•Thermal conductivity and viscosity models of nanofluids were reviewed.•Metallic oxides nanofluids (Al2O3, CuO, SiO2 and ZnO) were considered.•Various shapes of nanoparticles were selected.•Thermal ...conductivity increased as temperature and concentration increased.•Nanoparticles shape has sufficient impact on thermophysical properties of nanofluids.
For over ten years, investigators focused on determining and modelling the effective thermal conductivity and viscosity of nanofluids. Lately, many theoretical and experimental investigations on convective heat transfer have been performed on the augmentation of heat transfer by utilizing suspensions of nanometer-sized solid particle materials (metallic or nonmetallic) in base fluids. The main purpose of this work is to determine the thermal conductivity and viscosity of various types of metallic oxides (Al2O3, CuO, SiO2 and ZnO) for nanoparticle concentrations of 1–5 vol% at temperatures of 300–320 K and nanoparticle shapes (blades, platelets, cylindrical, bricks, and spherical). The results illustrate that the effective thermal conductivity and thermal conductivity ratio of metallic oxide nanofluids increase with temperature and nanoparticles volume fraction but decreases nanoparticle size intensifies. Besides that, the results of effective viscosity and viscosity ratio obtained indicate a considerable rise with the increase of nanoparticles concentration. Thus, optimum nanoparticle concentration is essential to be determined in forming nanofluids that can enhance thermal systems performance. Finally, it is found that nanoparticles shape has great impact on the thermophysical properties of nanofluids.
The use of viscosity-sensitive fluorescent probes in biological imaging is becoming increasingly popular, and the first measurements in various different cell types, organelles and even live animals ...have recently been reported. Yet there remains gaps in the understanding of 'microviscosity' and the various viscosity-related fluorescence parameters used to measure it. In this thesis, I moved away from a generalised notion of cellular viscosity and towards measurement of highly localised viscosity environments in biological organelles. To do this, I employed time- and polarisation-resolved fluorescence imaging and spectroscopy, using the gold-standard of viscosity probes: boron-dipyrromethene (BODIPY)-based fluorescent molecular rotors (FMRs). The objective was to achieve a high degree of local viscosity domain separation. By combined use of chemical FMR-targeting and physical organelle extraction, I separated the two primary domains of mitochondria: matrix and membrane. This represented the first level of domain separation. Using fluorescence lifetime imaging (FLIM) and two FMRs (mitoBODIPY and BODIPY-C12), I found that both viscosity environments are responsive to small physiological or environmental changes. The second level of domain separation was achieved through combined FMR-FLIM and time-resolved fluorescence anisotropy imaging (TR-FAIM), using BODIPY-C12. The method was applied to lipid droplet organelles and artificial analogues. Two viscosity-related parameters, FMR lifetime and rotational correlation time, were determined in the same experiment; they were non-equivalent. Furthermore, molecular dynamics simulations from a collaborator found distinct orientations of the FMR within each system which connected to empirically determined fluorophore populations, resolving the two-component signal. Finally, I investigated a fundamental photophysical aspect of BODIPY FMRs, the transition dipole moment (TDM), which is crucial in the interpretation of TR-FAIM signals. Using the spectroscopic approach pioneered by Toptygin, I found a tilted emission TDM in the fundamental BODIPY FMR, phenyl-BODIPY. This was contextualised and explained by quantum chemical calculations carried out by a collaborator. Furthermore, I examined phenyl-BODIPY's seemingly viscosity-dependent r0, an anisotropy parameter indicative of the angle between the absorption and emission TDM. Similar behaviour was observed in non-FMR dyes. Through a combination of higher excited state experiments and quantum chemical simulations from a collaborator, I conclude the behaviour is due to a combination of torsional vibrations and ultra-fast librations.
The dissipation of kinetic energy through viscosity provides one mechanism by which the solar atmosphere may be heated. Although isotropic, Newtonian viscosity is a common feature of many coronal ...simulations, the proper form of viscosity in a highly magnetised plasma is anisotropic and strongly coupled to the local magnetic field. This thesis investigates the differences between isotropic viscosity and a novel family of models of anisotropic viscosity, the switching model, when applied to simulations of the kink and fluting instabilities in a coronal loop, a slowly stressed magnetic null point, and the Kelvin-Helmholtz instability in the fan plane of a null point. This switching model provides a method of resolving previously unresolved regions of isotropic viscosity near null points by essentially removing the perpendicular and drift terms from the Braginskii model of anisotropic viscosity and modifying the coefficients of the remaining terms. A number of potential switching models are presented, with one showing particular promise for use in numerical modelling of the solar corona, that based on the coefficient of the parallel term in the Braginskii model. The choice of viscosity model strongly affects the stability and evolution of the studied instabilities, and the heating generated in their development. The use of anisotropic viscosity generally diminishes viscous heating, enhances Ohmic heating, produces small scales in flow and current structures, results in more energetic instabilities and an overall increase in reconnection rate.
Viscosity model is important for the simulation of flow and recovery behaviour of different hydrocarbon systems. Various semi-theoretical models such as Friction-Theory and cubic Equation of ...State-based models have been found satisfactory for lighter crudes. However, for heavier hydrocarbon systems e.g. heavy oils, bitumens, these models are not reliable; one possible reason is that they are not reliable for heavier components. The objective of this research is to develop a viscosity model sensitive to molar mass and density of components and a mixture of hydrocarbons.
In this work, a Cubic Equation of Viscosity model where P-ρ-T form of cubic equation (Abbott, 1973) is converted into P-μ-T form of cubic equation, is developed with desired sensitivity to density and molar mass. The model requires three parameters, which are optimized by viscosity data matching. Separate sets of parameters are developed for hydrocarbon groups such as paraffins, naphthenes, and aromatics. Viscosity estimation for mixture requires mixing of the parameters and not the viscosity values of individual components.
The carbon number of heaviest component used in the model is 64. The P-μ-T viscosity model has AARD of 2.91%, 3.06% and 5.68% for paraffins, naphthenes, and aromatics respectively in comparison of 33.95%, 19.6%, and 48.9% from T-μ-P (Guo et al., 2001) model. Friction Theory (Quinones-Cisneros et al., 2000) based model results in 26.38% AARD for paraffins. For 19 paraffinic mixtures, AARD from P-μ-T is 5.56% in comparison to 29% from T-μ-P (Guo et al., 2001) model and 316% from Friction Theory (Quinones-cisneros et al., 2000) model.
Viscosity-temperature property of coal ash slag plays the key role for stable and long term operation of entrained flow gasifiers, which is the quantitative parameter for slag tapping process. It is ...described by a curve of slag viscosity as a function of temperature, which includes three aspects: viscosity value dependence on temperature, temperature of critical viscosity (TCV), and pattern of slag viscosity-temperature curve. A clear and comprehensive understanding of viscosity-temperature property of coal ash slag and its influencing factors is really important for slag tapping, operation and design of a gasifier. This review begins with essence of slag viscosity-temperature property and requirement for slag tapping, and then focused on utilization of basic oxides to adjust slag viscosity-temperature property. It was found that TCV of a crystalline slag is vitally dependent on crystallization behavior of slag, and crystallization kinetics of slag needs further to be investigated in the future. In addition, residual char in slag, water vapor in syngas, and temperature program in viscosity measurement significantly affect the slag viscosity-temperature property and slag tapping process. Finally, based on results reported in the literatures, several perspectives were proposed for future studies on slag viscosity-temperature property of coal ash slag.
•Synergistic effect is found between CaO and Na2O on slag structure.•Occurrence of TCV is essentially affected by slag crystallization.•Crystallization kinetics strongly influences formation of solid phase.•More efforts should focus on practical factors during gasifier running.
Due to the presence of asphaltene, the flow assurance of high viscosity crude oil becomes more challenging and costly to produce in wellbores and pipelines. One of the most effective ways to reduce ...viscosity is to blend heavy oil with light oil. However, the viscosity measurement of diluted heavy crude is either time-consuming or inaccurate. This work aims to develop a more accurate viscosity model of diluted heavy crude based on machine learning techniques. A multilayer neural network is used to predict the viscosity of heavy oil diluted with lighter oil. The input data used in the training include temperature, light oil viscosity, heavy oil viscosity, and dilution ratio. In this modeling process, 156 datasets were retrieved from the available iterature of various heavy-oil fields in China. Part of the data (80%) is used to train the developed models using Adam optimizer algorithms, while the other part of the data (20%) is used to predict the viscosity of heavy oil diluted with lighter. The performance and accuracy of the machine learning models were tested and compared with the existing viscosity models. It was found that the new model can predict the viscosity of diluted heavy oil with higher accuracy, and it performs better than other models. The absolute average relative error is 10.44%, the standard deviation of the relative error is 8.45%, and the coefficient of determination is R2 = 0.95. The viscosity predicted by the neural network outperformed existing correlations by the statistical analysis used for the datasets available in the literature. Therefore, the method proposed in this paper can better estimate the viscosity of diluted heavy crude oil and has important promotion value.
The behavior of lubricants at operational conditions, such as at high pressures, is a topic of great industrial interest. In particular, viscosity and the viscosity-pressure relation are especially ...important for applications and their determination by computational simulations is very desirable. In this study, we evaluate methods to compute these quantities based on fully atomistic molecular dynamics simulations, which are computationally demanding but also have the potential to be most accurate. We used the 9,10-dimethyloctadecane molecule, main component of PAO-2 base oil as the lubricant for our tests. The methods used for the viscosity simulations are the Green-Kubo equilibrium molecular dynamics (EMD-GK) and nonequilibrium molecular dynamics (NEMD), at pressures of up to 1.0 GPa and various temperatures (40-150 degrees Celsius). We present the theory behind these methods and investigate how the simulation parameters affect the results obtained, to ensure viscosity convergence with respect to the simulation intervals and all other parameters. We show that, by using each method in its regime of applicability, we can achieve good agreement between simulated and measured values. NEMD simulations at high pressures captured zero shear viscosity successfully; while at 40 degrees Celsius, EMD-GK is only applicable to pressures up to 0.3 GPa, where the viscosity is lower. In NEMD, longer and multiply repeated simulations improve the confidence interval of viscosity, which is essential at lower pressures. Another aspect of these methods is the choice of the utilized force field for the atomic interactions. This was investigated by selecting two different commonly used force fields.
In this study, static tests and core experiments were carried out to evaluate heavy oil (high viscosity oil) production performance using low viscosity oil as a potential injection, as well as the ...coupling effects of viscous fingering and viscosity reduction on the displacement efficiency. Results show that 30% was the optimal maximum dilution ratio when considering economy and efficiency. With the low viscosity oil injecting, the displacement front came to breakthrough around 0.3 pore volume (PV), and then the effluents’ viscosity and the viscosity distributions along the core came to a sharp decline, indicating that low viscosity oil has already mixed thoroughly with heavy oil. The low viscosity oil displacements and heavy oil reverse displacements revealed a key instruction for the field application: The final total recovery of heavy oil was up to 65%, while it was almost 100% near the injection port. The injected low viscosity oil could be almost 100% retrieved for recycle, the larger displacement rate facilitated the faster growth of viscous fingering, further assisting low viscosity oil better dissolving into heavy oil and reducing the flow resistance. The study demonstrated a promising and practical strategy of low viscosity oil injection on enhancing heavy oil recovery.
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•The low viscosity oil displacement front advancing process was suggested.•The potential of low viscosity oil in recovering heavy oil was analyzed.•The retrieval of the injected low viscosity oil and the reusing possibility was discussed.•New insights into the coupling effects of viscosity reduction by dilution and viscous fingering were given.•The positive effects of viscous fingering on the spread efficiency was identified.
In a pilot‐scale bubble column operating with low and moderate viscosity hydrocarbons, the effect of pressure on the total and axial gas holdup as well as the regime transition velocity was ...investigated. Experiments were performed for two air‐Ketrul D100 and air‐Hydroseal G250 HL gas‐liquid hydrocarbon systems. It was found that increasing pressure increased gas holdup at the heterogeneous regime, and this effect was more pronounced for the low‐viscosity liquid. Moreover, increasing pressure further stabilized the homogeneous regime, and again, this stabilizing effect was more significant for the low‐viscosity liquid. Also, as a response to the pressure increasing, the axial gas holdup became more uniform in the case of the low‐viscosity liquid and less uniform in the case of the moderate‐viscosity liquid.
•Relation between drag reduction and viscoelasticity of polymers is investigated.•Drag reduction correlates with extensional viscosity and Weissenberg number.•Drag reduction does not correlated with ...small-amplitude oscillatory shear.•For large degradation, extensional viscosity increases with decreasing strain rate.
The relation between the drag reduction (DR) performance of several water-soluble polymers and their viscoelastic properties was investigated. Polymers with a flexible molecular structure including three grades of polyacrylamides (PAM), and a polyethylene oxide (PEO) were investigated. Xanthan gum (XG) and carboxymethyl cellulose (CMC), each with a rigid molecular structure, were also considered. The rheology was characterized using steady shear-viscosity measurement, capillary break-up extensional rheometer (CaBER), and small-amplitude oscillatory shear measurement at the concentration of the drag-reduced solution. To isolate the effect of shear viscosity, the concentration of the polymers was adjusted to produce solutions with a similar shear viscosity at high shear rates. Using pressure drop measurements in a turbulent pipe flow, the DR of each polymer solution was determined. With identical high-shear-rate viscosities, the flexible PAM solutions resulted in an initial DR of 50–58%, while the initial DR of PEO was 44%, and the rigid polymers provided the least DR of 12%. The rigid polymers demonstrated negligible degradation of DR over a period of 2 h. Of the flexible polymers, PAM showed moderate degradation, while the DR of PEO quickly diminished after 20 min. Drag reduction correlated with extensional viscosity and Weissenberg number obtained from CaBER. A strong correlation was not observed between DR and the viscoelastic moduli obtained from small-amplitude oscillatory shear. The large mechanical degradation of PEO was associated with a continuous extensional thickening, in which extensional viscosity increased with decreasing strain rate until the filament broke up.
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