Modelling of Metal-Coating Delamination Incorporating Variable Environmental Parameters

A mathematical model for metal-coat delamination of degrading metal was developed incorporating multiple variable environmental parameters. Metal-coat delamination not only depends on the electrochemical reactions at metal-coat interface but also on the factors like the type of propagating metal ions and their varying concentration with annual weather changes, time of exposure of the coated objects, type of coated objects are stationary or mobile vehicles, frequency with which certain vehicles are operating in various environments e.g. controlled or uncontrolled in terms of environmental conditions. A cutting edge model has been developed to calculate the varying environmental conditions using iteration algorithm, time dependent uncertain position of objects like vehicle in various environments using stochastic approach, effect of seasonal changes on ionic compound's concentration using algebraic method and instantaneous failure probability due to varying conditions. Based on the developed model a detailed simulation study was conducted to investigate the metal-coat delamination process and the ways to regress the under coat metal corrosion

Development in paraffin based thermal storage system through shell and tubes heat exchanger with vertical fins

Researchers are committed to develop robust and responsive technologies for renewable energy sources to avert from reliance on fossil fuels, which is the main cause of global warming and climate change. Solar energy based renewable energy technologies are valued as an important substitute to bridge the gap between energy demand and generation. However, due to varying and inconsistent nature of solar energy during weather fluctuations, seasonal conditions and night times, the complete utilisation of technology is not guaranteed. Therefore thermal energy storage (TES) system is considered as an imperative technology to be deployed within solar energy systems or heat recovery systems to maximise systems’ efficiency and to compensate for varying thermal irradiance. TES system can capture and store the excess amount of thermal energy during solar peak hours or recover from systems that would otherwise discard this excess amount of thermal energy. This stored energy is then made available to be utilised during solar off peak hours or night times. Phase change material (PCM) based TES system is appraised as a viable option due to its excellent adoption to solar and heat recovery systems, higher thermal storage density and wide range of materials availability. However, due to its low thermal conductivity (≅ 0.2 W/mK), the rapid charging and discharging of TES system is a challenge. Therefore, there is a need for efficient and responsive heat exchange mechanism to boost the heat transfer within PCM. In this study, transient analysis of two-dimensional computational model of vertical shell and tube based TES system is conducted. Commercial grade paraffin (RT44HC) is employed in shell as thermal storage material due to its higher thermal storage density, thermo-physical stability and compatibility with container material. Water is made to flow in tubes as heat transfer fluid. In this numerical study, the parametric investigations are performed to determine the enhancement in charging rate, discharging rate and thermal storage capacity of TES system. The parametric investigations involve geometrical orientations of tubes in shell with and without fins, inlet temperature and mass flow rate of HTF. It is evident from numerical results that due to increase in effective surface area for heat transfer by vertical fins, the charging and discharging rate of paraffin based TES system can be significantly increased. Due to inclusion of vertical fins, conduction heat transfer is dominant mode of heat transfer in both charging and discharging processes. Furthermore, vertical fins do not restrict natural convection or buoyancy driven flow as compared to horizontal fins. Similarly, the inlet temperature has a noticeable impact on both charging and discharging process. In melting process, the sensible enthalpy is boosted due to rise in inlet temperature and thus the whole system thermal storage capacity is enhanced. Likewise, the effect of mass flow rate of HTF on charging and discharging rate is moderate as compared to inlet temperature of HTF. The numerical results are validated by experimental results. To conclude, these findings present an understanding into how to increase charging and discharging rate of TES system so as to provide feasible design solutions for widespread domestic and commercial utilisation of TES technology

Rolling Contact Wear of Hybrid Ceramic Bearings with Refrigerant Lubrication.

Silicon nitride Si3N4 bearing elements have shown practical advantages over traditional steel elements due to their mechanical and physical properties. Leading technology and demands for high efficiency have caused loading bearing contacts in all kinds of machinery to be subjected to high speeds, high contact stresses and severe conditions of lubrication. In addition the introduction of a new generation of hydrocarbon refrigerants in various systems, where these rolling contact silicon nitride bearing elements are employed raises further demands to evaluate the rolling contact fatigue performance of these elements with refrigerant lubrication. Obtaining material wear properties of these refrigerants used in mechanical applications is difficult due to high saturation pressure of the refrigerants. It is important to investigate the influence of these refrigerants as lubricants on the rolling contact fatigue performance of ceramic bearing elements. This research responds to the need for bench testing of rolling contacts using the new generation refrigerants as lubricants. A novel pressurised chamber was designed to achieve a liquid state of the refrigerant as fluid for the rolling contact fatigue experiments. A high-speed rotary Tribometer was used for rolling contact fatigue tests. Experimental study of the influence of the liquid refrigerant lubrication on rolling contact wear of the silicon nitride/steel elements is presented. Investigations of the lubricated contact of silicon nitride rolling elements using the pressurised chamber reveal that wear rate is affected by the nature and geometry ofthe induced defect. A residual stress survey was also performed on failed ceramic elements. Analysing the relationship of residual stress with rolling contact fatigue is an important study which will provide guidelines on the design process and manufacturing of these elements. The residual stress field analysis shows that residual stresses are relieved due to sub-surface damage and are inversely related to stress cycles. Maximum tensile stresses at the edges of the contact path cause a weaker residual stress field at the sub-surface crack front

Dynamic simulation of a mobile manipulator with joint friction.

Mission criticality in disaster search and rescue robotics highlights the requirement of specialized equipment. Specialized manipulators that can be mounted on existing mobile platforms can improve rescue process. However specialized manipulators capable of lifting heavy loads are not yet available. Moreover, effect of joint friction in these manipulators requires further analysis. To address these issues, concepts of model based design and concurrent engineering are applied to develop a virtual prototype of the manipulator mechanism. Closed loop manipulator mechanism actuated by prismatic actuators is proposed herein. The mechanics model of the manipulator is presented here as a set of equations and as multibody models. Mechanistic simulation of the virtual prototype has been conducted and the results are presented. Combined friction model that comprises Coulomb, viscous and Stribeck friction is used to compute frictional forces and torques generated at each one degree of freedom translational and rotational joints. Multidisciplinary approach employed in this work improves product design cycle time for complex mechanisms. Kinematic and dynamic parameters are presented in this paper. Friction forces and torques from simulation are also presented in addition to the visual representation of the virtual prototype

Maximising the interfacial toughness of thin coatings and substrate through optimisation of defined parapmeters

The influence of three parameters, i.e. interfacial roughness λ, coating thickness h and impurity radius r at the coating–substrate interface on interfacial toughness, has been investigated within the framework of two approaches, i.e. thermodynamics and fracture mechanics. The governing equations for both the approaches have been derived independently and then fused to form a governing law for evaluating the interfacial toughness. The analysis in this paper which considers three parameters (λ, h and r) has been divided into three setups. Each setup is used to analyse the effect of one variable parameter on interfacial toughness while keeping the other two parameters constant. Three samples for each setup were prepared considering the requirements of constant and variable parameters for each setup. Simulation techniques founded on the experimental studies have been developed during this research in order to find the optimised values of three parameters. These optimised values act as critical values (boundary point) between coating fail-safe and coating fail conditions. The experiment employed ASTM-B117 test, which is used to analyse the interfacial toughness of samples under each setup. These experiments showed excellent, quantitative agreement with the simulation trends predicted by the theoretical model

Thermodynamic modelling and analysis of a solar organic Rankine cycle employing thermofluids

This paper presents thermodynamic modelling and simulation study of a small scale saturated solar organic Rankine cycle (ORC) which consists of a stationary, flat plate solar energy collector that is utilised as a vapour generator, a vane expander, a water-cooled condenser and a pump. Simulations are conducted under constant condensing temperature/pressure and various cycle pressure ratios (PR) for 24 organic thermofluids including Hydrocarbons (HCs), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), Hydrofluoroethers (HFEs) and Hydrofluoroolefins (HFOs). Special attention is given to the influence of PR and fluids’ physical properties on the solar ORC performance as well as fluids’ environmental and safety impacts including global warming potential (GWP), flammability and toxicity. The simulation results indicate that when the same fluid is considered, pressure ratio of the cycle leads to various operating conditions such as collector (evaporating) pressure which results in various collector, expander and cycle efficiency. For instance, increasing the pressure ratio of the cycle enhances the net work output and the thermal efficiency of the cycle, whereas it decreases the flat plate collector efficiency. The results also indicate that the proposed system produces the maximum net work output of 210.45W with a thermal efficiency of 9.64% by using 1-butene. Furthermore, trans-2-butene, cis-2-butene, R600, R600a, R601, R601a and neopentane (HC), R227ea and R236fa (HFC), RC318 (PFC) and R1234ze (HFO) show promising solar ORC thermal performances. However, the flammability problem of HCs and global warming potential issue of HFCs and PFCs limit their applications, owing to the safety and environmental concerns. On the other hand, in terms of the environmental impact, thermofluids such as RE347mcc, RE245fa2 (HFEs) and R1234ze, R1233zd (HFOs) offer an attractive alternative, yet they were neither the most efficient, nor generated the highest amount of net work output. This paper provides thermofluids’ selection guidelines to achieve maximum efficiency within solar thermal energy technologies while keeping environmental impacts into considerations

Friction and wear performance analysis of hydrofluoroether-7000 refrigerant as lubricant

The disquiet about global warming has triggered the formulation and introduction of new generation of refrigerants. Hydrofluoroethers (HFEs) are within the family of newly developed environmentally friendly refrigerants with a wide range of application areas. Hydrofluoroethers reportedly have better heat transfer and thermodynamic properties. In addition to an understanding and knowledge of the thermodynamic properties of refrigerants, it is essential to understand the tribological properties of refrigerants within the context of sustainable development. Tribo-performance of refrigerants applied in refrigeration, air-conditioning and energy systems directly influences the durability, reliability and cost effectiveness of the system. HFE-7000 has considerable potential for engineering applications in green energy and low carbon technologies. In this research, a detailed investigation has been performed to assess friction and wear performance of HFE-7000 (HFE-347mcc3). HFE-7000 has been employed as lubricants. Experimental results indicate the formation of tribo-films on the topmost surfaces. Energy-Dispersive X-ray Spectroscopic (EDS) and X-ray Photoelectron Spectroscopic (XPS) analyses on the tested samples revealed significant presence of oxygenated and fluorinated anti-wear tribo-films. These oxygen and fluorine containing tribo-layers prevent metal to metal contact and contribute to the reduction of friction and wea

A Review of Theoretical Analysis Techniques for Cracking and Corrosive Degradation of Film-Substrate Systems

This paper contains a review of the most vital concepts regarding the analysis and design of film systems. Various techniques have been presented to analyse and predict the failure of films for all common types of failure: fracture, delamination, general yield, cathodic blistering, erosive and corrosive wear in both organic and inorganic films. Interfacial fracture or delamination is the loss of bonding strength of film from substrate, and is normally analysed based on the fracture mechanics concepts of bi-material systems. Therefore, keeping the focus of this review on bonding strength, the emphasis will be on the interfacial cracking of films and the corresponding stresses responsible for driving the delamination process. The bi-material characteristics of film systems make the nature of interfacial cracks as mixed mode, with cracks exhibiting various complex patterns such as telephone cord blisters. Such interfacial fracture phenomenon has been widely studied by using fracture mechanics based applicable analysis to model and predict the fracture strength of interface in film systems. The incorporation of interfacial fracture mechanics concepts with the thermodynamics/diffusion concepts further leads to the development of corrosive degradation theories of film systems such as cathodic blistering. This review presents suggestions for improvements in existing analysis techniques to overcome some of the limitations in film failure modelling. This comprehensive review will help researchers, scientists, and academics to understand, develop and improve the existing models and methods of film-substrate systems