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뉴튼유체 및 비뉴튼 유체중에서의 섬유집단의 운동특성에 관한 연구 -정지상태의 수중 및 고분자 유체중에서의 연속낙하거동 비교-
송기원,Song, Ki-Won 한국섬유공학회 1996 한국섬유공학회지 Vol.33 No.7
In order to clarify the motion of fibers in Newtonian and non-Newtonian fluids, the free falling behavior of a group of cylindrical slender bodies was experimentally investigated in stationary water and polymeric fluids by means of continuous photographing technique using a motor drive-equipped camera, and an analysis method was developed to evaluate the actual motion of the slender bodies. In this paper, interferential effect between the bodies on the falling behavior was reported in detail. Furthermore, the difference between the motion in Newtonian and non-Newtonian fluids was interpreted by comparing the results in water and polymeric fluids. Main findings obtained from this study can be summarized as follows : (1) In whatever fluid, water or polymeric fluids, the slender bodies perform an interferential motion with changing momentarily their mutual attitudes. (2) In water, no slender body behaves independently free from the interference of other bodies, and the pattern approaching to a horizontal direction with damped oscillation takes place frequently. (3) In polymeric fluids, most of the slender bodies show an independent falling behavior at the beginning of their motion. However, the degree of interference between the bodies becomes greatly increased as the motion is continued. (4) In the more concentrated polymer solutions, interferential effect decreases because the flow region occurring due to the motion of the slender bodies becomes smaller.
폴리에틸렌옥사이드 수용액의 유변학적 특성 평가(I) -대진폭 진동 전단 변형하에서의 선형 점탄성 응답한계 및 비선형 거동-
송기원,장갑식,김철범,이장우,백종승 한국섬유공학회 1996 한국섬유공학회지 Vol.33 No.12
Using a Rheometrics Fluids Spectrometer, the nonlinear viscoelastic behavior of aquaous poly(ethylene oxide)(PEO) solutions with large amplitude oscillatory shear deformation has been investigated by analyzing the strain amplitude dependence of the storage modulus and dynamic viscosity. In this paper, the strain limits of linear viscoelastic response were determined and the effect of angular frequency on these values was examined. The behavior of the storage modulus and dynamic viscosity with increasing strain amplitude waIn also compared in nonlinear viscoelastic region. Further, the nonlinear behavior was interpreted by introducing the nonlinear viscoelastic functions derived from the Fourier expansion of the stress wave. Finally, the nonlinear behavior indices were defined and the effect of angular frequency on these values was discussed. Main results obtained from this study can be summarized as follows : (1) The storage medulus has a much stronger dependence on the strain amplitude and begins to show a nonlinear behavior at a smaller strain amplitude range than does the dynamic viscosity. (2) The strain limits of linear response of the storage modulus and dynamic viscosity are ${\gamma}$$_{EL}$ = 40~50% and ${\gamma}$$_{VL}$ = 80~100%, respectively. These values increase with decreasing angular frequency at frequency range lower than the inverse of the characteristic time. (3) The nonlinear behavior takes place at strain amplitude range larger than the limits of linear response, where the higher harmonic terms of the nonlinear viscoelastic functions show an obvious effect. (4) The nonlinear behavior indices have the maximum values at a specific angular frequency, and the elastic behavior shows more remarkable dependence on the angular frequency than does the viscous behavior.
정지상태의 비뉴튼 점탄성유체중을 자유낙하하는 원통형 섬유의 운동특성(II) -낙하특성에 미치는 초기회전각, 유체 유동특성 및 섬유 밀도의 영향-
송기원,김태헌 한국섬유공학회 1995 한국섬유공학회지 Vol.32 No.9
In order to clarify the influence of various factors on the motion of a fiber in non-Newtonian viscoelastic fluids, the free frilling behavior of a cylindrical slender body has been experimentally investigated in stationary polymer solutions. In this paper, experimental results on the effects of initial angle, fluid flow property, and body density on the frilling trajectory, horizontal and vertical velocities, and variation of attitude off slender body were reported in detail. Furthermore, the hydrodynamic mechanism of the results was discussed by considering the rheological properties of polymer solutions and introducing a quid boundary layer theory. Main findings obtained firm this study can be summarized as follows (1) The initial angle inonces the flee frilling behavior of a slender body only in the small region where the body starts its motion. Beyond this region the motion of a body is independent of the initial use. (2) Both the horizontal and vertical velocities of a body become smaller for the more concentrated polymer solutions. In addition, the final orientation angle of a body becomes closer to vertical direction as the solution concentration increases. (3) With increasing the body density, translational velocities of a body become larger but the final orientation an인e remains unchanged. (4) Falling behavior of a slender body can be inteivreted by a new mechanism introducing the competition between inertia and viscoelastic effects as well as a supercritical flow theory around a body.
폴리에틸렌옥사이드 수용액의 유변학적 특성 평가(II)-정상류점도와 동적점도, 복소점도의 상관관계-
송기원,장갑식,김철범,이장우,백종승 한국섬유공학회 1998 한국섬유공학회지 Vol.35 No.8
Using a Rheometrics Fluids Spectrometer (RFS II), the steady shear flow viscosity and dynamic viscoelastic properties of aqueous poly(ethylene oxide) (PEO) solutions have been measured over a wide range of shear rate and angular frequency. In this paper, the relationship between the steady flow viscosity and dynamic viscosity was investigated, and the property of a conversion factor was determined from the data. Further, the validity of the Cox-Merz rule was examined by comparing the steady flow viscosity and the magnitude of the complex viscosity. The influence of a coil overlap parameter on the applicability of the Cox-Merz rule was discussed finally. Main results obtained from this study can be summarized as follows : (1) At higher range of shear rate and angular frequency, tile dynamic viscosity decreases more rapidly than does the steady flow viscosity. A conversion factor between the steady flow viscosity and dynamic viscosity increases with increasing shear rate and angular frequency (2) At relatively lower polymer concentration, the steady flow viscosity is higher than the complex viscosity, which is reversed at highly concentrated solutions. (3) A coil overlap parameter has an effect on the validity of the Cox-Merz rule. Especially, the use of a coil overlap parameter including the molecular weight distribution can be regarded as an effective method to evaluate the Cox-Merz rule for all kinds of linear polymer solutions.
폴리에틸렌옥사이드 수용액의 유변학적 특성 평가(IV) -일단계 대변형하에서의 비선형 응력완화거동-
송기원,예상호,장갑식 한국섬유공학회 1999 한국섬유공학회지 Vol.36 No.5
In order to investigate the nonlinear stress relaxation behavior of viscoelastic polymer liquids at large shear deformations, the relaxation modulus G(t, r) of concentrated aqueous poly(ethylene oxide) (PEO) solutions has been measured with a Rheometrics Fluids Spectrometer (RFS II) over a wide range of shear strain magnitudes. The strain dependence of G(t, r) at various molecular weights and concentrations was reported in detail, and the result was interpreted using the Doi-Edwards theory. In addition, the time-strain separability (or factorability) of the nonlinear relaxation behavior was examined by superposing the G(t, r) curve on the linear relaxation modulus G(t) surve through a simple vertical shift. The experimentally determined damping function h(r) was compared with the results calculated from some empirical equations proposed by earlier researchers, and finally the effects of molecular weight and concentration on h(r) were discussed. Main results obtained from this study can be summarized as follows : (1) The G(t, r) curve at small range of strain magnitudes shows a linear relaxation behavior, which is independent of the deformation magnitude. As the strain magnitude is increased, however, the G(t, r) curve deviates from the linear relaxation behavior and falls successively below the G(t) curve. (2) When sufficiently large strain magnitude is imposed on the highly concentrated solutions polymer of high molecular weight, the G(t, r) curve shows a more complex shape having the two inflection points. This behavior is due to the occurrence of a new relaxation process, and can be accounted for by the retraction process of primitive polymer chains in the tube, as predicted by the Doi-Edwards theory. (3) The G(t, r) is separable (or factorable) into a time-dependent function G(t) and a strain-dependent function h(r) when the time region is longer than the experimentally determined material time constant ${\lambda}_{k}$. The ${\lambda}_{k}$ increases with increasing molecular weight and concentration. (4) The empiricisms proposed by Wagner and Osaki cannot provide an adequate description to predict the nonlinear relaxation behavior. In contrast, both the Zapas and Soskey-Winter relationships are in excellent agreement with the experimentally determined h(r). The h(r) shows a stronger dependence on the strain magnitude with increasing molecular weight and concentration.