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김시조 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.3
It is of great importance to understand and predict Residence Time Distribution (RTD) during a singlescrew extrusion process for extruder design and operation optimization purposes. RTD depends on the extruder geometry, operating conditions, and material properties of non-Newtonian fluids. This paper presents the proper dimensionless parameters and RTD for the three-dimensional circulatory flow. These dimensionless parameters were expressed in terms of physical and geometrical parameters such as flow rate, pressure gradient along down channel direction, aspect ratio, helix angle, and power-law index. RTD computations and analysis were based on the finite element method. This dimensionless parameter study is found to be very useful for extruder designers to understand and to predict the RTD systematically.
커튼 코팅 공정에서 자동격자생성 기법을 이용한 비정상 유동 해석을 위한 유한요소법 개발
김시조 한국섬유공학회 2024 한국섬유공학회지 Vol.61 No.1
In this study, the transient curtain coating process is computationally carried out via the in-house code developed using a finite element method(FEM). Incorporating sophisticated auto-remeshing techniques, our numerical implementaion for FEM not only captures the complex flow dynamics inherent in this curtain coating process but also adapts to the rapid deformations observed at important flow zones in the curtain coating flow. The stability and accuracy of the proposed computational model have been rigorously tested againsta spectrum of flow rates, viscosities, and substrate speeds, proving its robustness and reliability. As we continue our research, we aim to further enhance these simulation algorithms identifying optimal operating conditions that could be key in ensuring consistent qualityacross materials with different rheological properties in the curtain coating process.
이상(Two-phase) 유체의 변형거동에 대한 실험적 연구
김시조,황덕철,임영빈 한국군사과학기술학회 1999 한국군사과학기술학회지 Vol.2 No.2
본 논문에서는 얇은 직사각형 단면 형상을 가지는 세 가지 서로 다른 유동로 안에서 움직이는 공기버블의 변형 거동에 대한 실험을 수행하였다. 압력 차이로 유체는 유동되며, 유동장을 따라서 변형하는 버블의 정상상태 모양을 관찰하였다. 벽면효과를 알아보기 위해 세 종류의 얇은 사각단면을 사용하였으며, 두 가지 종류의 작동 유체, 버블의 초기 크기, 작동 유체의 유량 등을 변화시켰을 때 이에 대한 공기 버블의 변형을 체계적으로 관찰하고 이들의 관계를 고찰하였다. 실험데이타를 정량화하여 캐필러리 수에 대한 버블의 무차원 속도비와의 관계를 상세하게 고찰하였다. 글리세린의 경우는 항상 버블 선단부의 곡률이 후단의 곡률보다 더 작게 나타났으며 실리콘 오일의 경우와 반대 경향이 관찰되었다. 두 경우 모두 캐필러리 수에 대한 속도비와 세장비 값은 1 보다 큰 값을 가졌다. 실리콘 오일의 경우는 주어진 Ca 수에 대하여 속도비가 글리세린의 경우보다 더 크게 나왔으며 버블 크기에 따른 속도비 분산도가 더 조밀하게 나타났다. 사각 단면 폭이 감소할수록 벽면 효과는 증대되었으며 같은 폭에 대해서는 버블 변형이 축소관의 경우가 가장 크게 나타났다.
미끄럼현상을 갖는 입자충전 플라스틱재료의 압출공정 수치해석
김시조,권태헌 대한기계학회 1994 대한기계학회논문집 Vol.18 No.10
Many particle filled materials like Poweder/Binder mixtures for poweder injection moldings, have complicated rheological behaviors such as an yield stress and slip phenomena. In the present study, numerical simulation programs via a finite element method and a finite difference method were developed for the quasi-three-dimensional flows and the two-dimensional flow models, respectively, with the slip phenomena taken into account in terms of a slip velocity. In order to qualitatively understand the slip effects, typical numerical results such as vector plots, pressure contours in the cross-channel plane, and isovelocity controus for the down-channel direction were discussed with respect to various slip coefficients. Slip velocities along the boudary surfaces were also investigated to find the effects of the slip coefficient and processing conditions on the overall flow behavior. Based on extensive numerical calculations varying the slip coefficients, pressure gradient, aspect ratio, and power law index, the screw characteristics of the extrusion process were studied in particular with comparisons between the slip model and non-slip model.
관유동에서의 이상 폴리머 혼합물의 액적 변형 특성 연구
김시조,임영빈 한국섬유공학회 2000 한국섬유공학회지 Vol.37 No.5
It is of great importance to characterize the deformation of droplets in various polymer processing. In the present paper, as a basic study, the deformation of a non-Newtonian or Newtonian droplet dispersed in a Newtonian medium in pipe flow was analyzed using the finite element method(FEM). Numerical simulations were extensively performed on this two-phase flow and the results were presented in terms of droplet size, viscosity ratio, and Ca number for both the non newtonian and Newtonian droplets. In particular, the effects of non-Newtonian droplets on deformation were intensively discussed in comparison with those of Newtonian droplets on deformation were intensively discussed in comparison with those of Newtonian droplets. The effect of non-Newtonian droplet in deformation increased with increasing Ca number, droplet size, and viscosity ratio. Moreover, non-Newtonian droplets under the assumption of the present rheological model produced smaller deformation than the corresponding Newtonian droplet(λ=2.04) for the given droplet size and Ca number.
김시조,권태헌 대한기계학회 1994 대한기계학회논문집 Vol.18 No.10
This paper suggests a simple approach to determining the screw characteristics for a three0dimensional flow in a channel with a finite aspect ratio(ratio of a width to a depth, W/H) by introducing a Total Shape Factor($F_t$) to correct a two-dimensional flow analysis for a channel with an infinite aspect ratio. In the present study, the Total Shape Factor($F_t$) was defined as a ratio of a net flow rate obtained by the three-dimensional analysis to that by the two-dimensional analysis. In the proposed approach, the quantity, $ \frac{{\partial}F_t}{\partial(H/W)}$ turns out to be almost constant and to play an important role in understanding the effects of the flights. Therefore, $ \frac{{\partial}F_t}{\partial(H/W)}$ are extensively reported in this paper in terms of several dimensionless parameters. This simple approach with such database will be very useful for extruder designers to predict the screw characteristics.
이상 폴리머 혼합물에서의 액적 변형 해석을 위한 자동격자생성기법이 포함된 유한요소법 개발
김시조 한국섬유공학회 2000 한국섬유공학회지 Vol.37 No.4
The deformation of droplets dispersed in a liquid in a cylindrical tube is of great importance to characterize the rheological behavior in the polymer processing. Research on to two phase flows employing the boundary element method (BEM) is abundant. However, in order to simulate the non-Netwonian flow of the two-phase polymeric mixture a finite element method should be employed. In this regard, numerical analysis programs were developed via the finite element method by means of the penalty function considering the interfacial valence condition of the two-phase flow. In addition, moving boundaries between the medium and the droplet were solved via the auto-remeshing technique. The present paper presents detailed numerical methods together with the auto-remeshing generation and discusses essential numerical results. The proper generation of auto-remeshing was proved to be crucial to obtain the accurate and stable numerical solutions for two-phase flows and the results obtained by our numerical methods were in good agreement with the previous results by BEM in the literature. The present work can be applicable to the study of the deformation characteristics for complex systems frequently encountered in polymer blending.