The application of thermal energy storage technology in scenarios requiring rapid heat storage and release is of critical importance. This study introduces a novel composite thermal energy storage configuration, comprising a solid-phase change material (PCM) in the lower half and water in the upper section. By utilizing density variations induced by PCM phase change, the design facilitates natural convection between the two media, thereby enhancing heat transfer efficiency. The investigation focuses on the impact of unsteady pulsating heat fluxes on heat and mass transfer dynamics during the charging process. A comparative analysis of experimental and numerical results delineates the evolution of the solid-liquid interface within the PCM and the total melting time, validating the proposed thermal model. The findings demonstrate that the amplitude of the pulsating heat flux significantly influences the mean energy storage rate (ESR), while having a negligible effect on the total thermal energy absorbed by both water and PCM. Compared to a reference configuration with a heat source amplitude of 2.5 K, a half-period of 25 s, and a base temperature of 334.15 K, the Taguchi-optimized thermal storage structure exhibits a 28 % and 30 % improvement in the average ESR for the PCM and water, respectively, along with a 20 % reduction in the total melting time.

This study assesses Monel 400 ' s corrosion behavior in liquid and vapor phases in hydrofluoric (HF), hydrochloric (HCl), and mixed HF-HCl acid environments. Through mass loss testing and electrochemical measurements, the alloy's degradation was evaluated under varying acid concentrations, temperatures, gas atmospheres (N2, O2), and metal ion contaminants (Cu2+, Fe3+). Electrochemical measurements (ASTM G59/G102) and mass loss (ASTM G31/G1) were used for corrosion testing. The findings demonstrate that corrosion rates are considerably increased by vapor-phase exposure, especially in combined HF-HCl vapors (up to 0.8 mm center dot y- 1), because of combined fluoride and chloride chemical attack. Improved anodic dissolution and decreased passivation are confirmed by electrochemical data, particularly when oxidizing conditions (O2) and Cu2+ and Fe3+ ions are present. Significant surface deterioration, dealloying, and the development of corrosion products rich in fluoride and chloride were discovered by SEM/EDS investigations. The addition of CuCl2 and FeCl3 changed the surface chemistry and increased localized corrosion. Similar degradation trends were shown by industrial validation in a condensing heat exchange unit employing Monel 400, where concentrated acidic condensates promoted rapid material loss and corrosion deposits consisting of chlorides. The findings emphasize the limitations of Monel 400 in HF-HCl systems, notably under vapor-phase and oxidizing conditions, and propose mitigation measures such as alternate Ni-Cr-Mo alloys, protective coatings, and oxygen exclusion to improve durability in harsh fluorinated environments.

Heat recovery systems (HRS) exist in conceptual configurations which encompass a set of energy-using processes installed on a particular site, a set of waste heat recovery technologies and all potential recirculation of material and energy streams with the overall aim to generate an overall benefit related to improvement in energy efficiency. A specific example of HRS are those that contain thermal energy storage (TES) components. In the context of the development of computational models, this type of HRS is modelled according to a dynamic simulation and optimisation perspective, owing to the transient state-based nature of these systems. This work presents the development and further analysis of an optimisation model developed according to the dynamic programming (DP) methodology for an HRS set to be implemented in a process industry plant. Such model was developed with the Modelica language, being an integral part of the ThermWatt simulation and optimisation tool. The developed model proved to be useful for the proposed objective of analysing transient state-based heat recovery systems, allowing an accurate modelling of the physical phenomena occurring during the time of operation of these systems. A relative reduction of 20.80% energy-related operational costs has been assessed for the system's optimal configuration, which corresponds to a 0.51 M & euro;/year absolute reduction (from 2.38 M & euro;/year to 1.87 M & euro;/year). This work is set to compensate for a knowledge gap related to the inexistence of studies approaching the use of mathematical programming methods for the dynamic (transient state-oriented) optimisation of thermal energy storage-based heat integration systems.

This paper reports the construction of a composite phase change energy storage unit that incorporates water and phase change material (PCM). The presence of water expedited the solidification process of the PCM above it while serving as a sensible heat medium. The influence of heat sink fluctuations on the heat transfer dynamics was investigated during the internal heat release process of the energy storage unit. A comprehensive numerical model was developed, and the Taguchi method was utilized to optimize the design of heat sink parameters. Findings indicated that the contact phase change of water at the unit base significantly accelerated the solidification process of the PCM. Yet, a hard-to-melt region persisted in the upper right corner of the unit at the conclusion of the PCM solidification. Fluctuating heat sinks irregularly impacted water convection at the unit base, although the PCM temperature remained consistent with solidification under a steady heat sink with a given boundary temperature. The influence of sinusoidal heat sink parameters (Foundation Tw, Amplitude (A), half-time period (z)) was examined using the Taguchi method, revealing that Foundation Tw exerted the most significant influence on solidification time, the average heat release rate of PCM, and the average heat release rate of water, with clear interactions between amplitude and time period. Amplitude and time period affected the sensible heat release process of PCM, while latent heat release remained unaffected by fluctuations due to multiple thermal influences from heat sink, water, and natural convection. Water demonstrated faster heat release compared to PCM owing to its high thermal conductivity, although its fluctuation characteristics were more perceptible. When compared to Case 5 (Foundation Tw = 304 K, A = 7.5 K, z = 40 s), the solidification time for PCM in Cases 10 (Foundation Tw = 296 K, A = 7.5 K, z = 50 s) and 11 (Foundation Tw = 296 K, A = 1.5 K, z = 10 s), was reduced by 27.1% and 27.6%, respectively, with a corresponding increase of 43.1% and 44.4% in average heat release rate of PCM, and a 63.8% and 61.7% increase in the average heat transfer rate of water.

Home to some of the highest solar radiation levels globally and a strategic export location, Saudi Arabia ranks among the top countries for green hydrogen potential. However, widescale deployment remains constrained by the challenge of designing a supply chain that can effectively balance trade-offs between economic, environmental, and safety/risk objectives. This study presents a multi-objective, multi-period optimisation model for the design of a green hydrogen supply chain (HSC) network in the Northwestern region of Saudi Arabia, considering various production technologies (electrolyser types), storage options, and transportation modes. A novel dynamic framework is developed to simultaneously optimise cost, carbon footprint, and safety/risk. Within this framework, a hybrid AHP-MILP approach is integrated to capture stakeholder preferences and their evolution over time through time-dependent weightings, enabling the relative importance of economic, environmental, and safety criteria to adapt across planning periods in line with changing stakeholder priorities. Four planning periods are considered in this study: establishment phase (T1); early operations phase (T2); steady operations phase (T3) and mature system (T4) - with low, medium, and high demand scenarios analysed in each period. Results showed that as hydrogen demand increases, production technologies converge in performance because their individual strengths and weaknesses counterbalance each other, while storage and transportation technologies diverge as scale amplifies the advantages of various criteria.

This paper presents a systematic review of machine learning (ML) applications in liquid-based photovoltaic-thermal (PV/T) systems, a topic that remains largely unaddressed in the existing review literature despite the growing importance of these hybrid systems in renewable energy. A total of 72 publications are analyzed and categorized across three methodological families: artificial neural networks (ANNs), ensemble methods, and other ML techniques. The review is complemented by a patent landscape analysis covering liquid-based PV/T technologies and a critical assessment of the experimental foundations underlying the reviewed ML models.The analysis reveals that ANNs dominate PV/T modeling at 63% of reviewed studies, with Multilayer Perceptron being the most frequently applied architecture. Ensemble methods, particularly Random Forest and XGBoost, achieve the highest prediction accuracies with R2 values up to 0.999. Across all ML categories, prediction accuracies exceed R2 = 0.95 in most applications, confirming the effectiveness of ML in capturing the complex thermal-electrical interactions characteristic of PV/T systems. Nanofluid-enhanced and phase change material configurations consistently demonstrate significant performance improvements over conventional water cooling.The review traces the evolution of ML methods in PV/T research from foundational ANN studies in 2012 through recent Transformer-based and reinforcement learning architectures in 2025. Critical research gaps are identified, including prevalent small dataset sizes in most studies, limited experimental validation of nanofluid ML models, and the absence of ML-related patent activity indicating a disconnect between academic research and commercial deployment. Future research directions are proposed covering standardized datasets, transfer learning, IoT integration for real-time control, and explainable AI for engineering interpretation.

This work presents a study of transient transfer processes of water droplets evaporating in flue gas, including spectral radiation absorption and droplet slip. The results of numerical modelling of condensation, transitional and equilibrium evaporation regimes of water droplets in flue gas at temperatures ranging from 633 to 1833 K are presented. The modelled radiative transfer is based on geometrical optics theory. Convective heating and evaporation of the droplet are defined by the empirical Clift correlation for Reynolds numbers Re < 400. The interaction between transient processes and the dependence of the physical and optical spectral properties of a warming droplet on temperature are taken into account. The numerical iterative scheme defining the average instantaneous temperature of the droplet's surface and working according to the fastest descent method is based on the balance of heat fluxes. The influence of Stefan flow, evaluated by the Spalding heat- and mass-transfer parameters, is made universal for different droplet phase change regimes by carefully assessing the dynamics of the temperature gradient within the droplet. It was verified that the competing effects of droplet slipping and the absorption of radiation are essential for the interaction between droplet transfer processes. The internal heat transfer in a droplet is affected by absorbed radiation and influenced by water circulation. Due to the effect of absorbed radiation, the evaporation rate of a large water droplet more than doubles in flue gas at 818 K and increases up to fourfold at 1133 K. These simulation results agree with the experimental data.

Industry sector within the European Union (EU) accounts for approximately 25 % of final energy use, where the steel industry accounts for 10 % of the total energy consumption in the industry sector. The steel industry and similar process industries are facing significant challenges to reduce their greenhouse gas emissions due to recent climate change legislations. One method to achieve this, is via the implementation of waste heat recovery systems. The paper presented focuses on a steel plant located in Slovenia, where significant amounts of thermal energy are lost through exhaust gases from a natural gas furnace. The novel multi-sink gravity-assisted Heat Pipe Heat Exchanger (HPHE) aims to recover and reuse waste heat and generates two useful heat sinks. The novel HPHE consists of air and water heat sink sections with an average energy recovery efficiency of 47 %. The recovered energy from the air section provides preheated combustion air to the burners, whereas the recovered energy from the water section opens the possibility for district heating. The thermosyphons in the exhaust-air section were arranged in a counterflow arrangement with Dowtherm A and distilled water as the working fluid, whereas the exhaust-water sections were arranged in a crossflow, with distilled water as the working fluid. The novel HPHE features a bypass, allowing complete flexibility for the end user to deactivate the exhaust-water section. To ensure replicability of the HPHE, a theoretical model has been developed and validated through experimental results, the model exhibited a good agreement with the results within an error of 15 %. Both air and water sections recovered 1677 MWh and 753 MWh annually, operating at 8050 and 5750 h respectively. The implementation of the HPHE equates to an overall reduction in CO2 emissions of 334 tCO2 per annum. Moreover, the unit highlights a benchmark for the technology due to its readiness within industry due to a reported Return on Investment (ROI) of under 10 months.

Water recycling and reusing strategies in industries have been promoted to reduce freshwater consumption. In addition, Heat Pipe Heat Exchanger technology has been employed successfully, resulting in the reduction of natural gas consumption and mitigating greenhouse gas emissions. It is important to assess the true benefits of the application of these Circular Economy strategies. Therefore, this work assesses the integration of a Heat Pipe Condenser Economiser (HPCE) and a water treatment system in a ceramic industry. Additionally, rooftop rainwater harvesting is integrated into the industry. The CE assessment methodologies and selected indicators measure the efficiency of the transition from a linear to a circular economy and identify strategies for optimisation. However, the interactions between human and natural systems related to the abstraction of resources and release of outflows are not considered. This is important to understand potential disruptions when implementing circular actions. Therefore, the assessment focuses on circular principles such as resource traceability and value created by implemented actions, and through resource flow and circular action indicators, the intrinsic circularity of system integration is quantified. The assessment showed the integration of both systems and the rooftop rainwater harvesting increased the Circular Water Flow and the Water Withdrawal Reduction up to 33.73 % and 22.88 %, respectively. Moreover, it demonstrates that the HPCE integration increased the Recovered Energy Contribution up to 19.98 %. This indicates the system's integrations increased circular performance over the baseline scenario. Additionally, the assessment enabled a scenario analysis which aided in identifying further strategies to improve the circular actions, such as reducing freshwater withdrawal.

Skin and subcutaneous diseases represent a significant public health burden, profoundly impacting quality of life, social interactions, mental health, and daily activities-raising concerns worldwide. In modern cryogenics, cryosurgery is among the therapeutic approaches employed by healthcare professionals to address this broad and complex range of diseases. Over the past four decades, cryosurgery has evolved into a valuable treatment option, used alone or as an adjunct therapy, and is adaptable to the needs of various special populations. This approach offers distinct advantages over established treatments due to its safety, efficiency, feasibility, and cost-effectiveness. However, a comprehensive, up-to-date review of cryosurgery's applications is lacking, which limits research dissemination and recognition among dermatologists. This review aims to provide an overview of cryosurgery principles and its current clinical practice in dermatology, covering a broad range of benign, premalignant, and malignant cutaneous conditions, and highlighting its potential as an essential approach in global healthcare.

Interim storage of spent nuclear fuel is a very important part of the overall nuclear power generation cycle. At Ignalina NPP, spent nuclear fuel is stored in interim storage facilities in specially designed casks before being transferred to a geological repository. The internal structure of spent nuclear fuel casks and the processes involved are quite complex. Therefore, simplifying and optimizing simulations for evaluating decay heat removal from the cask is worthwhile. In this paper, the effect of computer model simplifications on the thermal characteristics of the CONSTOR RBMK-1500/M2 cask stored in building-type and open-type storage facilities is presented. The modeling was carried out using the ANSYS Fluent code. The analysis showed a substantial impact of solar insolation. Also, in the case of the homogenization of the SNF load in the basket, higher temperatures are obtained compared with the case when detailed modeling of the internal basket structure is performed. Hence, it was demonstrated that the homogenization model can be used in safety assessment as a conservative approach for the modeling of decay heat removal from the cask.

The presentation reviews hydrothermal carbonization of digested sludge as a complementary technology for sludge management at wastewater treatment plants. The motivation for expanding the knowledge of hydrothermal carbonization is the challenges of wastewater treatment plants: the increasing volume of sludge, high moisture content, the presence of organic and inorganic contaminants, rising disposal costs, and legislative amendments. Hydrothermal carbonization makes it possible to convert wet sludge under conditions (160–250 °C,10–30 bar) into hydrophobic hydrochars, but also liquids and gases, eliminating the need for drying. The process also offers heat recovery and integration into existing wastewater treatment plant infrastructure. A key aspect of implementing hydrothermal carbonization is understanding the impact of individual process parameters and their interactions on chemical reaction pathways, and optimizing operating conditions for specific applications. The presentation discusses two pathways for hydrochar utilization: as soil additives or as fuels in thermal processes, assessing their environmental and legal potential. Process liquids were evaluated as a source of valuable resources that can be recovered or used in situ. Despite the compatibility of hydrothermal carbonization with Green Deal policies, challenges related to energy efficiency, legislative compliance, public acceptance, and high investment costs for integrated thermal technologies still need to be addressed. Overcoming these barriers will enable the implementation of hydrothermal carbonization as a sustainable technology in a circular economy.

Membrane distillation (MD) is a temperature-driven technology suitable for treating industrial wastewater, especially when utilizing low-grade heat sources like waste heat or renewable energy. Despite its potential, large-scale application of MD faces challenges due to high energy demands and operational instability caused by membrane fouling and wetting, particularly when surfactants are present. This study evaluated the thermal performance of a lab-pilot MD system using two commercial PTFE membranes. Initial experiments used saline feed solutions at varying feed and permeate temperatures. Subsequent tests introduced a non-ionic surfactant (Triton X-100), with and without NaCl, to investigate membrane fouling and wetting behavior. Results showed that higher feed temperatures increased permeate flux across all conditions, but also accelerated fouling and wetting, thereby shortening operational time. Notably, in the absence of NaCl, membrane degradation occurred more slowly, resulting in more stable performance. The novelty of this study lies in revealing the combined effect of salinity and non-ionic surfactants on the fouling and wetting performance of commercially available PTFE membranes in membrane distillation. Using a comprehensive two-stage experimental approach, the work systematically correlates MD system performance with membrane degradation mechanisms under feed conditions representative of real industrial wastewater. This dual focus not only uncovers the interplay between surfactants and salts but also provides practically relevant insights into the reliability and applicability of PTFE membranes in industrial MD operations.

The adoption of clean hydrogen is expected to transform the global energy landscape, reducing greenhouse gas emissions, bridging gaps in renewable energy integration, and driving innovation across multiple sectors. In the medical and pharmaceutical industries, hydrogen offers unique opportunities for transformative progress. This review critically examines recent advances in three domains: hydrogen fuel cells as reliable, scalable, and sustainable energy solutions for hospitals; molecular hydrogen as a therapeutic and preventive medical gas, particularly for brain disorders; and hydrogenation technologies for the efficient and sustainable pharmaceutical production. Despite encouraging advancements, widespread adoption remains limited by economic constraints, regulatory gaps, and limited clinical evidence. Addressing these barriers through technological innovation, largescale studies, and life-cycle sustainability assessments is essential to translate hydrogen's full potential into clinical and industrial practice. Responsible adoption of green hydrogen is poised to reshape the clinical approach to global health and enhance the quality of life for people worldwide.

The low thermal conductivity of phase change materials (PCMs) has limited their large-scale energy storage applications. This paper focuses on the rapid heat storage process of phase change energy storage. A composite heat storage structure is proposed, in which 50 % of solid-PCMs are filled at the bottom and water is at the top. During the melting process, heat is continuously exchanged through the mixture of water and liquid PCM to enhance heat transfer. A computational model (Case 1) is established using the computational fluid dynamicsvolume of fluid (CFD-VOF) numerical method and compared with the Case 0 structure with 50 % water at the bottom. The reliability of the numerical model is verified through experiments, and the two-phase flow state of wax and PCM in the Case 1 structure is observed. Further, through numerical studies, the liquid phase evolution, temperature distribution, and internal flow velocity during the heat transfer process of different composite melting structures were analyzed, and the melting performance and energy storage performance were quantitatively evaluated. In addition, the melting characteristics of this novel energy storage structure at different wall temperatures are discussed in detail. The results show that compared with Case 0, the melting time of PCM in Case 1 is shortened by 51.75 %, while the average velocity of PCM and the average velocity of water are increased by 100.75 % and 67.33 % respectively, compared with Case 0. However, compared with Case 0, the total heat storage capacities of PCM and water in Case 1 are reduced by 3.17 % and 19.27 % respectively. Finally, the response surface method is used to optimize and predict the comprehensive heat storage rate and heat storage time, and the accuracy of the optimization results exceeds 98.995 %.

Phase change thermal energy storage (TES) represents a crucial technology for enhancing the efficiency of solar energy utilization, and optimizing the heat transfer performance of TES units has attracted significant interest. In this investigation, a computational model of a horizontal tube-and-shell TES unit was used to analyze heat transfer performance under both active and passive enhancement methods involving the integration of metal foam and the application of rotational conditions, and a rotating TES experimental platform was constructed to verify the numerical model. Meanwhile, the charging performance of composite phase change material (CPCM) under various rotational speeds was investigated. Optimal rotational conditions were selected by comparing parameters such as complete melting time, heat storage rate, heat storage capacity, temperature response rate, and liquid phase, temperature, and velocity distributions. The results indicate that the inclusion of metal foam improves the heat storage efficiency of the phase change material (PCM), resulting in a reduction of the total melting time for CPCM device by a factor of 36 compared with pure PCM device under stationary condition. Additionally, the melting rate of the rotational setup is improved compared to the stationary setup, particularly for CPCM units. Subsequently, a detailed analysis of TES units under various rotational speeds revealed that as the rotational speed increases, the complete melting time decreases. Specifically, at a rotational speed of 0.6 rpm, the melting time decreases by 12 %. Moreover, the rotational mechanism also enhances the temperature uniformity within the TES unit. Notably, further increasing the rotational speed beyond 0.6 rpm does not alter the complete melting time.

Hydrothermal carbonization (HTC) is a promising alternative to conventional sludge drying, enhancing energy recovery in wastewater treatment plants (WWTPs). This study examines how temperature, residence time, and sludge collection point influence HTC product properties. Experiments were conducted at 200-250 degrees C for 30-120 min using digested sludge collected before filtration, after thickening, and after dewatering. Results show that sludge collection point strongly affects hydrochar's higher heating value (HHV), while temperature and residence time influence the biomethane potential (BMP) of HTC liquids. The highest HHV (16.31 MJ/kg) was obtained from dewatered sludge (19.8 % TS) at 250 degrees C, 75 min, while the highest BMP (506 mlCH4/g NPOC) was observed from HTC liquids of thickened sludge (11.1 % TS) at 200 degrees C, 30 min. Findings highlight that sludge pretreatment (thickening, dewatering) plays a crucial role in HTC efficiency, influencing both solid and liquid fractions. From a WWTP perspective, dewatered sludge processed under mild HTC conditions provides the best trade-off between hydrochar quality, HTC liquid valorization, and operational costs. These insights support the optimization of sludge-to-energy strategies, essential for implementing HTC in WWTPs.

Located in the Arabian Gulf, Kuwait is a renewable-abundant country ideal for producing hydrogen via solar energy (green hydrogen). With a global transition away from fossil fuels underway due to their adverse environmental impacts, hydrogen is gaining significant traction as a promising clean energy alternative for the transport sector. Despite this, there are still various challenges associated with implementing a hydrogen supply chain, particularly with regard to the conflicting objectives of minimising cost, environmental impact and risk. This study determines the feasibility of implementing a green hydrogen supply chain in Kuwait based on a multiobjective design, to determine which combination of production (electrolysis type), storage method and transportation method is the most optimal for Kuwait. Three objective functions were considered in this study: the hydrogen supply chain cost, environmental impact, and safety/risk. A mathematical formulation based on mixed integer linear programming (MILP) was used, involving a multi-criteria approach where the three considered objectives must be optimised simultaneously, i.e., cost, global warming potential and safety/risk. The multiobjective optimisation approach via the weighted sum method was applied in this study and solved via GAMS. To account for the ranking of multi-objective criteria, a hybrid AHP-TOPSIS approach was used. Results showed that medium and high demand scenarios better reflect the comparative advantages of each considered method in terms of their multi-objective trade-offs. In particular, it was found that higher hydrogen demand amplifies the impact of higher efficiency and operational savings within several production, storage and transportation methods, and that despite higher initial capital investments, these costs are at some point offset by superior operational efficiency as hydrogen production volumes increase. Conversely, using highly efficient electrolysers or transportation methods at low demand was found to limit their performance.