An experimental investigation was conducted to evaluate the influence of geometric orientation on the thermal performance of a cylindrical phase change material energy storage system incorporating concentric heat transfer fluid tubes. Three configurations—vertical, inclined, and horizontal—were systematically examined to determine their effects on heat transfer characteristics, melting dynamics, and energy storage capacity. The phase change material was subjected to charging processes using heat transfer fluid inlet temperatures of 60℃, 70℃, and 80℃ at a constant mass flow rate of 1 kg/min, while discharging experiments were performed under identical flow conditions to ensure consistency. It was observed that the melting time was significantly reduced in the vertical configuration, exhibiting a decrease of 29.2% compared to the horizontal arrangement and 19.4% relative to the inclined configuration at an inlet temperature of 80℃. This enhancement was attributed to the intensification of natural convection within the molten phase change material region. Furthermore, at a charging duration of 140 minutes, the total thermal energy stored in the vertical configuration was found to be approximately 4.4%, 17.4%, and 19.4% higher than that of the horizontal configuration for heat transfer fluid inlet temperatures of 60℃, 70℃, and 80℃, respectively. The results demonstrate that the optimization of system orientation plays a critical role in enhancing both the charging rate and storage capacity of phase change material-based thermal energy storage systems. These findings provide valuable design insights for the development of high-efficiency latent heat storage units in renewable energy and thermal management applications.

Residual wastewater produced during the utilization of high-energy propellants presents a power-driven engineering problem in which reaction efficiency, energy input, and thermophysical stability must be jointly controlled. An integrated, mobile treatment system coupling electrochemical oxidation (ECO) with disc-tube reverse osmosis (DTRO) was designed and assessed from a system-level thermophysical perspective. A model-driven framework was employed to guide the engineering design of the electrochemical reactor, membrane unit, and pipeline network under constraints associated with power input, hydraulic behavior, and structural reliability. The ECO reactor equipped with boron-doped diamond (BDD) electrodes was operated under high-current conditions, and the effects of current density and energy input on degradation behavior were examined. Experimental results show that, at a current density of 70 mA·cm⁻², the integrated system achieved a unsymmetrical dimethylhydrazine (UDMH) removal efficiency of 99.2% within 3 h while maintaining stable thermal and mechanical states. The downstream DTRO unit enabled effective separation of reaction intermediates and residual contaminants, resulting in stable effluent quality during continuous high-load operation. These results demonstrate that the ECO–DTRO configuration constitutes a feasible power-driven treatment pathway for high-energy propellant residues, characterized by controlled energy utilization and satisfactory thermophysical stability, and provides engineering guidance for the design of coupled electrochemical–membrane systems.

The integration of hydrogen electrolyzers into weak and very weak electrical grids introduces significant power quality challenges, including harmonic distortion and stability fluctuations. This systematic review and meta-analysis evaluated studies published between 2015 and 2025 to quantify the effectiveness of mitigation strategies for improving total harmonic distortion (THD) performance in grid-connected hydrogen production systems. The methodology followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020, screening 6,189 records and including 12 eligible studies for quantitative synthesis. A random-effects model was applied, using log-ratio effect size computation to assess THD of current or voltage reduction and stability improvements across varying Short Circuit Ratio conditions. Results indicated a pooled effect size of 1.321 and an average THD reduction of 82.53%, with the highest performance observed in moderate short-circuit ratio (SCR) of the grid at the point of common coupling environments. Funnel plot symmetry and Egger’s test (p = 0.243) confirmed minimal publication bias, supporting statistical reliability. The discussion highlights that performance strongly correlates with converter topology, control sophistication, and filtering strategy, with active front-end and grid-forming configurations outperforming passive solutions. The meta-analytic evidence suggests that hydrogen systems can operate effectively in weak grids when supported by harmonics-aware control frameworks. This study concludes that while feasibility has been established, future research should prioritize standardization and cost-effective deployment pathways to enhance the effectiveness of this approach.

This study highlights how the analysis of the long-term performance of solar reflective materials used both as roofing and flooring solutions to mitigate urban overheating has recently become more important. European and Italian legislations focus just on initial properties, but actual energy efficiency depends on durability over time. The objective is the development and the validation of characterization methodologies that consider performance degradation due to aging, providing reliable guidance for designers and policy makers. This study integrates standard thermophysical characterization methods with natural and accelerated aging protocols. Solar reflectance (SR) measurements can be performed by using ultraviolet-visible-near-infrared spectrophotometer, solar spectrum reflectometer and pyranometer/albedometer, while thermal emissivity can be measured with infrared emissometers. Natural aging was implemented at the Energy Efficiency Laboratory structure of the University of Modena and Reggio Emilia, operational since 2017. Accelerated methods include the standard protocol for surface soiling and an innovative method for biological growth. The analysis reveals significant degradations in SR, with reductions of between 10% and 40% after three years of natural exposure. Bituminous membranes show the most marked degradation, while ceramic materials present the best stability. Accelerated methods show interesting correlations with natural aging. The doubling of the standard accelerated cycle, designed on North American climatic conditions, is more representative of European climatic conditions characterized by greater air pollution. It must be recalled that evaluation based just on initial performance significantly underestimates long-term behaviour. The results suggest the need to update regulations by introducing requirements based on post-ageing performance. New materials design should be focus on durability by integrating into new materials both self-cleaning properties and improved stability over time. While, during design process, materials with certified long-term stability, analyzed through durability and degradation analysis should be considered in energy and economic assessments.

Repurposing deep abandoned oil and gas wells for advanced adiabatic compressed air energy storage (AA-CAES) has attracted increasing attention; however, reliable performance assessment is challenged by the complex thermal behaviour induced by the large aspect ratio of deep wells and the long-term interaction between the gas column and surrounding formations. In particular, simplified heat transfer assumptions commonly adopted in existing models may lead to non-negligible deviations in capacity and efficiency predictions. To address this issue, a coupled thermodynamic framework is established that accounts for gas column gravity effects, geothermal temperature gradients, and unsteady heat conduction in the surrounding rock. Different wellbore heat transfer boundary representations and operational strategies are systematically examined to clarify their influence on the thermal and energetic performance of deep-well AA-CAES systems. The analysis indicates that under low mass flow rate conditions, the extended wellbore length promotes effective heat exchange between the compressed air and the surrounding rock, restricting the average temperature variation along the wellbore and leading to compression and expansion processes that deviate markedly from ideal adiabatic behaviour. When a constant wall temperature boundary is employed to represent long-term formation heat transfer, the predicted storage capacity is reduced by 6.12% compared with conventional adiabatic assumptions. In addition, sliding-pressure operation exhibits superior adaptability to the thermal characteristics of deep wells, increasing the round-trip efficiency (RTE) from 48.82% to 60.99 relative to constant-pressure operation. At low flow rates, extended thermal relaxation further enhances heat dissipation, resulting in a modest increase in effective energy storage density (ESD). These results highlight the role of surrounding rock formations as a distributed thermal buffer and underscore the importance of incorporating realistic heat transfer modelling and appropriate operational strategies in the thermodynamic design of deep-well AA-CAES systems.