Multiphase Computational Fluid Dynamics of Rotary Shaft Seals

Background: The use of electric vehicles is expected to increase day by day. The operating conditions of the rotary shaft seals used in the powertrain of electric vehicles are more challenging than those of internal combustion engines. The maximum operating temperature of seal used in electric vehicles is 150℃ and the maximum operating speed is 16,000RPM. It is impossible for a standard seal with a garter spring not to leak under these operating conditions, which has led us to turn to alternative designs. Objective: The objective of starting this study is to develop a new generation rotary shaft seal to be used in electric vehicles with finite element analysis (FEA) and optimization. Methods: During this study, finite elements, optimization and geometry development methods were used. First of all, alternative spiral knurled seal that can operate at high speeds was designed in this study. Secondly, our alternatively designed seal was tested to determine lifetime. Results: When we checked the results coming from test machines, the first design seal had approximately 5g of leakage at the end of 7 days. In the examinations made after the experiment, it was observed that the spirals were deleted at the end of 7 days. A finite element model of the first designed seal was created and radial load control was performed. When the radial load value obtained from the finite element model and the experimental radial load value are compared, it is seen that there is a deviation of around 4.3%. In the light of these data, the accuracy of the FEA model created in the Abaqus has been proven. The created finite element model was optimized within the boundary conditions with the help of Isight. A prototype of the optimized design seal was produced and a life-time test was carried out. The prototype seal of the optimized design had approximately 4g of leakage after 13 days under the same test conditions. Since the lifetime requested by the customer is 10 days, the optimization made on the seal is considered appropriate. The lifetime of the seal was approximately 95% improved. Conclusion: As a result, a new generation rotary shaft seal that can be used in electric vehicles, which is the aim of our study, has been developed. The prototype rotary shaft seal has been validated according to DIN 3761 specification.

The aim of this paper is to model the steady-state condition of a rotary shaft seal (RSS) system. For this, an iterative thermal-mechanical algorithm was developed based on incremental finite element analyzes. The behavior of the seal’s rubber material was taken into account by a large-strain viscoelastic, so called generalized Maxwell model, based on Dynamic Mechanical Thermal Analyses (DMTA) and tensile measurements. The pre-loaded garter spring was modelled with a bilinear material model and the shaft was assumed to be linear elastic. The density, coefficient of thermal expansion and the thermal conductance of the materials were taken into consideration during simulation. The friction between the rotary shaft seal and the shaft was simplified and modelled as a constant parameter. The iterative algorithm was evaluated at two different times, right after assembly and 1 h after assembly, so that rubber material’s stress relaxation effects are also incorporated. The results show good correlation with the literature data, which state that the permissible temperature for NBR70 (nitrile butadiene rubber) material contacting with ~80 mm shaft diameter, rotating at 2600/min is 100°C. The results show 107°C and 104°C for the two iterations. The effect of friction induced temperature, changes the width of the contact area between the seal and the shaft, and significantly reduces the contact pressure.

Process intensification of multiphase flow and reaction system: Perspectives

A number of particle models that are suitable for simulating multiphase fluid flow and biogeochemical processes have been developed during the last few decades. Here we discuss three of them: a microscopic model – molecular dynamics; a mesoscopic model – dissipative particle dynamics; and a macroscopic model – smoothed particle hydrodynamics. Particle methods are robust and versatile, and it is relatively easy to add additional physical, chemical and biological processes into particle codes. However, the computational efficiency of particle methods is low relative to continuum methods. Multiscale particle methods and hybrid (particle–particle and particle–continuum) methods are needed to improve computational efficiency and make effective use of emerging computational capabilities. These new methods are under development.

Electricity generated by nuclear power is now common in Japan. The present commercialized status of nuclear power generation technology has been established due to efforts of many engineers and also as a result of information accumulated from other advanced countries. Presently 23 percent of total electricity generated in Japan depends on nuclear power, and in the long run, this proportion is expected to increase further. Although accumulation of various important technological knowledge is required in nuclear power generation, the conversion of heat generated in nuclear reactors into electrical energy by means of a working medium is one of the most essential problems in the relevant technology. This paper deals with rotary shaft seals used in the circulation pump for the primary coolant, as an important functioning component in such a system. Once this sealing system causes trouble such as excessive leakage, it results in quite serious social problems; i.e., not only power failure but also possibly radioactive contamination. This paper explains the significant points of the development carried out on the shaft seal system for the primary coolant circulation pumps in PWR (pressurized water reactor) type nuclear power plants and describes the present status of design technology and results of practical operation.

Summary Cold heavy oil production with sand (CHOPS) technique has successfully improved oil recovery from heavy oil reservoirs due to high permeability channels resulted from sand failure and foamy oil flow enhancing heavy oil movability. However, impacts of the sand failure and the foamy oil flow on multiphase fluid flow features are still not properly understood. In this paper, an effective and systematic framework has been proposed to characterize the multiphase fluid flow and determine the three-phase relative permeability of CHOPS processes. A recently developed sand failure criterion and a relative permeability model have been integrated with a reservoir simulator to simulate the CHOPS process. The unknown parameters involved in the systematic framework are intelligently determined by an iterative ensemble smoother (IES) algorithm, which also enables sensitivity analysis on CHOPS production profiles. Subsequently, the proposed framework is tested through a laboratory CHOPS experiment. We obtained not only fairly history-matched production data (i.e., cumulative oil, gas, and sand production), but also satisfactorily converged three-phase relative permeability curves by iteratively assimilating production profiles of the CHOPS experiment. It has also been found that using two sets of three-phase relative permeability is capable of representing the segment-type nature of the multiphase flow and reproducing the transition stage on the production profiles. Furthermore, the comparison between two sets of three-phase relative permeability indicates that the sand failure phenomenon yields a reduced residual oil saturation and an increased oil/gas relative permeability. In addition, the sensitivity analysis demonstrates that the segment-type nature of production profiles results from the variation of key impact factors dominating the multiphase fluid flow in CHOPS processes. Overall, the proposed systematic framework can not only reproduce the physical phenomena of sand failure and foamy oil, but also provide a convenient tool to characterize the multiphase flow in CHOPS processes.

Natural gas hydrate is ice‐like mixture of gas (mostly methane) and water that is widely found in sediments along the world's continental margins and within and beneath permafrost and glaciers in a near‐surface depth interval where the pressure is sufficiently high and temperature sufficiently low for gas hydrate to be stable. We categorize the myriad of geological gas hydrate deposits into five characteristic types. We then review the multiple quantitative models that have proposed to describe the genesis of these deposits and describe how each may have formed. We emphasize the importance of coupling multiphase flow (free gas and liquid water) and multicomponent reactive transport with geological history to describe the dynamical processes of gas hydrate formation and evolution in geological systems. A better insight into the kinetics of methane formation from microbial biogenesis and the processes of multiphase flow at the pore scale will advance our knowledge of how these systems form. By understanding the generation and evolution of gas hydrate through time, we will better decipher the role of gas hydrate in the carbon cycle, its potential to contribute to climate change and geohazards, and how to design optimal strategies for gas production from hydrate reservoirs.

TOUGH–RDCA modeling of multiple fracture interactions in caprock during CO2 injection into a deep brine aquifer

In the present study, a Computational Fluid Dynamics (CFD) model was set up to analyse the dynamic behaviour of LNG (Liquefied Natural Gas) tanks adopted in heavy trucks refuelling stations in normal operating conditions or during process upsets. The CFD model was based on the Volume-Of-Fluid (VOF) method to simulate the transient behaviour of a multi-phase flow in a 100 m3 vertical cylindrical tank. The model first considered a fully insulated vessel, and subsequently it was modified to take into account possible damages of the insulation layer, this being a critical upset scenario. The CFD model allowed predicting the dynamic pressure build up in the damaged tank, thus obtaining key indications for the evaluation of the vessel mechanical resistance and set up of safety measures. The model also provided the prediction of vapor temperature with respect to time and external heat source, that is a key issue to assess the effectiveness of the thermal insulation.

The numerical treatment of free surface problems in ferrohydrodynamics is considered.Starting from the general model, special attention is paid to field–surface and flow–surfaceinteractions. Since in some situations these feedback interactions can be partly or even fullyneglected, simpler models can be derived. The application of such models to the numericalsimulation of dissipative systems, rotary shaft seals, equilibrium shapes of ferrofluid drops,and pattern formation in the normal-field instability of ferrofluid layers is given. Ournumerical strategy is able to recover solitary surface patterns which were discoveredrecently in experiments.

Rotary shaft seals

The paper describes an investigation to establish the mechanism by which sealing is achieved in the conventional synthetic rubber oil seal when used on a rotating shaft. After demonstrating that the contact between the seal and the shaft cannot be dry contact—that there is in fact what appears to be a coherent film of oil between the sealing lip and the rotating shaft—further experiments are described to find out why the oil in the film does not flow out past the seal. The conclusion is reached that there is a meniscus at the oil/air interface and that retention of the oil in the oil film is effected by the surface tension of the oil.

Experimental study on gas transportation in radial shaft seals

Shaft seals made from polytetrafluoroethylene (PTFE) materials, called PTFE lip seals, have been successfully used for decades in the chemical industry. Owing to their chemical and thermal stability, PTFE lip seals are used instead of elastomeric lip seals in many automotive and hydraulic applications. This paper deals with the fundamental tribological properties and effects of filled PTFE materials employed in rotary shaft seals, mainly on the basis of experimental work done in the authors' laboratory. The tribological components of a sealing system and the main influences on the sealing function are briefly surveyed. The test methods and conditions used are also described. The experimental results show that the fillers used in the PTFE compounds, as well as the topography of the shaft, play a crucial role in fluid sealing.

Rotary Shaft Seals