Papers by Rubens R Fernandes
Chemical Engineering Science, 2019
The removal of toothpaste layers by static and moving water jets and falling films is studied. Th... more The removal of toothpaste layers by static and moving water jets and falling films is studied. The adhesive removal model predicts the cleaning rate and cleaning front shape. The removal force of soaked soils and the effect of soaking on cleaning are quantified. Measurements of the falling film thickness agree with Kapitza theory. Channeling in the falling film is more important at low flow rates. a b s t r a c t The cleaning of thin toothpaste soiling layers from vertical glass surfaces by horizontal impinging water jets and the falling films created by the draining liquid were studied. The effect of soaking time on the rheological properties of the soil material, the force required to remove it, and the cleaning behaviour were determined. The adhesive removal model reported by) gave a good description of the cleaning behaviour, including the shape of the cleaning front generated by jets from static and moving nozzles. This model was also applied to removal by the falling liquid film: when soaking kinetics are taken into consideration, it gives a good description of this process as well. This is the first study considering the effect of soil soaking on cleaning by water jets and falling films.
Chemical Engineering Science, 2019
Journal of Petroleum Science and Engineering, 2019
Drilling fluids are complex materials that display elastoviscoplastic and thixotropic characteris... more Drilling fluids are complex materials that display elastoviscoplastic and thixotropic characteristics. Rotational viscometers that impose discrete rotational velocities, such as the Fann 35A, are traditionally employed to evaluate the rheological properties of drilling fluids in field operations due to their robustness and low cost. These viscometers are used to measure the steady-state shear stresses by imposing different shear rates and the transient stress overshoot as an estimation of the fluid's gel strength. In the current work, two synthetic drilling fluids and two bentonite suspensions were tested in a Fann 35A viscometer and in a rotational rheometer to check how accurate the Fann 35A viscometer results can be in comparison to rheometer data. Although the steady-state shear stresses measured by the Fann 35A were corroborated by the corresponding values obtained from the rheometer, the accuracy of Fann 35A on measuring the stress overshoots depends on the fluid rheo-logical characteristics. Two hypotheses were proposed to explain the difference on the stress overshoots: (i) wall slip and (ii) the inappropriate control of the shear rate.
Rheologica Acta, 2017
Drilling fluids are suspensions of solid particles and present thixotropic and elastoviscoplastic... more Drilling fluids are suspensions of solid particles and present thixotropic and elastoviscoplastic behaviors simultaneously , which turn their rheological characterization into a challenging task. Rotational rheometers are widely employed to determine the properties of these fluids, and one major challenge in rheometric tests carried out with thixotropic fluids is to obtain repeatable results. Submitting the fluid specimen to a known shear history by performing a pre-shear procedure is commonly used to achieve repeatable results with thixotropic fluids. In this paper, the effect of different pre-shearing conditions on the rheological measurements of an oil-based drilling fluid was investigated using cross-hatched parallel plates. Firstly, an adequate aging time to ensure complete fluid restructuring was determined by monitoring the storage modulus, G′, over an oscillatory time sweep experiment. Shear-rate controlled start-up tests were then conducted to evaluate the gel strength and the steady-state shear stress. Nine different pre-shearing conditions were evaluated, and each experiment was performed three times. Finally, the results were analyzed by using two statistical tools: a two-way analysis of variance (ANOVA) and the Tukey's range test. The analysis shows that despite the good repeatability achieved when the same pre-shear condition is applied, the pre-shearing affects not only the gel strength but also the steady-state shear stress. The ANOVA also revealed that the effect of the pre-shearing shear rate on the fluid rheological behavior is statistically more significant than the effect of the pre-shearing time. The same analysis was performed after 10 s and 10 min of aging, and similar results were obtained.
The common dimension (ComDim) chemometric method for multi-block analysis and hierarchical cluste... more The common dimension (ComDim) chemometric method for multi-block analysis and hierarchical cluster analysis (HCA) were used to evaluate the data obtained from the physico-chemical and rheological characterization of 42 commercial fruit pulps. The physico-chemical characteristics and the rheological behavior of the pulps were found to be considerably different. The Herschel-Bulkley equation was fit to the steady-state flow curves of the fruit pulps, and it was found to appropriately describe the materials, which showed a wide range of yield stresses. The soluble solids content and the yield stress were the main factors responsible for the sample discrimination in the multivariate statistical analysis. The ComDim model indicates that these parameters may have a direct correlation. Namely, the soluble solids amount can influence the viscosity, as demonstrated by the similar scores of the samples in both common components, and this corroborated with the HCA analysis.
Wear, 2019
Kaye et al. (1995) conducted an experimental investigation of the cleaning of thin soil layers by... more Kaye et al. (1995) conducted an experimental investigation of the cleaning of thin soil layers by water jets generated from stationary nozzles of diameter 0.25–2mm and velocities ranging from 6 to 40m s−1. The soil layers were prepared by drying a commercial cleaning suspension on polymethylmethacrylate plates. Several of their data sets have been re-analysed and are shown to fit the ‘strong soil’ model for cleaning by peeling reported by Bhagat et al. (2017). The model is demonstrated to be able to explain the trends in cleaning efficiency observed by Kaye et al. quantitatively, including the transition in efficiency observed at longer times. Kaye et al. also investigated the case of cleaning by a moving nozzle for one set of jet conditions, and reported an increase in cleared area with nozzle velocity. This behaviour is not predicted for the ‘strong soil’ and the model was modified to incorporate a contribution from the milling action of the jet in its impingent zone. This ‘very strong soil’ result gave good agreement with the data for the area cleared and the shape of the cleared region.
Journal of Rheology, 2017
Elastoviscoplastic materials present a transition from a gel-like to a liquidlike state induced b... more Elastoviscoplastic materials present a transition from a gel-like to a liquidlike state induced by shearing: While the first is primarily elastic, the second is predominantly viscous. The point that characterizes this transition is usually known as the yield point, which is associated to critical quantities such as yield stress and/or yield strain. Another characteristic of elastoviscoplastic materials is the transition from linear to nonlinear viscoelasticity. In the current work, a commercial hair gel, which is an elastoviscoplastic material, was tested in two rotational rhe-ometers in order to evaluate these two transition points. Stress oscillatory amplitude sweeps at different frequencies were performed and a Fourier-Transform analysis was applied to the results in order to determine the linear viscoelastic limit. The linear viscoelastic limit stresses and strains at different frequencies were then compared to quantities that are usually associated to the yield point: The extrapolated zero-shear-rate stress obtained from the equilibrium flow curve, the minimum stress required to start up flows in creep experiments, the stress overshoot reached in constant shear rate experiments and the G 0-and-G 00 crossover stress determined through oscillatory amplitude sweeps. The results showed that the stresses and strains obtained as the linear viscoelastic limits were smaller than the critical quantities associated to the yield point for all evaluated cases. Although the critical quantities depend on the experimental condition, the linear viscoelastic limit strain was remarkably constant. Additionally, the linear viscoelastic limit strain was found to be in the same order of magnitude of the strain that characterizes the onset of plastic behavior in recovery experiments. This suggests that the beginning of the transition from a completely structured state of elastoviscoplastic materials to an unstructured state might be associated to the threshold of nonlinear viscoelasticity.
The rheological characterization of drilling fluids is crucial to ensure an adequate performance ... more The rheological characterization of drilling fluids is crucial to ensure an adequate performance of drilling operations. These materials show elastoviscoplastic and thixotropic behaviors simultaneously so that its gel strength is highly affected by the aging time to which the sample is subjected. This work presents experimental evidences of a correlation between the stress overshoot observed in flow start-up rheometric experiments after different aging times and the storage modulus, G , monitored during a low amplitude oscillatory sweep over the aging time. A comparison of the correlation with the measured data at five different shear rates show that results lie within error bands of 10%. The results also suggest that the stress overshoot for different aging times can be estimated by using only two rheometric tests: an oscillatory sweep and a controlled shear rate experiment.
Drilling fluids usually gel at rest in order to avoid cuttings to precipitate over the drill bit ... more Drilling fluids usually gel at rest in order to avoid cuttings to precipitate over the drill bit when circulation is interrupted. At flow start-ups, pumping pressures higher than the steady-state circulation pressure are usually required to surpass the gel strength. The gel-liquid transition may have significant importance, especially in ultra-deep waters where high pressures and low temperatures take place. In the current work, controlled shear rate rheometric tests were conducted to investigate the yielding of an oil based drilling fluid. An algebraic equation, that accounts for both shear rate and shear history, is proposed to predict the gel breaking. This equation requires less fitting parameters than the current structural kinetic models available in literature, and is quite useful to represent the pressure peaks that take place during drilling fluid flow start-ups. The equation fit to rheometric data and is able to predict satisfactorily the start-up shear stress of a gelled drilling fluid at different shear rates.
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Papers by Rubens R Fernandes