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Xiang Lin, Jiong Liu, Changqing Wu, Mengmeng Wu, Dongyun Ren, Jun Zhang
Experimental evaluation of the pressure sensitivity of molten polymer viscosity with a triple-stage capillary rheometer

Appl. Rheol. 28:2 (2018) 25503 (8 pages)

A triple pressure-stage capillary rheometer was individually developed for providing an insight of pressure effect on polymeric melts viscosity during steady and continuous flow. Three capillary dies with identical/varied diameters and aspect ratio were assembled in series along the flow direction, relying on which the flow was divided into three zones with varied pressures under the same flow rate. Several polymeric melts, such as low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP) as well as its nanocomposites of PP/CaCO3, PP/Mg(OH)2, and PP/ halloysite nanotubes (PP/HNTs) were taken as the experimental samples. The principles for calculating the pressure sensitivity of shear viscosity in capillary flow were discussed, including methods based on constant shear rate (CSR), constant shear stress (CSS), and curve superposition (CSP). For the several polymer melts adopted in this work, a sequence of pressure dependence of viscosity was revealed as PS > PP > LDPE, which is typically acknowledged.

Cite this publication as follows:
Lin X, Liu J, Wu C, Wu M, Ren D, Zhang J: Experimental evaluation of the pressure sensitivity of molten polymer viscosity with a triple-stage capillary rheometer, Appl. Rheol. 28 (2018) 25503.

Jingsi Zhang, Simon J Haward, Zhigen Wu, Xiaohu Dai, Wenquan Tao, Zhuo Li
Evolution of Rheological Characteristics of High-solid Municipal Sludge during Anaerobic Digestion

Appl. Rheol. 26:3 (2016) 32973 (10 pages)

Rheological characterization of high-solid sludge is a fundamental requirement for optimizing the mixing and transport of high-solid sludge during anaerobic digestion in waste water treatment systems. We investigate the time evolution of physicochemical properties and rheological characteristics of high-solid digested sludge with total solids (TS) 15−20 wt.% during anaerobic digestion. A series of experiments are carried out over a period of 26 days during the operation of an anaerobic sequencing batch reactor. In equilibrium flow curves, high-solid digested sludge exhibits shear thinning behavior with a yield stress. Strong viscoelastic behavior is exhibited in the linear and non-linear regimes in dynamic and creep tests. A critical shear stress is found in the equilibrium flow curve, which accounts for the viscoelastic property. To accurately model the flow curves, a piecewise Herschel-Bulkley function separated by the corresponding critical shear rate is proposed. The digestion time plays an important role in determining the rheological behavior. Longer digestion times lead to a decreased yield stress in creep tests, and a decreased viscosity and a reduced critical shear stress in the steady flow curve. In addition, the storage modulus G' and the loss modulus G'' are reduced as digestion proceeds, leading to a shorter linear viscoelastic regime. Moreover, we find that the storage modulus G' varies linearly with the concentration of total organic matter in the sludge, suggesting that G' could be used as a new control parameter for monitoring of the anaerobic digestion process.

Cite this publication as follows:
Zhang J, Haward SJ, Wu Z, Dai X, Tao W, Li Z: Evolution of Rheological Characteristics of High-solid Municipal Sludge during Anaerobic Digestion, Appl. Rheol. 26 (2016) 32973.

Jinjun Zhang, Liping Guo, Houxing Teng
Evaluation of thixotropic models for waxy crude oils based on shear stress decay at constant shear rates

Appl. Rheol. 20:5 (2010) 53944 (7 pages)

Thixotropy is an important rheological behavior of waxy crude oils. The objective of this paper is to demonstrate existing model's abilities to describe shear stress decay behaviors of waxy crude oils at constant shear rates. Seven models specially developed for or currently used to waxy crude oils are reviewed as well as two viscoelastic-thixotropic models for human blood. Stress decay behaviors were measured for four waxy crude oils and at various temperatures. Each of the models was used to fit the stress decay plots at a single shear rate, and at multiple shear rates, respectively. Globally, Zhao's model, a complex viscoplatic model with two structure parameters and twelve physical & fitting parameters,matched the experimental plots better than other compared models. While the three models with viscoelastic backgrounds were not quite successful. For use of models, one may make choice by comprehensively considering a model's complexity in mathematic form and abilities to describe the rheological behaviors.

Cite this publication as follows:
Zhang J, Guo L, Teng H: Evaluation of thixotropic models for waxy crude oils based on shear stress decay at constant shear rates, Appl. Rheol. 20 (2010) 53944.


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