What would happen if a drop of oil was placed on water? Relate to a real world oil spill that students may have observed, such as gasoline or oilfilm on a wet road. How can we find the volume of a single drop of oil? Review the process of drop calibration that students learned earlier by questioning. Allow students to articulate the process of calibration by using pictures or demonstrations.
design parameters on the minimum filmthickness of hydrodynamic journal bearing. In one of the paper the authors have designed the bearing on the basis of heat balance i.e. heat generated inside the bearing should be nearly equal to the heat dissipated from the bearing housing to the surroundings. As it is an iterative process, this analysis also includes computer aided bearing design. Matlab programming provides easy, accurate and fast results. This paper gives the effect of bearing design parameters such as oil grades, lubrication systems, bearing housing geometry, R/C and L/D ratios on the minimum oilfilmthickness of hydrodynamic journal bearing.
The effect of lubricants properties in oilfilmthickness was evaluated and linked to performance limitations in view of cavitation appearance, its initia Ccapacitance tion and development. The piston-ring and the cylinder liner interface are characterized in terms of oilfilmthickness measurements. Study of cavitation in lubricants and its rheology were presented in previous studies and results of different lubricants, speed, load, temperature and piston-ring curvatures were assessed to achieve useful tribological engine data that apply to the piston-cylinder assembly. The evaluation of new designs that can be applied to the ring/liner interface and many future parametric studies that can be combined with surface modifications in both parts of the assembly are under examination. The use of a simplified single-ring test rig that utilizes a steady piston-ring section of overall width 5 mm placed under a flat liner surface that reciprocates instead, takes advantage of significantly less uncertainties when compared to engine experiments. Minimum oilfilmthickness measurements (MOFT) is studied for different lubricants as a variation of temperature and simultaneously friction high temperature results for the whole stroke length are presented. Measurement transducers for the separation of the metal surfaces (liner and piston-ring) and the friction force developed in the contact surfaces were the conventional methods used. Within certain parts of the stroke where friction reaches its maximum value, a greater focus is given to evaluate the effect of different operating conditions. Useful conclusions are drawn regarding lubricants behavior under cavitation that can be used to new additives design and enhancement of lubricant physical-chemical properties that have the potential to conform to the even stricter emission regulations that will apply in the future.
Ultrasonic The transducer consists of a piezo- ment in a waterproof housing. The transducer was a nominal 10 MHz, focused (the centre frequency was at 8.8 MHz), and 90% bandwidth. In this work it is necessary to focus the wave onto the oilfilm (normal contact transducers would result in spreading of the beam and reflection from regions surrounding the film). Focusing is achieved by means of a concave lens bonded to the piezo- element. The transducer has a focal distance of 75 mm in water and a corresponding focal area of diameter ~520m. The piston ring has a thickness of 2 mm with a slight crowning. The ultrasonic spot size falls within a region of the ring face that is virtually flat. Reference  describes in more detail the focusing of ultrasonic waves and the resulting spatial resolution.
Experiments have been performed on a model EHL contact between a ball and a flat surface. A transducer is mounted above the contact such that the ultrasonic wave is focused onto the oilfilm. The reflected signals are captured and passed to a PC for processing. Fourier analysis gives the reflection spectrum that is then used to determine the stiffness of the liquid layer and hence its thickness. In further testing, an ultrasonic transducer has been mounted in the housing of a deep-groove ball bearing to measure the film generated at the outer raceway as each ball passes. Results from both the ball-flat and ball bearing measure- ments agree well with steady-state theoretical EHL predictions. The limits of the measuring technique, in terms of the measur- able rolling bearing size and operating parameters, have been investigated.
Experiments have been performed on a model ehl contact between a ball and a flat surface. A transducer is mounted above the contact such that the ultrasonic wave is focused onto the oilfilm. The reflected signals are captured and passed to a PC for processing. Fourier analysis gives the reflection spectrum which is then be used to determine the stiffness of the liquid layer and hence its thickness. In further testing, an ultrasonic transducer has been mounted in the housing of a deep groove ball bearing to measure the film generated at the outer raceway as each ball passes. Results from both the ball-flat and ball bearing measurements agree well with steady state theoretical ehl predictions. The limits of the measuring technique, in terms of the measurable rolling bearing size and operating parameters, have been investigated.
Figure 6 shows a simulation of the measurement system obtained using this approach. The acoustic properties of the media and transducer characteristics used in the simulation are shown in table 2 and 3 respectively. A source plane (50 × 50 mm) was defined with a spatial sampling interval of 25 µ m (i.e. ∆ x= ∆ y=25 µ m). Figure 6(a) shows the amplitude distribution at the focal plane (i.e. plane 2) obtained by equation 14 as well as the size of the lubricated contact region in a 6016 ball bearing for a 15 kN radial load from equation 3. From figure 6(a), it can be seen that the assumption that the majority of the acoustic field is within the contact ellipse is reasonable. Figure 6(b) shows the predicted reflection coefficient distribution and weighted sum reflection coefficient for various oil-films. To generate this figure equations 17 and 18 were used to calculate the displacement distribution and weighted sum at the transducer. Simulations were performed for both the thin-film case and the reference case (i.e. steel-air) and used in equation 10 to compute reflection coefficient (using R ref = 1.0000). For the reflection coefficient distribution, equation 10 was
In order to weaken the instantaneous starvation phenomenon, the non-Newtonian fluid was investigated. The viscosity improver additive (PMA) was added to base oil (PAO), which can form non-Newtonian fluid. Figure 12 gives the oilfilm interference images of Newtonian and non- Newtonian fluid. In this case, the speed is equal to 0.107m/s and the load is equal to 200N. As shown in figure 12, it can be found that the fluctuation of light intensity apparently weakens for non-Newtonian fluid, although two kinds of lubricants have the similar kinematic viscosity before experiment. Figure 13 gives the filmthickness at the specified point, it can be found that the filmthickness of non-Newtonian fluid is apparently lower than that of Newtonian fluid. This is because shear-thinning behavior exists in non-Newtonian fluid under high shear stress which can cause temporary loss of viscosity. In addition, air–oil meniscus didn’t appear for the non-Newtonian fluids which indicate that the oil supply volume of non-Newtonian fluid is larger than that of Newtonian fluid. This is because the effective kinematic viscosity of non-Newtonian fluid didn’t fully recover during operation. Therefore, non-Newtonian fluid can weaken the instantaneous starvation.
This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrodynamic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oilfilm and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oilfilm stiffness that can be readily converted to filmthickness. Whilst the reflected amplitude of the wave is dependent on the frequency component, the measured filmthickness is not; this indicates that the quasi-static assumption holds.
There were severe pitting corrosions on the surface of transmission gears in diesels. The cause of metal fatigue pitting of gear surface is analyzed in the paper, which based on the contact fatigue experiment of 18Cr2Ni4WA carburizing and quenching gears used in the diesel engine. Causes of pitting on harden tooth surface are studied from three aspects: gear surface residual stress field, oilfilm pressure and carburizing thickness, which according to the morphology of test gear fatigue fracture and the surface hardening properties of carburizing and quenching gears. The reasons of experimental gears' contact fatigue pitting were analyzed and conclusions were as follows: The depth of the diffusion layer, surface carbon concentration and the carbon concentration gradient of layer were the key to improve the ability to resist wear surface fatigue pitting.
occurs. However, this is a challenging measurement as typically the load is carried by an extremely thin oilfilm over a small lubricated region. For example in a 6016 ball bearing (shaft diameter 80 mm, ball diameter 12.7 mm) the contact ellipse is 0.3 x 3 mm under typical (15 kN) operating load, and the oilfilmthickness is in the range 0.1-1.0 m . In this range, either electromagnetic or optical methods have been used to measure the lubricant filmthickness. However, these techniques suffer from serious drawbacks. The resistance  and capacitance methods [4,5] require either an insulated surface mounted sensor, or complete electrical isolation of the contact elements. These methods are generally limited to lubricant films above about 1 m in thickness [6,7]. Optical interferometry  and optical fluoresence techniques  have also been used in test bearings but these require a transparent window though which to make the measurement. These requirements mean that both electromagnetic and optical methods are rarely used outside the laboratory.
Figures 9(a) and (b) show the variation in measured filmthickness measured ultrasonically (at the leading edge outer pad radius 80:20 position) as the bearing load and operating speeds are varied. Note that here the bearing loads quoted here have been scaled as if the bearing were a true full compliment of thrust pads. The data has some degree of uncertainty since it is based on calibration (the data of figure 7c) which itself has an inherent error; ±10µm is the expected level of accuracy in this data. Much higher accuracy can be achieved when the intermediate layers can be separated out.
The thickness of the oilfilm in tribological components is a key parameter. If the film is too thin then surface contact can occur resulting in high friction and wear. If the film is too thick energy is expended needlessly in overcoming churning loses. The film is usually so thin that it is small compared to elastic distortions of the bearing elements. For this reason, measurement of the bulk separation of the bearing components is not usually sensitive enough to deduce the oilfilmthickness. Electrical resistance and capacitance have proved useful methods, as have optical methods. However, both these approaches require modifications to the bearing machinery that frequently preclude their application outside of the laboratory [1-5].
differences between fa s t and slow contacts we cannot simply extrapolate this research to our case. When velocities are low, heat originating in surface friction has enough time fo r being conveyed into the surround and into the substrate. That is why the rise o f temperature caused by friction on sliding surfaces at low velocities is negligible, but it has an important or even prevailing influence when velocities are higher. A higher temperature substantially influences the lubricating oilfilm viscosity as well. The oilfilmthickness is strongly dependent on the velocity o f the sliding surfaces. It becomes thicker with higher velocities, therefore in such case there usually exists an elasto-hydrodynamic lubrication, whereas at low velocities a mixed lubrication prevails. These are the main reasons why, fo r evaluation o f wear in slow sliding-rolling contacts, we cannot use results which are valid fo r fa st contacts. Hence, new efforts are being made to form an adequate rating method fo r slow running gears [1-5] in numerous institutions all over the world.
Fig. 13 shows the effect of vane tip radius of curvature on oilfilmthickness for FVA2 mineral oil at 1.5 mm vane thickness, 60 o C and 150 bar for three different vane speeds. Curves show that increasing of vane speed affects the FVA2 oilfilmthickness much more than FVA1 oil type. Oil properties plays great rule on hydraulic vane machines performance. Fig. 14 shows the effect of vane tip radius of curvature on oilfilmthickness for FVA1 mineral oil at 1.5 mm vane thickness, 60 o C and 3500 rpm for three different operating pressures. Curves show that increasing of vane tip radius of curvature significantly enhances oilfilmthickness. Increases of operating pressure have negative impact on oilfilmthickness. It should be mentioned that the TEHL-model is designed only to deal with oilfilm between vane tip and cam-ring assuming that came ring as a circular contour.
Filtered cathodic vacuum arc  was used to prepare different types of amorphous and nanocrystalline carbon films. Bonding structure of the films was controlled through controlling the negative substrate bias during the deposition. In order to fabricate carbon thin films with nanocrystals of preferred orientation, a carbon film deposited at 300-V substrate bias was irradiated by a sin- gle pulse of a 248-nm excimer laser with a pulse width of 23 ns. The laser energy was kept at 460 mJ/cm 2 . FE was tested in a parallel plate configuration with an in- dium tin oxide-coated glass as the cathode with an anode-cathode spacing of 100 μm in a pressure lower than 5 × 10 −6 Torr. In order to check the repeatability of the data, two samples were prepared at each condition. FE tests have been done on two different positions of every individual sample. More than ten measurements have been done on each test spot.
Figure 27 shows a schematic front view of a spherical vacuum chamber used construct the mathematical models. The black dot in the middle of the vacuum chamber indicates a point deposition source. A point deposition source is a infinitesimal small piece of film material with a mass and density. In this case it is placed in the middle of the vacuum chamber, hereby, the particles will escape the film material and subject proportional to cooler surfaces all around the chamber. This assumption is made for convenience, the mathematical models can also be constructed for different type of deposition sources. The red horizontal line in the upper half of the sphere represents the sample holder. In this case, the shape of the sample holder round and mounted inside the vacuum chamber against the wall. Another assumption is perfect vacuum inside the chamber. This allows particles to follow a perfect straight path (directional) and proportional distribute inside the chamber. A summary of the assumptions:
New techniques have been developed for measuring filmthickness in the recent year (2011), [16-18]. In , silicon nitride tips are fixed to the end of a triangular cantilever to sense the filmthickness during the operating conditions. This technique is based on the deflection movements of the beam (lever in tribology machine) which is monitored by microprojector. The microprojector is connected to the computer to convert the captured images into filmthickness readings. A calibration was needed to gain accurate results for each sample used. One of the limitations of this technique is that the accuracy of the measurement is not good at low uniformity of the lubricant. In addition, it has three steps of calibration (deflection signal, microprojectos signal, and filmthickness) to gain the required thickness measurement. In the current technique, there is one conversion step which is the strain gauges reading into filmthickness. This could reduce the error in readings compared to the previous technique in . In other works [17, 18], an optical test apparatus was used to measure the filmthickness. The main limitation of this technique is the counterpart should be glass which allows the xenon flash lamp to trigger the filmthickness. In the current adopted technique, all types of tribological materials can be used which give more advantages to it compared to the optical technique.
loaded polymer film has a dramatic waves when tested in the same electrolytic solution. A well defined redox response was obtained and exhibited a thin layer behavior. The electrocatalytic activity of the modified electrode for the oxidation of methanol, propanol and formaldehyde in aqueous acidic solution was studied by using cyclic voltammetry. Results showed that, poly AQ/Pt modified electrode can improve the activity of Pt towards the oxidation of these small organic molecules, showing the possibility of attaining good electrocatalytic anodes for fuel cells.
The purpose of this thesis is to describe the analysis and experiments performed on a proposed micro-scale heat transfer device, in which silicone oil is actuated using an electrical field. Initial analysis covers heat transfer of the device and formulates a dimensionless group that appears to be related to the heat transfer potential. The device used in this research is composed of a Hele-Shaw cell formed by two parallel vertical glass plates coated on one side with indium-tin-oxide such that the Hele-Shaw cell functions as a capacitor. The Hele-Shaw cell device is placed within a reservoir of silicone oil of 10 cSt viscosity which is heated to prescribed temperatures. Capillary pressures cause the silicone oil to rise within the Hele-Shaw cell forming a silicone oil-air interface. A power source and function generator are used to induce an electrical field in the Hele-Shaw device, applying electrohydrostatic pressure to the silicone oil and inducing actuation. Several actuation periods are analyzed to determine the effect of the dimensionless group on the heat transfer of the device. Analysis of the experimental data reveals that increasing the actuation frequency increases the temperature rise observed from the heated silicone oil. Differences between observed results indicate a dependence on temperature which may be related to the properties of the fluid and the formation of a thin film on the surface of the Hele-Shaw cell.