Temperature-viscosity Effects Research Articles

Analysis of Thermo-Hydrodynamic Lubrication of Three-Lobe Semi-Floating Ring Bearing Considering Temperature–Viscosity Effect and Static Pressure Flow

Analysis of Thermo-Hydrodynamic Lubrication of Three-Lobe Semi-Floating Ring Bearing Considering Temperature–Viscosity Effect and Static Pressure Flow

Analysis of lubrication performance and flow field for lead-bismuth bearings considering the temperature-viscosity effect

Lead-bismuth bearing performance and dynamic properties are crucial for ensuring the steady operation of lead-bismuth liquid metal pumps since they are one of the primary supporting elements in the lead-bismuth cold fast reactor system. To study and analyze the lubrication performance of lead-bismuth bearings as well as the influence of the viscous-temperature property of lead-bismuth medium on the bearing load performance, a hydrodynamic model based on CFD (Computational Fluid Dynamics) is established. The performance of lubrication comprises addressing the static and dynamic properties of lead-bismuth bearings. The pressure and temperature flow fields of the Lead-bismuth bearing under various working conditions were determined by solving the N-S equation and energy equation. The numerical findings demonstrate a clear strip-like distribution in the temperature and pressure flow fields of the lead-bismuth bearing. The pressure flow distribution in the working and feedback grooves is symmetrical, the temperature flow distribution is isotropic, and the temperature increase is mostly proportional to the rotation speed. As the rotation speed becomes larger, the force in the y-direction, power loss, and leakage flow rate all increase. Bearings with small radius clearance and greater rotation speeds have superior stability than those with big radius clearance and lower speeds. The findings of this paper serve as a point of reference for the study of the viscosity-temperature effect and lubrication theory of lead-bismuth bearings and supply the foundation for subsequent rotor dynamics calculations.

Steady-State Characteristics of Spiral Groove Floating Ring Gas-film Seal Considering Temperature-Viscosity Effect

During the operation of the floating ring gas film seal, a certain amount of heat is generated inside the seal gap, giving rise to thermal deformation of the seal rings, and further leading to operation unstable and increased leakage rate. Based on the gas lubrication theory, the control equations of gas pressure and gas film thickness of the floating ring gas film seal are obtained. And the energy and temperature-viscosity equation are also introduced. The above equations were solved by the finite difference method and their correctness was verified by experiments. The variation of opening force, leakage rate, friction force, and gas film temperature rise with rotating speed, inlet pressure, and eccentricity were analyzed. The results reveal that, for leakage rate, the difference between the modeled and tested values is only 2.94% at high speeds, taking into account the influence of the temperature-viscosity effect. The experiment substantiates that the temperature-viscosity effect model is scientifically valid. Operation parameters also have different effects on sealing performance. Compared with isothermal flow, the pressure distribution in the gas film flow field will change significantly with increasing gas temperature, which means that the temperature-viscosity effect cannot be neglected in the flow field calculation. These results provide grounds for further study of the thermoelastic effect of air film seal of floating ring and have important engineering significance.

Lubrication analysis of the piston ring of a two-stroke marine diesel engine considering thermal effects

Thermal deformation of the cylinder liner (TDCL) and the temperature–viscosity effect (TVE)of the lubricating oil are two common thermal effects which impact the lubrication properties of the piston-ring–liner tribological pair. In this study, the influence of these two thermal effects in a low-speed two-stroke diesel engine on piston ring lubrication performance are discussed in detail. For the TDCL, a steady-state heat-transfer model based on sequential fluid–solid coupling is used to solve for the heat-transfer coefficient and temperature on the coupling surface between the cylinder liner and the cooling water jacket. The boundary condition used to calculate the TDCL is the temperature distribution on the inner surface of the cylinder liner calculated empirically and verified experimentally. For the TVE, experimental data measured using capillary viscometers are used to determine the coefficients in four different empirical viscosity–temperature formulas, then the experimental and simulation results for TVE are compared using correlation coefficients and average absolute relative errors. Ultimately, the American Society for Testing and Materials (ASTM) model is selected to describe the viscosity–temperature characteristics of the lubricating oil used in this research. The results of the TDCL and the ASTM model are used in the lubrication model to analyze how the thermal effects influence the lubrication performance of the piston-ring–liner tribological pair.

Effects of thermal and elastic deformations on lubricating properties of the textured journal bearing

Hydrodynamic journal bearing is an important part of rotary machine and faces many challenges such as high rotating speed, heavy specific pressure, and large temperature rise with the development of industry. These challenges lead to notable thermal and elastic deformations of the journal bearing. Surface texture has been proved to be a valid method to promote bearing lubricating properties. However, effects of thermal and elastic deformations on lubricating properties of the textured journal bearing have not been clearly analyzed. Based on this, the article presents a method to transform thermal–structural–fluid interaction into thermal–structural interaction and thermal–fluid interaction based on textured journal bearing model. Cavitation and temperature-viscosity effects are also considered. Based on this method, action mechanisms of surface texture on lubricating properties are discussed considering elastic and thermal deformations, and effects of elastic and thermal deformations on the textured journal bearing are also investigated. The results show that the load carrying capacity and the maximum oil film pressure of the textured journal bearing both increase when elastic and thermal deformations are considered. Optimal texture parameters can enhance the backflow effect in dimples and restraint cavitation phenomenon in the oil film rupture region. Meanwhile, inertial and cavitation effects caused by surface texture have significant effects on elastic and thermal deformations of the journal bearing.

Influence of temperature – viscosity effect on ring-journal speed ratio and stability for a hydrodynamic floating ring bearing

Purpose The purpose of this paper is to study the influence of lubricant temperature-viscosity on the performance for a hydrodynamic journal floating ring bearing (FRB), including ring-journal speed ratio and stability. Design/methodology/approach The finite difference method was used to solve computational models of Reynolds equation, energy equation and temperature–viscosity equation. Dynamic coefficients were obtained based on the floating ring balance. The dynamic model of journal and floating ring was established to deduce the stability criterion of single mass symmetrical rigid FRB rotor system by the Routh–Hurwitz method. The outlet temperature and ring-journal speed ratio under different journal speeds were compared to experimental data. Findings The temperature–viscosity effect reduces the ring-journal speed ratio and stability of rotor system. According to theoretical and experimental results, the outlet temperature rises and ring-journal ratio drops when the journal speed rises. Originality/value The temperature–viscosity effect is combined with dynamic characteristics to analyze the stability of the rotor system and lubrication mechanism for an FRB. Influence of temperature–viscosity on the ring-journal ratio and multi-stable regions of system are studied.

Combined effects of Coriolis force and temperature-viscosity dependency on hydro-viscous transmission of rotating parallel disks

Abstract The temperature rise of hydro-viscous film in rotating parallel disks is usually controlled by imposing throughflow for keeping high film viscosity, but the Coriolis effect induced by throughflow can resist hydro-viscous transmission in return. In this work, the combined effects of Coriolis force and temperature-viscosity dependency on the hydro-viscous transmission are investigated. Firstly, the momentum and energy equations are established and the temperature-viscosity relationship is given, meanwhile, the numerical method is introduced. Then the combined effects on temperature rise and viscous transmission are analyzed and partly validated in experiment. The results reveal that with throughflow rate increasing the resistant effect of Coriolis force can be more and more significant relatively to temperature-viscosity effect, so their balance should be highlighted.

A novel quasi-3D thermodynamic model of oil film bearing with non-Newtonian and temperature-viscosity effects

PurposeThe purpose of this paper is to propose a quasi-three-dimensional (3D) thermohydrodynamic (THD) model for oil film bearings with non-Newtonian and temperature-viscosity effects. Its performance factors, including precision and time consumption, are investigated.Design/methodology/approachTwo-dimensional (2D), 3D and quasi-3D numerical models are built. The thermal and mechanical behaviors of two types of oil film bearings are simulated. All the results are compared with solutions of commercial ANSYS CFX.FindingsThe 2D THD model fails to predict the temperature and pressure field. The results of the quasi-3D THD model coincide well with those of the 3D THD model and CFX at any condition. Compared with the 3D THD model, the quasi-3D THD model can greatly reduce the CPU time consumption, especially at a high rotational speed.Originality/valueThis quasi-3D THD model is proposed in this paper for the first time. Transient mechanical and thermal analyses of high-speed rotor-bearing system are widely conducted using the traditional 3D THD model; however, the process is very time-consuming. The quasi-3D THD model can be an excellent alternative with high precision and fast simulation speed.

Thermodynamics and Stability Analysis of High-Speed Hydrodynamic Journal Bearing

The thermodynamic model of the high-speed hydrodynamic journal bearing is established to analyze the influence of the temperature-viscosity effect on the oil film in aspects of dynamic characteristics and stability. The coupling governing equations of the bearing including the Reynolds equation, energy equation and viscosity-temperature equation are solved to obtain the pressure distribution, temperature distribution and viscosity distribution, according which the stiffness coefficients and damping coefficients are acquired. Then the stability analysis of the bearing is processed based on Routh-Hurwitz stability criteria. The result indicates that when temperature-viscosity effect is taken into account, the dynamic characteristics, threshold speed and threshold mass show distinct decrease, and the degree of which is positive relative to the rotating speed, the eccentricity and the aspect ratio.

Influence of particles on the loading capacity and the temperature rise of water film in Ultra-high speed hybrid bearing

Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant and ultra-high speed of hybrid bearing, which cannot be ignored under the high speed and micro-space conditions of ultra-high speed water-lubricated hybrid bearing. Considering the impact of solid particles in lubricant, turbulence and temperature viscosity effects of lubricant, the influences of particles on pressure distribution, loading capacity and the temperature rise of the lubricant film with four-step-cavity ultra-high speed water-lubricated hybrid bearing are presented in the paper. The results show that loading capacity of the hybrid bearing can be affected by changing the viscosity of the lubricant, and large particles can improve the bearing loading capacity higher. The impact of water film temperature rise produced by solid particles in lubricant is related with particle diameter and minimum film thickness. Compared with the soft particles, hard particles cause the more increasing of water film temperature rise and loading capacity. When the speed of hybrid bearing increases, the impact of solid particles on hybrid bearing becomes increasingly apparent, especially for ultra-high speed water-lubricated hybrid bearing. This research presents influences of solid particles on the loading capacity and the temperature rise of water film in ultra-high speed hybrid bearings, the research conclusions provide a new method to evaluate the influence of solid particles in lubricant of ultra-high speed water-lubricated hybrid bearing, which is important to performance calculation of ultra-high speed hybrid bearings, design of filtration system, and safe operation of ultra-high speed hybrid bearings.

A Nonisothermal Fluid-Structure Interaction Analysis on the Piston/Cylinder Interface Leakage of High-Pressure Fuel Pump

In this paper, a nonisothermal fluid-structure interaction mathematical model for the piston/cylinder interface leakage is presented. Full account is taken of the piston eccentricity, elastic deformations of the piston pair, the nonisothermal flow in the interface, and the physical properties of the fluid such as the pressure-viscosity and temperature-viscosity effects. The numerical method for the solution of the model is given, which can simultaneously solve for the fluid pressure distribution and leakage rate in the interface. The model is validated by comparing the calculated leakage rates with the measurements. Results show the good accuracy of the model. The impacts of parameters such as the piston diameter, the initial clearance between the piston pair, and the piston velocity on the leakage rate are discussed. Some of the conclusions provide good guidance for the design of high-pressure fuel pumps.

Analysis on pressure characteristics of pump turbine guide bearing rotating sump based on VOF model

With the technology of Computational Fluid Dynamics (CFD), this paper conducts a 3D numerical simulation for the oil and gas flow field in the Pump turbine guide bearing rotating sump. VOF model is adopted in this simulation. This study calculates distribution of the oil-air phase and characteristics of the pressure. The influence of sump rotating speed, oil level and oil viscosity on the pressure at the inlet of oil-immersion plate are discussed. The results demonstrate that the static pressure at the inlet is roughly proportional to oil level. Too low level may result in the separation between lubrication oil and supply hole on the oil-immersion plate, which then disables the oil supply. The static pressure at the inlet increases parabola as the sump rotating speed increases. To ensure the supply pressure, the unit is not suitable for long time operation under low rotating speed. The temperature-viscosity effect of the lubricant oil has little influence on the oil pressure at the supply hole. This paper provides a theoretical base for the safe design and operation of the pump turbine rotating sump, and offers the inlet boundary condition for the analysis of the oil film dynamic characteristics of the turbine guide bearing.

Numerical and experimental research of bidirectional thrust bearings used in pump-turbines

A three-dimensional thermo-elasto-hydro-dynamic model for bidirectional thrust bearings used in pump-turbines taking into account the temperature-viscosity effect as well as thermal-elastic deformations in the pad and runner surface was set up. The finite difference method was employed to solve the thermo-hydro-dynamic model, and the thermal-elastic deformations in the pad and runner were obtained by the finite element software ANSYS11.0. The data transfer between the thermo-hydro-dynamic model and ANSYS11.0 was carried out automatically by an interface program. Laboratory test was performed on the Harbin Electric Machinery 3000 ton thrust bearing test rig. A detailed comparison between the experimental results and numerical predictions showed quite good overall agreement on the oil film thickness, pressure and temperature, which provided an evidence of validation of the three-dimensional thermo-elasto-hydro-dynamic model coupled with finite difference method and finite element method developed in this article.

On the Glass in Coal Fly Ashes: Recent Advances

ABSTRACTRecent advances in the characterization of the glassy aluminosilicate phases in coal fly ashes are reviewed and discussed in terms of the development of new models describing their mechanism of formation, composition, structural relationships and chemical reactivity. Characterization techniques such as electron microscopy, x-ray diffraction, infrared and Raman spectroscopy, nuclear magnetic resonance and Mössbauer spectroscopies, thermal analysis, acid dissolution, silanation, and density fractionation have been used as experimental probes, and reveal a range of information relating to the glass phases from the macro, through the micro, to the nano-structural levels. Complex inter- and intra-particle heterogeneity in ash is observable not only in bulk chemical and mineralogical analyses but also at the molecular level in the constituent glasses. Remarkable relationships between ash particle size, density and glass composition have been observed and lead to a new proposed mechanism for ash morphogenesis based on temperature-viscosity effects in the mineral precursor melts in the boiler flame. A glass-ceramic model for fly ash particle structure is proposed and discussed in terms of phase relations in the CaO–SiO2–Al2O3 and FeO–Fe2O3–A12O3–SiO2 systems, modification of the aluminosilicate glasses by alkali and alkaline earth metal cations, and microheterogeneity involving glass devitrification and phase separation.