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.

Dimensionless analysis of three-dimensional residence time distribution in single-screw extrusion processes

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.

압출공정 스크류특성 결정을 위한 전체형상계수 ( A Total Shape Factor for Determining Three-Dimensional Screw Characteristics of Extrusion Processes )

김시조,권태헌 대한기계학회 1993 대한기계학회 춘추학술대회 Vol.- No.-

압출공정에서의 균일한 혼합체 제조를 위한 카오스 혼합 연구 ( 새로운 수치 사상법 개발 ) ( Study of Chaotic Mixing for Manufacturing Uniform Mixtures in Extrusion Processes ( Development of a New Numerical Mapping Method ) )

김시조,김은현 대한기계학회 1996 대한기계학회 춘추학술대회 Vol.- No.-

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.

압출공정 스크류특성 결정을 위한 전체 형상계수

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.

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.

Transient stresses of two-dimensional model droplet emulsions subjected to simple shear flow by numerical simulations

김시조,황욱렬 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.3

We investigated numerically effects of the capillary number, the droplet size and the viscosity ratio on the transient stress responses of a Newtonian droplet suspended in a Newtonian liquid in a sliding bi-periodic frame that represents a flow of two dimensional droplet emulsions in simple shear flow. Understanding the relationship between the droplet deformation and the transient stress responses such as the bulk shear stress and the first normal stress is particularly emphasized, using this computational model problem, where the rheological properties of medium and droplet fluids and flow conditions can be accurately controlled.

Two-Phase Hele-Shaw 유동의 실험과 수치비교

김시조,황덕철,임영빈 安東大學校 工業技術硏究所 1999 공업기술연구논문집 Vol.6 No.1

얇은 사각단면을 가지는 관을 통하여 움직이는 버블 변형에 대한 실험을 수행하였으며, 수치적으로 비교하였다. 유동장은 압력 구동장이며, 유동장 내부를 버블이 진행할 때 버블의 변형하는 모양과 정상상태 모양을 관찰하였다. 이러한 정상상태 버블의 모양은 기존에 보고된 모양과 일치하였고, 유동장 평균속도에 대한 정상상태의 버블 속도의 비를 계산하여 수치 계산한 값과 비교하여 정상적으로 일치함을 보였다. 특히, 긴 버블의 경우에 막 두께는 현저하게 발달하였다. 실험적으로 얻은 결과는 기존의 보고된 자료와 비교하여 실험적/수치적으로 일치함을 알 수 있었다. The study of bubble deformation through a thin channel with rectangular cross-section was experimentally performed. The motion was driven by pressure drop and then the shapes of steady and deforming bubble were observed. The results demonstrated that the shape of steady-state bubble had good agreement with that of previous reports. In addition, the average values of velocity ratio was also qualitatively agreed with other studies. It was significant that film thickness was developed, especially in the long bubble.

이상 폴리머 유동 해석을 위한 그래픽 소프트웨어의 개발

김시조,우병철 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-

The prediction of the drop deformation of a dispersed two-phase polymer blends is very important in the industrial fields, especially in the polymer processing such as injection molding and extrusion. Very recently S. J. Kim has developed FEM computer codes for this problem[3,4,5]. With this source program, a new graphic software was developed to treat the pre, solver, post processing in the PC base by using OpenGl and MFC. In solving the system equations, an unstructured mesh generator and auto-remeshing technique were used to show the deformation shapes of drops under the application program window.