Thermo-hydraulic assessment of non-Newtonian MWCNT nanofluid flows inside microchannels with different cross-sections

In the present study, the convective heat transfer of MWCNT/water nanofluid was investigated along microchannels with different cross-sectional geometries. This class of carbon-based nanofluid exhibited a notable non-Newtonian shear-thinning behavior, which made them suitable for different heat transfer applications. A two-phase mixture model with a well-tuned non-Newtonian viscosity function was adapted. The effects of the volume fraction of nanoparticles, Reynolds number, and the geometrical shape of the cross-section were examined on the pressure drop and heat transfer rate across various microchannels. The obtained results showed that the microchannel cross-section geometry had a significant effect on the thermal performance of MWCNT/water nanofluids under certain thermal conditions. Moreover, it was deduced that for all Reynolds numbers and nanoparticle volume fractions considered, the flattened geometry exhibited the most superior thermal performance, which is around 19.03% larger than the circle geometry at Re = 1000 and volume fraction of 2%.

Effect of botanical origin on stability and crystallization of honey during storage

PurposeThe purpose of this paper was to study the effect of botanical origin on the characteristics of single-flower honeys (assa-peixe, coffee, eucalyptus, laranjeira and vassourinha), polyfloral (silvestre), extrafloral (sugarcane) and honeydew (bracatinga) during storage.Design/methodology/approachThe honeys were stored at 14 °C, and the analysis of water activity, color, absorbance, rheological behavior and microscopic analysis were performed during 6 months (T0, T30, T60, T90, T120, T150 and T180 days); quantification of sugars (fructose (F) and glucose (G)), moisture (M), F/G and G/M ratio only at T0.FindingsAll honeys showed changes during storage, and sugarcane honey stood out for presenting greater crystallization, influenced by the high content of glucose and fructose. Coffee honey showed the least crystallization. The crystallization of honeys influenced the increase in water activity, Newtonian viscosity, color and absorbance. The composition of the honeys directly influenced the crystallization process during storage.Originality/valueCrystallization is a natural process that occurs spontaneously in honey. Thus, the knowledge of the crystallization rate of honeys from different origins (botanical and geographical) during storage, is of great importance and interest for the industry, beekeepers and consumers, since each type of honey crystallizes in different ways and periods.

Rheological stratification in impure rock salt during long-term creep: morphology, microstructure, and numerical models of multilayer folds in the Ocnele Mari salt mine, Romania

At laboratory timescales, rock salt samples with different composition and microstructure show variance in steady-state creep rates, but it is not known if and how this variance is manifested at low strain rates and corresponding deviatoric stresses. Here, we aim to quantify this from the analysis of multilayer folds that developed in rock salt over geological timescale in the Ocnele Mari salt mine in Romania. The formation is composed of over 90 % of halite, while distinct multiscale layering is caused by variation in the fraction of impurities. Regional tectonics and mine-scale fold structure are consistent with deformation in a shear zone after strong shearing in a regional detachment, forming over 10 m scale chevron folds of a tectonically sheared sedimentary layering, with smaller folds developing on different scales in the hinges. Fold patterns at various scales clearly indicate that during folding, the sequence was mechanically stratified. The dark layers contain more impurities and are characterised by a more regular layer thickness compared to the bright layers and are thus inferred to have higher viscosities. Optical microscopy of gamma-decorated samples shows a strong shape-preferred orientation of halite grains parallel to the foliation, which is reoriented parallel to the axial plane of the folds studied. Microstructures indicate dislocation creep, together with extensive fluid-assisted recrystallisation and strong evidence for solution–precipitation creep. This provides support for linear (Newtonian) viscous rheology as a dominating deformation mechanism during the folding. Deviatoric stress during folding was lower than during shearing in the detachment at around 1 MPa. We investigate fold development on various scales in a representative multilayer package using finite-element numerical models, constrain the relative layer thicknesses in a selected outcrop, and design a numerical model. We explore the effect of different Newtonian viscosity ratios between the layers on the evolving folds on different scales. By comparing the field data and numerical results, we estimate that the effective viscosity ratio between the layers was larger than 10 and up to 20. Additionally, we demonstrate that the considerable variation of the layer thicknesses is not a crucial factor to develop folds on different scales. Instead, unequal distribution of the thin layers, which organise themselves into effectively single layers with variable thickness, can control deformation on various scales. Our results show that impurities can significantly change the viscosity of rock salt deforming at low deviatoric stress and introduce anisotropic viscosity, even in relatively pure layered rock.

Continuum Scale Non Newtonian Particle Transport Model for Hæmorheology

We present a continuum scale particle transport model for red blood cells following collision arguments, in a diffusive flux formulation. The model is implemented in FOAM, in a framework suitable for haemodynamics simulations and adapted to multi-scaling. Specifically, the framework we present is able to ingest transport coefficient models to be derived, prospectively, from complimentary but independent meso-scale simulations. For present purposes, we consider modern semi-mechanistic rheology models, which we implement and test as proxies for such data. The model is verified against a known analytical solution and shows excellent agreement for high quality meshes and good agreement for typical meshes as used in vascular flow simulations. Simulation results for different size and time scales show that migration of red blood cells does occur on physiologically relevany timescales on small vessels below 1 mm and that the haematocrit concentration modulates the non-Newtonian viscosity. This model forms part of a multi-scale approach to haemorheology and model parameters will be derived from meso-scale simulations using multi-component Lattice Boltzmann methods. The code, haemoFoam, is made available for interested researchers.

Rheological stratification in impure rocksalt during long-term creep: morphology, microstructure and numerical models of multilayer folds in the Ocnele Mari salt mine, Romania

Analysis and prediction of deformations in salt tectonics and salt engineering require information about the mechanical properties of rocksalt at time scales far longer than possible in the laboratory. It is known that at laboratory time scales, rocksalt samples with different composition and microstructure show a variance in steady-state creep rates, but it is not known how this variance is manifested at low strain rates and corresponding deviatoric stresses. Here, we aim to quantify this from the analysis of multilayer folds that developed over geological time scale. We studied excellent exposures of layered, folded rocksalt in the Ocnele Mari salt mine in Romania. The formation is composed of over 90 % of halite, while distinct multiscale layering is caused by variation in the fraction of impurities. Regional tectonics and mine-scale fold structure are consistent with deformation in a shear zone, after strong shearing in a regional detachment, forming over ten meter-scale chevron folds of a tectonically sheared sedimentary layering, with smaller folds developing on different scales in the hinges. Morphology of the fold pattern at various scales clearly indicates that during folding the sequence was mechanically stratified. The dark layers contain more impurities and are characterized with a more regular layer thickness as compared to the bright layers and, thus, are inferred to have higher viscosities. Optical microscopy of Gamma-decorated samples shows a strong shape preferred orientation of halite grains parallel to the foliation, which is reoriented parallel to the axial plane of the folds studied. Microstructures indicate dislocation creep, together with extensive fluid-assisted recrystallization and strong evidence for solution-precipitation creep indicative for linear (Newtonian) viscous rheology during folding. Deviatoric stress during folding was lower than during shearing in the detachment, around 1 MPa. We investigate fold development on various scales in a representative multilayer package using finite element numerical models, constrain the relative layer thicknesses in a selected outcrop and design a numerical model. We explore the effect of different Newtonian viscosity ratios between the layers on the evolving folds on different scales. Through the comparison of the field data and numerical results, we estimate that the effective viscosity ratio between the layers was larger than 10 and up to 20. Additionally, we demonstrate that the considerable variation of the layer thicknesses is not a crucial factor to develop folds on different scales. Instead, unequal distribution of the thin layers, which organize themselves into effectively single layers with variable thickness can trigger deformation at various scales. Our results show that impurities can significantly change the viscosity of rocksalt deforming at low deviatoric stress and introduce anisotropic viscosity, even in relatively pure, layered rock.

Snow water equivalents exclusively from snow depths and their temporal changes: the Δsnow model

Reliable historical manual measurements of snow depths are available for many years, sometimes decades, across the globe, and increasingly snow depth data are also available from automatic stations and remote sensing platforms. In contrast, records of snow water equivalent (SWE) are sparse, which is significant as SWE is commonly the most important snowpack feature for hydrology, climatology, agriculture, natural hazards, and other fields. Existing methods of modeling SWE either rely on detailed meteorological forcing being available or are not intended to simulate individual SWE values, such as seasonal “peak SWE”. Here we present a new semiempirical multilayer model, Δsnow, for simulating SWE and bulk snow density solely from a regular time series of snow depths. The model, which is freely available as an R package, treats snow compaction following the rules of Newtonian viscosity, considers errors in measured snow depth, and treats overburden loads due to new snow as additional unsteady compaction; if snow is melted, the water mass is stepwise distributed from top to bottom in the snowpack. Seven model parameters are subject to calibration. Snow observations of 67 winters from 14 stations, well-distributed over different altitudes and climatic regions of the Alps, are used to find an optimal parameter setting. Data from another 71 independent winters from 15 stations are used for validation. Results are very promising: median bias and root mean square error for SWE are only −3.0 and 30.8 kg m−2, and +0.3 and 36.3 kg m−2 for peak SWE, respectively. This is a major advance compared to snow models relying on empirical regressions, and even sophisticated thermodynamic snow models do not necessarily perform better. As such, the new model offers a means to derive robust SWE estimates from historical snow depth data and, with some modification, to generate distributed SWE from remotely sensed estimates of spatial snow depth distribution.

Numerical study on the energy cascade of pulsatile Newtonian and power-law flow models in an ICA bifurcation

The complex physics and biology underlying intracranial hemodynamics are yet to be fully revealed. A fully resolved direct numerical simulation (DNS) study has been performed to identify the intrinsic flow dynamics in an idealized carotid bifurcation model. To shed the light on the significance of considering blood shear-thinning properties, the power-law model is compared to the commonly used Newtonian viscosity hypothesis. We scrutinize the kinetic energy cascade (KEC) rates in the Fourier domain and the vortex structure of both fluid models and examine the impact of the power-law viscosity model. The flow intrinsically contains coherent structures which has frequencies corresponding to the boundary frequency, which could be associated with the regulation of endothelial cells. From the proposed comparative study, it is found that KEC rates and the vortex-identification are significantly influenced by the shear-thinning blood properties. Conclusively, from the obtained results, it is found that neglecting the non-Newtonian behavior could lead to underestimation of the hemodynamic parameters at low Reynolds number and overestimation of the hemodynamic parameters by increasing the Reynolds number. In addition, we provide physical insight and discussion onto the hemodynamics associated with endothelial dysfunction which plays significant role in the pathogenesis of intracranial aneurysms.