Interlayer dwell time is a critical but often under optimized parameter in wire arc additive manufacturing (WAAM), as it governs heat accumulation, solidification kinetics, solute redistribution and the final performance of deposited alloys. In this work, Inconel 625 wall structures were fabricated by cold metal transfer (CMT) based WAAM using interlayer dwell times of 10s, 50s and 90s. A sequentially coupled thermo-mechanical finite element model, with experimentally validated thermal predictions, was combined with numerical stress-distortion analysis, multiscale microstructural characterization, tensile testing, wear analysis, and electrochemical corrosion evaluation. The results show that a short dwell time intensifies thermal accumulation, extends the mushy zone and promotes Nb/Mo segregation into interdendritic Laves-rich regions. Increasing the dwell time to 90s enhanced heat extraction, reduced the solute boundary layer thickness and refined the solidification structure, decreasing the primary dendrite arm spacing (PDAS) from ∼40 to ∼15 μm and the grain size from ∼610 to ∼180 μm. This refined and chemically more homogeneous microstructure increased hardness from 225 to 290 HV0.2 and improved tensile performance through combined solid solution, grain boundary, dislocation and precipitate strengthening. The 90s condition also exhibited superior tribological response, with the wear mechanism transitioning from severe oxidative-delamination wear to milder oxidative-abrasive wear. Corrosion resistance in 3.5 wt.% NaCl improved markedly with dwell time, as the corrosion current density (i_corr) decreased from 71.40 to 22.50 nA/cm⁻², the corrosion rate decreased from 27.86 × 10⁻³ to 8.77 × 10⁻³ mpy, and the pitting potential increased from 290 to 550 mV. These findings establish interlayer dwell-time control as an effective route for simultaneously improving dimensional stability, microstructural integrity, strength, wear resistance and corrosion performance in WAAM Inconel 625.

Additive manufacturing (AM) enables the fabrication of complex internal cooling channels for high-temperatureaerospace applications, but the rough as-built surfaces strongly influence flow. Understanding and predicting theseeffects is critical for accurate thermal–hydraulic design of AM-based cooling components. This study investigates therole of surface roughness on pressure drop and friction factor in an AM rectangular channel fabricated from Haynes230, a nickel-based superalloy. The cooling channel, with a hydraulic diameter of 1.995 mm, was tested in a closed-loop nitrogen flow facility at different mass flow rates, corresponding to Reynolds numbers in the range of 104 - 105.The test facility was developed under the MERiT+ project funded by Swedish National Space Agency at KTH Royal Institute of Technology, with industry partners from Siemens Energy and GKN Aerospace. Pressure drops wererecorded using multiple taps located along axial direction, and the Darcy friction factor was determined from localpressure drops. Complementary optical measurements of cross-sections at different streamwise locations wereperformed to assess variations in hydraulic diameter, while white light interferometry was employed to quantify surface roughness parameters, including Sa, Sq ,Ssk, and Sku. Numerical simulations were carried out in ANSYS Fluent usingthe pressure-based steady solver. Simulations were conducted with equivalent sand-grain roughness height, ks, derivedfrom characteristic parameters. Comparison between experimental and numerical results demonstrated consistenttrends in pressure drop and validated the approach for implementing hydraulic roughness in CFD. The data was furtheranalyzed to establish a predictive correlation between measured roughness parameters and equivalent sand-grainroughness. Several log-linear model forms were evaluated, and fitting was performed by minimizing errors in predictedfriction factors using the Haaland equation. The final correlation expresses (ks/Dh) as a function of normalized RMS roughness, and skewness, providing a compact, physically interpretable model. This work demonstrates a combinedexperimental, metrological, and numerical methodology for quantifying and predicting friction factor in AM channels.The proposed correlation, calibrated for Haynes 230 LPBF channels in the turbulent regime, bridges advanced surface characterization with classical fluid mechanics and offers a foundation for more reliable hydraulic design of AM-based cooling systems.

In present work, the melting performance of triplex-tube latent heat thermal energy storage (LHTES) unit was numerically studied using equal volumes of PCM and metal foam composite PCM (CPCM) in various arrangements. For the n-eicosane (as PCM), the study was conducted at the fixed Rayleigh number (Ra) = 4.08x107, Prandtl number (Pr) = 62.9, and Stefan number (Ste) = 0.14. The results showed that positioning the metal foam on the bottom side and distributing segmented CPCM with alternating PCM zones effectively improved the system performance. Moreover, this also prevents the overheating of thermal layers in the LHTES unit. While the model labelled M2 exhibited the highest economic efficiency among all isotropic models, its low dimensionless thermal energy storage (TES) density (i.e., q’ ∼ 0.6) led this study to focus on models falling under the category having a TES density of ∼ 0.8. Compared to a pure PCM model, the configurations under equal volume ratio category demonstrated up to ∼ four times higher TES rate (p’) and the significant reduction of ∼ 75 % in melting time. The optimized isotropic model achieved the highest TES rate per unit cost with peak value of ∼ 3 at a price ratio (N) of 1. Lastly, the testing of metal foam anisotropy on the chosen design showed a substantial increase in melting/heat storage rates. The largest drop of ∼ 33 % in the total melting time was noticed for model M2 as compared to isotropic case.

This review article provides a comprehensive overview of the fundamentals, modelling approaches, experimental studies, and challenges associated with hydrogen gas flow in pipelines. It elucidates key aspects of hydrogen gas flow, including density, compressibility factor, and other relevant properties crucial for understanding its behavior in pipelines. Equations of state are discussed in detail, highlighting their importance in accurately modeling hydrogen gas flow. In the subsequent sections, one-dimensional and three-dimensional modelling techniques for gas distribution networks and localized flow involving critical components are explored. Emphasis is placed on transient flow, friction losses, and leakage characteristics, shedding light on the complexities of hydrogen pipeline transportation. Experimental studies investigating hydrogen pipeline transportation dynamics are outlined, focusing on the impact of leakage on surrounding environments and safety parameters. The challenges and solutions associated with repurposing natural gas pipelines for hydrogen transport are discussed, along with the influence of pipeline material on hydrogen transportation. Identified research gaps underscore the need for further investigation into areas such as transient flow behavior, leakage mitigation strategies, and the development of advanced modelling techniques. Future perspectives address the growing demand for hydrogen as a clean energy carrier and the evolving landscape of hydrogen-based energy systems.

The melting/solidification performance of a latent heat based thermal energy storage (TES) system is impeded due to the poor thermal conductivity of phase change materials (PCMs). To circumvent this limitation, several approaches have been adopted such as incorporation of nanoparticles including carbon nanotubes, fins/extended surfaces, heat pipes, metal foam, etc. This work presents an innovative design optimization technique for the solidification (discharging) enhancement by embedding the porous copper metal foam in PCM (referred as composite PCM) inside a triplex-tube heat exchanger unit. Equal volume ratio (0.5 v/v) of PCM and composite PCM was considered inside the annular space. Fifteen different configurations (M-1 to M-15) of composite PCM under the four broad classes based on the relative positioning and arrangement of metal foam were investigated and compared. Transient drop in melt fraction during solidification, temperature contours, instantaneous solidification contours, and total energy change in the solid PCM have been discussed. Numerical experiments demonstrated that the segmentation of porous metal foam zone in TES units significantly improves the discharging performance. The results suggest that upon maintaining a direct contact of the composite PCM zone with the flowing heat transfer fluid further improves heat dissipation and leads to an enhancement of ∼3.2 times (M-15) as compared to the pure PCM case (M-1). The overall performance is improved when the metal foam is placed above the pure PCM in TES unit. Typical results predict ∼97.5% and ∼ 91.1% reduction in solidification time for model M-2 (fully filled with metal foam of porosity 0.95) and M-11 (uniform segmentation of metal foam of porosity 0.95 into 4 zones), respectively, when compared with pure PCM (M-1). An evaluation of the rate of the total energy released per unit cost of material used during discharging reports that model M-11 outperforms (the maximum value of ∼8.9) all other models having identical mass of PCM and/or composite PCM.

The present study investigates magnetorheological grease flow in a rectangular channel with two rotating cylinders. Along with a heat transfer analysis, the study focuses on the effect of a magnetic field on the flow of the grease dispersed with two different weight fractions of carbonyl iron particles. With increasing pressure, it has been observed that velocity increases at all locations of the channel. The presence of a magnetic field leads to a reduction in flow velocity. This is explained based on the formation of strong field-induced chain-like networks which increases the resistance to flow. The pressure drop across the channel is dependent on magnetic field strength as the rate of drop decreases in the vicinity of the zone where the magnetic field is applied. Temperature contours suggest that heat dissipation is directly related to the field strength. As the interaction time between the grease and heated walls of the cylindersin the channel increases due to reduced motion, better heat dissipation takes place. Velocity distribution at different locations of the channel is studied to understand the effect of magnetic field strengthand rotation of cylinder walls on the flow. The velocity profile is near parabolic downstream of the magnetic zoneand a higher velocity is offered by magnetorheological grease with a lower weight percentage of carbonyl iron particles.

This work presents an investigation of magnetohydrodynamic flow in a novel double restriction seal configuration using micro-Particle Image Velocimetry (µPIV). A conventional seal design has been modified to impart magnetic effects in the flow of magnetorheological grease, which is prepared with 5% by weight of carbonyl iron particles dispersed in NLGI 3 grade lithium-soap-based grease. Rectangular bar magnets are fitted on the seal to induce an external magnetic field strength greater than 0.8 T. The grease flows between two restrictions in the annular domain, and the velocity field is captured by a µPIV technique. Experimental results predict that flow velocities are considerably lower in the presence of the magnetic field. Carbonyl iron particles orient themselves in the direction of the magnetic field and form strong chains which increase the yield stress of the grease medium. Maximum velocities are obtained in the vicinity of the shaft. Further, a numerical model has been developed to predict the velocities at different locations in the annular grease domain at varying rotational speeds of the shaft.

In this work, we present a novel magnetohydrodynamic flow study using micro-Particle Image Velocimetry (m-PIV) in a rectangular channel under the effect of a uniform transverse magnetic field. This study is the first of its kind to explore the use of magnetorheological grease in machine components such as bearings. Rheological characterisation of grease samples establishes the non-linear relationship between the shear rate and shear stress and thus confirms the non-Newtonian behaviour of the grease. The flow follows a parabolic path away from the magnetic field. Experimental studies reveal that the flow velocities reduce considerably from 11.9 m/s to 1.7 m/s in the vicinity of the magnetic zone due to the formation of strong field-induced chains. These chains are responsible for an increase in localized yield stress of grease thereby causing a surge in the resistance to flow. Further, numerical and analytical models are developed to predict the velocity field under a magnetic field. The analytical model can accurately predict the flow velocity for different magnetic field strengths. It can be deduced that the obtained correlation is a suitable model for estimating the velocity values at different magnetic field strengths for flow in similar configurations. Numerical results predicted by a finite volume method-based solver are in good agreement with the experiments on the upstream side. Flow velocities increase with flow rate and decrease with the onset of the magnetic field. Pressure drop along the channel length shows an abrupt change in the magnetic zone. This is because of the disturbance of the normal flow regime due to the presence of the magnetic field. The grease flow disturbs the distribution of magnetic field lines resulting in flow-induced field strength of B = 0.1 T against an applied external magnetic field strength value of B = 0.3 T. The present study analyses the effects of an external field on the flow patterns of magnetorheological grease. It confirms that magnetorheological grease provides controllability in applications, because flow properties can be varied by tuning the magnetic field strength.

Thermorheological characterizations of magnetorheological (MR) grease thickened with polytetrafluoroethylene (PTFE) and molybdenum disulphide (MoS2) used as an additive for two different greases prepared with 50% (MRG50) and 70% (MRG70) weight fractions of spherical carbonyl iron (CI) particles, respectively, are presented. The magnetic properties and glass transition temperature of prepared MR greases (MRGs) have been measured using vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC), respectively. The MR properties are investigated at different temperatures ranging from 25 °C to 65 °C at magnetic fields ranging from 0 to 0.75 T under rotational and oscillatory sweep tests using a magnetorheometer. It is observed that for MRG70, the shear stress and apparent viscosity increase with increasing temperature. This is explained based on the formation of monolayers of MoS2 as it interacts with MRG and the effect of thermal conductivity on magnetorheology. Yield stress of PTFE-based MRG has been shown to increase with temperature and magnetic field. Formation of PTFE particle clusters decreasing the localized heat dissipation has been explained to be the reason for this. With increasing magnetic field strength, the flow properties show an increasing trend. ON-state storage and loss modulus are studied to understand the effect of temperature and magnetic field on the viscoelasticity of PTFE-based MRG.

This work presents a numerical model for predicting flow behaviour and temperature distribution of polytetrafluoroethylene thickened grease in a roller bearing configuration of obstructed flow. A finite-element code with a laminar flow multiphase mixture model is used to predict the flow patterns and volume fraction distribution of a thickener in a rectangular channel with two cylindrical rollers rotating at constant angular speeds ranging from 50  to 200 r/min. A heat transfer analysis has been done to study the temperature variation near the rollers. Simulations are carried out for 5%, 10% and 20% concentrations of the thickener. Rheological characterisation of the proposed grease samples is done. An experimentally developed rheological model is incorporated in the numerical model. The rheological characteristics of the samples follow the Herschel–Bulkley model. The velocity profiles obtained from the present numerical model are compared with the nearest available experimental microparticle image velocimetry profiles for lithium complex grease to find qualitative similarity. The variation of volume fraction distribution and temperature at different times and locations of the channel is predicted. The rotation of rollers affects the local distribution of a thickener as well as the rate of homogenisation with the oil. As polytetrafluoroethylene grease is able to maintain its rheology even at elevated temperatures, most of the channel portion is thermally unaffected due to heat dissipation up to 5 W.