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Lubricants for the Disk Drive Industry
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Spindle motors have evolved to fluid dynamic bearings, which provide much smoother rotation with comparable or better stiffness than ball bearings. Stiffness is provided by the relative motion between a shaft and a sleeve, one of which contains a pattern of grooves on its surface. The grooves pressurize a several micron thick film of oil. This chapter highlighted two key properties of the fluid bearing oil: viscosity and vapor pressure. Present fluid bearing oils have a low enough vapor pressure so that the evaporation loss of oil is small over the lifetime of the drive. However, there is a tradeoff between the vapor pressure and oil viscosity such that the lowest operating temperature of the drive is limited by the maximum power of the motor and the oil viscosity. Attempts to use lower-viscosity oils result in oils with a higher vapor pressure, and this appears to be a physical constraint of oils in general. Detailed thermodynamic analysis of the relationship between oil vapor pressure and viscosity was reviewed. The flow- and vaporization-activation energies are linked to one another by interaction forces between the oil molecules. There is, however, in principle, some chance of reducing the viscosity without altering the activation energies if a molecular structure could be found which has a large positive rotational component of the flow-activation entropy. Molecular structures examined have so far provided limited insight into how this may be accomplished.
Hydraulic Fracturing from the Groundwater Perspective
Published in M. Thangarajan, Vijay P. Singh, Groundwater Assessment, Modeling, and Management, 2016
Ruth M. Tinnacher, Dipankar Dwivedi, James E. Houseworth, Matthew T. Reagan, William T. Stringfellow, Charuleka Varadharajan, Jens T. Birkholzer
Operating wells (whether used for production or injection/disposal) can serve as transport pathways for subsurface migration in a similar fashion to deteriorated abandoned wells. Failures in well design and construction may allow migration of gas and fluids from the reservoir, or from shallower gas and fluid-bearing formations intersected by the wellbore. Pathways can be formed due to inadequate design, imposed stresses unique to stimulation operations, shear failure due to subsidence, or other forms of human/operator error. Class II deep injection wells with casing or cement inadequacies would also have similar potential for contamination as a failed production well or a well that fails due to stimulation pressures. Examples of potential subsurface releases through wells are illustrated in Figure 7.6.
Petroleum Geophysical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
A dense and compact rock generates more pulling force, resulting in a greater gravity anomaly than soft and porous rock. A feeble gravity anomaly is generated due to unconsolidated soft sedimentary rock. A basement rock that has been pushed up into sedimentary rock gives rise to an appreciable anomaly, due to reduced distance from the surface and the denser character of the rock. Different underground structures (denser rock, anticlines, synclines, salt domes, folds, faults, porosity and fluids) generate gravity anomalies differently so they are identifiable. Salt rock is less dense and softer and has little impact on gravity reading, so the presence of a salt dome can be established. Fault-, fold- and fluid-bearing rock gives different anomalies.
Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area, eastern margin of the Ordos Basin, China
Published in Australian Journal of Earth Sciences, 2018
Y. Y. Huyan, X. Q. Pang, T. S. Liu, F. J. Jiang, X. Z. Chen, X. Q. Ma, L. L. Li, X. H. Shao, D. Y. Zheng
NMR is a non-destructive technique that has been widely used in the petroleum industry (Meng, Ge, Ji, & Wang, 2016). The NMR relaxation is based on the response of fluids to magnetic excitation. Before applying a frequency pulse to fluid-bearing samples, the fluid (water, gas, oil) is polarised in a static magnetic field. The frequency pulse stimulates the hydrogen protons and generates the phenomenon of NMR. Then, by removing the frequency pulse, an exponentially attenuating signal is recorded. The nuclear magnetic signal contains two important parameters, the longitudinal relaxation time, T1, and transverse relaxation time, T2. Generally, the T2 spectrum is used to investigate the fluid distribution in pores (Li et al., 2017a).
Research on Effects of Groove Shape Optimization on Cavitation and Lubricating Characteristics for Microgroove Rotary Seal
Published in Tribology Transactions, 2018
Bing Xue, Chao Wei, Ji Bin Hu, Yi Min Zhao
Cavitation may occur in the divergent gap region. For a whole hydrodynamic groove of a rotary seal, the convergent and divergent gaps coexist; hydrodynamic effects in the convergent gap are enhanced with increasing speed, and negative effects in the divergent gap are also enhanced. When the pressure in the divergent gap is lower than the cavitation pressure, cavitation will occur in the oil film will occur. In the cavitation region, the viscosity of a lubricant (air) is very small compared to that of the fluid, which weakens the hydrodynamic effect and leads to a decrease in fluid bearing capacity. Therefore, cavitation plays an important role in the lubrication performance of rotary seals and research on cavitation is meaningful. In order to eliminate the negative effects and improve the lubrication performance of rotary seals, it is necessary to optimize the rotary seal groove shape structures and molded lines.
A Review of Morton Effect: From Theory to Industrial Practice
Published in Tribology Transactions, 2018
Recall that ME is an inherent feature of a rotor with a fluid bearing/seal system. In most cases, the rotors are well balanced and thus exhibit satisfactory vibration levels. The satisfactory level can be maintained as long as the factors that influence the differential heating remain the same. However, the incubation time of ME will come to an end under certain circumstances; for example, relocations (De Jongh and van de Hoeven (22)) or upgrades of rotor systems (Faulkner, et al. (4)).