Defect and Diffusion Forum Vol. 449

Abstract: Wire-net stainless steel (WS) is an alternative material used to enhance heat transfer in solar air heater (SAH) by inducing swirling or rotating airflow as air passes through its pores. In this study, WS with varying porosity—corresponding to pore per inch (PPI) of 16, 20, and 25—and a constant pitch distance (P) of 0.06 m was installed within the flow channel of the SAH, and air was used as the working fluid under turbulent flow. The results showed that WS significantly improved heat transfer performance, though accompanied by increased pressure drop. An increase in PPI resulted in a maximum of Nusselt number and friction factor by factors of 13.81 and 238.61, respectively, compared to SAH without WS. The highest thermal enhancement factor of 2.48 was observed at PPI=20.

Abstract: Heating networks are a crucial part of modern urban infrastructure, delivering heat to residential, commercial, and industrial consumers efficiently and reliably. Ensuring their safe and continuous operation is essential for maintaining comfort and supporting daily urban life. The integration of digital twins has become increasingly important, as they allow operators to monitor network behavior in real time, predict potential failures, and implement corrective actions promptly. By reducing response times and minimizing the frequency of accidents, digital twins help ensure a stable and uninterrupted heat supply. For a digital twin to be effective, it must be based on accurate numerical models that capture fluid flow, heat transfer, and pressure distribution throughout the network. Proper design and modeling enable efficient use of resources, including pumping power and pipe sizing, while reducing energy waste and operational costs. This study presents a comprehensive approach to optimizing heating networks. Control variables such as pipe diameters, pump pressure, and the settings of bypass and radiator valves for each consumer are defined. A constraint aggregation function ensures that no consumer experiences freezing, while the objective is to minimize both the initial installation costs and long-term operational expenses. Advanced numerical solvers were used to perform the calculations, enabling efficient optimization of large and nonlinear networks. This approach demonstrates how careful modeling and control can improve the efficiency, reliability, and cost-effectiveness of heating networks.

Abstract: Ethylene carbonate (EC) is essential for forming a passivating film on graphite, whereas practical electrolytes dilute EC with linear carbonates that modify that film. Here, we isolate an EC-only medium and track film formation by in situ electrochemical atomic force microscopy during slow-scan cyclic voltammetry on the basal plane of highly oriented pyrolytic graphite in EC with lithium perchlorate. A two-stage pathway is resolved: during the cathodic sweep a subsurface pre-insertion regime develops and transitions near 0.8 V vs Li/Li⁺; the subsequent anodic sweep produces a particulate precipitate layer. After the first cycle, the effective precipitate-layer thickness is approximately 20 nm; a second cycle increases it to approximately 30 nm with marked lateral heterogeneity and edge-proximal coarsening. These observations delineate the potential-dependent switch and provide quantitative benchmarks for the early growth of the EC-derived film. Minimizing the dwell time near the transition may suppress overgrowth and improve interfacial stability, thereby establishing an EC-only baseline for interpreting mixed-carbonate electrolytes.

Abstract: Lithium iron phosphate (LFP) is a commonly used cathode material in lithium-ion batteries, particularly for electric vehicle (EV) battery energy storage systems. To support sustainability and the principles of a circular economy, recycling spent LFP batteries is essential. This study focuses on the direct regeneration of spent LFP cathode material using an aqueous relithiation method conducted at low temperature, followed by post-annealing. The waste precursors and regenerated LFP were fully characterized for its structural, morphological, and compositional properties. Fourier-transform infrared (FTIR) analysis confirmed the presence of additive carbon and electrolyte residues in the spent LFP. XRD analysis revealed that certain components of the LFP structure in the as received spent cathode material decomposed, as evidenced by the presence of impurity peaks due to FePO₄ and P₂O₅, which disappeared after relithiation. The lattice parameter values (a=4.6897 Å and c=10.3211 Å) of the regenerated LFP were also found to be close to the theoretical (a=4.6925 Å and c=10.3253 Å), suggesting successful structure repair after regeneration. SEM indicated that regenerated LFP particles appeared to be more well-dispersed and finer than spent LFP particles. EDS mapping revealed a relatively homogeneous elemental distrbution of the major identified elements. ICP analysis further confirmed the successful restoration of Li content. The composition of the spent cathode, initially Li_0.85FePO₄, transformed to Li_1.03FePO₄ after regeneration, corresponding to an increase in Li content from the as-received 3.75 to 4.53 wt% Li after relithiation.

Abstract: The increasing demand for energy and the environmental challenges posed by CO₂ emissions necessitate the development of innovative solutions for utilizing natural gas reservoirs with high CO₂ content. In Southeast Asia, over 13 trillion cubic feet of natural gas remain undeveloped due to their high CO₂ content, reaching up to 87%. Current CO₂ separation technologies, though effective in removing CO₂, are energy-intensive and economically unfeasible. In the present work, monolith multilayer catalytic membrane is utilized to directly converting CO₂-rich natural gas permeate streams into syngas and co-generated energy. The membrane consists of a gas conversion, ion-selective and ion-conducting layers to optimize syngas production and improve energy efficiency. Experimental results show that increasing the operating temperature from 600°C to 800°C significantly enhances the conversion of methane (CH₄) and CO₂, yielding higher amounts of CO and H₂, with improved CO selectivity. Additionally, electrochemical performance evaluations demonstrate relatively higher current densities and power outputs at elevated temperatures. These findings underscore the multilayer catalytic membrane's potential to provide an economically viable and environmentally sustainable solution for converting CO₂-rich natural gas into valuable products, while also reducing CO₂ emissions. The membrane offers a promising route for syngas and energy production, contributing to the development of more efficient, low-emission energy technologies.