scholarly journals The Lubricity and Rheological Properties of Magnetorheological Fluids

2016 ◽  
Vol 39 (1) ◽  
pp. 141-158
Author(s):  
Emil Nowiński

Abstract The article presents results of tribological research carried on four ball tester and dynamic rheometer for different magnetorheological fluids. The wear test was conducted with and without magnetic field. The dynamic rheology measurement was done at wide range of velocity. The inteligent fluids differed from each other by an amount of solid phase and kind of base liquid.

Author(s):  
Yurui Shen ◽  
Dezheng Hua ◽  
Xinhua Liu ◽  
Weihua Li ◽  
Grzegorz Krolczyk ◽  
...  

Abstract In order to study the rheological properties of aqueous magnetorheological fluids (MRFs) from microscopic point of view, an experimental observation method based on the fluorescence confocal laser scanning microscope is proposed to clearly produce the chain shape of the magnetic particles. Firstly, the mathematical model of the magnetic particles is established in a magnetic field using the magnetic dipole theory, and the MRFs with different fraction volumes and different magnetic fields are investigated. Furthermore, an aqueous MRFs experiment is prepared, in which the magnetic particles are combined with Alexa 488 fluorescent probe. On this basis, an observation method is innovatively developed using two-dimensional (2D) and three-dimensional (3D) image analysis by the fluorescence confocal microscope. The rheological mechanism of the aqueous MRFs is investigated using four different types of MRFs in an external magnetic field. The analysis results demonstrate that the simulation and experimental rheological properties of the MRFs are consistent with the magnetic dipole theory. Moreover, the proposed method is able to real-time observe the rheological process of the MRFs with a very high resolution, which ensures the correctness of the analysis results of the rheological mechanism.


Tribologia ◽  
2016 ◽  
Vol 269 (5) ◽  
pp. 41-49 ◽  
Author(s):  
Wojciech HORAK ◽  
Józef SALWIŃSKI ◽  
Marcin SZCZĘCH

Magnetic fluids are substances whose rheological properties can be actively influenced by treatment with a magnetic field. Two main types of magnetic fluids can be distinguished: ferromagnetic fluids, and magnetorheological fluids. Ferrofluids are mostly used in sealing engineering, whereas magnetorheological fluids are usually applied in controlled systems for the dissipation of mechanical energy, like brakes and dampers. The ability to control the rheological properties of magnetic fluids opens new horizons for development in machine design, among others in the areas of bearing engineering. The paper presents a comparative analysis of the rheological characteristics of selected magnetic fluids with a focus on the possible areas of the application of these substances in bearing engineering.


2005 ◽  
Vol 19 (01n03) ◽  
pp. 593-596 ◽  
Author(s):  
J. M. HE ◽  
J. HUANG

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological properties. Upon application of a magnetic field, MR fluids have a variable yield strength. Altering the strength of the applied magnetic field will control the yield stress of these fluids. In this paper, the method for measuring the yield stress of MR fluids is proposed. The curves between the yield stress of the MR fluid and the applied magnetic field are obtained from the experiment. The result indicates that with the increase of the applied magnetic field the yield stress of the MR fluids goes up rapidly.


2020 ◽  
Vol 32 (1) ◽  
pp. 49-64
Author(s):  
Yongbo Peng ◽  
Pei Pei

To predict the shear stress of magnetorheological fluids (MRFs) under magnetic field and shear flows, a meso-microscale shear model is proposed based on the entire course of particle aggregates and chains. For this purpose, a systematic study on the microstructure evolution and rheological properties of MRFs is conducted by using molecular dynamics simulations. An efficient chain identification technique is introduced to count the number of particle chains within the suspension system. From the perspective of particle-level simulations, the microstructured behavior of MRFs involving particle aggregation and internal structure evolution of magnetorheological suspensions are addressed. Shear properties of MRFs derived by the proposed model are studied, and model verification by comparison with previous experimental data and predictions of the existing structural viscosity model is included as well. It is revealed that the proposed meso-microscale shear model exhibits satisfactory accuracy and efficiency for describing the rheological properties of MRFs. Besides, the critical factors linked with rheological properties of MRFs such as magnetic field strength, particle volume fraction and shear rate, are analyzed, further demonstrating the applicability of the proposed model in design and optimization of MRFs.


Magnetic nanofluid (Ferrofluid) is a magnetic colloidal suspension consisting of base liquid and magnetic nanoparticles with a size range of 5–15 nm in diameter coated with a surfactant layer. The effect of magnetic field on fluids is worth investigating due to its numerous applications in a wide range of fields. The study of interaction of the magnetic field or the electromagnetic field with fluids have been documented (e.g., among nuclear fusion, chemical engineering, medicine, and transformer cooling). The goal of nanofluid is to achieve the highest possible thermal properties at the smallest possible concentrations by uniform dispersion and stable suspension of nanoparticles in host fluids. In this chapter, the influence of external magnetic field on ferrofluid flow and heat transfer is investigated. Both effects of Ferrohydrodynamic (FHD) and Magnetohydrodynamic (MHD) have been taken in to account. So, the effects of Lorentz and Kelvin forces on hydrothermal behavior are examined.


Tribologia ◽  
2016 ◽  
Vol 269 (5) ◽  
pp. 51-61 ◽  
Author(s):  
Wojciech HORAK ◽  
Józef SALWIŃSKI ◽  
Marcin SZCZĘCH

Magnetic fluids belong to the class of materials in which rheological properties can be controlled by magnetic fields. Magnetic fluids are suspensions of ferromagnetic particles in a carrier fluid, and the magnetic field can change their internal structure. This phenomenon is fully reversible, almost instantaneously. The test results of a hydrostatic bearing lubricated by magnetic fluid are shown in the publication [L. 7]. It has been shown that the use of MR fluids as a lubricant allows high stiffness of the bearing to be obtained regardless of the height of the bearing gap. The publication [L. 8] presents the results of a thrust bearing lubricated by magnetic fluid with no external feed pump. The load capacity of the bearing was achieved by a self-sealing effect. This effect is associated with the ability to hold a magnetic fluid in a predetermined position through the magnetic field. This is caused by the appropriate geometry of the bearing surface. This effect retains the flow of the magnetic fluid out of the bearing gap as a result of the occurrence of a magnetic barrier, which counteracts the movement of the magnetic fluid. This barrier is a result of a local increase or decrease in magnetic induction similar to magnetic fluid seals. Another phenomenon highlighted in [L. 9, 10, 11] is the generation in the magnetic fluid of additional pressure due to the interaction of the magnetic field gradient. The result is an additional buoyancy force. When selecting a magnetic fluid for application in the thrust bearing, a number of factors should be taken into account. In addition to the parameters describing the typical lubricant, such as lubricity, corrosion properties, and work at high temperatures, the magnetic fluid used in the friction zone should allow a wide range of the rheological properties to be obtained due to changes in the magnetic field intensity. It is also important that the magnetic fluids have the ability to generate the appropriate value of the normal force due to the magnetic field.


Tribologia ◽  
2019 ◽  
Vol 285 (3) ◽  
pp. 45-50
Author(s):  
Wojciech HORAK ◽  
Marcin SZCZĘCH

The operating state of thrust plain bearings is a function of many parameters, both geometric and related to load conditions. Besides the methods of controlling bearings of this type used so far, new possibilities of modelling their operating characteristics by using substances with controlled rheological properties as a lubricant can be pointed out. Magnetorheological fluids create such a possibility. These are suspensions of particles with magnetic properties in a carrier fluid (usually in mineral or synthetic oil). The influence of magnetic field on this type of fluids changes their rheological properties. This process is almost instantaneous and fully reversible. The paper presents the results of investigations of a thrust squeeze bearing lubricated with magnetorheological fluid. The aim of the study was to determine the influence of selected factors on the axial force as a result of the oscillatory squeeze load.


2017 ◽  
Vol 17 (1) ◽  
pp. 197-201
Author(s):  
J. Kolczyk ◽  
Ł. Jamrozowicz ◽  
N. Kaźnica

Abstract The results of investigations of the rheological properties of typical ceramic slurries used in the investment casting technology - the lost wax technology are presented in the paper. Flow curves in the wide range of shear velocity were made. Moreover, viscosity of ceramic slurries depending on shearing stresses was specified. Tests were performed under conditions of three different temperatures 25, 30 and 35°C, which are typical and important in the viewpoint of making ceramic slurries in the investment casting technology. In the light of the performed investigations can be said that the belonging in group of Newtonian or Non - Newtonian fluid is dependent on content of solid phase (addition of aluminum oxide) in the whole composition of liquid ceramic slurries.


Author(s):  
Wanning Zhu ◽  
Xufeng Dong ◽  
Hao Huang ◽  
Min Qi

The improvement of properties of magnetorheological fluids and mechanism study has long been a classic area within the field of magnetorheological materials. This article was undertaken to dope the iron nanoparticles synthesized by direct current electric arc discharge with the traditional carbonyl iron powders to prepare bimodal magnetorheological fluids with different doping ratios. Their rheological properties and sedimentation stability were evaluated to explore the influence rules and mechanisms. The results indicate that the effect of the addition of iron nanoparticles on rheological properties under magnetic field is a combination of two opposing factors such as the strengthening of the structure and the weakening of magnetization. The sedimentation stability of the bimodal magnetorheological fluids improved significantly with the increase in the proportion of iron nanoparticles, which is attributed to the help of both free state and adsorbed state iron nanoparticles in magnetorheological fluids. Furthermore, within a specific magnetic field strength range, the bimodal magnetorheological fluids with a small proportion of iron nanoparticles can achieve an improvement in both rheological property and sedimentation stability compared with carbonyl iron particles–based magnetorheological fluids.


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