Steady Apparent Viscosity Research Articles

Development of a mathematical model of viscosity for prediction of emulsion of Water/Wax crude oil

The degree of emulsification of oil-water is the main influencing factor for the steady apparent viscosity of water/waxy crude oil emulsions. The steady apparent viscosity of the emulsion gradually increases with the increase of the stirring rate, and gradually increases first with the increase of the stirring time and then remains unchanged. A conditional parameter relationship for describing the process of preparing the emulsion has been established by viscous flow entropy production, and the mathematical relationship between the apparent steady viscosity and the viscous flow entropy production value is analyzed. A model for quantitatively describing the relationship between the preparation conditions of the emulsion and the steady apparent viscosity has been established by the method of multiple statistical regression. This model can provide theoretical guidance for the preparation of a crude oil emulsion.

A Microbial Exopolysaccharide Produced by Sphingomonas Species for Enhanced Heavy Oil Recovery at High Temperature and High Salinity

Microbial exopolysaccharides secreted by microorganisms during metabolic processes have been widely used in biotechnology because of their environmentally friendly and renewable nature. This study evaluates the potential of a novel microbial exopolysaccharide, diutan gum, which is produced by Sphingomonas species, for enhanced heavy oil recovery at high temperature and high salinity. In addition, two conventional polymers [xanthan gum and partially hydrolyzed polyacrylamide (HPAM)] used in oil exploitation are compared under the same conditions. It is found that the steady apparent viscosity and dynamic modulus of aqueous diutan gum solutions are not sensitive to the temperature and virtually independent of the salinity, while those of xanthan gum and HPAM significantly decrease at high temperature and high salinity. The retention values of the apparent viscosity and the dynamic modulus of diutan gum at 90 °C and 244 121 mg·L–1 salinity are greater than 90%. The gel-like structure of diutan gum is depende...

Research on rheological properties and extrusion behavior of aqueous alumina paste in paste-extrusion-based SFF processes

In this work, the rheological properties and extrusion behavior of aqueous alumina paste which can be used in paste-extrusion-based solid freeform fabrication (SFF) processes are presented. According to the analysis of dynamic viscoelastic properties, the aqueous alumina paste with solid loading of 50 vol% can be treated as a viscous–elastic–plastic body in the extrusion process. The paste shows the viscoelastic feature before yielding and viscoplastic feature after yielding. Although the paste possesses shear-thinning behavior, it can be extruded steadily due to relatively steady apparent viscosity within the range of shearing rate in the actual paste extrusion process. The ram extrusion experiments show that the variation of extrusion pressure is essentially determined by the rheological behavior of paste. The average extrusion pressure in steady extrusion stage can be estimated by Benbow–Bridgwater model. However, there exists a ram velocity threshold (0.1 mm/s in this study) below which the liquid phase migration will be significant and the extrusion pressure is hardly estimated. Due to the viscoplastic fluid feature of paste, the extrudate velocity cannot immediately reach to the expected value when paste extrusion starts and stops, and it could result in the imprecise deposition and “die drooling,” which can be improved by the operation of pulling back of ram.

Influence of Morphology on the Rheological Behavior of Semi-Solid A356 Aluminum Alloy

The morphology of semi-solid alloy is one of the key influence factors on the rheological behavior of slurry during die filling and the mechanical properties of formed parts. However, it is difficult to study such effect due to hard controlling of morphology in semi-solid state. In this paper, a self-developed Searle-type viscometer was used to determine the rheological behavior of A356 aluminum alloy in different morphology, which was refined with the salts mixture of K2TiF6 and KBF4. The results indicated that the flow behavior of refined A356 alloy in the semi-solid state possesses obviously thixotropic behavior under isothermal shearing condition with less time to reach steady state and lower steady apparent viscosity as compared to that of the A356 alloy. During continuous cooling at a constant shearing rate, the apparent viscosity of refined A356 slurry in the same solid fraction decreased with the content of Ti. It is shown from quantitative image analysis that the primary α-Al grain in the refined alloy evolves from dendrites to rosettes or sphericitys, and then tends to be rounder and finer in higher Ti content. The mechanism of the influence of morphology on rheological behavior was also discussed in this paper.