Increase In Film Temperature Research Articles

Thermo-Hydrodynamic Effect of Gas Split Floating Ring Seal with Rayleigh Step Grooves

The force equilibrium and moment equilibrium play a significant role on the sealing performance of gas split floating ring seals. A small deflection angle may generate seriously wear on sealing surface and cause seal failure. Therefore, the thermo-hydrodynamic lubrication analysis of gas split floating ring seal with Rayleigh grooves is investigated considering the deflection angle and frictional heat of surface contact, which is beneficial to grasp the hydrodynamic characteristics and rules under high-temperature and high-speed conditions. Pressure and temperature distributions of sealing rings are numerically calculated for the cases with different deflection angle, rational speed, seal pressure and ambient temperature. Then, the hydrodynamic effect and sealing performance are analyzed. The obtained results show that, the surface Rayleigh step grooves do not present obvious hydrodynamic effect when split seal ring has no deflection. While, a significant hydrodynamic effect can be obtained when the split seal ring presents a deflection angle about dozens of micro radians. Here, a 10% increase of opening force is achieved when the deflection angle reaches 80 μrad in the case of speed 30,000 r/min and seal pressure 0.2 MPa. Moreover, the hydrodynamic effect becomes obvious with increasing deflection angle as well as rotational speed. Meanwhile, the growth of rotational speed results in an obvious increase of film temperature. The increase of ambient temperature has a significant influence on the decrease of leakage rate. When the ambient temperature increases from 340 K to 540 K, the leakage rate reduces exceeding 50%, however, it does not present obvious effect on the opening force. The proposed model has the potential to provide the theoretical basis and design guidance for surface grooves of gas split floating ring seal in the future.

Calculation and influence analysis of tooth surface friction coefficient of planetary gear system in mixed lubrication condition

Based on the gearing theory, the calculation formulas of comprehensive curvature radius, relative sliding speed and tooth surface contact stress of internal and external meshing gear pair of the planetary gear system are deduced in this paper. Combined with load sharing theory and thermal elastohydrodynamic lubrication analysis method, the oil film thickness, film bearing ratio and friction coefficient are solved and the effects of roughness and input power on the friction coefficient are studied. The results show that with the increase of tooth surface roughness, the film bearing ratio decreases and friction coefficient increases; As the input power increases, the film temperature increases, the oil viscosity and film thickness decreases, which causes the tooth surface friction coefficient increases.

Effect of liquid drainage on heat transfer from a heated surface to flow of aqueous foam

According to global studies, application of macro aqueous foam flow as a coolant seems promising and complex at the same time. Research of the heat transfer between a heated horizontal flat surface at the bottom of the channel and a longitudinal flow of aqueous foam was performed in this investigation. The distribution of the foam temperature in various cross-sections along the heated surface was found experimentally. A significant change in temperature was observed only in the bottom 1/4 part of the cross-section. The liquid drained from foam and formed a moving film which covered the heated surface. The inflow of lower temperature liquid into the film of drained liquid inhibited the intensive increase in film temperature. This influenced the character of cooling intensity of the heated surface. Analytically obtained formulas to calculate the amount of liquid draining from the foam and the developed methodology were verified in the experimental research.

Revisiting Threshold Fouling Models for Crude Oil Fouling

Threshold crude oil fouling models use activation energy in the deposition rate term to predict the initial fouling rates. It has been reported in the literature that fluid velocity has a strong influence on activation energy, which does not agree well with the principles of chemical reaction engineering. Besides, the existing threshold fouling models always predict an increase in the fouling rate with an increase in film temperature. Several studies reported in the literature reveal that many test crude oils exhibited a decrease in fouling rate with an increase in film temperature caused by an increase in bulk temperature. It is, therefore, necessary to develop a threshold fouling model that is free from the use of activation energy in the model, and that predicts the initial fouling rates correctly for all types of crude oils and fouling mechanisms. In the present study, a modified threshold fouling model has been proposed by introducing a bulk temperature-dependent constant in the place of activation energy and validated with experimental data from our laboratory and data from the literature.

Matching the relationship between rotational speed and load-carrying capacity on high-speed and heavy-load hydrostatic thrust bearing

PurposeRotational speed and load-carrying capacity are two mutual coupling factors which affect high precision and stable operation of a hydrostatic thrust bearing. The purpose of this paper is to study reasonable matching relationship between the rotational speed and the load-carrying capacity.Design/methodology/approachA mathematical model of relationship between the rotational speed and the load-carrying capacity of the hydrostatic bearing with double-rectangle recess is set up on the basis of the tribology theory and the lubrication theory, and the load and rotational speed characteristics of an oil film temperature field and a pressure field in the hydrostatic bearing are analyzed, reasonable matching relationship between the rotational speed and the load-carrying capacity is deduced and a verification experiment is conducted.FindingsBy increasing the rotational speed, the oil film temperature increases, the average pressure decreases and the load-carrying capacity decreases. By increasing the load-carrying capacity, the oil film temperature and the average pressure increases and the rotational speed decreases; corresponding certain reasonable matching values are available.Originality/valueThe load-carrying capacity can be increased and the rotational speed improved by means of reducing the friction area of the oil recess by using low-viscosity lubricating oil and adding more oil film clearance; but, the stiffness of the hydrostatic bearing decreases.

Thermo Elastohydrodynamic Lubrication with Liquid-Solid Lubricant

This paper presents the performance characteristics of thermo-elastohydrodynamic lubrication (TEHL) in line contact with non-Newtonian liquid–solid lubricant. The time independent Reynolds equation, energy equation, elastic equation and load carrying with solid particle equation were formulated for compressible fluid. Newton-Raphson method and multigrid technique were implemented to obtain film thickness, film pressure, film temperature, friction coefficient and load carrying with solid particle equation in the contact region at various concentrations of solid lubricant and applied loads. The simulation results showed that film thickness and film temperature increase but film pressure decreases when solid particles are added into liquid lubricant. The maximum film temperature and load carrying of solid particle increased but friction coefficient decreased when concentration of solid particle increased. For increasing applied loads, the minimum film thickness decreases but maximum film temperature and friction coefficient increase for all liquid lubricant and liquid-solid lubricants.

Characterization of the microscopic mechanics in falling film evaporation outside a horizontal tube

In order to get a deep insight of the heat transfer mechanism of falling film evaporation outside a horizontal tube, the characterization of the microscopic mechanics was numerically investigated. A numerical model was developed to obtain the dynamic and heat transfer performance including film thickness, film velocity, film temperature and local heat transfer coefficient. The simulated results were found to be in a good agreement with the reported data. The results show that the convection plays an important role in the thin film evaporation even at low Reynolds number through the analysis on the profiles of the local film velocity and local heat transfer coefficient in the falling film. The distribution of the thermal developing region and thermal developed region along the tube circumference for a single tube and a tube bundle was predicted. The local film temperature increases and local heat transfer coefficient stabilizes at the top thermally developing region while the former stabilizes and the latter decreases at the fully thermal developed region which is at the bottom part of the tube.

Electromigration Reliability of Electroplated Gold Interconnects

ABSTRACTThe electromigration lifetimes of a very large quantity of passivated electroplated Au interconnects were measured utilizing high-resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with current density limited to 2 MA/cm2 and oven temperatures in the range of 300°C to 375°C prevented large Joule-heated temperature gradients and electrical overstress failures. A Joule-heated Au film temperature increase of 10°C on average was determined from measured temperature coefficients of resistance (TCRs). A failure criterion of 50% resistance degradation was selected to avoid thermal runaway and catastrophic open circuit failures. All Au lifetime distributions followed log-normal statistics. An activation energy of 0.80 ± 0.05 eV was measured from constant-current electromigration tests at multiple temperatures. A current density exponent of 1.91 ± 0.03 was extracted from multiple current densities at a single constant temperature.

Theoretical Investigation of Transient Lubrication in Spur Gear

This paper presents performance characteristics of transient thermo-elastohydrodynamic lubrication (TEHL) in line contact with Newtonian fluids. The time-dependent modified Reynolds equation, energy equation and elasticity equation with initial conditions were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel method for an involutes spur gear to obtain the film pressure profiles, film thickness profiles, film temperature and friction coefficient in the contact region. In this analysis, the load is applied on either two pairs or one pair of gear teeth. The simulation results show that at approach point, the film thickness is minimized and film temperature rapidly increases. Film temperature and friction coefficient were suddenly increase when the transition from two pairs to one pair and vice versa are modeled as a step variation of load. The friction coefficient and film temperature were occurrence at pitch point. Film temperature and friction coefficient increase but film thickness decreases when applied load increases. For increasing of speeds, film thickness and film temperature increase but friction coefficient decreses.

Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A Model Anchored to Test Data

The paper introduces a thermohydrodynamic (THD) model for prediction of gas foil bearing (GFB) performance. The model includes thermal energy transport in the gas film region and with cooling gas streams, inner or outer, as in typical rotor-GFBs systems. The analysis also accounts for material property changes and the bearing components’ expansion due to temperature increases and shaft centrifugal growth due to rotational speed. Gas inlet feed characteristics are thoroughly discussed in bearings whose top foil must detach, i.e., not allowing for subambient pressure. Thermal growths determine the actual bearing clearance needed for accurate prediction of GFB forced performance, static and dynamic. Model predictions are benchmarked against published measurements of (metal) temperatures in a GFB operating without a forced cooling gas flow. The tested foil bearing is proprietary; hence, its geometry and material properties are largely unknown. Predictions are obtained for an assumed bearing configuration, with bump-foil geometry and materials taken from prior art and best known practices. The predicted film peak temperature occurs just downstream of the maximum gas pressure. The film temperature is higher at the bearing middle plane than at the foil edges, as the test results also show. The journal speed, rather than the applied static load, influences more the increase in film temperature and with a larger thermal gradient toward the bearing sides. In addition, as in the tests conducted at a constant rotor speed and even for the lowest static load, the gas film temperature increases rapidly due to the absence of a forced cooling air that could carry away the recirculation gas flow and thermal energy drawn by the spinning rotor; predictions are in good agreement with the test data. A comparison of predicted static load parameters to those obtained from an isothermal condition shows the THD model producing a smaller journal eccentricity (larger minimum film thickness) and larger drag torque. An increase in gas temperature is tantamount to an increase in gas viscosity, hence, the noted effect in the foil bearing forced performance.

Thinning transitions in free-standing liquid-crystal films as the successive formation of dislocation loops.

We describe a model for the layer-thinning transition in free-standing liquid-crystal films based on the successive, spontaneous formation of dislocation loops. As the film temperature increases and the smectic order and layer compressional modulus decrease, the condition for creating a dislocation loop of critical radius is met and a thinning is nucleated. The resulting equation for N, the number of smectic layers, as a function of temperature yields good fitting results to the thinning transitions obtained from several fluorinated compounds.

The effect of electrical current (DC) on gold thin films

We studied changes induced by electrical current (DC) on gold thin films by using a combination of scanning tunnelling microscopy and grazing incidence X-ray diffraction. The results show that the process inducing device failure is based on surface diffusion that produces the growth of microcrystals at the expense of mechanically strained microcrystals. The de-percolation and loss of adherence to the substrate reduce the heat transfer which in turn produce an increase of film temperature. This temperature increase induces a large mechanical stress due to the differential dilatation of substrate and film. The result of these processes is the final failure of current conduction by the film.

Thermoelastohydrodynamic Analysis of Fixed Geometry Thrust Bearings Including Runner Deformation

A thermoelastohydrodynamic theory for the analysis of sector thrust bearings is presented. The analysis includes the generalized Reynolds equation and a fully elliptic three-dimensional energy equation in the film. In addition, full three-dimensional heat transfer is allowed in the pad while axisymmetric conduction is allowed in the runner. Three-dimensional elastic deformation due to mechanical and thermal loading is allowed in the pad while axisymmetric mechanical elasticity is allowed in the runner. The performance of a parallel tapered-land thrust bearing including runner deformation effects is analyzed as a function of different models. It is seen that mechanical deformation of the pad affects the operating characteristics only slightly while thermal deformation of the pad can cause large increases in operating temperature. The runner deformation effects can include a reduction of the maximum film temperature at slight deformation or a large increase in film temperature at the inner radius of the pad at larger deformations.

Dynamics of ablation of polymethyl methacrylate films by near ultraviolet light of an Ar+ laser

The dynamics of cw near ultraviolet (NUV) laser ablation of polymethyl methacrylate (PMMA) films are investigated by recording the time dependence of the reflected light power. A new phenomenon in cw light ablation of PMMA, which is similar to 'incubation' pulses in excimer laser ablation, is recognized as the 'incubation' period of ablation, when polymer fragments are accumulated up to a critical density followed by a volume explosion. The incubation time is found to decrease when the light intensity in the film and/or the film temperature increases. However, for sufficiently high light intensities the incubation time depends only upon the film temperature. A dynamic model of the ablation process during the incubation time is proposed which accounts for the main features of our observations and provides a consistent quantitative description of the mechanism underlying the initial stage of ablation, i.e. before the volume explosion.