Korea-Australia Rheology Journal最新文献

The occurrence of barite sag in drilling fluids has relatively often been the cause for gas kicks in oilwell drilling. The subsequent absorption of gas into drilling fluid could lower the density and reduce the viscosity of the drilling fluid, thereby aggravating both pressure control and hole cleaning. In this paper, we present experimental measurements of rheological properties and barite sag in a typical North Sea oil-based drilling fluid at downhole pressure and temperature conditions. A new experimental apparatus was setup for barite sag measurements at static condition with operational temperature and pressure capabilities up to 200 °C (392°F) and 1000 bar (14,503.8 psi), respectively. Rheometry measurements were conducted on fluid samples with and without barite particles at operating conditions up to 90 °C and 100 bar. We observed that at a typical shear rate of 250 s⁻¹, which is experienced in 8.5″ hole annulus, the viscosity of fluid sample with barite increased nearly three times as that of the fluid sample without barite as the temperature and pressure increased. However, temperature effect on viscosity dominates at high shear rates compared to pressure effect. Furthermore, the fluid samples showed more shear-thinning effect with increasing yield stress as the temperature increased. On the other hand, barite sag measurements revealed that whereas fluid samples under high pressure are less prone to sag, high temperature fluid samples, however, promote sag significantly. The data from this study are useful to validate extrapolations used in computational models and to improve understanding and operational safety of sag phenomena at downhole conditions. We also discuss the importance of this study in optimizing drilling operations.

Optimisation design of composite structures requires an accurate predictive model for forming behaviour. The simulation process contains a number of model parameters which include transverse and longitudinal viscosities of continuous fibre-reinforced viscous composites, fundamental to predicting the shear rheology. Shearing the unidirectional composite along the fibre direction gives a measure of the longitudinal viscosity (LV), whilst shearing across or transverse to the fibre direction gives a measure of the transverse viscosity (TV). Numerous experimental work was conducted in the past to measure these two viscosities for various materials. However, conflicting measurements by different test methods were obtained and these apparent discrepancies had not yet been systematically investigated in any single study. This paper reviews previous work on characterisation techniques to further understand the cause of such discrepancy, and hence to improve measurement accuracy, which would benefit future work on theoretical modelling of the composite viscosities and optimisation simulation of composites forming. Some important findings, such as effects of resin-rich areas, contributory factors of elastic effects, non-Newtonian behaviour for composites with Newtonian matrix, aspect ratio and end effects of test samples, geometry effects of fibres and fibre rearrangement during shearing, existence of a mathematical relationship between LV and TV and necessary benchmarking exercise using Newtonian matrix composites, were summarised.

We study the flow behavior of a Newtonian fluid in a planar 4:1 contraction channel using two numerical methodologies: the two-relaxation time lattice Boltzmann method (TRT-LBM) and the finite element method (FEM). To confirm the validity of the TRT-LBM, hydrodynamic quantities such that velocity, pressure, and vortex are carefully investigated at the wide ranges of Reynolds numbers (Re = 0.1–100). At first, we analyze the velocity along the channel. The results of TRT-LBM look reasonable and also coincide with the analytical solution and FEM results. Richer features are observed in the pressure profile along the flow direction. At low Reynolds numbers, the one-step change of the slope in the pressure profile is observed near the contraction region. The slope gradually grows up with the increase of Reynolds numbers, and eventually, this evolves the two-step change. Non-monotonic behavior is observed in the characteristics of the vortex. The size of the vortex non-linearly decreases as the Reynolds number increases. Also, the center of the vortex gradually moved toward the corner of the channel as an increase of Reynolds numbers with non-linearity. Not only the velocity and the pressure profiles but also the characteristics of the vortex quantitatively coincide in TRT-LBM and FEM results. Through this study, we confirm the robustness of the TRT-LBM as a simulation tool to investigate inertial flow in a planar contraction geometry.

Thermoplastic resin transfer molding (T-RTM) of polyamide 6-based composite is one of the promising process to mass-produce an environmentally friendly textile composite with recyclable thermoplastic resin, in which ε-caprolactam monomer with low viscosity is injected and in situ polymerized into the fabric. The side reactions caused by water in the anionic polymerization process of the monomer is a crucial problem for fabricating the composite with a high quality. In this study, we introduced zeolite, a porous ceramic water-absorbing particle, into the ε-caprolactam to improve the moisture sensitivity during the anionic polymerization. The selective water-absorbing effect of zeolite particle was verified by measuring the monomer conversion, viscosity-average molecular weight, and viscosity change during polymerization, and mechanical properties of the resultant carbon fiber reinforced polyamide composite were investigated. It is expected that processability of the T-RTM is remarkably improved by reducing both the drying time during process and quality deviation of the composite by variation of humidity, which can make T-RTM process a viable technology for mass-production of thermoplastic composites.

Among various nanomaterials, cellulose nanocrystals (CNCs) are regarded as the most suitable reinforcing fillers for hydrogels owing to their high dispersibility in water and favorable hydrogen bonding with water-dispersible polymers. Herein, CNC-laden polyvinyl alcohol (PVA)/borax (P/CNC) hydrogels were prepared by solution mixing, and their mechanical and rheological properties were investigated in terms of CNC loading of 0–60 w/w%. PVA/borax hydrogels are known to exhibit self-healing ability based on the dynamic nature of the borate–diol complex, which is dependent on the rheological response because the rheological chain dynamics dominantly affect the self-healing process. In mechanical testing, the Young’s modulus of the P/CNC hydrogels sharply increased above 40 w/w% CNC, indicating that the stiffening effect of CNC was enhanced above the critical loading. From a rheological perspective, the increases in the viscosity and storage modulus were further accelerated above 40 w/w%. In particular, the chain flow relaxation time (τ_f), a quantitative parameter closely related to the self-healing performance, was observed for the P/CNC hydrogels with CNC amounts of 0−40 w/w% (1.6−97.3 s); whereas, there is no τ_f for the P/CNC hydrogels with 45−60 w/w% CNC within a reasonable time scale we observed at 25 °C. Consequently, the incorporation of less than 40 w/w% CNCs affords high mechanical stiffness while maintaining self-healing ability.

The relationship between microstructure changes and rheological properties in suspensions containing boehmite particles, which are well applied in various industrial wash-coating processes, was investigated by changing pH condition. The boehmite particles in suspensions were either well dispersed or aggregated depending on the pH, owing to the relative contributions of repulsive interaction between particles as well as hydrolysis and condensation reactions. Four groups of boehmite suspensions were classified as very low, intermediate, almost zero charge, and high pH regimes based on their colloidal behaviors, and their microstructural differences were investigated using transmission electron microscopy (TEM) and multi-speckle diffusing wave spectroscopy (MSDWS). For gel-like suspensions of three groups, various rheological properties such as shear viscosity, viscoelastic modulus, yield stress, and recovery behavior were extensively compared, and the results clearly demonstrated that a suspension with high yield stress was not fully recovered into the original state when disturbed at high shear rates.

The present work investigates the effect of plate gap on the rheological properties of shear thickening fluid (STF) and proposes a phenomenological model to predict the viscosity curve of STF for different values of plate gap and temperature. Multiwalled carbon nanotube (MWCNT) reinforced silica-based STF (MWCNT/SiO₂-STF) containing 0.8 wt% MWCNT and 20 wt% SiO₂ nanoparticles was prepared using polyethylene glycol as a dispersion medium and tested for its steady and dynamic rheological behavior at different plate gaps. The peak viscosity of MWCNT/SiO₂-STF follows the characteristic behavior of an initial increase followed by a subsequent decrease corresponding to the increase in plate gap. A maximum viscosity of 198.89 Pa s was recorded at a plate gap of 1.0 mm. Although significant shear thinning in the dynamic rheological response of MWCNT/SiO₂-STF was noticed at a 1.0 mm gap, the storage and loss modulus were better than those at 0.5 mm gap. The proposed model based predicts the shear thinning and thickening behavior of STF at low and high shear rates for different values of plate gap with reasonable accuracy. The model also provides a very good fit for the viscosity of STF at different temperatures. Thus, the proposed model is suitable for numerical simulations as well as theoretical analysis in the vibration control field.