Defect and Diffusion Forum

Preface

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453

Forging Process of Graphite Lubricated LED Lamp Heat Sink

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Tung Sheng Yang, Meng Wei Ke
The stress-strain curves for AL-1050 were experimentally determined through compression tests. The friction factor between the AL-1050 aluminum alloy and the die material was subsequently obtained via ring compression tests, with graphite serving as the lubricant during the LED lamp heat sink forging process. The design of the forging dies for the LED lamp heat sink carefully considered several critical factors, including product geometry, parting line, die fillet radius, shrinkage, and flash. Subsequently, die dimensions, the stress-strain curve, the friction factor, and initial billet dimensions were utilized as input parameters for the finite element analysis (FEA) of the LED lamp heat sink's forging. The FEA successfully predicted the maximum forging load, effective stress distribution, and die-filling behavior of the LED heat sink during the forging process. Following the parameters established by the simulation, an LED lamp heat sink was fabricated using a forging machine. The experimental results showed excellent agreement with the simulation predictions, thereby validating the accuracy of the FEA model in forecasting the forging process.

Ductile Fracture Analysis of Lubricated Magnesium Alloy Sheet during Hemispherical Deep Drawing Process at Elevated Temperatures

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Tung Sheng Yang, Guo Zhou Cheng
This study utilized a computerized universal testing machine to obtain the stress-strain curves and fracture behavior of AZ31 magnesium alloy at various temperatures. Additionally, friction coefficients were determined through friction tests conducted at these different temperatures. Ductile fracture analysis was performed during the graphite-lubricated hemispherical deep drawing process at various elevated temperatures. By employing finite element simulation combined with ductile fracture criteria, we determined the forming load, punch stroke, and fracture location for AZ31 sheet metal forming at different working temperatures. Finally, the predicted values from the simulation were compared with experimental results obtained during the hemispherical deep drawing process. The simulation results showed good agreement with the experimental values for both the punch stroke and the fracture location during the hemispherical deep drawing process. This consistency confirms the feasibility of the method for predicting ductile fracture during deep drawing at various elevated temperatures.

Feasibility Study of Friction Stir Drilling of Pet Recycled Nonwoven Sheets

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Chien Te Liu, Yuh Ping Chang, Jun Ting Guo, Wei Liang Kuo
Non-woven fabrics are made of fiber mesh and carded or spun. They have the advantages of low cost, high output, easy production. The manufacturing process has a small carbon footprint and environmental benefits, which is in line with today's environmental issues and the important value of a circular economy. However, non-woven fabrics are thin and not very hard. They are usually assembled with other materials by vibration welding or adhesion, but they often lose their replaceability. This study attempts to develop a nonwoven fabric locking method and explore the impact of different friction stir drilling parameters on the formation of the boss and bushing.

Fatigue Life Prediction of a CNC Machine Spindle Support Shaft under Realistic Loading Using RecurDyn Simulation

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Yunn Lin Hwang, Arslan Munir
The current paper presents a comprehensive fatigue analysis of the steel column shaft spindle in a model CNC machine tool under prototypical cyclic loading conditions. The study integrates multi-body dynamic simulation with RecurDyn and stress-based as well as strain-based fatigue life prediction procedures. The geometry of the shaft, achieved through CAD and meshed as a deformable body using the RFlex interface, was loaded with eight-point force-controlled cyclic loading mimicking operation machining forces. Stress-based analysis made use of Manson-Coffin life criterion along with Gerber and Goodman mean stress correction models, whereas strain-based analysis made use of the Brown-Miller and Morrow criteria along with corresponding mean stress corrections. Material characterization was enabled by developing an S-N curve for the shaft steel, enabling accurate estimation of life. Fatigue damage accumulation was evaluated using Miner's Rule, and damage contour plots to find critical locations. Results indicated maximum damage values of the order 10⁻⁹ for stress-based and 10⁻¹⁰- 10⁻⁸ for strain-based models, which correspond to predicted fatigue lives in excess of 10¹³ cycles under the applied boundary conditions. Gerber and Goodman criteria-based safety factor analysis also provided minimum values of 6.12 and 4.93, respectively, which indicate a substantial margin against fatigue failure. The approach provides an experimentally validated framework for the evaluation of machine tool structural elements' durability, enabling optimal support schemes and longer life of operation.

Dynamic Analysis of CNC Machine Tool Structures Using FBGMT and R-Flex Flexible Multibody Dynamics Approaches

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Yunn Lin Hwang, Nabeel Ahmad
This study presents an integrated rigid flexible dynamic analysis of a CNC machine tool column using the Full Body General Motion Transfer (FBGMT) method and R-Flex flexible body modeling in RecurDyn, validated through comparison with ANSYS finite element modal results. The FBGMT approach simulated the vertical translation of the spindle head driven by a ball screw linear guide system, generating realistic motion data for structural evaluation. The R-Flex model converted the column into a flexible body using an RFI-based contact method, enabling the assessment of deformation, stress, and strain at three distinct tool head positions top, mid, and bottom. Modal analysis was performed in both RecurDyn and ANSYS under matched geometry, mesh density, and boundary conditions to verify frequency and mode shape consistency. Results show that displacement and stress increase as the tool head moves downward, with all responses remaining within elastic limits. Frequency deviation between RecurDyn and ANSYS remained within engineering tolerance, and mode shapes demonstrated strong correlation. This integrated workflow demonstrates a robust methodology for predicting CNC structural performance under realistic motion induced loading.

Assessing Barely Visible Impact Damage in Thermoplastic Composites through the Logarithmic Slope Histogram Sequence

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Pusan Dhar, Manoj Rijal, David Amoateng-Mensah, Richard Amevorku, Mannur Sundaresan
Thermoset and thermoplastic composites are extensively used in aerospace because of their exceptional mechanical properties. Compared to thermoset composites, thermoplastic matrix composites offer excellent chemical and physical damage resistance and are more cost-effective to produce. However, barely visible impact damage (BVID) poses a critical risk to thermoplastic Carbon Fiber Reinforced Polymer (CFRP) aerospace structures due to its limited surface manifestation and significant effect on compressive strength. This study presents a thermographic nondestructive evaluation (TNDE) approach based on Thermographic Signal Reconstruction (TSR) fingerprints to enable repeatable depth and area estimation of impact-induced damage. A data-driven threshold is derived from the logarithmic slope histogram sequence, allowing consistent separation of sound and damaged regions without relying on contrast extrema or operator-dependent frame selection. The method is first validated using flat-bottom holes (FBH) of known geometry and then applied to an industrial thermoplastic composite demonstrator subjected to multiple impact energies. Quantitative comparisons with ultrasonic C-scan measurements demonstrate convincing correlation and stable trends, with error magnitudes consistent with known physical limitations of flash thermography for deeper or structurally constrained defects. The results demonstrate that the proposed methodology offers a resilient, contactless alternative for swift BVID screening and comparative damage quantification in aerospace composite inspection.

Failure Analysis of Cast Iron Overlay Material in Grinding Rollers by SEM/EDS and XRD Characterization

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Nebbar Mohamed Chaouki
Grinding rollers are critical components of the cement manufacturing process, with the grinding rollers experiencing heavy mechanical and chemical stresses that can cause early failure. The present research aimed to analyze a failed roller specimen, which included a backing material and an overlay layer, to determine the root causes of deterioration. The research method adopted combined visual examination, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) analysis. Macroscopic investigation determined pitting, cracking, heavy corrosion, and wear patterns on the overlay material. Investigations by SEM/EDS found significant concentrations of chlorine (Cl) and sulfur (S) within the damaged interface and within fissures, consequently proving their roles as potent corrosive agents. Moreover, oxygen (O) was detected in substantial amounts, advocating massive oxidation processes. The results of the XRD examination of the corroded area revealed products of corrosion that correspond to oxide and chloride phases. The results demonstrate that grinding roller failure results from a combined effect of mechanical fatigue and chemical corrosion, with specific vulnerability being evident in the overlay layer. The outcome emphasizes the need for better material selection, optimal overlays deposition, and the utilization of protection treatments to enhance the service life of grinding rollers within the cement manufacturing industry.

Vacancy Formation and Trapping by Carbon in Ferritic Iron: A First‑Principles Study

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Olga Kulitckaya, Vladislav Kulitckii
The vacancy-carbon interactions control defect kinetics and the properties of ferritic iron. Here we use spin‑polarized density‑functional theory on 3×3×3 bcc‑Fe supercells with one to four carbon atoms in octahedral interstitial sites to quantify how carbon modifies vacancy energetics. Two limiting families are considered: dilute configurations with C far from the vacancy and compact VCₙ clusters (n=1-4) with C placed in the nearest octahedral shell. For the dilute case, the vacancy formation energy remains close to that of pure Fe. In contrast, for compact clusters the effective formation energy of a vacancy bound to carbon, Ef_VC, decreases markedly with increasing n, while the total binding energy increases and then saturates. The incremental stabilization Eadd stays positive up to n = 3 and turns negative for n=4. Etrap is small and positive for n=1-2, but becomes negative for n ≥ 3, consistent with carbon‑rich microenvironments biasing vacancies into VCₙ states. Increasing n moderately reduces N(EF), particularly in the minority-spin channel, which is consistent with strengthened Fe-C hybridization and the larger binding energies of the VCn complexes. Finally, using a Seydel thermodynamic trapping model parameterized by our ab initio Ebind (VCn) we predict effective vacancy diffusivities Dv_eff(T,Ctot) that exhibit trends in line with prior analyses, while reflecting the stronger trapping implied by our energetics. Consistent with our DOS analysis, increasing carbon content strengthens Fe-C hybridisation, shifts Fe d states to lower energies and reduces N(EF), indicating a gradual transition from metallic Fe-Fe bonding to a more covalent Fe-C bond character. This work closes an important gap between electronic-structure data and mesoscale modelling by providing a consistent set of vacancy-carbon energetics and effective vacancy diffusivities for dilute C in α-Fe, which serves as a model system for ferritic Fe-based alloys.

Influence of Nickel on Microstructure and Property in Die-Cast Ductile Iron

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Nidchanan Wanmai, Arisara Wanalerkngam, Krittapart Sriboonrueang, Worachot Boonyarit, Kandit Amatachaya, Sirintra Mangmee, Kittirat Worakhut, Sarum Boonmee
This study examines the influence of nickel (Ni) additions on the microstructure and hardness of Ductile Iron (DI) produced in permanent molds, where higher cooling rates significantly affect solidification behavior. Ductile iron melts were prepared in a 100-kg induction furnace with varying Ni levels (0.06–12.30 wt.%), and Y-block castings were produced in accordance with ASTM A536. Optical microscopy and image analysis were employed to evaluate graphite morphology and matrix phases, while color etching was used to differentiate bainite and martensite. Results show that increasing Ni reduced the nodule count but promoted the formation of primary graphite due to hypereutectic solidification. The matrix evolved sequentially from ferrite to pearlite, and then to bainite and martensite with higher Ni content. At Ni levels above 9–12 wt.%, retained austenite was observed. Hardness increased with Ni additions up to ~10 wt.% but decreased slightly at higher contents due to the presence of retained austenite. These findings demonstrate that controlled Ni additions can produce ductile iron with comparable hardness to the Austempered Ductile Iron (ADI) without heat treatment.

Vacancy Formation and Diffusion in FeCr Alloys

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Olga Kulitckaya, Vladislav Kulitckii
In this work we investigate the effect of chromium on the self‑diffusion of Fe and Cr in binary bcc FeCr alloys using ab initio (density‑functional) calculations. While diffusion data for FeCr systems exist, most are limited to selected compositions or rely on semi-empirical parameterisations, and a consistent ab initio assessment of vacancy-mediated Fe and Cr transport across the dilute to intermediate Cr range is still lacking. We also analyse the influence of chromium concentration on the lattice parameter of these alloys. The lattice parameter shows a clearly non‑linear dependence on Cr content: it increases steeply with chromium addition up to about 8 at.% and then remains almost constant up to the highest considered concentration of 25 at.%. The vacancy formation energy on Cr sites decreases markedly from 2.27 eV to 1.95 eV as the chromium content is raised from 7.4 at.% to 26 at.%. In contrast, the vacancy formation energy on Fe sites exhibits only a small increase between 7.4 at.% and 11 at.% Cr and then remains nearly unchanged up to 26 at.% Cr. These results indicate that chromium additions strongly facilitate the formation of vacancies on Cr sites and therefore are expected to enhance Cr self‑diffusion, whereas the self‑diffusion of Fe is only weakly sensitive to composition in the studied range. Based on the calculated activation energies, Arrhenius‑type temperature dependences were constructed for the Fe and Cr diffusion coefficients in five model alloys: Fe-7.41 at. % Cr, Fe-11.11 at. % Cr, Fe-18.52 at. % Cr and Fe-25.93 at. % Cr. The resulting diffusion coefficients are in good agreement with available experimental and theoretical data, which supports the reliability of the present ab initio-based approach for describing vacancy‑mediated transport in α‑FeCr alloys. Combining the calculated vacancy formation energies with literature data on vacancy migration energies allows us to construct Arrhenius‑type estimates for Fe and Cr self‑diffusion coefficients in α‑FeCr alloys, which are relevant for modelling microstructural evolution in ferritic steels.

Conjugate Heat Transfer Analysis of Teflon-Coated Steel Surfaces Exposed to Premixed Flame Jets

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Panit Kamma, Kittipos Loksupapaiboon, Juthanee Phromjan
Composite material systems involving impinging flame jets on flat surfaces are critical in applications requiring precise thermal management and energy efficiency. A prominent example is Teflon-coated steel cookware, where the Teflon layer not only provides a nonstick surface but also influences thermal performance. Optimal coating thickness is essential: excessive thickness can reduce heat transfer efficiency, while insufficient thickness may compromise adhesion and durability. This study investigates the thermal interaction between a premixed flame jet and a Teflon-coated steel substrate using high-fidelity simulations in OpenFOAM. A conjugate heat transfer approach captured the coupled heat fluxes between the flame, steel substrate, and Teflon layer. Teflon thicknesses ranging from 0.01 to 0.20 mm were systematically analyzed to evaluate their effect on heat transfer performance. Simulation results enabled the development of a thermal efficiency model as a function of Teflon thickness, achieving a high correlation (R² = 0.9923). The proposed model offers quantitative guidance for optimizing coating thickness, providing a practical tool for the design and manufacturing of thermally efficient cookware.

Comparative Study of Rhodium Recovery from Plating Solutions via Cementation, Chemical Precipitation and Electrowinning

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Tapany Patcharawit, Chatisa Kansomket, Napat Mahiwan, Sumita Chailoi, Thanapon Chandakhiaw, Loeslakkhana Sriklang
Rhodium plating is currently in appreciable demand not only for automotive as in catalyst converter but also for jewelry industry due to its silvery-white appearance, allergy-friendly, durable, scratch and tarnish-resistant. In accordance with circular economy, to assure efficient reuse and deviating from primary resource reliance, rhodium recovery is therefore of significance as the secondary resources. This research investigated comparative study of rhodium recovery from the plating solution via three techniques: cementation, chemical precipitation and electrowinning. The fresh plating solution prepared from rhodium concentrate and additive solutions was diluted to 0.1, 0.2 and 0.4 g/L of rhodium and used as the equivalent spent plating solutions. It was found that both cementation using zinc powder and chemical precipitation using sodium hydroxide and ammonium hydroxide did not yield notable recovery and gave low purity recovered products. Electrowinning has shown be more effective among the three techniques. For electrowinning, the diluted solutions were used as electrolyte, while the current density was controlled at 0.08-0.14 A/cm2 for 2-24 h. Rhodium could be obtained at the cathode, giving the average rhodium content of 94.02 wt.% and the purity of greater than 98%. At the greater rhodium concentration of 0.4 g/L, deposition of rhodium metal was uniform appearing as clusters of particles on the cathode surface where nucleation and growth are competitive.

A Numerical Simulation on Effect of Surface Roughness towards Heat Transfer Performance

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Hein Htet Aung Ahmed
Surface roughness plays a major factor in energy conversion, which impacts both heat transfer and energy losses. The word “Roughness” is defined due to variations in height of the surface arising from geometry or waviness, which directly impacts the thermal–hydraulic performance of heat exchangers. In this research, the study aims to determine the impact of surface roughness on heat transfer characteristics in a double-pipe heat exchanger. The numerical simulation was conducted using ANSYS CFD Fluent for one smooth surface and four rough surfaces with sand grain roughness values ranging from 0.5 mm to 2 mm, applied to the inner pipe wall boundary. The result proved that increasing the roughness surface will have an effect in the heat transfer coefficient and Nusselt number, which was calculated mathematically for the data derived from the outlet temperature of the Numerical Simulation. In addition to these, higher roughness also has a major effect on pressure drop and heat loss within the system. This study demonstrates that controlled application of surface roughness can significantly improve the thermal performance of heat exchangers, providing both economic and ecological benefits for industrial applications.

Statistical Characterisation of Pressure Drop Fluctuation in Two-Phase Air-Water Flow Downstream of a Minichannel T-Junction

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Untung Surya Dharma, I. Gusti Ngurah Bagus Catrawedarma, Indarto Indarto, Deendarlianto Deendarlianto
The movement of gases and liquids in a minichannel with a T-junction during two-phase flow is also important in fields like medicine, chemistry, and thermal management. The dynamics of the influence of the bend radius on the downstream pressure difference are not well comprehended. This paper examines the statistical characterisation of the pressure drop downstream of a horizontal T-junction in a minichannel, considering the observed flow patterns. The geometric parameters of the T-junction involved are variations of the ratio of the bend radius to the hydraulic diameter (r/Dh = 0.5, 0.7 and 1.0). Air and water are used as test fluids, with superficial velocities ranging from 0.59 to 2.96 m.s-1 for air (Jg) and 0.63 to 3.19 m.s-1 for water (Jl). The pressure sensors are used to measure pressure drop signals (ΔP2-3), which are recorded by a data collection device at 1000 Hz. A high-speed camera is also used to record the flow and verify the flow regime. There are six downstream flow regimes identified, and they include: Bubbles, Bubble to Slug, Slug, Elongated Slug, Churn to Elongated Slug, and Churn. These flow patterns are characterised using statistical, spectral, and nonlinear analysis methods. The findings suggest that as the bend radius increases, the amplitude of fluctuations also increases and the probability distribution becomes wider. However, there is a possibility that larger bend radii decrease chaos levels, resulting in a characteristic regime pattern. Additionally, there are artificial neural networks (ANN) that utilise wavelet energy variance as input, achieving a classification accuracy of 85.5%. The ordered association between statistical characterisation and regime classification through ANN is useful in comprehending the impact of the instability due to the bend radius in multiphase flow. These results complement the basic knowledge and predictive modelling of pressure drops in minichannels with horizontal T-junctions.

Multiphase Flow Analysis of Hydraulic Conveying of Coal Reject from Pulverized Coal Combustion

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Agung K.N. Sartono, Haslinda Kusumaningsih, Winarto Winarto
A hydraulic conveying system utilizing a jet pump is commonly employed for the transportation of coal rejects from the PCCB (pulverized coal combustion boiler) unit. This study applies CFD (computational fluid dynamics) combined with the DEM (discrete element method) to simulate solid-liquid two-phase flow in the jet pump. The coal reject particles were modeled as perfect spheres with a diameter 55 mm a mass flow rate of 5 kg/s. The hydraulic jet pump was supplied with water at a pressure of 12 bar and a flow velocity of 3 m/s. The diameter of nozzle was varied at 26-, 36-, 46-, 56-, and 66 mm to evaluated the effects on particle velocity, residue buildup, and the flow characteristics. The simulation results indicate that increasing the nozzle diameter leads to lower particle velocities and decreases the amount of coal reject residue in the jet pump. The nozzle diameter also influences to the multiphase flow behaviors in the outlet pipe.

Thermal Characteristics and Heat Balance Analysis of the FASSIP-06 Ver.3 Rectangular Natural Circulation Loop under Single-Phase Flow Conditions

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Sunandi Kharisma, Deendarlianto Deendarlianto, Shendy Akbar Maryadi, Kukuh Prayogo, Arif Adtyas Budiman, Adhika Enggar Pamungkas, Putut Hery Setiawan, Mulya Juarsa
Natural circulation is a passive cooling mechanism that is attractive for application in thermal engineering systems and advanced nuclear reactors because it is simple, reliable, and does not require pumps or external power sources. However, detailed studies on the thermal characteristics and energy balance of medium-scale experimental facilities remain limited, even though such investigations are essential to validate system performance and support the development of numerical models. This study aims to analyze the performance of the FASSIP-06 Ver.3 facility, which is configured as a rectangular loop with a height of 3.4 m and a width of 0.85 m, operated under single-phase conditions with heater power variations ranging from 750 to 1550 W. Experimental results show that increasing heater power leads to a rise in fluid temperature along the loop until a quasi steady-state condition is achieved. The temperature distribution demonstrates a clear gradient between the hot leg and cold leg, with the highest temperature observed at the heater outlet and the largest drop at the cooler inlet. Heat loss analysis indicates that the major contributions occur at the cooler, the BRT, and the visualization window, while other sections are relatively well insulated. Energy balance evaluation shows that the difference between heater input power and total measured heat loss consistently remains below ±10%, indicating that the system achieves thermal equilibrium.

Heat Transfer Characteristics Simulation Based on Power Input Variation in a Natural Circulation U-Top Rectangular Loop

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Shendy Akbar Maryadi, Deendarlianto Deendarlianto, Sunandi Kharisma, Mulya Juarsa
Increasing demand for reliable and passive thermal management in modern energy systems, particularly in nuclear reactors, has elevated interest in natural circulation loops. Among the influencing factors, loop geometry and heating power are critical in natural circulation systems. This study investigates the effect of heating power on heat transfer in a rectangular VHVC natural circulation loop with an enlarged upper elbow radius of 350 mm. The analysis was conducted using CFD under steady-state conditions, employing a pressure-based solver with the realizable k-epsilon turbulence model and energy equation to simulate buoyancy-driven flow. Three power inputs 750 W, 1100 W, and 1540 W were applied to evaluate their effect on temperature distribution and energy absorption. Results show that increasing the heating power enhances buoyancy forces, leading to higher mass flow rate and stronger natural circulation within the loop. The fluid temperature difference between the heating and cooling sections rises with power input, which directly increases the convective heat transfer coefficient. Consequently, the obtained Nusselt number increased from 25.69 at 750 W to 31.23 at 1540 W. This finding confirms that higher heating power significantly improves the loop heat transfer performance, providing insight into the optimization of passive cooling systems in nuclear safety applications.

The Effect of Variations in Mass Fraction of Al2O3 Nanofluid on Thermal and Electrical Efficiency in Photovoltaic Thermal Systems Using Computational Methods

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Asaad Belal Othman, Hassan Barrie, Redi Bintarto
This study examines the enhancement of Photovoltaic Thermal (PVT) systems through the application of nanofluids containing hexagonal boron nitride (Al2O3) nanoparticles. PVT systems, which integrate photovoltaic cells with thermal collectors, offer a dual-function solution by generating both electricity and heat, thereby maximizing the utilization of solar energy. The research specifically focuses on optimizing the thermal and electrical efficiencies of PVT systems by adjusting two critical parameters: the inlet velocity of the nanofluids and the concentration of Al2O3 nanoparticles. Computational simulations were performed using ANSYS Fluent software to analyze the impact of these variables on temperature distribution within the systems. The simulations revealed that both higher inlet velocities and increased nanoparticle concentrations lead to significant improvements in system performance. The most notable gains were observed at a nanoparticle concentration of 0.05% and an inlet velocity of 0.08 m/s, where thermal efficiency reached 74.80%, and electrical efficiency increased to 14.43%. The study confirms that the enhanced thermal conductivity of nanofluids due to the presence of Al2O3 nanoparticles plays a pivotal role in improving heat transfer and cooling processes. This optimization leads to the photovoltaic cells operating at more efficient temperatures, thus elevating both the output and overall efficiency of the PVT systems. The findings suggest that carefully controlled adjustments to the nanofluid properties can effectively optimize PVT systems, making them a more viable and efficient solution for simultaneous heat and electricity production from solar energy.

Turbulent Flows of Kerosene, Water, and Air through Copper Ducts with Variable Outlet Geometries: Insight into Turbulent-Mixing, Stress-Redistribution, Pressure-Losses, Secondary-Flows, and Energy-Dissipation

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Isaac Lare Animasaun
Studying turbulent mixing, stress redistribution, pressure losses, secondary flows, and energy dissipation enhances industrial process efficiency, improves equipment durability, minimizes operational costs, optimizes fluid transport systems, supports design and promotes energy conservation. However, little is known about the influence of outlet geometry on turbulence characteristics (i.e. turbulent kinetic energy, turbulent intensity, effective viscosity , and effective thermal conductivity) in air, water, and kerosene flowing through Y-shaped copper ducts featuring regular, converging, and diverging outlets. A hybrid geometric configuration incorporating angular inlets and asymmetric outlets enables detailed analysis of turbulent mixing, stress redistribution, pressure losses, and secondary flow development in complex internal flow regimes. Numerical simulations were conducted using ANSYS Fluent 2023 R2, employing the shear stress transport (SST) turbulence model for accurate resolution of adverse pressure gradients and boundary-layer effects. High-quality meshing, grid independence validation, and robust solver configurations ensured numerical reliability and convergence. The results demonstrate that outlet geometry significantly influences turbulence intensity, effective viscosity, and thermal conductivity across different working fluids. For air, increasing inlet velocity enhances turbulent kinetic energy and turbulence intensity at the regular outlet, while the diverging outlet exhibits peak turbulence at higher cold-fluid velocities. In water flows, the converging outlet shows substantial turbulence growth under increased velocity conditions, highlighting the role of geometric restriction in enhancing mixing and energy dissipation. For kerosene, the regular outlet achieves maximum effective thermal conductivity due to improved fluid interaction and turbulence under elevated velocity conditions, whereas the diverging outlet exhibits lower viscosity as a consequence of geometric flow dispersion. Overall, the findings underscore the critical role of outlet configuration in determining turbulence behavior and thermal-fluid transport characteristics.

Enhancement of Thermal Performance of a Solar Chimney Power Plant Using Phase Change Material: A Numerical Study

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Hidayet Meroua Sefiani, Faycal Bouzit, Mohamed Bouzit
This study investigates the effect of incorporating Phase Change Material (PCM) into the collector of a Solar Chimney Power Plant (SCPP). Numerical simulations were conducted using a 2D axisymmetric geometry, considering transient, turbulent, and radiative heat transfer. The results show that the PCM-enhanced system maintains higher temperatures at the collector outlet, with an average increase of approximately 6%. This thermal regulation enhances buoyancy-driven airflow, raising the chimney base velocity from 2.5 m/s in the conventional system to 3 m/s in the PCM configuration, with a corresponding increase in mass flow rate of 0.013 kg/s. Furthermore, the collector efficiency improves significantly, reaching 23% with PCM compared to 11% without. These findings demonstrate that integrating PCM into the collector effectively boosts thermal energy retention and system performance.

Comparative Numerical Analysis of Melting Enhancement in a Triplex Tube Latent Heat Storage Unit Using Rectangular Fins and Copper Nanoparticles

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Aymen Abdellah Lasri, Fayçal Bouzit, Mohamed Bouzit
This study presents a computational investigation of melting enhancement in a triplex tube heat exchanger TTHX with rectangular fins considering RT-82 as the phase change material (PCM) and copper as nanoenhanced PCM (NEPCM). The number of fins was increased from 8 to 12, and copper nanoparticles were dispersed at a volume fraction of 2% and 3% to assess their effect on thermal energy storage TES. The evolution of the solid–liquid interface was simulated using the enthalpy–porosity formulation, and the system performance was evaluated in terms of liquid fraction, total melting time, and melting efficiency, defined as the ratio of latent heat absorbed to the input energy. Raising the number of fins from 8 to 12 reduced melting time by 30% relative to the reference case with eight fins only, indicating enhanced heat conduction and faster initial melting. The use of copper nanopcm with 3 vol% further cuts melting times by 55% compared with the same reference case due to the increase in effective thermal conductivity. Hence, in brief, moderate fin numbers coupled with 3 vol% copper rendered the fastest melting rates and highest storage efficiencies among those tested.

Thermal Regulation of Photovoltaic Panels Using Aluminum Fins and RT Phase Change Materials: A Numerical Study

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Abdelhafid El Ouassidi, Abdelkader Mir, Majdouline Alla, Hind Talbi, Omar Ghoulam, Kamal Amghar, Ismael Driouch, Bilal El Monhim
Thermal management of solar panels is a major challenge, particularly in hot climates, and has attracted growing interest from both researchers and professionals in the photovoltaic (PV) sector. In this study, a two-dimensional numerical analysis was conducted to evaluate the thermal performance of an aluminum box filled with a phase change material (PCM) used for cooling a solar panel. The impact of integrating horizontal fins placed either on one side or on both sides of the PV/PCM system, was also examined to optimize heat transfer and stabilize temperature. The simulations indicate that a configuration with five fins arranged on one side, spaced 18.25 mm apart, provides effective cooling. The use of RT25 PCM maintains the surface temperature at 28 °C for 100 minutes before it gradually increases without exceeding 65 °C. Similarly, RT35 also demonstrates good thermal performance, maintaining the temperature between 35 and 43 °C for 252 minutes before eventually reaching a peak of 61 °C. These results highlight the effectiveness of the fins and the critical role of PCM selection in enhancing the thermal regulation of solar panels.

Coupled Effects of MHD, Solar Radiation, and Arrhenius Chemical Reaction on Third-Grade Hybrid Nanofluid Mixed Convection Flow through a Porous Medium

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): O.A. Ajala, O. Adebisi, A.O. Akindele, A.A. Yahaya, A.D. Ohaegbue, M.O. Afolabi, A.W. Ogunsola
The increasing need for efficient and sustainable thermal systems has driven the exploration of non-Newtonian models such as third-grade fluids, which capture the nonlinear, memory-dependent behavior of many real-world industrial and biological fluids. This study aims to analyze the thermal and flow behavior of a third-grade fluid under the combined influences of mixed convection (through thermal and concentration Grashof numbers), Arrhenius-type chemical reactions, solar radiation, and a transverse magnetic field, while also considering slip boundary effects and a porous channel structure. The model accounts for buoyancy-driven forces coupled with externally imposed flow, as well as temperature-sensitive reaction rates governed by the Arrhenius relation, making it highly relevant to solar energy systems, catalytic reactors, and advanced heat exchangers. The resulting non-linear partial differential equations (PDEs) describing the flow are reduced to ordinary differential equations (ODEs) using suitable similarity transformations. These ODEs, along with their boundary conditions, are numerically solved via the Galerkin Weighted Residual Method (GWRM) implemented in MATHEMATICA 11.3. The findings show that mixed convection significantly enhances heat and mass transfer, while Arrhenius chemical reactions alter the temperature and concentration fields, influencing flow stability. Moreover, strong magnetic fields and thermal radiation improve energy transport, offering key insights into optimizing third-grade fluid-based thermal systems for solar and industrial applications. Keywords: Third-grade fluids, Hybrid nanofluids, Mixed convection, Solar radiation, Solar Radiation, Magneto-hydrodynamics. Nomenclature and abbreviations list

Transient Flow Conjugated with Mixed Convection in a Vertical Channel

Tue, 14 Jul 2026 00:00:00 +0200

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Sofiane Boulkroune, Abdelfetah Belaid, Abdelkader Filali, Omar Kholai, Tawfiq Chekifi, Mawloud Guermoui, Reski Khelifi
Transient laminar mixed convection of air (Pr = 0.71) in a vertical plane channel is numerically investigated for opposing buoyancy at Re=100. The channel walls include symmetric, discrete, isothermal heated sections applied on the external side of a central wall zone, resulting in a conjugate heat-transfer problem through the solid wall and the fluid domain. The two-dimensional unsteady Navier–Stokes and energy equations are solved using a finite-volume method on a staggered grid with SIMPLE pressure–velocity coupling. The Grashof number is varied over 103 ≤ Gr ≤ 105. Instability onset is identified using a quantitative criterion based on the growth and persistence of velocity/temperature fluctuations and a domain-integrated fluctuation energy. The effects of wall thickness Δ and heated length Lh on the critical Grashof number are reported. Increasing Lh lowers the instability threshold, whereas increasing Δ stabilizes the flow by damping thermal gradients transmitted to the fluid. The results provide a stability map and physical interpretation of the transition from steady to unsteady mixed convection at low Reynolds number.