Home About us Contact
|
Home About us Contact | ||
|
|
||
Fluid Viscosity (fluid + viscosity)
Selected AbstractsEstimation of Joule heating effect on temperature and pressure distribution in electrokinetic-driven microchannel flowsELECTROPHORESIS, Issue 3 2006Reiyu Chein Professor Abstract In this study we present simple analytical models that predict the temperature and pressure variations in electrokinetic-driven microchannel flow under the Joule heating effect. For temperature prediction, a simple model shows that the temperature is related to the Joule heating parameter, autothermal Joule heating parameter, external cooling parameter, Peclet number, and the channel length to channel hydraulic diameter ratio. The simple model overpredicted the thermally developed temperature compared with the full numerical simulation, but in good agreement with the experimental measurements. The factors that affect the external cooling parameters, such as the heat transfer coefficient, channel configuration, and channel material are also examined based on this simple model. Based on the mass conservation, a simple model is developed that predicts the pressure variations, including the temperature effect. An adverse pressure gradient is required to satisfy the mass conservation requirement. The temperature effect on the pressure gradient is via the temperature-dependent fluid viscosity and electroosmotic velocity. [source] Impact of transition zones, variable fluid viscosity and anthropogenic activities on coupled fluid-transport processes in a shallow salt-dome environmentGEOFLUIDS (ELECTRONIC), Issue 3 2009F. MAGRI Abstract In the Schleswig,Holstein region (S,H) of Germany, most observed near-surface saline ground waters originate from dissolution of shallow salt domes. Previous numerical simulations of thermohaline flow clarified the major mechanisms controlling large-scale density-driven flow. It has been found that, in addition to topographically driven flow, gravitational and thermohaline convection are the primary mechanisms for extensive solute exchange between shallow and deep aquifers. Geological features such as glacial channels control recharge/discharge processes at the surface. Here we address several previously unresolved issues: (i) the impact of a permeable unit (transition zone) between the salt and adjacent units; (ii) the role of variable brine viscosity in affecting regional- (i.e. km-) scale heat and mass patterns; and (iii) the influence of anthropogenic activities such as pumping stations on density-driven flow. We found that geophysical factors play a major role in determining the dynamics of fluid processes. The transition zone significantly influences the flow field and the distribution of heat, slowing the formation of highly concentrated salty plumes. The impact of variable fluid viscosity on the coupled heat and brine flow is twofold. In a colder and highly concentrated environment, such as a shallow salt-dome crest, it retards brine flow. In a less saline environment, variable fluid viscosity enhances thermally induced upward fluid flow. Groundwater extraction from production wells only affects brine and heat flow locally within the upper aquifers. [source] Seismic wave properties in time-dependent porosity homogeneous mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007G. Quiroga-Goode SUMMARY It is quantified the properties of seismic waves in fully saturated homogeneous porous media within the framework of Sahay's modified and reformulated poroelastic theory. The computational results comprise amplitude attenuation, velocity dispersion and seismic waveforms. They show that the behaviour of all four waves modelled as a function of offset, frequency, porosity, fluid viscosity and source bandwidth depicts realistic dissipation within the sonic,ultrasonic band. Therefore, it appears that there is no need to include material heterogeneity to model attenuation. By inference it is concluded that the fluid viscosity effects may be enhanced by dynamic porosity. [source] Near-lithostatic pore pressure at seismogenic depths: a thermoporoelastic modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Francesca Zencher SUMMARY A model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure. This configuration is thought to be pertinent to the South Iceland seismic zone (SISZ) and to other tectonically active regions of recent volcanism, where volatiles are continuously released by ascending magma below the brittle,ductile transition. Poroelastic parameters are computed for basaltic rock. The model is 1-D, the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium. Environment conditions are considered, pertinent to basalt saturated with water at shallow depth (case I) and at mid-crustal depth (case II). If the intrinsic permeability of the rock is high, no significant effects are observed in the pressure field but advective heat transfer shifts the brittle,ductile transition to shallower depths. If the intrinsic permeability is low, the pressure-dependent permeability can propagate near-lithostatic pore pressures throughout most of the transition layer, while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition. Geometrical parameters characterizing the fracture distribution are important in determining the effective permeability: in particular, if an interconnected system of fractures develops within the transition layer, the effective permeability may increase by several orders of magnitude and near-lithostatic pore pressure propagates upwards. These modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the SISZ, in connection with the two 2000 June M= 6.5 earthquakes, including: (i) fluid pressure pulses in deep wells, (ii) low resistivity at the base of the seismogenic layer, (iii) low VP/VS ratio and time-dependent seismic tomography, (iv) heterogeneity of focal mechanisms, (v) shear wave splitting, (vi) high b -value of deep foreshocks, (vii) triggered seismicity and (viii) Radon anomalies. [source] Empirical slip and viscosity model performance for microscale gas flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005Matthew J. McNenly Abstract For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier,Stokes solution in the non-continuum non-equilibrium regime. In this investigation, the optimal modifications are found by a linear least-squares fit of the Navier,Stokes solution to the non-equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non-equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non-zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L2 error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger. Copyright © 2005 John Wiley & Sons, Ltd. [source] A COMPARATIVE STUDY OF THE PERFORMANCE OF SELECTED IN-LINE VISCOMETERS ON NEWTONIAN AND SHEAR-THINNING FLUIDS,JOURNAL OF TEXTURE STUDIES, Issue 2 2001LAURA A. ZIMMER Three commercial instruments for in-line process measurement of fluid viscosity (an oscillating sphere viscometer, a tube viscometer and a coaxial cylinder viscometer) were evaluated using a Newtonian (60% sucrose) and two shear-thinning fluids (0.5% xanthan gum and 2% hydroxypropyl methylcellu-lose). The oscillating sphere viscometer required little or no calibration to measure the viscosity of Newtonian fluids. Otherwise, when compared to results given by analytical off-line rheometry, the in-line viscometers were found to be grossly inaccurate in predicting viscosity. A methodology is presented to correct the flow curves generated by each in-line instrument such that the output measurements are consistent with that given by off-line rheometry. Additional characteristics of each instrument that should be considered when choosing an instrument for in-line process application are presented. [source] Wet clutch transmission fluid for AWD differentials: base fluid influence on friction characteristicsLUBRICATION SCIENCE, Issue 1 2006Rikard Mäki Abstract During the past few years several electronically controllable automotive transmission systems, where wet clutches are used as intelligent differentials, have emerged in the market. In this type of application the anti-shudder properties of the lubricants are of vital importance. This paper investigates the influence of base fluids on the anti-shudder properties of transmission fluids for wet clutches in all-wheel-drive systems. The investigated all-wheel-drive system featuring a wet multi-plate clutch with a sintered brass-based friction material is described. The test equipment used to determine the frictional characteristics of the transmission fluid is described. The parameters studied include base fluid type and base fluid viscosity. It is shown that the choice of base fluid has no impact on torque capacity, but that the base fluid influences the temperature dependence of the dynamic friction and the anti-shudder properties. It is also shown that the major effect on the friction characteristics is caused by additive effects rather than base fluid effects. Copyright © 2006 John Wiley & Sons, Ltd. [source] Role of pleural viscosity in the differential diagnosis of exudative pleural effusionRESPIROLOGY, Issue 2 2007Ozkan YETKIN Objective and background: Determining the aetiology of an effusion involves assessing if it is an exudate or a transudate. However, a reliable test for determining the aetiology of a pleural effusion is lacking. Pleural viscosity has a high sensitivity and specificity and a high positive and negative predictive value for discriminating exudative and transudative pleural effusions. The aim of this study was to use pleural fluid viscosity to discriminate between various aetiologies of exudative effusions, namely malignant, parapneumonic and tuberculous. Methods: Seventy consecutive patients (24 women, 46 men, mean age = 67 years) with exudative pleural effusion due to pneumoniae in 24 patients, tuberculous pleurisy in 21 and lung cancer in 25 were studied prospectively. Measurements of pleural fluid and plasma viscosity were performed using Brookfield DV-II viscometer. Results: Pleural viscosity and pleural LDH were highest in the tuberculous pleurisy patients and lowest in the lung cancer patients. Pleural viscosity ,1.57 was found to be indicative of tuberculous pleurisy with a sensitivity of 100% and specificity of 95%. Pleural viscosity <1.39 was found to be indicative of lung cancer with a sensitivity of 100% and specificity of 94%. Pleural viscosity was significantly correlated with pleural albumin (r = 0.34, P = 0.004), protein (r = 0.40, P = 0.001), LDH (r = 0.70, P < 0.001) and plasma viscosity (r = 0.44, P < 0.001), having the most significant value with pleural LDH. Conclusion: The pleural fluid viscosity of patients with parapneumonic, tuberculous and malignant effusions are significantly different from each other. Among these groups, tuberculous effusions had the highest viscosity, and malignant effusions from lung cancer the lowest. [source] Mixing Time in a Short Bubble ColumnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2003M Ravinath Abstract Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D , 5) with different spargers and for different clear liquid height to diameter (HC/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter-cell exchange velocity, Ve, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers. On a effectué des mesures de temps de mélange dans une colonne à bulles courte de 0,2 m de diamètre intérieur (Hc/D , 5) munie de différents aérateurs et pour différents rapports entre la hauteur de liquide clair et le diamètre (HC/D). On a fait varier la vitesse de gaz superficielle dans la gamme de 0,01-0,1 m/s. L'effet de la viscosité en masse du fluide sur le temps de mélange est également étudié. On a utilisé le modèle de zones de circulation, comprenant deux paramètres calés, à savoir le nombre de zones de circulation, S, et la vitesse d'échange entre les zones, Ve, pour prédire et expliquer la variation du temps de mélange et le profil d'écoulement dans la colonne à bulles courte pour différents types d'aérateurs. [source] Slot die coating of dilute suspensionsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Yi-Tsun Lin Abstract An experimental study was carried out to investigate slot die coating of dilute suspensions. Polymethyl methacrylate (PMMA) particles of different sizes were added to glycerol solutions as test fluids. The coating flow experiment was performed on a lab coater. The operating window, which is a domain in which only a stable and uniform coating solution is possible, was determined experimentally. It was found that adding particles has little effect on the physical properties of glycerol solutions, as only the fluid viscosity increases slightly. Two coating defects are commonly observed; ribbing which is caused by flow instability refers to lateral waves on the coated surface, and air entrainment which implies that air bubbles are trapped in the coating solution. Adding particles has little effect on the operating window if the coating defect is ribbing. However, the operating window can be expanded substantially if the coating defect is air entrainment. Higher the particle concentration, or the smaller the particle size, more significant is the expansion of the operating window. The maximum coating speed may increase to 80% for high suspension particle density number. A previous study reported that there exists an optimal particle size which has the largest operating window for a given pure solution; this was not found in the present work. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Insulating effect of coals and organic rich shales: implications for topography-driven fluid flow, heat transport, and genesis of ore deposits in the Arkoma Basin and Ozark PlateauBASIN RESEARCH, Issue 2 2002J.A. Nunn ABSTRACT Sedimentary rocks rich in organic matter, such as coal and carbonaceous shales, are characterized by remarkably low thermal conductivities in the range of 0.2,1.0 W m,1 °C,1, lower by a factor of 2 or more than other common rock types. As a result of this natural insulating effect, temperature gradients in organic rich, fine-grained sediments may become elevated even with a typical continental basal heat flow of 60 mW m,2. Underlying rocks will attain higher temperatures and higher thermal maturities than would otherwise occur. A two-dimensional finite element model of fluid flow and heat transport has been used to study the insulating effect of low thermal conductivity carbonaceous sediments in an uplifted foreland basin. Topography-driven recharge is assumed to be the major driving force for regional groundwater flow. Our model section cuts through the Arkoma Basin to Ozark Plateau and terminates near the Missouri River, west of St. Louis. Fluid inclusions, organic maturation, and fission track evidence show that large areas of upper Cambrian rocks in southern Missouri have experienced high temperatures (100,140 °C) at shallow depths (< 1.5 km). Low thermal conductivity sediments, such as coal and organic rich mudstone were deposited over the Arkoma Basin and Ozark Plateau, as well as most of the mid-continent of North America, during the Late Palaeozoic. Much of these Late Palaeozoic sediments were subsequently removed by erosion. Our model results are consistent with high temperatures (100,130 °C) in the groundwater discharge region at shallow depths (< 1.5 km) even with a typical continental basal heat flow of 60 mW m,2. Higher heat energy retention in basin sediments and underlying basement rocks prior to basin-scale fluid flow and higher rates of advective heat transport along basal aquifers owing to lower fluid viscosity (more efficient heat transport) contribute to higher temperatures in the discharge region. Thermal insulation by organic rich sediments which traps heat transported by upward fluid advection is the dominant mechanism for elevated temperatures in the discharge region. This suggests localized formation of ore deposits within a basin-scale fluid flow system may be caused by the juxtaposition of upward fluid discharge with overlying areas of insulating organic rich sediments. The additional temperature increment contributed to underlying rocks by this insulating effect may help to explain anomalous thermal maturity of the Arkoma Basin and Ozark Plateau, reducing the need to call upon excessive burial or high basal heat flow (80,100 mW m,2) in the past. After subsequent uplift and erosion remove the insulating carbonaceous layer, the model slowly returns to a normal geothermal gradient of about 30 °C km,1. [source] | ||||||||||||||||