급개시 전단유동장에서 천연 다당류 잔탄검 농후용액의 과도적 레올러지 거동 : Wagner 구성방정식을 사용한 응력도약현상 예측 (Transient Rheological Behavior of Natural Polysaccharide Concentrated Xanthan Gum Solutions in Start-up Shear Flow Fields : Prediction of a Stress Overshoot Phenomenon Using the Wagner Constitutive Eq)

서지정보

· 발행기관 : 한국섬유공학회
· 수록지 정보 : 한국섬유공학회지 / 56권 / 6호 / 386 ~ 401페이지
· 저자명 : 안혜진, 최근석, 김용석, 송기원

초록

The present study has been designed to theoretically predict the transientrheological behavior of concentrated xanthan gum systems in start-up shear flow fieldsusing the Wagner constitutive equation. Using an Advanced Rheometric Expansion System(ARES), a number of constant shear rates were suddenly imposed to aqueous xanthan gumsolutions with different concentrations and then the resultant shear stress responses weredetected with time. The linear and nonlinear stress relaxation moduli at various deformationmagnitudes were also measured to determine the damping function. The linear relaxationmodulus was characterized by a power-law expression to determine the memory functionand a time-strain separability of the nonlinear relaxation moduli was employed to predictthe nonlinear response. The experimentally obtained damping function was compared withthe fitted results calculated from the two mathematical forms of the Wagner and Soskey-Winter equations in order to examine the effect of damping function on the predictiveperformance of the Wagner model. The overall applicability of the Wagner model forpredicting the whole procedures of a transient rheological behavior at start-up of steadyshear flow was discussed in depth. The main findings obtained from this study aresummarized as follows : (1) The Wagner model has a predictive ability to qualitativelyexpress the whole procedures of a transient rheological behavior of concentrated xanthangum solutions for all shear rates imposed, regardless of selecting a damping function. (2)The values of the maximum reduced stress predicted by the Wagner model employing theWagner damping function exhibit an almost equal magnitude, irrespective of the shearrates imposed, whereas those predicted by the Wagner model employing the Soskey-Winter damping function are gradually decreased with an increase in imposed shear rate.
(3) For all shear rates applied, the Wagner model having the Wagner damping function hasa fairly good ability to predict the time at which the maximum stress occurs, tmax, while theWagner model having the Soskey-Winter damping function predicts a much faster value oftmax. (4) The Wagner model using both of the Wagner and Soskey-Winter damping functionshas a weakness with respect to predicting a stress decay which always show a slowerdecrement than does the predicted results by the Wagner model using the two differentforms of a damping function. (5) The Wagner model adopting the Wagner dampingfunction exhibits a superior performance to the Wagner model adopting the Soskey-Winterdamping function for predicting the whole steps of a transient rheological behavior.

영어초록

The present study has been designed to theoretically predict the transientrheological behavior of concentrated xanthan gum systems in start-up shear flow fieldsusing the Wagner constitutive equation. Using an Advanced Rheometric Expansion System(ARES), a number of constant shear rates were suddenly imposed to aqueous xanthan gumsolutions with different concentrations and then the resultant shear stress responses weredetected with time. The linear and nonlinear stress relaxation moduli at various deformationmagnitudes were also measured to determine the damping function. The linear relaxationmodulus was characterized by a power-law expression to determine the memory functionand a time-strain separability of the nonlinear relaxation moduli was employed to predictthe nonlinear response. The experimentally obtained damping function was compared withthe fitted results calculated from the two mathematical forms of the Wagner and Soskey-Winter equations in order to examine the effect of damping function on the predictiveperformance of the Wagner model. The overall applicability of the Wagner model forpredicting the whole procedures of a transient rheological behavior at start-up of steadyshear flow was discussed in depth. The main findings obtained from this study aresummarized as follows : (1) The Wagner model has a predictive ability to qualitativelyexpress the whole procedures of a transient rheological behavior of concentrated xanthangum solutions for all shear rates imposed, regardless of selecting a damping function. (2)The values of the maximum reduced stress predicted by the Wagner model employing theWagner damping function exhibit an almost equal magnitude, irrespective of the shearrates imposed, whereas those predicted by the Wagner model employing the Soskey-Winter damping function are gradually decreased with an increase in imposed shear rate.
(3) For all shear rates applied, the Wagner model having the Wagner damping function hasa fairly good ability to predict the time at which the maximum stress occurs, tmax, while theWagner model having the Soskey-Winter damping function predicts a much faster value oftmax. (4) The Wagner model using both of the Wagner and Soskey-Winter damping functionshas a weakness with respect to predicting a stress decay which always show a slowerdecrement than does the predicted results by the Wagner model using the two differentforms of a damping function. (5) The Wagner model adopting the Wagner dampingfunction exhibits a superior performance to the Wagner model adopting the Soskey-Winterdamping function for predicting the whole steps of a transient rheological behavior.

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