Surface specific asperity model for prediction of friction in boundary and mixed regimes of lubrication

Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaussian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions

Thermo-Mixed Hydrodynamics of Piston Compression Ring Conjunction

The final publication is available at http://link.springer.com.A new method, comprising Navier-Stokes equations, Rayleigh-Plesset volume fraction equation, an analytical control-volume thermal mixed approach and asperity interactions is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring-cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors

Atomic Scale Friction in the Function of Modified Eyring Activation Energies

At microscale, friction is better understood fundamentally through hydrodynamic and elastohydrodynamic lubrication. However, the mechanisms governing friction at nanoscale remains a subject of interest. With the emergence of small-scale devices such as Microelectromechanical Systems (MEMS)and Nanoelectromechanical Systems (NEMS), there is a need to improve on the fundamental understanding of friction at diminishing gaps. Therefore, the paper investigates the friction of a simple fluid (n-hexadecane 99%) using an atomic force microscope. The measurements areinterpreted using modified Eyring’s thermal activation energy approach in order to examine the effect of molecular solvationat the assumed smooth summit of asperities. It is found out that solvation for a sliding contact could be observed through the shear stress activation volume due togenerated thermal energy, which indicates the movement of the fluid molecules intoand outof the contac

Prediction of Load and Shear of Ultra-Thin Multi-Species Surface Films

Unless protected by an inert gas atmosphere, micro-scale conjunctions are often separated by molecularly-thin adhered films. Therefore, predicting contact load, friction or adhesion, must consider the contribution of this layer to the overall contact problem. The contribution of an adhered layer can be accounted for using a simplified solution (e.g. an adjustment to the energy of adhesion to account for the liquid film). However, these methods cannot account for layers consisting of multiple species of molecules. The most common approach, which accounts for inter-molecular forces between molecules of various species, is a molecular dynamics simulation. However, this is time consuming, and therefore, often limited for small volumes of fluid and small scale contacts. The current paper proposes an alternative approach, where the pressure and shear between two smooth surfaces separated by an ultra-thin film is predicted using a statistical mechanics based model. This method accounts for the chemical structure of each species of molecules comprising the ultra-thin film, their concentration, intermolecular forces and adsorption to the wall. This approach is very fast, therefore, it can be easily included in a larger scale code predicting the behavior of the entire micro-scale mechanism. It was found that for a specified material of the solid boundary the model can predict the optimal concentration of each species of molecule in the intervening ultra-thin film, to minimize friction or adhesion.</jats:p

Multivariate optimisation study and life cycle assessment of microwave-induced pyrolysis of horse manure for waste valorisation and management

The increasing amount of waste generated globally due to industrialisation and economic activities require a proper and efficient waste management route. Turning waste to energy via pyrolysis pathway is a promising solution to reduce the amount of waste while generating useful end products. In the present study, microwave pyrolysis of horse manure for the production of bio-fuels and bio-chemicals is conducted and optimised using a lab-scale reactor. Pyrolytic products derived from optimised parameters show that the energy density of bio-char increased by 38.7% with a surface area of 799.57 m2g-1. The bio-oil was found to be enriched with phenolic content while the gaseous product contained high syngas proportion (67.17 vol%). A life cycle assessment (LCA) on the microwave pyrolysis of horse manure for a modelled pyrolysis plant located in Peninsula Malaysia has been conducted to evaluate the energy consumption, operation cost and environmental impact of each unit processes involved. Processing of horse manure via microwave-induced pyrolysis is demonstrated to be more advantageous as compared to the conventional pyrolysis of swine manure from the aspects of higher conversion efficiency, lower energy consumption and reduced environmental risk. Overall, the LCA of horse manure on microwave pyrolysis shows positive environmental impact as compared to other biowaste treatment methods such as composting and incineration

Microwave pyrolysis for valorisation of horse manure biowaste

© 2020 Elsevier Ltd Biomass-based feedstock is an attractive alternative to fossil fuel due to its sustainability and potential as a clean energy source. The present work focuses on the valorisation of horse manure biowaste to produce bioenergy via microwave-assisted pyrolysis technique. The thermal decomposition process is conducted by considering the effects of pyrolysis temperature, catalyst loading and carrier gas flow rate on the yield and quality of end products. The pyrolysed gaseous product contains up to 73.1 vol% of syngas components. The solid biochar obtained contains a heating value of 35.5 MJ/kg with high surface to pore volume ratio. The relatively high specific energy contents of gaseous products and biochar indicate their potential as biofuels. The liquid product is found to contain oxygenated phenolic compound of up to 79.4 wt%. In spite of an overall energy deficit achieved when comparing the total energy of end products with the feedstock, the energy balance analysis indicates the optimum production parameters. The least energy deficit is achieved at the reactive conditions of 350–450 °C and manure-to-catalyst ratio of 1:1. A reaction mechanism pathway for the pyrolysis of horse manure is presented to show the production route for bioenergy and valuable chemicals

Nanoscale elastoplastic adhesion of wet asperities

Accurate prediction of friction is crucial for design and efficient operation of many devices, comprising various contacts. In practice, contacting surfaces are rough and often wet. There are several mechanisms, which contribute to friction, including viscous shear of a coherent fluid film, as well as that of a thin adsorbed layer of boundary active molecular species. Additionally, adhesion and elastoplastic deformation of asperities on counterface surfaces may occur. Traditional friction models are based on statistical representation of surface topography as well as description of boundary shear films based on the theoretical lubricant film Eyring shear stress. The study reports a more realistic friction model than the traditional ones, which do not take into account the wet nature of the asperities. The fluid–surface interaction is a main contribution of the article, not hitherto reported in literature. It is shown that ignoring the effect of surface wetness can lead to the over-estimation of boundary friction and under-estimation of contact load-carrying capacit