The Bair and Winer, Gecim and Winer, Circular and Cardiff limiting shear stress models are compared and contrasted under different load, viscosity, limiting shear stress, surface velocities, Young's modulus, relative radius of curvature and temperature. Isothermal comparisons show that limiting shear stress rheology reduces the pressure gradients in the centre of the contact. Also a localised increase in film thickness in the inlet and a reduction near the exit of the contact occur. The bulk oil temperature significantly influences the limiting shear stress features developed. As a result a full thermal approach was adopted that includes the heat generated, by slip, at the fluid-surface interface. Regions where limiting shear stress and temperature effects dominate are identified under optical interferometry operating conditions. The heat generated during contact was included in the thermal approach. Sinusoidal roughness features promoted contact and the temperature responses were compared using different coefficients of friction. Contact develops higher temperatures than those generated in full film regions, with much greater temperature rises for higher coefficients of friction. Thermal and isothermal gear meshes are simulated using equivalent roller and involute geometries with rough and smooth surfaces. Roughness data taken from gear teeth are linked to the numerical involute used in the simulation, allowing roughness features to be used in the correct part of the gear mesh. Smooth and rough surface results are obtained for three different meshes. 'Running in' was investigated by measuring the amount of surface modification and contact developed between two rotating disks using 'in situ' Talysurf profiles and contact resistance measurements respectively. 'Running in' occurred quickly, with temperature effects reducing the films prolonging the contact period. Comparisons using the software developed incorporating actual roughness profiles, bulk disk and bulk oil temperatures, gave good agreement between the numerical and experimental approaches.

The flow is studied of a fluid film originating from a source at the apex of a right circular cone, and flowing under gravity over its outer surface. A modified Orr-Sommerfeld equation is derived for the flow. This and the corresponding boundary conditions contain terms introducing distance along the cone generator as a parameter. The system of equations is solved for small wave number to give e. stability criterion, which shows the flow to be unstable for all practical values of Reynolds number. Results of experiments on a 60 included angle cone are presented, giving the pattern of behaviour of the main film and waveform characteristics. Mean film thickness is expressed as a function of Reynolds number only and found to be less than that of an undisturbed laminar film. Wave amplitude is shown to reach a limiting value and thereafter decline. Wave number is shown to be linearly related to a non-dimensional parameter incorporating viscosity, surface tension and slope derived from one proposed by Berbente and Ruckonstein whose theory also matches well the limiting amplitudes measured. Wave speed and wavelength are also measured and discussed.

As rotating machines become larger, an increasing number of plain journal bearings operate in the turbulent regime. The addition of small amounts of high molecular weight polymers to the lubricant offers an attractive method of counteracting the increased power loss. This effect has previously been investigated for turbulent flow in pipes. Experiments are described on the operation of a four-inch diameter bearing lubricated with a very dilute, aqueous solution of poly(ethylene oxide).It is shown that the film extent in large clearance bearings is very dependent on the operating parameters, A numerical analysis based on the Reynolds equation indicates that a minimum dissipation principle can be used to explain the delay in the formation of a full width film. The transition to turbulence occurred at a Reynolds number of 2000. There was little evidence of Taylor vortices. The bearing friction was significantly affected by the angular momentum of the leakage flow. Very low concentrations of polymer were found to be effective in reducing the friction. Typically, 0.005% by weight causing a reduction of k5% at a Reynolds number of 3500, The bearing was also significantly stabilised against whirling, although the pressure distribution was unchanged. The polymer became ineffective after approximately twenty passes through the bearing. The degradation caused by shearing will probably be the factor limiting commercial exploitation of friction reduction in turbulent bearings.

This investigation is concerned with the elasto-hydrodynamic squeeze-films generated by the normal approach of two surfaces. It is inspired by the excellent functioning of healthy animal joints under the adverse conditions of high load and low, or even zero, sliding speeds. The effects on the film of four features are examined from both the theoretical and experimental viewpoints. These four features are the elasticity of the materials bounding the film, the permeability of these materials, an extreme interpretation of the concept of "weeping" lubrication and the presence of a lubricant enrichment in the film. This latter feature is considered only in its theoretical aspects. It is shown experimentally that when a thin layer of rubber is used as the soft boundary of the film, entrapment occurs, due to the high poisson's ratio involved. The agreement between theoretical predictions and experimental results for the effects of permeability and of a "weeping" mechanism is good. The models, as examined, are found to be dominated by viscous forces rather than the inertia of the moving surfaces. It is found that high permeability of the surfaces tends to decrease film life and that high flexibility tends to increase it. However, very low permeability material appears to promote slight "weeping" tendencies and hence prolong film lives. The effect of an additive confined to motion in the fluid flow is found to be small unless present at extremely high concentrations and in joints it seems likely to be effective only at very thin films. When the additive is confined not only to the film but also prevented from flowing in the film, squeeze times are found to be increased by several times. The increase is not considered to be enough to make the mechanism totally convincing as a mode of operation of an animal joint.

Vibrational analysis performed on a common design of pin-on-disk tribometer showed that high frequency oscillatory friction forces were generated between the pin and the disk during a test. These resulted in the tribometer exhibiting friction-induced vibration, during which it oscillated at a natural frequency. This oscillation had two effects; firstly the friction data generated between the pin and the disk was modified such that the recorded friction data was not an accurate representation of 'real' data. The second effect was that the tribometer modified the sliding conditions being tested, leading to a disparity in the recorded friction data, when compared to data obtained with the sliding conditions held at a constant value. For meaningful friction data to be recorded the influence of the tribometer must be kept to a minimum. A dynamic model of a tribometer was constructed to investigate the coupling between oscillatory friction data and the tribometer's dynamics, and the influence it had on the accuracy of the recorded friction data. The model quantified the influence that the tribometer had on the recorded friction data and the deviation in sliding conditions. Using the model a stiffer design of the tribometer was designed and constructed with the aim of minimising the influence of the dynamic characteristics on the friction data. Vibrational analysis of the modified stiffer tribometer set-up showed that it was still exhibiting friction-induced vibration, and as such the dynamics of the tribometer still had a significant impact on the accuracy of the friction data produced. There were significant differences in the way the tribometer's dynamics influenced the friction data for the two set-ups. Friction testing with the two set-ups showed that both set- ups produced repeatable friction data, but with very different average friction coefficients and variations in the friction data during a test.

To run both smoothly and efficiently, high-speed machines need stable, low friction bearings to support their rotor. Being oil-free, self-acting gas film bearings are often the choice in high speed rotating machinery. Although plain aerostatic journal bearings carry more load and have superior lift characteristics, they suffer from instability problems, and one can add grooves to 'increase that stability. The research describe a mathematical model developed for small eccentricities, to predict the steady state and stability of enhanced capacity air bearings which combine external pressurisation and aerodynamic effects by adding grooves. This theory was than tested in a practical bearing design application. With the aid of a computer program geometry and thus load capacity, stiffness and stability were optimised. A prototype bearing based on a standard aerostatic bearing spindle, was designed, produced and tested. Stiffness, load capacity, pressure distribution and stability were monitored experimentally. The effects of the attitude angle on stability are discussed and it is concluded that the attitude angle is an unreliable predictor of bearing stability. Experimental dynamic stability studies have been carried out and the initial bearing spindle was operated with known amounts of unbalance at speeds up to 105000 rpm, with a gas supply pressure of 6 bar. The spindle vibration amplitude was measured and coherence data and dynamic compliance functions of the bearing were determined. The critical speeds were determined by monitoring the natural frequency amplitudes of the bearing spindle. Having observed some positive dynamic benefits of a prototype hybrid spindle, the work was followed up with a further test on a hybrid spindle with improved bearing geometry. The natural frequencies were observed, and the critical speeds determined. The bearing successfully reached the maximum 120000 rpm speed predicted by the theoretical model for the bearing design, and at all speed the spindle remained stable. The main contribution is in improved stability and increased speed capacity of a hybrid externally pressurised bearing by adding optimised geometry grooves which further enhanced the control of pressure distribution for bearings used in high speed spindle applications.

The present study investigates, for the first time, the production of granular activated carbon (GAC) from date palm pits, a waste material. Reported data indicates.that the t. yearly production of dates in the Kingdom of Saudi Arabia (KSA) is more than 800 ktonnes of which a significant portion is de-stoned prior to sale. Hence the use of date palm pits for the production of GAC would confer two benefits, Le., reduction in waste disposal costs and concerns and production of a very useful material from this waste, Le., GAC, which at the present is imported in the KSA for several industrial applications.<br></br>Considering these facts, date palm pits from a local source were used for the production of GAC. Several GAC production variables were investigated in detail, to study their effect on the BET specific surface area (SSA_BET), porosity, and the pore size distribution of the produced material. Variables studied included sample predrying, time of carbonization, time of activation, strength of the activating agent (i.e., phosphoric acid), acid impregnation ratio, pH, and temperature. Nitrogen adsorption isotherm data was used for the determination of respective SSA_BET, and porosity values.<br></br>The optimum conditions that produced the best activated carbon were, H₃P0₄ concentration equal to 70%, acid to pits ratio of 1.6:1, and carbonization temperature of 500°C. Additionally, a maximum yield of 24% was noted for the best GAC sample which showed the following characteristics 590 kg m^-3 bulk density, 0.5% ash content, 1100 mg g^-1 iodine number, and 1319 m² g^-1 SSA_BET. Furthermore, this GAC sample showed substantial capability to adsorb phenol and 2-Methylphenol (o-cresol) from the aqueous phase. The respective adsorption data fitted well to the Freundlich adsorption isotherm. Several continuous column studies (using operational variables including flowrate, initial pollutant concentration, pH, temperature and dissolved oxygen) were also conducted to find the suitability of the produced optimum GAC sample for the removal of phenol and 2-Methylphenol from the aqueous phase. For example, the adsorption of both phenol and 2-Methylphenol was influenced both by the flowrate and the initial pollutant concentration. Also, the breakthrough time decreased when the flowrate and the initial concentration values were increased, probably due to insufficient pollutant residence time. The respective optimum activated carbon was also successfully used for the reduction of total organic carbon from an industrial wastewater sample.<br></br>Furthermore, to minimize waste disposal cost and concerns related to the exhausted GAC, an attempt was also made to regenerate the used GAC sample from the present work using chemical and electrochemical desorption methodologies. The electrochemical desorption method, which so far has been scantly investigated in the literature, was noted to successfully regenerate the used GAC sample, using a current density value of 50 rnA cm^-2. Factorial experimental design and optimization of parameters for the production of GAC from date pits, using Response Surface Methodology (RSM), was also completed. The respective results were acid to pits ratio of 1.5:1, carbonization temperature of430°C, and H₃P0₄ concentration of 55%.<br></br> In summary, a high efficiency GAC sample was successfully produced from an otherwise waste material i.e., the palm date pits. The produced GAC was also noted to be very efficient for the removal of organic pollutants from the aqueous phase. It is suggested that the use of activated carbon produced from date pits would be economical, since date pits are a waste product and available in large quantity in the Kingdom of Saudi Arabia, and phosphoric acid is manufactured from local resources in the Kingdom.

The presence of lubricant mist in the piston assembly of an automotive engine has been known of for many years, but has not been specifically investigated. This study, therefore, focuses on understanding the lubricant misting process and its effect on the engine in terms of lubricant degradation. Informed by existing literature, it was hypothesised that mist is formed in the piston ring gaps. A laboratory rig was designed and built to simulate this environment, producing and measuring representative mist flows. Using this rig, the contribution of the components of a commercial lubricant to its misting properties was studied. Base oil viscosity and molecular weight, and the presence of polymeric viscosity modifiers were identified as being the key parameters controlling the tendency of an oil to form mist. Further investigation using viscosity modifiers of varying size and molecular structure was performed, indicating differences between the behaviour of linear and star polymers. Measurements of the droplet flows in the crankcase of an engine were made using a particle sizer. These confirmed the dependency of misting properties on viscosity, and validated the hypothesis that lubricant mist in the crankcase is formed in the piston assembly by a similar mechanism to that produced in the laboratory rig. Longer engine tests were used to investigate the effect of lubricants with varying misting tendency on lubricant degradation. A range of chemical and rheological analyses were performed to compare fresh and used lubricant samples in different flows and positions in the engine. These tests were not able to differentiate between the degradation of the different lubricants tested, though the degradation of lubricant in different positions in the engine varied significantly. It was shown that lubricant mist is formed in the piston assembly and that lubricant misting is a significant lubricant transport mechanism.

The objective of the research presented in this thesis was to investigate and quantify the impact of biofuel ethanol and the associated water contamination into a commercially available automotive gasoline engine lubricant on the frictional response of piston ring/cylinder liner contacts and the resulting implications for fuel economy under problematic cold-start/warm-up/short-journey driving conditions. Whilst road transport is a major driver of global economic growth, it is also a primary user of fossil fuel based energy and a major emitter of Carbon Dioxide (C02). Therefore, increasingly stringent legislation demanding the use of biofuels in conjunction with conventional fossil fuels has been put in place. Even though biofuels are being blended into conventional gasoline and diesel at varying concentrations, information relating to the impact of these fuels on automotive engine lubrication, friction and fuel economy is scarce. A comprehensive and rigorous laboratory bench-top screening test programme using a reciprocating tribometer and Statistical Experimental Design was developed for the first stage of this investigation. Bespoke engine test programmes were also conducted to identify areas susceptible to ethanol and water dilution on the piston assembly and cylinder liner and to quantify fuel and water dilution into the lubricant present along the cylinder liner wall and in the sump. Tribometer investigations showed that significant reductions in friction resulted when the piston ring/cylinder liner contacts were lubricated with the lubricant-ethanol-water mixtures and the separated phases of these mixtures compared to the formulated lubricant. Temperature measurements on a single cylinder gasoline engine highlighted that lubricant present on the piston skirt, the connecting rod and on the intake side of the cylinder liner was highly susceptible to ethanol and water contamination under cold-start/warm-up conditions. Fuel dilution measurements on the same engine revealed that lubricant present on the upper cylinder liner, at top dead centre, was highly contaminated with ethanol, gasoline and water compared to that present lower down the cylinder, mid-stroke and bottom dead centre, and in the sump. again under cold-start/warm-up conditions.

No description available.