Search Results (78)

Both ground source heat pumps (GSHPs) and energy underground structures are engineered systems that utilize shallow geothermal energy. However, due to the construction complexity and associated costs of energy tunnels, their heat exchange efficiency relative to GSHPs remains a topic worthy of in-depth investigation. In this study, a thermal–hydraulic (TH) coupled finite element model was developed based on a section of the Torino Metro Line in Italy to analyze the differences in and influencing factors of heat transfer performance between energy tunnels and GSHPs. The model was validated by comparing the outlet temperature curves under both winter and summer loading conditions. Based on this validated model, a parametric analysis was conducted to examine the effects of the tunnel air velocity, heat carrier fluid velocity, and fluid type. The results indicate that, under identical environmental conditions, energy tunnels exhibit higher heat exchange efficiency than conventional GSHP systems and are less sensitive to external factors such as fluid velocity. Furthermore, a comparison of different heat carrier fluids, including alcohol-based fluids, refrigerants, and water, revealed that the fluid type significantly affects thermal performance, with the refrigerant R-134a outperforming ethylene glycol and water in both heating and cooling efficiency. Full article

The transition towards sustainable energy systems demands efficient utilization of low- and medium-temperature thermal sources, which offer a promising alternative to pollutant energy carriers like fossil fuels. Among these, solar thermal, geothermal, and residual heat emerge as leading candidates for clean energy generation. Organic Rankine Cycles (ORCs) stand out as robust technologies capable of converting these thermal sources into electricity with high efficiency. A critical factor in ORC performance lies in the effective transfer of heat from the thermal source to the working fluid. This study systematically evaluates various thermal oils as intermediate heat transfer media, aiming to optimize their selection based on key performance indicators. The analysis focuses on thermal and exergetic efficiencies, alongside mass and volumetric flow rates of both the working fluid and the thermal oil. The findings reveal that the integration of thermal oils notably boosts the exergetic efficiency of the ORC system, underscoring their pivotal role in maximizing energy conversion from sustainable heat sources. Full article

The global shortage of freshwater resources and the energy crisis have propelled solar-driven interfacial evaporation (SDIE) coupled with photocatalytic technology to become a research focus in efficient and low-carbon water treatment. Graphene-based materials demonstrate unique advantages in SDIE–photocatalysis integrated systems, owing to their broadband light absorption, ultrafast thermal carrier dynamics, tunable electronic structure, and low evaporation enthalpy characteristics. This review systematically investigates the enhancement mechanisms of graphene photothermal conversion on photocatalytic processes, including (1) improving light absorption through surface morphology modulation, defect engineering, and plasmonic material compositing; (2) reducing water evaporation enthalpy via hydrophilic functional group modification and porous structure design; (3) suppressing heat loss through thermal insulation layers and 3D structural optimization; and (4) enhancing water transport efficiency via fluid channel engineering and wettability control. Furthermore, salt resistance strategies and structural optimization significantly improve system practicality and stability. In water treatment applications, graphene-based SDIE systems achieve synergistic “adsorption–catalysis–evaporation” effects, enabling efficient the degradation of organic pollutants, reduction in/fixation of heavy metal ions, and microbial inactivation. However, practical implementation still faces challenges including low steam condensation efficiency, insufficient long-term material durability, and high scaling-up costs. Future research should prioritize enhancing heat and mass transfer in condensation systems, optimizing material environmental adaptability, and developing low-cost manufacturing processes to promote widespread application of graphene-based SDIE–photocatalysis integrated systems. Full article

Aviation is one of the most important industries in the current global scenario, but it has a significant impact on climate change due to the large quantities of carbon dioxide emitted daily from the use of fossil kerosene-based fuels (jet fuels). Although technological advancements in aircraft design have enhanced efficiency and reduced emissions over the years, the rapid growth of the aviation industry presents challenges in meeting the environmental targets outlined in the “Flightpath 2050” report. This highlights the urgent need for effective decarbonisation strategies. Hydrogen propulsion, via fuel cells or combustion, offers a promising solution, with the combustion route currently being more practical for a wider range of aircraft due to the limited power density of fuel cells. In this context, this paper designs and models a nitrogen–hydrogen heat exchanger architecture for use in an innovative hydrogen-propelled aircraft fuel system, where the layout was recently proposed by the same authors to advance sustainable aviation. This system stores hydrogen in liquid form and injects it into the combustion chamber as a gas, making the cryogenic heat exchanger essential for its operation. In particular, the heat exchanger enables the vaporisation and superheating of liquid hydrogen by recovering heat from turbine exhaust gases and utilising nitrogen as a carrier fluid. A pipe-in-pipe design is employed for this purpose, which, to the authors’ knowledge, is not yet available on the market. Specifically, the paper first introduces the proposed heat exchanger architecture, then evaluates its feasibility with a detailed thermodynamic model, and finally presents the calculation results. By addressing challenges in hydrogen storage and usage, this work contributes to advancing sustainable aviation technologies and reducing the environmental footprint of air travel. Full article

Ion-adsorption-type rare-earth element (iREE) deposits, a primary source of global heavy REE (HREE) ores, have attracted wide attention worldwide due to their concentrated distributions and irreplaceable role in the field of cutting-edge technologies. In recent years, iREE mineralization has been reported in the overlying weathering crust of the Mosuoying granites within the Dechang counties, Sichuan Province, Southwest China, suggesting great potential for the formation of iREE deposits. The Mosuoying granites, acting as the primary carrier of REE pre-enrichment, govern the contents and distribution patterns of REEs in their weathering crust. Therefore, investigating the sources and enrichment mechanisms of REEs in the parent rocks will provide a critical theoretical basis for the scientific exploitation and utilization of iREE deposits. In this study, we investigated the migration and enrichment of REEs in the Mosuoying granites (850–832 Ma) using petrography, geochronology, geochemical, and Sr-Nd-Hf isotopic data. The results reveal that the REE enrichment in the Mosuoying granites might be associated with both the melting of crustal felsic rocks and the magmatic-hydrothermal evolution. On the one hand, the granites exhibit different REE patterns. Compared to the light REE (LREE)-rich granites, the HREE-rich granites feature higher SiO₂ contents, higher differentiation index (DI), lower Nb/Ta and Zr/Hf ratios, and more significant negative Eu anomalies, indicating that the crystal fractionation of magmas governed the differentiation of REEs. Furthermore, the hydrothermal fluids further promoted the formation of the HREE-rich granites. On the other hand, the geochemical characteristics suggest that they are A-type granites. Regarding the isotopic characteristics, the Mosuoying granites exhibit negative whole-rock εNd(t) and zircon εHf(t) values, suggesting an evolved crustal source. Therefore, we suggest that the high REE contents in the Mosuoying A-type granites might originate from the partial melting of felsic rocks in a shallow crustal source under high-temperature and low-pressure conditions. Specifically, the high-temperature A-type granitic magmas caused the partial melting of the felsic crustal materials to release REEs; concurrently, these magmas enhanced the solubility of REEs in melt during magmatic evolution, inhibiting the separation of REE-bearing minerals from the melts. These increased the REE contents of the granites. The high-temperature heat source might be associated with the process where the asthenospheric mantle experienced upwelling along slab windows and heated continental crust in the Neoproterozoic extensional setting. Full article

This study employs computational fluid dynamics (CFD) to analyze the in-flight dynamics of particles in an Ar–H₂ atmospheric plasma spray (APS) torch with a modified diverging-type nozzle. The focus is on optimizing injection parameters—plasma gas flow rates, input power, and carrier gas flow rates—to enhance coating microstructure and deposition efficiency by achieving superheated molten metal droplets. Using a discrete phase model, the heat and momentum transfer of Ni/Al/C (2 wt.% diamond) composite powders (30–110 µm) within the plasma jet were simulated. Results show that particle characteristics, such as temperature and oxidation, can be controlled by adjusting plasma jet temperature (T∞) and velocity (U∞). Smaller particles heat faster, reaching higher temperatures with increased evaporation and oxidation rates. The modified nozzle enables Ni-based alloy particles to reach ~2500 °C, reducing oxygen inclusion in the plasma jet core. This setup allows for the control of the onset of carbon and oxygen reactions, wherein carbon serves as a sacrificial element, protecting the base alloy elements (such as aluminum) from excessive oxidation. Full article

Depending on the obturation technique, the tooth and surrounding tissues may heat up during root canal filling, particularly with warm methods. This study aimed to analyze the temperature increase in the periradicular and -apical region during various warm obturation techniques with a present simulated periodontal blood flow. Seventy-five extracted human teeth were shortened to 11 mm (cut-grinder Primus diamond cutting device; Walter Messner GmbH, Oststeinbek, Germany) and prepared using the ProTaper Gold system (Dentsply Sirona Inc., Charlotte, NC, USA) ISO size 40/.06. Specimens were prepared to ensure stable fluid circulation in an artificially created periodontal space, and the procedure was recorded with a thermal infrared camera (VarioCAM HD; InfraTec GmbH Infrarotsensorik und Messtechnik, Dresden, Germany). The following obturation methods were applied: I, cold single-cone obturation (control group); II, gutta-percha-coated rigid carrier technique (GuttaFusion); III, squirting technique (injection technique); IV, continuous wave technique; and V, Schilder technique. Statistical analysis was performed using the Kruskal–Wallis test, followed by the Mann–Whitney pairwise test using the sequential Bonferroni procedure for significant differences (p < 0.05). The Schilder technique with 0 mL/min showed the lowest temperature change, with a median of 0.00 °C (max. 0.00 °C, min. 0.00 °C, IQR 0.00 °C). In contrast, the continuous wave technique at a circulation rate of 2.6 mL/min exhibited the highest temperature change, with a median of 3.76 °C (max. 5.33 °C, min. 2.42 °C, IQR 1.46 °C). Although warm obturation techniques can increase surface temperature, none of the methods produced changes that were potentially damaging to the periodontium or surrounding bone. Full article

The storage of thermal energy has been hindered by the low heat-transfer rate of the solid phase of the phase-changing materiel. With water being the heat-transfer fluid as well as the liquid phase in the liquid–solid two-phase system, a novel type of fluidized bed is designed in this study. Numerous hollow spheres are fabricated with phase-changing materiel encapsulated. Adding the solid–liquid phase-change material capsules to the flowing fluid, the capsules are dispersed suspended in the carrier. The large spheres, 25 mm in present experiment, possess the merits of guaranteeing energy-storage density and tolerating internal interface chaotic motion. Both the fluidization status and phase-changing process are recorded by photography combined with image-processing technology. It is found that the large spheres, with density less than water, can be fluidized by the downward flowing fluid. As the flow rate increases, the expansion ratio of the solid phase increases and the regimes of incipient fluidization and bubbling fluidization can be observed. In comparison to the fixed bed, the oscillation of pressure drop across a fluidized bed is more severe, but the averaged value is less than the fixed bed. The melting and solidifying can be accelerated by 22.6% and 50%, respectively, thus proving the superiority of the fluidized bed in improving the heat-transfer rate while charging/discharging the thermal energy. Three types of basic movement of the spheres are shown to contribute to the enhanced phase-changing rate, which are shifting, colliding and rotating. Full article

Hydrogen energy is a green and environmentally friendly energy source, as well as an excellent energy carrier. Hydrogen storage technology is a key factor in its commercial development. Solid hydrogen storage methods represented by using metal hydride (MH) materials have good application prospects, but there are still problems of higher heat transfer resistance and slower hydrogen absorption and release rate as the material is applied to reactors. This study innovatively proposed an array-type MH hydrogen storage reactor based on external water-cooled jacket heat exchange, aiming to improve the heat transfer efficiency and absorption reaction performance, and optimize the absorption kinetics encountered in practical applications of LaNi₅ hydrogen storage material in reactors. A mathematical model was built to compare the hydrogen absorption processes of the novel array-type and traditional reactors. The results showed that, with the same water-cooled jacket, the hydrogen absorption rate of the array-type reactor can be accelerated by 2.78 times compared to the traditional reactor. Because of the existence of heat transfer enhancement limits, the increase in the number of array elements and the flow rate of heat transfer fluid (HTF) has a limited impact on the absorption rate improvement of the array-type reactor. To break the limits, the hydrogen absorption pressure, as a direct driving force, can be increased. In addition, the increased pressure also increases the heat transfer temperature difference, thereby further improving heat transfer and absorption rate. For instance, at 3 MPa, the hydrogen absorption time can be shortened to 147 s. Full article

Ground heat pump systems (GHPSs) are esteemed for their high efficiency within renewable energy technologies, providing effective solutions for heating and cooling requirements. These GHPSs operate by utilizing the relatively constant temperature of the Earth’s subsurface as a thermal source or sink. This feature allows them to perform greater energy transfer than traditional heating and cooling systems (i.e., heating, ventilation, and air conditioning (HVAC)). The GHPSs represent a sustainable and cost-effective temperature-regulating solution in diverse applications. The ground heat exchanger (GHE) technology is well known, with extensive research and development conducted in recent decades significantly advancing its applications. Improving GHE performance factors is vital for enhancing heat transfer efficiency and overall GHPS performance. Therefore, this paper provides a comprehensive review of research on various factors affecting GHE performance, such as soil thermal properties, backfill material properties, borehole depth, spacing, U-tube pipe properties, and heat carrier fluid type and velocity. It also discusses their impact on heat transfer efficiency and proposes optimal solutions for improving GHE performance. Full article

In this study, cargo boil-off gas (BOG) re-liquefaction systems for ammonia-fueled liquefied carbon dioxide (LCO₂) carriers were analyzed. These systems use cold energy from ammonia to reliquefy the CO₂ BOG. In this study, a system that can completely reliquefy the CO₂ BOG at all engine loads using only one heat exchanger is proposed, instead of the existing cascade system that requires multiple components. R744, which has a low global warming potential, was used as the working fluid for the refrigeration cycle in the CO₂ BOG re-liquefaction system. The organic Rankine cycle (ORC) was used to reduce the net power consumption of the system. The existing and proposed systems were classified into Case 1 (existing system), Case 2 (our proposed system), and Case 3 (Case 2 combined with an ORC). Thermodynamic and economic analyses were conducted. Case 2 is a system with a simpler configuration than Case 1, but it has a similar thermodynamic performance. Case 3 has a higher exergy destruction rate than Cases 1 and 2, owing to the ORC, but it can significantly reduce the net power consumption. The economic analysis shows that Cases 2 and 3 reduce the total annual costs by 17.4% and 20.1%, respectively, compared to Case 1. The proposed systems are significantly more advantageous for long-term operation than existing systems. Full article

To achieve net-zero objectives, the expansion of renewable energy sources is anticipated to be accompanied by an increased use of carbon-free fuels, such as hydrogen. Internationally, there are proposals for transporting hydrogen by synthesizing it into carriers like ammonia or Liquid Organic Hydrogen Carriers (LOHCs). However, considering the energy consumption required for hydrogenation and dehydrogenation processes and the need for high-purity hydrogen production, the development of liquid hydrogen transportation technologies is becoming increasingly important. Liquid hydrogen, with a density approximately one-sixth that of liquid natural gas and a boiling point roughly 90 K lower, poses significant challenges in suppressing and managing boil-off gas during transportation. Slush hydrogen, a mixture of liquid and solid phases, offers potential benefits. with an approximate 15% increase in density and an 18% increase in thermal capacity compared to liquid hydrogen. The latent heat of fusion of solid hydrogen effectively suppresses boil-off gas (BOG), and the increased density can reduce transportation costs. This study experimentally validated the long-duration storage and transportation concept of slush hydrogen by adapting NASA’s (National Aeronautics and Space Administration) proposed IRAS (Integrated Refrigeration and Storage) technology for compact and mobile tanks. Slush hydrogen was successfully produced by reaching the triple point of hydrogen, resulting in a composition of 47% solid and 53% liquid, with a density of approximately 80.9 kg/m³. Most importantly, methodologies were presented to observe and measure whether the hydrogen was indeed in the slush state and to determine its density. Additionally, CFD (Computational Fluid Dynamics) analysis was performed using solid hydrogen properties, and the results were compared with experimental values. Notably, this analytical technique can be utilized in designing large-capacity tanks for storing slush hydrogen. Full article

To analyze the heat transfer characteristics of oil shale under different in situ pyrolysis methods from a microscopic perspective, a combination of experimental and simulation approaches was employed. Initially, high-temperature in situ pyrolysis experiments on single-fracture oil shale were conducted using high-temperature steam and electrical methods. Subsequently, micro-CT scanning technology was utilized to obtain digital rock cores under different in situ pyrolysis conditions. Finally, these digital rock cores were seamlessly integrated with COMSOL 6.0 to achieve numerical simulations of high-temperature steam convective heating and electrical conductive heating in the in situ state. The relevant conclusions are as follows: Firstly, during the in situ pyrolysis of oil shale with high-temperature steam convective heating, the overall temperature increase is uniform and orderly. Heat is conducted gradually from the pores and fractures to the matrix. The uneven distribution of pores and fractures causes an uneven temperature field, but no localized overheating occurs, which can effectively enhance the pyrolysis efficiency. Secondly, the heat transfer direction in electrical conductive heating is primarily inward along the normal direction of the heat source end face. The closer the section is to the heat source end face, the higher the rate of temperature increase. Within 1 s, the temperature rise at 100 μm (near the heat source end face) is 2.27 times that at 500 μm (near the farthest cross-section from the heat source end face). The heat transfer effect of high-temperature steam convective heating consistently surpasses that of electrical conductive heating. The T_c value initially increases and then decreases as pyrolysis progresses, reaching a maximum of 1.61331 at 0.4 s, but T_c remains greater than 1 throughout. Finally, in the initial stages of pyrolysis, the high-temperature region formed by conductive heating is superior to that of convective heating. However, once the heat carrier fluid flow stabilizes, the volume of the high-temperature region formed by convective heating grows rapidly compared to that of conductive heating. At 1 s, the volume of the high-temperature region formed by convective heating reaches 5.22 times that of the high-temperature region formed by conductive heating. Full article

Geothermal energy piles or ground heat exchange (GHE) systems embrace a sustainable source of energy that utilizes the geothermal energy naturally found inside the ground in order to heat and/or cool buildings. GHE is a highly innovative system that consists of energy loops within foundation elements (shallow foundations or piles) through which a heat carrier fluid circulates, enabling heat extraction or storage in the ground. Despite the innovation and potential of GHE systems, there are significant challenges in harmonizing their thermal and mechanical designs due to the complex interactions involved. This review critically examines state-of-the-art design methodologies developed to address these complexities, providing insights into the most recent advancements in GHE performance and design. Key findings include innovative techniques such as advanced numerical modeling to predict thermomechanical behavior, the use of different pipe configurations to optimize heat transfer, and strategies to minimize thermal stress on the foundation. Additionally, this review identifies research gaps, including the need for more comprehensive full-scale experimental validations, the impact of soil properties on system performance, and the long-term effects of thermal cycling on pile integrity. These insights aim to contribute to a better understanding of the thermomechanical behavior of energy piles, ultimately facilitating more accurate and effective design solutions. Full article

Highly indium-rich group-III nitrides are attracting attention for advancing our capacity to create highly effective optical emitters at extended visible/IR wavelengths or for enhancing bandgap engineering possibilities within the group-III nitride material framework. Current methods of synthesis are constrained in their efficacy, partially owing to the low decomposition temperature of indium nitride. Implementation of a new design of a vertical high-pressure spatial chemical vapor deposition (HPS-CVD) reactor with six separated precursor source zones and a rotating wafer carrier disk carrying four 2-inch wafers is proposed and analyzed using COMSOL Multiphysics as a commercial computational fluid dynamics (CFD) program to study the fluid phenomena inside the numerical domain. This study focuses on understanding the different flow patterns within the chambers at super-atmospheric conditions (5 atm to 30 atm) and identifying suitable operating conditions under which smooth and dominant vortex-free flow is achieved. Four 2-inch wafers are heated to maintain a temperature of 1200–1300 K at each pressure and gas type. Three different gas types (nitrogen, hydrogen, and ammonia) are used, and the impacts of different inlet flow velocities and rotational speeds are investigated and discussed. An operating matrix is presented for each analyzed system pressure providing suitable combinations of these operational variables for smooth flow in the chambers. Each gas type was identified to have a range of suitable rotational and inlet velocity regimes at each operating pressure. Overlap of these three gas-specific operating condition windows resulted in the identification of a generally suitable operating condition for smooth flow patterns in the system regardless of the gas type used, as required for the growth of group-III nitride materials. Full article