선,박이동,Yoo, H.,Pak, E.-T. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.1

In order to establish a theoretical basis for the analyses of transient behaviors in stratified thermal storage tanks, analytical approaches to an improved one-dimensional model are made. In the present model the storage tank is treated as a finite region with an adiabatic tank exit, whereas it has been considered as a simple semi-infinite region previously. Application of the Laplace transformation and the Inversion theorem to the governing equations makes it possible to obtain an exact infinite-series solution, which is convergent only at sufficiently large time. Accordingly a complementary solution which is available for short times, i.e., the time range of this study is sought by an approximate method. The approximate solution which is rigorously validated through the examination of neglected terms in the solution procedure agrees quite well with the exact one. Moreover, it is simpler to use and more convenient to interpret the physical meaning of the solution. Comparison of the present solution with the previous ones shows relatively large difference near the tank bottom, which results from the more realistic boundary condition adopted in the present model. Some representative results by the approximate solution including effects of the Peclet number on temperature distrbutions are illustrated to show the utility of this study. In consequence, it is expected that the present results based on the improved model replace the foregoing ones as a new theoretical reference for studies of thermal stratification fields.

완전혼합영역을 갖는 성층축열조의 충전과정에 대한 이론적인 해석

유호선,박이동,Yoo, H.,Pak, E.T. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.2

A theoretical one-dimensional model for the charging process in stratified thermal storage tanks is established presuming that the fluid ensuing from the tank inlet creates a perfectly mixed, layer above the thermocline. Both the generic and asymptotic closed-form solutions are obtained via the Laplace transformation. The asymptotic solution describes the nature of the charging pertaining to the case of no thermal diffusion, whereas the generic solution is of practical importance to understand the role of operating parameters on the stratification. The present model is validated through comparison with available experimental data, where they agree well with each other within a reasonable limit. An interpretation of the exact solution entails two important features associated with the charging process. The first is that an in-crease in the mixing depth $h_m$ causes a relatively slow temperature rise in the perfectly mixed region, but on the other hand it results in a faster decay of the overall temperature gradient across the thermocline. Next is the predominance of the mixing depth in the presence of the prefectly mixed region. In such a case the effect of the Peclet number is marginal and there-fore the thermal characteristics are solely dependent on the mixing depth paticularly for large $h_m$. The Peclet number affects significantly only for the case without mixing. Variation of the storage efficiency in response to the change in the mass flow rate agrees favorably with the published experimental results, which confirms the utility of the present study.

Ice Ball형 빙축열조에서 Brine의 유동방향에 따른 축열, 방열 특성의 실험적 연구

허은(E. Heo),박이동(E. T. Pak),김철주(C. J. Kim),조금남(K. N. Cho) 대한설비공학회 1995 대한설비공학회 학술발표대회논문집 Vol.1995 No.11

온수 저장조 내 유동 특성과 온수 추출에 관한 연구

조운(W.Cho),박이동(E.T.Pak),황영규(Y.K.Hwang) 대한설비공학회 1993 대한설비공학회 강연회 및 기타간행물 Vol.- No.-

원심형 회전차내의 난류유동에 관한 수치해석적 연구

강보경(B.K.Kang),박이동(E.T.Pak),김철주(C.J.Kim),황영규(Y.K.Hwang) 대한설비공학회 1995 대한설비공학회 학술발표대회논문집 Vol.1995 No.11

축열시스템의 온수이용 예측에 관한 연구

조운(W.Cho),박이동(E.T.Pak) 한국태양에너지학회 1998 한국태양에너지학회 논문집 Vol.18 No.3

실내 유입 냉기의 열류동 특성에 관한 실험적 연구

장영근(Y.G.Jang),박정원(J.W.Pak),박이동(E.T.Pak) 한국태양에너지학회 1998 한국태양에너지학회 논문집 Vol.18 No.1

쾌적한 실내환경을 유지하고, 공기조화 설비에 있어서 냉방동안 에너지를 절약하기 위한 실내로 유입되는 냉기의 열유동 특성에 관한 연구이다. 실물 크기의 모형room에 대하여 실내로 유입하는 냉기의 유속(1,2,3 m/s)과 실내온도와 유입냉기와의 기준온도차(10,20,30℃)를 변화시키고, 또한 유입구 형상을 아네모스형과 베인형으로 하면서 실내의 온도분포를 파악하여 열유동 특성 및 혼합특성에 대하여 고찰하였다.<br/> 연구 결과, 아네모스형이 베인형보다 혼합이 빨리 진행되었고 유입속도에 의한 영향이 기준온도차에 의한 영향보다 지배적이었다. A study on a buoyancy effect by the temperature difference between a inner room air and a inflowing cool air and also by inlet velocity can contribute greatly to enhance performance of air conditioning system, so the study on the distribution characteristics of inflowed cool air is important to analyze the cool air storage in a room.<br/> For this study, in the real-sized model room, the temperature differences between inflowing cool air and inner room air are 10, 20, 30°C, and the inlet velocities of inflowing cool air are 1, 2, 3m/s respectively as dynamic parameters. Also, an anemos and a vane type diffuser are used as inlet geometric conditions.<br/> Following conclusions have been obtained through this study.<br/> I) In case of the anemos type diffuser, it is found that a dimensionless temperature profile is low and the distribution of the inflowed cool air is uniform and also, all diffuusers have a low temperature of the inner room as increasing the inlet velocity.<br/> 2) A mixing takes place rapidly in case of the anemos type diffuser when the temperature difference is low ??T=l0°C and the inletvelocity is high V= 3m/s. and the mixing degree is higher with the anemos type diffuser than the vane.