scholarly journals Effects of Nanoparticle Enhanced Lubricant Films in Thermal Design of Plain Journal Bearings at High Reynolds Numbers

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1353 ◽  
Author(s):  
Abdollahzadeh Jamalabadi ◽  
Alamian ◽  
Yan ◽  
Li ◽  
Leveneur ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Rise ◽  
Rotational Speed ◽  
Volume Fraction ◽  
Journal Bearings ◽  
Thermal Design ◽  
Average Shear Stress ◽  
Average Shear ◽  
Dissipation Power

Performance investigation of oil journal bearings is of particular importance given the growing use of them as a support for rotary components in a wide range of industrial machines. Frictional forces and shear stresses, which are proportionate to the velocity of lubricating layers at different points in the bearing space, provide the basis for changing temperature conditions. Various factors such as rotational velocity increase, slip width reduction, and small heat transfer coefficient of lubricant cause intensification of lubricant temperature changes. In the present study, with using computational fluid dynamic (CFD) thermohydrodynamic (THD) numerical simulations, the effect of nanoparticles on the performance features of plain journal bearings is evaluated. Particularly, 3D simulation of a journal bearing is implemented using CFD which considerably improves the accuracy of results, coupled with conjugate heat transfer model for metal parts of bearings. Reynolds equation model is used to calculate the oil-film pressure developed in hydrodynamic journal bearings by applying the nano-based lubricants. The configuration of thrust bearing consists of six pads in this study. In order to reduce the modeling complexity and computational cost and because of the symmetrical geometry of the pads, simulation of a single pad is considered instead of the entire domain. In this study, TiO2 nanoparticle with different volume fraction percentages are used. The parameters that are changed to evaluate the performance of the bearing include volume fraction percentage of the nanoparticle, type of lubricant, and rotational speed. Based on the results, for all different lubricant types, the dissipation power, average shear stress, and temperature rise are increased with augmenting the rotational speed. By increasing the rotational speed from 500 to 1500 rpm, the average shear stress increases by more than 100%, 120%, and 130% for DTE 26, DTE 25, and DTE 24 lubricant types, respectively. Moreover, by increasing the rotational speed from 500 to 1500 rpm, the dissipation power, and temperature rise are increased around 600% and 800%, respectively. Furthermore, increasing nanoparticles volume fraction from 0% to 10%, increases all parameters by approximately 10% for all lubricant types and in all rotational speeds.

scholarly journals Numerical Study of Fluid Dynamics in Suspension Culture of iPS Cells

2019 ◽  
Vol 17 (1) ◽  
pp. 73 ◽  
Author(s):  
Masaki Yano ◽  
Takuya Yamamoto ◽  
Yasunori Okano ◽  
Toshiyuki Kanamori ◽  
Mashiro Kino–oka
Keyword(s):  
Shear Stress ◽  
Suspension Culture ◽  
Numerical Study ◽  
Maximum Shear Stress ◽  
Ips Cells ◽  
Stirred Tanks ◽  
Average Shear Stress ◽  
Average Shear ◽  
Orbital Shaking ◽  
Induced Pluripotent

In a suspension culture of iPS cells, the shear stress generated during mixing is expected to promote differentiation of induced pluripotent stem (iPS) cells. The stress on the cells can be controlled by rotational rate and shape of impeller. However, it is difficult to optimize these operative parameters by experiments. Therefore, we have developed a numerical model to obtain the average and the maximum shear stress in two kinds of stirred tanks and an orbital shaking cylindrical container. The present results showed that the shear stress strongly depended on the type of mixing and lesser extent on the shape of the impeller. The average shear stress is larger in the shaking mode than that in the stirring mode. In contrast, the maximum shear stress is much smaller in the shaking than the stirring. These results suggest that stirring and shaking should be selectively used depending on the application

Study on the Characteristics of Flow and Heat Transfer of Polymeric-Fluid-Based Cu Nanofluids

2017 ◽  
Author(s):  
Weihua Cai ◽  
Yongyao Li ◽  
Yue Wang ◽  
Xin Zheng ◽  
Mengsheng Zhu
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Volume Fraction ◽  
Solution Flow ◽  
Flow And Heat Transfer ◽  
Wall Shear ◽  
Polymer Aqueous Solution

In this paper, we propose a new fluid: drag-reducing-fluid-based nanofluids (DRFBN), i.e., nanoparticles are added into polymer aqueous solution. In order to investigate the flow and heat transfer characteristics of this new fluid, the Reynolds stress turbulence model and equivalent viscosity model are used in the simulations. Wall shear stress and Nusselt number (Nu) are chosen to represent the effects of drag reduction and heat enhancement respectively. The numerical studies mainly focus on the effects of different parameters on wall shear stress and Nu. The results show that comparison with water flow, DRFBN flow still has remarkable drag-reducing effect; comparison with polymer aqueous solution flow, DRFBN flow has some improvement on heat transfer. Therefore, DRFBN has duel effects: drag reduction and heat transfer enhancement. Besides, it is found that the parameters of nanoparticle volume fraction, Reynolds number and drag-reducing parameter have remarkable effects on wall shear stress and Nu of DRFBN flow.

scholarly journals Mixed Convection of Hybrid Nanofluids in an Annulus

2018 ◽  
Vol 10 (2) ◽  
pp. 55 ◽  
Author(s):  
F. Selimefendigil ◽  
H. F. Oztop ◽  
Mohamed E. Ali
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Rotational Speed ◽  
Volume Fraction ◽  
Outer Cylinder ◽  
Hybrid Nanoparticles ◽  
Hybrid Particles ◽  
Volume Fractions ◽  
Hybrid Nanofluids

 In this study, mixed convection in an annulus formed by two horizontal isothermal cylinder surfaces and filled with hybrid nanofluids was examined with Galerkin weighted residual finite element method. The outer cylinder is rotating and inner cylinder is stationary. Influence of Rayleigh number, angular rotational speed of the outer cylinder, eccentricity of the inner cylinder, solid volume fractions of different nanoparticles (alumina, copper, hybrid particles between 0 and 0.02) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average heat transfer enhances with Rayleigh number, solid volume fractions of nanoparticles and eccentricity ratio and reduces as the angular rotational speed of the outer cylinder increases. Adding nanoparticles was found to be advantageous for lower values of Rayleigh number and higher values of angular rotational speed. At the highest volume fraction of Cu nanoparticles, average Nusselt number increases by 31.75 % when the inner cylinder center moves in +y direction. Nanofluid with hybrid nanoparticles gives heat transfer rates which are higher than that of with alumina and lower than that of with copper nanoparticles for the same volume fraction.

Analysis and Experimental Research on the Fluid–Solid Coupled Heat Transfer of High-Speed Motorized Spindle Bearing Under Oil–Air Lubrication

2020 ◽  
Vol 143 (7) ◽  
Author(s):  
Feng Gao ◽  
Weitao Jia ◽  
Yan Li ◽  
Dongya Zhang ◽  
Zhengliang Wang
Keyword(s):  
Heat Transfer ◽  
Temperature Rise ◽  
High Speed ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Phase Flow ◽  
Motorized Spindle ◽  
Two Phase ◽  
Spindle Bearing ◽  
Air Lubrication

Abstract For high-speed motorized spindle bearing, temperature rise is the primary factor that restricts the maximum speed of spindle and affects the stability of system. This paper addresses the lubrication and cooling of spindle bearing by exploiting the precise oil control and high cooling efficiency of oil–air lubrication. Enlightened by the bearing tribology and two-phase flow theory, a numerical model of oil–air two-phase flow heat transfer inside bearing cavity is created, with which the effects of operating condition and nozzle structure parameters on the temperature rise are studied. As the results show, with the elevation in speed, the heat generation increases rapidly, and despite the somewhat enhanced heat transfer effect, the temperature still tends to rise. Given the higher volume fraction of air than oil in the two-phase flow, the temperature rise of bearing is suppressed greatly as the air inlet velocity increases, revealing a remarkable cooling effect. When a single nozzle is used, the bearing temperature increases from the inlet to both sides, which peaks on the opposite side of the inlet. In case multiple evenly distributed nozzles are used, the high-temperature range narrows gradually, and the temperature distributions in the inner and outer rings tend to be consistent. With the increase in the nozzle aspect ratio, the airflow velocity drops evidently, which affects the heat dissipation, thereby resulting in an aggravated temperature rise. Finally, the simulation analysis is verified through experimentation, which provides a theoretical basis for selecting optimal parameters for the oil–air lubrication of high-speed bearing.

Model-Based Shear Stress Gradient in Realistic Vascular Flows and Its Relation to Arterial Macromolecular Permeability

2003 ◽  
Author(s):  
Jeffrey A. LaMack ◽  
Heather A. Himburg ◽  
Xue-Mei Li ◽  
Morton H. Friedman
Keyword(s):  
Shear Stress ◽  
Fluid Dynamic ◽  
Stress Gradient ◽  
Blue Dye ◽  
Infrarenal Aorta ◽  
Flow Measurements ◽  
Average Shear Stress ◽  
Average Shear ◽  
Time Average ◽  
Shear Stress Gradient

Evans blue dye (EBD) was injected into the carotid arteries of three anesthetized pigs and allowed to circulate for 90 minutes. At the conclusion of the 90-minute period, the animals were sacrificed and injection casts of the infrarenal aorta and iliac-femoral arteries were prepared. The casts with their surrounding arteries were removed and immersed in fixative. After fixation, the EBD-stained vessels were separated from the casts, which were used to construct computational meshes for simulation of the flow fields and wall shear stress distributions that had existed in the casted regions during the experiments. The inlet flow waves and flow partitions were based on flow measurements performed during each experiment. Based on a conceptual model of the relation between shear stress nonuniformity and permeability increase, the spatial and angular variation of the gradient of the time-average shear stress at the walls of the external iliac arteries was found from the computational fluid dynamic simulations for each experiment. Using affine transformations, the gradient and time-average shear stress results, and the EBD optical density distributions, were mapped to a common template, allowing pixel-by-pixel correlations of the hemodynamic stress parameters and local permeability. The results suggest that both shear stress gradient and time-average shear play a role in determining vascular permeability to macromolecules.

Analytical and numerical modelling of Newtonian and non-Newtonian liquid in a rotational cross-flow MBR

2012 ◽  
Vol 66 (11) ◽  
pp. 2318-2327 ◽  
Author(s):  
T. R. Bentzen ◽  
N. Ratkovich ◽  
S. Madsen ◽  
J. C. Jensen ◽  
S. N. Bak ◽  
...  
Keyword(s):  
Shear Stress ◽  
Laser Doppler Anemometry ◽  
Membrane Surface ◽  
Empirical Relationship ◽  
Tangential Velocity ◽  
Cross Flow ◽  
Weighted Average ◽  
Newtonian Liquid ◽  
Average Shear Stress ◽  
Average Shear

Fouling is the main bottleneck of the widespread use of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid cross-flow velocity. In rotational cross-flow MBR systems, this is attained by the spinning of, for example, impellers. Validation of the CFD (computational fluid dynamics) model was made against laser Doppler anemometry (LDA) tangential velocity measurements (error less than 8%) using water as a fluid. The shear stress over the membrane surface was inferred from the CFD simulations for water. However, activated sludge (AS) is a non-Newtonian liquid, for which the CFD model was modified incorporating the non-Newtonian behaviour of AS. Shear stress and area-weighted average shear stress relationships were made giving error less that 8% compared with the CFD results. An empirical relationship for the area-weighted average shear stress was developed for water and AS as a function of the angular velocity and the total suspended solids concentration. These relationships can be linked to the energy consumption of this type of systems.

Failure Pressure in Corroded Pipelines Based on Equivalent Solutions for Undamaged Pipe

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
M. Bony ◽  
J. L. Alamilla ◽  
R. Vai ◽  
E. Flores
Keyword(s):  
Shear Stress ◽  
Numerical Simulations ◽  
Wall Thickness ◽  
Yield Criteria ◽  
Failure Pressure ◽  
Average Shear Stress ◽  
Average Shear ◽  
Thin Walled ◽  
Von Mises

Simple and accurate approaches to predict failure pressures in corroded pipelines are outlined in this work. It is shown that failure pressures for corroded pipelines can be predicted from the solution for undamaged pipelines using an equivalent wall thickness. Three different yield criteria (Tresca, ASSY (average shear stress yield), and von Mises) are reviewed in the light of reported experimental burst pressures. At first, failure pressures for cylindrical vessels with an infinitely long groove are studied by means of numerical simulations. The effect of groove size (depth and width) over the pipeline performance is quantified through a model. Finally, the scheme is extended to estimate the failure pressure of thin walled vessels with irregular finite defects.

Non-Darcy Natural Convection From a Vertical Cylinder Embedded in a Thermally Stratified and Nanofluid-Saturated Porous Media

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
A. M. Rashad ◽  
S. Abbasbandy ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Shear Stress ◽  
Natural Convection ◽  
Volume Fraction ◽  
Vertical Cylinder ◽  
Physical Parameters ◽  
Porous Media Model ◽  
Local Shear ◽  
Local Shear Stress

In recent years, nanofluids have attracted attention as a new generation of heat transfer fluids in building heating, heat exchangers, plants, and automotive cooling applications because of their excellent thermal performance. Various benefits of the application of nanofluids include improved heat transfer, heat transfer system size reduction, minimal clogging, microchannel cooling, and miniaturization of systems. In this paper, a study of steady, laminar, natural convection boundary-layer flow adjacent to a vertical cylinder embedded in a thermally stratified nanofluid-saturated non-Darcy porous medium is investigated. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis, and a generalized porous media model, which includes inertia and boundary effects, is employed. The cylinder surface is maintained at a constant nanoparticles volume fraction, and the wall temperature is assumed to vary with the vertical distance according to the power law form. The resulting governing equations are nondimensionalized and transformed into a nonsimilar form and then solved by Keller box method. A comparison is made with the available results in the literature, and our results are in very good agreement with the known results. A parametric study of the physical parameters is made, and a representative set of numerical results for the velocity, temperature, and volume fraction, as well as local shear stress and local Nusselt and Sherwood numbers, are presented graphically. The salient features of the results are analyzed and discussed. The results indicate that, when the buoyancy ratio or modified Grashof number increases, all of the local shear stress, local Nusselt number, and the local Sherwood number enhance while the opposite behaviors are predicted when the thermophoresis parameter increases. Moreover, increasing the value of the surface curvature parameter leads to increases in all of the local shear stress and the local Nusselt and Sherwood numbers while the opposite behaviors are obtained when either of the thermal stratification parameter or the boundary effect parameter increases.

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