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Time-Dependent Optimal Heater Control Using Analytic and Numerical Methods
Yun-De Shen,Zhen-Zhe Li,Dong-Ji Xuan,Kwang-Su Heo,Seoung-Yun Seol 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.1
Thermoforming is one of the most versatile and economical processes to produce polymer products. The drawback of thermoforming is difficult to control thickness of final products. Temperature distribution affects the thickness distribution of final products, but temperature difference between surface and center of the sheet is difficult to be decreased because of low thermal conductivity of ABS material. In the first step, it was found out that timedependent variation of heat affects to the temperature difference between surface and center. An analytic solution was studied because the optimization time is remarkably large when optimal design is directly carried out using the analysis code developed in a previous study. Duhamel’s Theorem was used in order to solve a one-dimensional heat conduction with a time-dependent boundary condition when neglecting the effect of natural convection, but the analytic solution was difficult to be applied when the boundary condition is complicate or noncontinuous. In the following step, an optimal heating profile expressed by exponential function was recommended from 8 simple optimal cases using Duhamel’s Theorem, but the analysis results show that the effect of natural convection must be considered under the condition of setting the heat fluxes as suitable values. In order to consider the effect of natural convection with suitable heat inputs, Finite Difference Method was used. Through investigation, the optimal results using Finite Difference Method show that the temperature difference between surface and center of the sheet can be remarkably minimized with satisfying Temperature of Forming Window.
설승윤,Seol, Seoung-Yun 한국초전도저온공학회 2000 한국초전도저온공학회논문지 Vol.2 No.2
The stability of variable cross-sectional area HTS current lead is considered. The cross-sectional area is varied to have a constant safety factor which is defined as the ratio of operating current and critical current of superconductor. As the constant area HTS lead, the variable cross-sectional area HTS lead also has three steady states above the bifurcation point and only one steady state below the bifurcation point. The temperature profiles and current sharing ratios for each steady state are calculated. The heat dissipation into cryogenic system for super-conducting, intermediate, and upper states are compared. For Bi-2333 sheathed with silver-gold alloy 2m length of current lead, and the maximum temperature of upper state seems to be burn-out free below 5m length.
사이클론 집진기의 벽면구배에 따른 압력손실과 컷 사이즈 변화 예측 모델 개발
허광수(Heo Kwang-Su),설승윤(Seol Seoung-Yun) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
In previous studies, Convex cyclone are proposed to reduce pressure loss which are design cyclone wall with a single continuous curve. Studies about a prediction model for pressure loss and cut-size has focused on conventional cylinder-on-con cyclone. Therefore, the models do not perform well for uncommon design. In this study, a predict model for pressure loss and cut-size depend on cyclone wall curvature are developed. The tangential velocity below vortex-finder is obtained with consideration about friction area and momentum loss on the cyclone wall, and with this the variation of vortex-core and core velocity is obtained. Pressure loss is predicted using a Rankine vortex hypothesis. The prediction results are well agreed with experiments and CFD results.
연속적인 곡선으로 정의 되는 볼록한 형상의 사이클론에 대한 연구
허광수(Heo Kwang-Su),설승윤(Seol Seoung-Yun),리진철(Li Zhen-Zhe) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
A cyclone design concept named Convex cyclone was developed to reduce pressure losses. Contrary to conventional cylinder-on-con type cyclone, inner wall of Convex cyclone are defined with a continuous curve and it has convex shape body. The discontinuity of inner diameter variation rate of cylinder-on-con type cyclone cause additional pressure loss. Continuous wall of Convex cyclone prevent additional pressure loss. In order to verify Convex cyclone design concept, we make a comparative experiments between Stairmand HE and Convex cyclone. Experimental Convex cyclone designed based on Stairmand HE model, and inner wall are defined with circular arch. The experimental result clearly shows that Convex cyclone can achieve maximum 50% pressure loss reduction with a few percent of collection efficiency drop. In addition, the experimental results indicated the existence of optimum convexity, minimum pressure loss, of cyclone wall.
사이클론 집진기의 벽면 구배에 따른 압력손실과 등급집진효율에 대한 수치적 연구
허광수(Heo Kwang-Su),설승윤(Seol Seoung-Yun) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
A pressure loss and dust collection performance of a cyclone dust separator have a relationship that trade off each other. Therefore, the design of the cyclone dust separator is a process in a quest for reasonable balance between collection efficiency and pressure loss. A number of theories about collection efficiency and pressure drop are introduced. However, those theories do not complete enough to be used to find an optimal design for a given operation condition directly. Therefore, there is a wide range of cyclone geometries in use, studies on new cyclone geometry are conducted lively. Our previous experiments show that the Convex cyclones are very effective for pressure loss reduction. The body of Convex cyclones are designed with single continuous curve and convex shape as a substitute for cylinder-on-cone geometry. In this study, we perform CFD simulation for a in-depth comprehension about flow pattern and particle behaviour of Convex cyclone.
Time-dependent Optimal Heater Control in Thermoforming Preheating Using Dual Optimization Steps
Li, Zhen-Zhe,Heo, Kwang-Su,Seol, Seoung-Yun Korean Society for Precision Engineering 2008 International Journal of Precision Engineering and Vol.9 No.4
Thermoforming is one of the most versatile and economical processes available for shaping polymer products, but obtaining a uniform thickness of the final product using this method is difficult. Heater power adjustment is very important because the thickness distribution depends strongly on the distribution of the sheet temperature. In this paper, the steady-state optimum distribution of heater power is first ascertained by a numerical optimization to obtain a uniform sheet temperature. The time-dependent optimal heater input is then determined to decrease the temperature difference through the direction of the thickness using the response surface method and the D-optimal method. The optimal results show that the time-dependent optimum heater power distribution gives an acceptable uniform sheet temperature in the forming temperature range by the end of the heating process.
등급집진효율 곡선의 기울기가 2단 사이클론의 집진효율에 미치는 영향
허광수(Heo Kwang Su),설승윤(Seol Seoung-Yun),김민하(Kim Min Ha) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
A collection efficiency of cyclone is influenced by cut-size and slope of grade efficiency curve. It has been recognized that the collection efficiency is improved when the cut-size is reduced. However, effects of the slope have never been studied so far. In this study, we analyze a relationship between slope of grade efficiency and collection efficiency in two-stage cyclones. In single stage cyclones, higher slope cyclones have high efficiency. On the contrary to single stage cyclone, collection efficiency of two-stage cyclone have the maximum value when the first cyclone has a lower slope and second cyclone is high.
코어유동모델과 익형이론을 이용한 사이클론 동압회복 기구의 설계
허광수(Heo Kwang-Su),설승윤(Seol Seoung-Yun) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.9
Pressure loss of cyclone consists of cyclone body friction loss and dynamic pressure loss of vortex finder which hold most of cyclone pressure loss. The pressure recovery vane or rectifier is generally used mechanism to convert rotational flow in vortex finder into axial flow. Conventional circular arc rectifier has no theoretical design guide line and depends on trial error. In this paper, we propose a theoretical design method of pressure recovery vane to reduce pressure loss in cyclone vortex finder. Core flow model is used to decide the angle of attack and width of vane. Theory shows that there exists an effective width of vane. The shape of pressure recovery vane is borrowed from the static blade of axial blower using NACA airfoil data. The design method of axial blower static blade provides theoretical guide line that can decide number of vane and stagger angle.