Open Literature Research Articles

Effect of Heat Exchanger and Capillary Geometry on the performance of Joule- Thomson Refrigerators operating with different mixtures

Abstract Joule-Thomson (J-T) refrigerators or J-T cryocoolers are extensively used in many low-temperature applications. J-T refrigerators operating with nitrogen-hydrocarbon (N2-HC) refrigerant mixtures offer several advantages, such as low operating pressures (<20 bar), high exergy efficiency, no moving parts in the cold section, and low cost. The cooling power or cooling capacity of the J-T refrigerator depends on the hardware used as well as the refrigerant composition. The proposed work focuses on estimating the cooling capacity of a mixed refrigerant J-T (MRJ-T) refrigerator of the given hardware and specified refrigerant. An iterative steady-state full-cycle simulation procedure has been presented in this work to simulate the complete system and estimate the cooling capacity, taking into account the possibility of choking of the expansion capillary. Some of the results have been validated against experimental results of an MRJT refrigerator available in the open literature. The details of the simulation model and the results of our studies on the prediction of stable operating range, maximum cooling capacity, the effect of heat exchanger geometry, expansion capillary geometry, mixture composition, and choking of the refrigerant mixture on the performance of an MRJ-T refrigerator are presented in this paper

Lithium leach residue synthesis process of high crystallinity hydroxysodalite, NaX, NaA zeolites and solidification and migration of potentially toxic elements

Converting lithium leach residue (LLR) into zeolite can reduce environmental impacts while also producing high value-added products. However, the synthesis of zeolites by LLR under alkali fusion may result in the solidification and migration of potentially toxic elements with secondary environmental impacts. Systematic research into this subject is rare in the open literature and the mobility of toxic elements from LLR derived zeolites is yet to be understood. In this paper, we have investigated the highly crystalline synthesis of hydroxy sodalite, X-type zeolite (NaX), and A-type zeolite (NaA) without stencil agent and crystal species, which can be achieved by modulating the alkali fusion temperature, all three zeolites have greater than 90 % conversion of the major elements aluminum and silicon. Meanwhile, the leachability of thallium (Tl), beryllium (Be), and potentially toxic elements (lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), arsenic (As), barium (Ba), copper (Cu), nickel (Ni), cobalt (Co), zinc (Zn)) was monitored by pH-dependent leaching test for LLR and three kinds of synthesized zeolites according to the Chinese standard and the emission of toxic elements during the synthesis process was analyzed, to investigate the migration and quantify the distribution of the toxic elements in the LLR to the product zeolites and the cleaning wastewater. The migration efficiency of potentially toxic elements from LLR to the product zeolite and cleaning wastewater was explored. It was found that most of the toxic elements Tl, Be and potentially toxic elements were solidified in the structure of the zeolites by ion exchange (solidification rate > 90 %), and a small portion flowed into the cleaning wastewater. Although there are toxic elements solidified in the structure, there is no significant leaching under various pH conditions, which is in line with the Chinese standard (GB/T 5085.3–2007). Therefore, it is considered that LLR realizes environmentally friendly zeolite production and does not cause secondary pollution to the environment. This work demonstrates great potential for green recycling of LLR from the lithium extraction process and introduces an environmentally friendly slag treatment technology.

Selection of pure and binary working fluids for high-temperature heat pumps: A financial approach

High-temperature heat pumps are increasingly being recognized for decarbonizing industrial heat supply up to 200 °C. In the open literature, the operating conditions, working fluids and configurations of high-temperature heat pumps are typically optimized for achieving a maximum Coefficient of Performance (COP). This work however presents a method that optimizes the operating conditions, working fluid and configuration of the heat pump, based on a combined financial and technical appraisal. In this regard a financial model to calculate the levelized cost of heat (LCOH) of a heat pump unit is developed. The model screens a large set of working fluids and therefore allows for subcritical, transcritical and supercritical operation and includes (zeotropic) binary mixtures. The methodology is applied to a large set of generic temperature profiles, with process temperatures between 160 °C and 200 °C and heat source temperatures between 80 °C and 120 °C. The results indicate that designing a heat pump solely based on maximum COP may lead to a sub-optimal financial solution. Overall, binary mixtures, either zeotropic or azeotropic, of natural working fluids often performed best. The benefits of zeotropic mixtures are twofold: improved temperature matching and flexibility in their thermophysical properties. However, for industrial processes with high temperature glides, pure fluids operating in the transcritical regime proved to be the most promising. The study also highlights the sensitivity of the financial performance to the electricity price, annual operating hours and heating capacity.

Using technology broadcasting to explore market applications: The moderating role of a firm's domain‐specific and general knowledge

AbstractInnovative firms, like startups, are increasingly making use of technology broadcasting to explore market applications for their technology. While findings from previous studies suggest that these firms can get access to a large pool of suggestions for market applications through technology broadcasting, we lack empirical evidence on whether firms that use technology broadcasting will actually be able to process and explore these suggestions. The current study points to the distinct role of firms' domain‐specific and general knowledge base in this respect. It proposes that technology broadcasting is positively related to the number of market applications a firm explores. Moreover, it hypothesizes that this relationship is weakened by the firm's domain‐specific knowledge and strengthened by its general knowledge base. We use Poisson analyses on hand‐collected survey and secondary data on a sample of 205 Flemish startups. We find that technology broadcasting is positively associated with the number of market applications a firm explores. Furthermore, this positive relationship is stronger with increasing general knowledge, but weaker with increasing domain‐specific knowledge. These findings advance our understanding of the boundary conditions of technology broadcasting. Additionally, our study contributes to the open innovation literature which has called for more attention to the challenges an organization faces in managing its external knowledge search. Finally, our study provides important practical insights for innovative firms that are trying to find market applications for their technology.

Experimental study and neural network model based prediction of layer thickness influence on LPBF IN625 single track geometry

The performance of interacting metal surfaces having sliding motion is enhanced by fabricating microfeatures on-top of the surfaces. Laser powder bed fusion (LPBF) is used to fabricate the microfeatures of IN625 on-top of a flat surface. In LPBF, geometrical characteristics of microfeatures are based on the energy supplied and the volume of material melted (layer thickness) at that instant of time. There is very few research reported in open literature on the effect of layer thickness on microfeatures geometry during LPBF. In this work, a series of single tracks is fabricated with different combinations of laser power and scanning speed for 75 μm, 100 μm, and 125 μm layer thickness and its effect on single track geometrical characteristics and microstructure was evaluated. It has been found that laser power and scanning speed have a significant influence on the track geometry irrespective of layer thickness. The minimum linear energy density of 2.5 J/mm is considered to fabricate the continuous track formation for investigated layer thickness. From statistical analysis, it is observed that the laser power and scanning speed shows higher contribution on track width and remelting depth, respectively. Whereas, layer thickness shows a higher influence on track height and contact angle of single track as compared to laser power and scanning speed. In 125 μm layer thickness, the volume of material melting is increased which encourages the gravity effect to deform the melt pool and produces larger track width compare to 100 μm layer thickness. Further, the cell spacing is gradually increased with layer thickness resulting increase in the solidification period. The shape controllability of the single track is significantly increased with layer thickness, but as keeps on increasing layer thickness due to the larger volume of molten metal, the melt pool losses ability to maintain convex shapes. An Artificial Neural Network (ANN) model is developed to understand the relationship between the LPBF process parameters and single track geometrical characteristics to predict the responses for a wide range of process parameters. The multiple response neural network model shows excellent agreement with experimental results with R2 value greater than 0.95.

The Advent of Molecular Targeted Therapies Against Cancer. Toward Multi‐Targeting Drugs Through Materials Engineering: A Possible Future Scenario

The authors, actively engaged in the development of mesoporous silica‐based solutions, initially for modified drug release, later for the smart administration of conventional chemotherapeutic cytotoxic drugs, present the evolution of the concept of targeted therapy across different disciplines. They also discuss the diverse therapeutic needs and related challenges (adverse drug effects) that have unfolded over the last 30 years. Nanomedicine potentialities, mainly against cancers, that have emerged globally during the intense research activity of the last few decades, are critically discussed. The authors glimpse the growing potential of immune‐based therapeutic solutions, including those assisted by nanotechnology, as well as molecular targeted therapies (MTT) on which they focus. The advantages offered by targeted molecular therapies, despite the limits of monotargeted therapies, suggest the engineering of multi‐targeted therapies. Nanomedicine solutions such as ligand‐specific internalization and pH‐sensitive drug release that they have extensively tested and recently presented in open literature, still remain available instruments. According to the authors, MTT can offer shining perspectives in the near future that will depend on a thorough comprehension of nanostructures synthesis and tumor physiology. This article gives an interdisciplinary point of view tailored for non‐specialist readers imagining possible future scenarios in the field.

The effect of main dimensions on the preliminary design of motor yachts

The design process of motor yachts mainly relies on the experience of designers, who have confidence in the knowledge acquired from designing units with similar hull-form characteristics. However, once a new concept needs to be developed, the acquired experience on a standard platform is no longer sufficient to achieve in a short time a successful design. The design of a motor yacht implies considering multiple aspects of ship hydrodynamics: resistance, propulsion, seakeeping, and manoeuvring. Such factors have been widely discussed individually on different kinds of ships, but an appropriate joint investigation of hulls like motor yachts is missing in the open literature. Therefore, the present paper intends to cover this gap, providing guidelines for the design of motor yachts in a length range between 20 and 40 meters. As a preliminary study, a series of 15 yacht hulls has been developed, starting from a reference hull form. Seakeeping, manoeuvring, and propulsive performances have been evaluated at a reference environmental condition and speeds according to the ISO 22834:2022 guidelines. Such calculations allow for developing response surfaces of the hydrodynamic properties for the series of yachts as a function of the hull's main dimensions. As a final result, the obtained responses allow for identifying the best compromise solutions for the main dimension selection of a new motor yacht in the length range of 20-40 meters.

Magneto-Micropolar Nanofluid Flow Over a Convectively Heated Sheet with Nonlinear Radiation, Chemical Reaction, and Viscous Dissipation

A mathematical model is presented for analyzing the flow of magneto-micropolar nanofluid above a convectively heated permeable stretching sheet with nonlinear radiation, chemical reaction, and viscous dissipation. Similarity transformation is utilized to change the governing partial differential equations to the system of nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is sorted out mathematically by utilizing the shooting method with the Adams-Moulton method of fourth order, and the obtained mathematical outcomes are compared with published results. The obtained numerical results reflect very good agreement with those from open literature. Numerical values of physical quantities like skin friction coefficient, Sherwood number, and Nusselt number for emerging parameters such as Pr , Nb , Nt , Le , etc. are also computed and discussed in this work. The impact of pertinent flow parameters on nondimensional velocity, temperature, and concentration profiles is illustrated via tables and graphs.

Structural Optimization of Trusses in Building Information Modeling (BIM) Projects Using Visual Programming, Evolutionary Algorithms, and Life Cycle Assessment (LCA) Tools

The optimal structural design is imperative in order to minimize material consumption and reduce the environmental impacts of construction. Given the complexity in the formulation of structural design problems, the process of optimization is commonly performed using artificial intelligence (AI) global optimization, such as the genetic algorithm (GA). However, the integration of AI-based optimization, together with visual programming (VP), in building information modeling (BIM) projects warrants further investigation. This study proposes a workflow by combining structure analysis, VP, BIM, and GA to optimize trusses. The methodology encompasses several steps, including the following: (i) generation of parametric trusses in Dynamo VP; (ii) performing finite element modeling (FEM) using Robot Structural Analysis (RSA); (iii) retrieving and evaluating the FEM results interchangeably between Dynamo and RSA; (iv) finding the best solution using GA; and (v) importing the optimized model into Revit, enabling the user to perform simulations and engineering analysis, such as life cycle assessment (LCA) and quantity surveying. This methodology provides a new interoperable framework with minimal interference with existing supply-chain processes, and it will be flexible to technology literacy and allow architectural, engineering and construction (AEC) professionals to employ VP, global optimization, and FEM in BIM-based projects by leveraging open-sourced software and tools, together with commonly used design software. The feasibility of the proposed workflow was tested on benchmark problems and compared with the open literature. The outcomes of this study offer insight into the opportunities and limitations of combining VP, GA, FEA, and BIM for structural optimization applications, particularly to enhance structural efficiency and sustainability in construction. Despite the success of this study in developing a workable, user-friendly, and interoperable framework for the utilization of VP, GA, FEM, and BIM for structural optimization, the results obtained could be improved by (i) increasing the callback function speed between Dynamo and RSA through specialized application programming interface (API); and (ii) fine-tuning the GA parameters or utilizing other advanced global optimization and supervised learning techniques for the optimization.

Cattaneo–Christov heat and mass flux model and thermal enhancement in three‐dimensional MHD Jeffrey hybrid nanofluid flow over a bi‐directional stretching sheet with convective boundary conditions

AbstractInspired by the progressive relaxation characteristics of the Jeffrey model and its applied advantages in the rheological modeling of various dynamic fluids, the current study is focused to investigate the heat and mass transfer of magnetohydrodynamic (MHD) Jeffrey hybrid nanofluid flow over bi‐directional stretching sheet with convective boundary conditions. Additionally, the Cattaneo–Christov model of heat and mass flux is employed to take into consideration the time relaxation effects. The energy and concentration equation are taken into account to explore the effects of thermophoresis and Brownian motion. Homotopy analysis method (HAM) is employed for the solution of the current problem. Solution methodology is verified by comparing present results with those already published in open literature. The physical aspects of obtained graphical and numerical results are explained in detail to justify acquired trends. From the investigation, it is inferred that the magnetic and viscoelastic factors have a reducing influence on the flow profile along primary and secondary directions, while the stretching parameter has an increasing behavior on the flow profile in the secondary direction. Furthermore, the Brownian motion, magnetic parameter, and thermophoretic parameter have an escalating behavior on thermal distribution; however, the Brownian motion has a declining consequence on the concentration profile. The larger Biot number heightens the thermal and concentration distributions.

Prediction of Resonant Frequency of an Equilateral Triangular Microstrip Antenna Using Conformal Mapping Technique

In this manuscript, Conformal Mapping Technique (CMT) is applied to predict the resonant frequency of an Equilateral Triangular Microstrip Antenna (ETMA). The ETMA is mapped into a simple circular geometry with the aid of CMT. The wave equation is solved in the transformed domain using Galerkin technique to obtain the approximate solution of eigenfunction and eigenvalue. Twenty-three measured data are collected from the open literature to validate our theory. Our theoretical results are also compared with several CAD models to show the effectiveness of the present theory. It is found that our proposed theory can predict the resonant frequency of the ETMA with an error of less than 1.5%, whereas those CAD models can produce a large error (sometimes, 10-19% error). Internal field patterns, input impedance, far-field radiation patterns, quality factor, bandwidth gain, and directivity of the ETMA for the dominant mode are also investigated using CMT.

Enhancing security and privacy in smart agriculture: A novel homomorphic signcryption system

Technology driven Smart Agriculture is transforming modern day farming practices through digital tools and real-time data analysis. It monitors plant health in both soil and soilless cultivation, promoting environmentally responsible practices by utilizing integrated sensors and precision methods. Despite the significant potential benefits, challenges persist in ensuring data security in the smart agriculture frameworks. The existing research has explored various mechanisms to cater these issues, yet these solutions susceptible to known attacks i.e., Confidentiality, Authentication, Privacy preservation. Notably, the available schemes in open literature face performance deficiencies due to an overreliance on Rivest-Shamir-Adleman (RSA), bilinear pairing, and elliptic curve (EC). To comprehensively address these challenges, this study presents a novel approach via employing homomorphic Signcryption based on Hyper-Elliptic Curves (HEC). Our HEC based Signcryption technique enhances security with lower computational cost and communication overhead as compared to the existing techniques. Furthermore, our solution provides the best performance in terms of efficiency, addressing the privacy preservation issues with conformance to the (Confidentiality, Integrity, and Availability) CIA triad. For proof of concept and correctness, we have validated the results in Scyther tool, with the assurance that proposed scheme is correct, verified, and resistant against known set of attacks. The proposed scheme achieves a remarkable reduction in both computational and communication costs around 95.08 % and 89.28 % respectively, enhancing practicality and suitability for real-world implementation. Thus, making it a suitable candidate for employing in smart agriculture environments, encompassing both soil and soilless cultivation scenarios. This research contributes a robust, secure, cost effective, and efficient solution to the challenges posed by the evolving landscape of agriculture, paving the way for enhanced data protection and system resilience in smart agriculture systems.

Boosting firms’ absorptive capacity: the digital technologies edge

PurposeThis study aims to explore how firms can enhance their innovation processes by effectively utilizing external knowledge and employing digital technologies. Specifically, it emphasizes the role of absorptive capacity (ACAP) in external knowledge acquisition and assimilation (potential ACAP), as well as transformation and exploitation (realized ACAP), highlighting the necessity of equipping firms with digital technologies to support ACAP activities.Design/methodology/approachTo achieve the research purpose, we conducted a structured literature review of academic papers sourced from Scopus-Elsevier.FindingsThe key findings encompass the identification of common digital technologies supporting ACAP and explore how these technologies contribute to knowledge acquisition, assimilation, transformation and exploitation. The main results show that social media and online communities are the most studied technologies in relation to ACAP activities. Research predominantly centres on potential ACAP – with acquisition activity more studied than assimilation – rather than realized ACAP – with only social media and online communities demonstrating full support for transformation and exploitation activities.Research limitations/implicationsThis research represents a pioneering joint study of ACAP and digital technologies, advancing understanding beyond organizational perspectives and expanding open innovation literature by integrating ACAP role in technology collaborations. A call for qualitative investigations into the relationship between digital technologies and ACAP emerged.Practical implicationsThe findings offer valuable guidance to innovation managers, aiding them in selecting appropriate digital technologies to strengthen ACAP activities.Originality/valueThis work’s uniqueness lies in bridging the gaps between open innovation, ACAP and digital technologies, which are often studied in isolation.

Advances in enhanced geothermal systems: Integrating laboratory, numerical and field insights

An enhanced geothermal system is a designed and engineered thermal reservoir that has been deliberately stimulated to extract economically viable amounts of heat from geothermal resources having no natural permeability. Enhanced geothermal system projects are typically initiated to meet the industrial production standards, usually via techniques such as chemical stimulation, hydraulic fracturing, or thermal processes to enhance the permeability of the reservoir. The main aim of this study is to evaluate the current advancements in enhanced geothermal system through a comprehensive examination of laboratory experiments, numerical simulation, and fieldwork investigations from numerous studies that are insufficient captures and combined by current open literature. This study highlighted the critical importance of precisely developing fracture systems, whether natural or artificially induced, in ensuring the effectiveness of such projects. Notably, hydraulic fracturing techniques have been proven instrumental in enhancing the performance of enhanced geothermal systems. On the contrary, research conducted through numerical simulations has demonstrated consistent findings that it is beneficial to enhance the permeability of low-permeability rock for the efficient use of enhanced geothermal systems. Additionally, this study has highlighted the intricate and expensive nature of designing enhanced geothermal systems due to uncertainties in subsurface conditions especially from projects that are in initial stages of development. This study enables researchers and operators to improve the efficiency and safety of geothermal energy extraction, paving the way for more sustainable enhanced geothermal system projects in the future.

Limits of coefficient of performance of adsorption cooling cycle based on refrigerant’s type

This research work discusses how the thermodynamic properties of refrigerant constrain the upper limit of the coefficient of performance (COP) of adsorption cooling (AC) cycle. A mathematical model is developed based on the mass and energy balance across the adsorption bed and used to estimate the maximum COP. Langmuir model is used to derive the ideal COP. Besides, Carnot COP and exergy efficiency are derived to evaluate the adsorption cooling cycle further. These new parameters are applied to the available cycles in the open literature to assess how much room for improvement is still left in the adsorption technology based on the refrigerant type. Water, ammonia, methanol, ethanol, Butane, R134a, R32, CO2 and R1234ze are used in this study. The maximum cooling COP cannot exceed 1.0 for cooling applications and is always less than 2.0 for heat pumps. Results show that AC cycles using water or ethanol as refrigerants achieve the highest exergy efficiency. The AC cycle using water as an adsorbate and silica gel as an adsorbent has the highest relative COP, about 80 % at 85 °C regeneration temperature. In turn, CO2 exhibits the lowest one. This work is merely an attempt to save experimental effort and time by identifying the most suitable refrigerant based on its physical and thermal properties and the cycle operating conditions.

Gas viscosities from a semiconductor-manufacturing mass-flow controller

We obtain gas viscosities with a pressure-based mass-flow controller used for semi-conductor manufacturing, a rate-of-change approach, and a physics-based calculation. The novelty of this method is that it is used in an industrial process whose main goal is not to measure viscosities. In this way, for pressures of the order of 10 kPa and 25 ∘C and 35 ∘C, we obtain for seven gases viscosities with mean absolute errors with respect to reference viscosities of less than 1%. Using this method, we report viscosities for two semiconductor-manufacturing gases not available in the open literature: hexafluoroisobutene (CAS # 382-10-5) and 1,1,3,3,3-pentafluoropropene (690-27-7).

Investigation of Iron Dissolution Mechanism in Acidic Solutions with and without Dissolved CO2—Part I: Electrochemical Impedance Spectroscopy Measurements

Aqueous CO2 corrosion of mild steel is one of the major problems in the oil and gas industry. While current understanding primarily focuses on cathodic reaction mechanisms, less attention has been given to the impact of aqueous CO2 on the anodic iron dissolution reaction. In contrast, the mechanism of iron dissolution in strongly acidic environments has been thoroughly investigated. Among the reaction mechanisms found in the open literature, a multipath mechanism was identified that could explain the iron dissolution in strong acidic sulfate solution; both in terms of steady-state polarization sweeps and impedance data at various pH values and current densities. However, the role of aqueous CO2 in solutions containing chlorides on the mechanism of iron dissolution remained an open question. The present study used electrochemical impedance spectroscopy (EIS) as the main technique, to study the mechanism of iron dissolution in strong acid chloride solution with and without the presence of CO2. Results showed that the presence of chloride ions (0.5 M) decreased the rate of iron dissolution by competing with hydroxide ions to adsorb on the metal surface, forming chloride-containing intermediate species that participate in the iron dissolution reaction. The resulting decrease in the availability of hydroxide intermediates, which are more effective at enhancing the reaction rate compared to chloride-containing intermediates, leads to an overall decrease in the rate of iron dissolution. While the presence of CO2 increases anodic current density, EIS investigation revealed that neither aqueous CO2 nor other carbonic species directly react on the bare metal surface to form adsorbed intermediates involved in the anodic reaction. EIS investigation suggested that aqueous CO2 may induce changes in the chemical composition of adsorbed species, rate constants, and surface coverage, thereby altering the kinetics of the underlying reactions.

Numerical simulation for MHD Oldroyd-B fluid flow with melting and slip effect

This investigation reflects an examination of Oldroyd-B fluid flow over a permeable surface subjected to the effects of melting, slip effect, inclined magnetic field and chemical reactions. The governing equations are resolved using the bvp4c inbuilt MATLAB tool, the arithmetic computation for the momentum, thermal and concentration equations are executed. The results are exhibited graphically. Numerical outcomes are graphically depicted by aid of velocity, concentration, temperature profiles for several model variables. The achieved results exhibit a promising agreement with the previously established findings available in the open literature. The results obtained indicated that Deborah number β1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta_{1}$$\\end{document} reduces the momentum boundary layer thickness whereas Deborah number β2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta_{2}$$\\end{document} enhances the adjacent momentum boundary layer. Furthermore, temperature profile declined for melting parameter Me\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Me$$\\end{document}. The application of this study transcends various engineering disciplines, offering practical solutions and optimization opportunities in polymer processing, coating technologies, cooling systems, materials processing, biomedical and environmental engineering.

Elastic and Elastoplastic Contact Mechanics of Concentrated Coated Contacts

Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been predicted using classical Hertzian contact mechanics. However, the theory is only applicable when the contact between a pair of ellipsoidal solids of revolution may be considered as a rigid indenter penetrating a semi-infinite elastic half-space. Many coatings act as thin bonded elastic layers that undergo considerably higher pressures than those predicted by the classical theory. Furthermore, inelastic deformation of bonded solids can cause plastic flow, work-hardening, and elastoplastic behaviour. This paper presents a comprehensive, integrated contact mechanics analysis that includes induced sub-surface stresses in concentrated counterformal finite line contacts for all the aforementioned cases. Generated pressures and deformation are predicted for hard coated surfaces, for which there is a dearth of relevant analysis. The contact characteristics, which are of particular practical significance, of many hard, wear-resistant advanced coatings are also studied. The paper clearly demonstrates the importance of using efficient semi-analytical, detailed holistic contact mechanics rather than the classical idealised methods or empirical numerical ones such as FEA. The novel approach presented for the finite line contact of thin-layered bonded solids has not hitherto been reported in the open literature.

A comprehensive review on advancements in compliant structures of gas foil journal bearings

Gas foil journal bearings (GFJBs) are widely considered technically advanced bearings and a viable alternative to conventional rolling element and oil-lubricated bearings in high-speed rotating machinery. GFJBs offer advantages such as reduced maintenance, improved efficiency, and the ability to operate in challenging environments. A traditional GFJB consists of (i) a smooth top foil for the generation of hydrodynamic pressure, (ii) a compliant corrugated foil beneath the top foil for tailoring stiffness, and (iii) a bearing base to hold the foils together. The shape and geometry of corrugated thin foil are primarily designed for the essential stiffness and load-carrying capacity of the bearings. The thickness of thin foils is in the range of 100–150 μm. The fabrication of complaint thin foils to their desired shapes and sizes is quite challenging. Engineers and researchers around the world have designed and published various advanced design structures of GFJBs to improve their static and dynamic characteristics. The corrugated or compliant structure is the most significant component of GFJBs from design and fabrication point of view. Therefore, a modest attempt is made by the authors to review and report systematically on various foil journal bearings reported in open literature. The study covers four primary categories, which are centered around the design of compliant structures, materials, manufacturing processes, and coatings over the years. By analyzing the state-of-the-art advancements, this review aims to identify key areas for further research, explain technological trends, and underline the pivotal role of GFJBs in various high-speed applications across industries.