Hydrogen storage is vital to the development of renewables, especially in low-infrastructure countries. Metal hydrides offer a small but safe solid-state candidate for hydrogen storage at medium pressures and near-ambient temperature, yet large-scale applications face heat-management challenges. In this article, we numerically analyze examples of two large-scale lanthanum pentanickel (LaNi5)-based metal hydride reactor configurations with shell-and-tube heat exchangers. This research studies two large-scale shell-and-tube metal hydride reactor configurations: a tube-side cooling reactor with hydride powder packed in the shell and coolant flowing through internal tubes, and a shell-side cooling reactor using annular hydride pellets with coolant circulating through the shell. The thermal and kinetic performance of these large-scale reactors was simulated using COMSOL Multiphysics (version 6.1) and analyzed under different geometries and operating conditions typical of industrial scales. The tube-side solution provided 90% hydrogen absorption in 1500–2000 s at 30 bar, while the shell-side solution reached the same level of absorption in 430 s at 10 bar. Results show that tube-side cooling has higher storage, while shell-side cooling improves heat removal and kinetics. For energy and maritime transport applications, these findings reveal optimization insights for large-scale, efficient hydrogen storage systems.

The growing demand for green hydrogen underscores the importance of renewable energy sources such as wind. However, the water electrolysis process, crucial for producing green hydrogen, often experiences frequent shutdowns that can damage membranes and catalysts, diminishing both efficiency and longevity. The variability of wind power further complicates this, necessitating advanced control strategies to maintain system stability. Traditional rule-based control methods often struggle to effectively handle real-time power fluctuations and predict future wind conditions, limiting their adaptability. This study introduces an innovative rule-based control method that includes a 'target battery level' to balance reliability and productivity. Utilizing a bi-level optimization framework, it co-optimizes the system design and target battery level to create a more adaptable and efficient solution. Case studies in six regions reveal that the levelized cost of hydrogen is realistically 6-20% higher than scenarios assuming perfect wind foresight. Moreover, this new rule-based control strategy, aiming to maintain a target battery level above 90%, consistently outperforms traditional methods in terms of reliability and economic viability. This approach offers a robust and economically feasible solution for enhancing sustainable green hydrogen production under real-world conditions, addressing key challenges related to system stability and operational efficiency.

In the global pursuit of sustainable energy solutions, mitigating carbon dioxide (CO2) emissions stands as a pivotal challenge. With escalating atmospheric CO2 levels, the imperative of direct air capture (DAC) systems becomes evident. Simultaneously, green hydrogen (GH) emerges as a pivotal medium for renewable energy. Nevertheless, the substantial expenses associated with these technologies impede widespread adoption, primarily due to significant installation costs and underutilized operational advantages when deployed independently. Integration through sector coupling enhances system efficiency and sustainability, while shared power sources and energy storage devices offer additional economic benefits. In this study, we assess the economic viability of polymer electrolyte membrane electrolyzers versus alkaline electrolyzers within the context of sector coupling. Our findings indicate that combining GH production with solid DAC systems yields significant economic advantages, with approximately a 10

Metal hydrides are a class of materials that can absorb and release large amounts of hydrogen. They have a wide range of potential applications, including their use as a hydrogen storage medium for fuel cells or as a hydrogen release agent for chemical processing. While being a technology that can supersede existing energy storage systems in manifold ways, the use of metal hydrides also faces some challenges that currently hinder their widespread applicability. As the effectiveness of heat transfer across metal hydride systems can have a major impact on their overall efficiency, an affluent description of more efficient heat transfer systems is needed. The literature on the subject has proposed various methods that have been used to improve heat transfer in metal hydride systems over the years, such as optimization of the shape of the reactor vessel, the use of heat exchangers, phase change materials (PCM), nano oxide additives, adding cooling tubes and water jackets, and adding high thermal conductivity additives. This review article provides a comprehensive overview of the latest, state-of-the-art techniques in metal hydride reactor design and heat transfer enhancement methodologies and identifies key areas for future researchers to target. A comprehensive analysis of thermal management techniques is documented, including performance comparisons among various approaches and guidance on selecting appropriate thermal management techniques. For the comparisons, the hydrogen adsorption time relative to the reactor size and to the amount of hydrogen absorbed is studied. This review wishes to examine the various methods that have been used to improve heat transfer in metal hydride systems and thus aims to provide researchers and engineers working in the field of hydrogen storage with valuable insights and a roadmap to guide them to further explore the development of effective thermal management techniques for metal hydrides.

As the world is keen on cleaner and sustainable energy, hydrogen energy has the potential to be part of the green energy transition to replace fossil fuels and mitigate climate change. However, hydrogen energy storage is a difficult task since physical storage in the form of compressed gas under high pressure is associated with safety issues. Another form of hydrogen storage is material-based storage, which is the safest way to store hydrogen energy in a particulate matter, known as metal hydrides. Metal hydrides can store hydrogen at room temperature and use less volume to store the same amount of hydrogen compared to classical gas tanks. The challenges with the metal hydrides reactor are their slow charging process and the requirement of proper thermal management during the charging process. In this study, a metal hydride reactor model is developed in COMSOL Multiphysics, and the associated heat transfer simulations are performed. The main objective of this research is to optimize the cooling channel design in the metal hydride reactor, where the R-134a coolant rejects heat through both latent and sensible heat transfer. The study showed that the phase-changing coolant and varying convection coefficient along the length of tubes significantly reduce the hydrogen charging time and the peak temperature of the reactor during hydrogen absorption. The pumping power analysis for the R-134a flow was also conducted. The computation results reveal that coolant channel configurations with nine or more tube-passes require significantly large pumping power.

A brake disc decelerates the vehicle through friction with the brake pads. When the brake system is overheated, brake fade can occur, in which the friction coefficient drops significantly. Additionally, an over-heated brake system may cause vapor lock, in which the brake hydraulic fluid is vaporized. These phenomena can lead to the loss of braking power and cause a fatal accident. Therefore, brake systems must have stable braking and heat dissipation performance. Having through-holes and slits on the friction surface of the rotor has been adopted to improve the heat dissipation performance, but the holes become stress points and potentially cause cracks. Therefore, brake systems should be designed to have structural stability as well as good heat dissipation. In this study, finite element (FE) modeling was developed to analyze the structural stability and heat dissipation performance of a brake system, and structural and thermal simulations were performed in ANSYS, a CAE software package. In addition, to minimize concentrated stress and temperature, optimal design of the shape and pattern of holes and slits was carried out using PIAnO, an integrated optimal design software package. The first step of design optimization was performed while considering the shape and pattern of the disc holes and slits as design factors. Among the design factors, those with the largest effects on the objective functions were found and set as new design factors to perform the second step. The designs were compared to existing discs. Through the optimization presented in this paper, it is expected that the performance of the braking system will improve and the life of the brake parts will be increased.

Two-phase closed thermosyphons have been employed in roadway embankments in the arctic regions to prevent permafrost from thawing. Thermosyphons installed in the embankment reject heat during the cold season and help maintain the ground temperature below freezing. Despite their proven effectiveness, the use of thermosyphons is limited due to high installation cost. In this research, roadway embankments in permafrost regions were numerically investigated to seek an optimal spacing between neighboring thermosyphons. First, this work focused on the conventional evaporator design of a horizontal straight pipe. Additionally, the constructal theory-inspired Y- and T-shaped evaporators were studied. The volume-averaged ground temperature was computed for each design. The simulations showed that there exists an optimal spacing and that the proposed Y- and T-shaped designs outperform the conventional design. A Y- and T-shaped design with a higher bifurcation level showed better cooling performance than designs with a single bifurcation level.

We proposed a hybrid heating, ventilation, and air-conditioning (HVAC) system that integrates a solar thermal collector and a radiative cooling panel as a heat source and a heat sink, respectively. The annual performance of the proposed system was analyzed for a single-family house and compared with that of the conventional solar-assisted heat pump (SAHP) and radiative-cooling-assited heat pump (RAHP) sys-tems. We found that the seasonal coefficient of performance of the proposed system can be enhanced by 27.3% for cooling compared to the SAHP system in cold-dry climate and by 61.8% for heating compared to the RAHP system in hot-dry climate. The detailed analysis revealed that the sizes of the solar collector and the radiative cooling panel, and the total amount of water (i.e., working as a heat source or a heat sink for the proposed HVAC system) are the key parameters affecting the annual performance of the pro-posed HAHP system. By using an optimization technique, we showed that these parameters should be varied depending on climate zones for optimal operation. Interestingly, it was found that installing both solar collector and radiative cooing panel can be more efficient than the conventional systems regardless of climate conditions (i.e., cold-dry: Denver; hot-dry: Pheonix; and marine: Los Angeles). The sensitivity analysis of each parameter revealed that the annual power consumption is less sensitive to the tank water volume for cold-dry and hot-dry climates, but the tank volume becomes important for marine cli-mate. For considered three locations, the proposed system was found to be able to reduce the annual power consumption by about 3% ti 29% as compared to the conventional RAHP or SAHP system. (c) 2021 Elsevier B.V. All rights reserved.

An analysis was conducted on the feasibility of designing a unidirectional heat transfer cylindrical wall suitable for microgravity conditions. The heat transfer wall is unidirectional in the sense that heat is only allowed to flow in one direction, which is made possible by the principles of phase-change heat transfer (PCHT). The wall is to consist of two concentric cylindrical walls and is to direct heat from the outer wall to the inner wall radially. A mathematical model is presented for the proposed unidirectional heat transfer wall. Preexisting heat transfer correlations were utilized to calculate the heat transfer rate of the unidirectional heat transfer wall with R-134a as the working fluid. The present study demonstrates that the unidirectional heat transfer wall can switch from a heat conductor to a thermal insulator by adjusting the loading of the working fluid within the walls of the proposed device.

In this study, the effect of surfactants and liquid temperature on boiling regime transitions of high-temperature rod during quenching was examined using inverse heat transfer analysis. Liquid pools of the aqueous sodium dodecyl sulfate (SDS) and Triton X-100 solutions were used with pure water. In the present experimental range, the critical heat flux (CHF) and minimum film boiling (MFB) point for all test fluids increased as the liquid temperature decreased. On the other hand, the SDS and Triton X-100 surfactants suppressed the CHF and MFB point, which might be due to the enhancement of vapor film stability caused by reduced surface tension. Some previous experimental studies have reported that the surfactants enhance the boiling regime transitions, but their results seem to be contradictory to the present ones. Considering the present study with the previous works, the surfactants seem to have different effect on boiling phenomena depending on the boiling regime. In other words, in the aqueous surfactant solution, the boiling regime transition points seem to be markedly influenced by a path of boiling regime. In addition, boiling mode diagrams were presented for pure water and aqueous surfactant solutions.

Constructing surface facilities on permafrost soils is a substantial engineering challenge. Moreover, evading thaw-settlement on roadway embankments is not an easy task due to the shifting thermal regime of underground soil because of seasonal temperature variations. Of all engineered cooling solutions available to stabilize permafrost, thermosyphons have attracted many researchers because of the benefits of using this cooling method compared with other methods. In this paper, we describe the optimization of thermosyphons with a Y-shaped evaporator. The cooling effects were compared with those of a conventional parallel design. The optimal spacing between thermosyphons for both the parallel design and the proposed Y-shaped design are documented.

Rural communities throughout arctic and subarctic regions of the world have difficulties providing cost-effective means of growing produce during the winter months.Plants need light and heat in order to survive and grow, both of which are in short supply during the long, cold winters.The average temperature of the spring and fall seasons in Fairbanks, Alaska is only about 30 to 40°F, which provides unreliable conditions to grow most crops.The traditional growing season in northern areas is roughly four months long, which is too short for many plants to grow and/or produce fruit.The purpose of the present research is to evaluate the use of solar heat pipe vacuum collectors to elongate the growing season of greenhouses in the arctic regions.The greenhouse utilizes the collection and retention of solar heat and a thermal mass to store the heat during days and release during nights.The solar heat pipe captures solar radiation, which heats a water-propylene glycol mix to act as the carrying medium.This fluid is pumped into the adjacent greenhouse and through the thermal mass unit.The thermal mass consists of two concrete slabs and dissipates the stored heat to normalize temperature fluctuations between night and day.A test greenhouse was built with dimensions of 12 ft by 10 ft with a height of 6 to 8 ft in Fairbanks, Alaska.Data collections for a performance analysis were made in April 2017.The experiments showed that the temperature of the greenhouse was above 60°F, at an external temperature of 32°F.The solar heat pipe with thermal mass system increased the average greenhouse temperature by 11°F.

As hydrogen generation technologies using renewable energy sources are being developed, considerable attention is paid to storage and transportation of hydrogen gas. Metal hydride alloys are considered as promising materials because they are viewed as an attractive alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas cylinder, which requires compression of hydrogen at high pressures, metal hydride alloys can store the same amount of hydrogen at nearly room pressure. However, this hydrogen absorption necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, fin structures are employed to enhance the heat transfer of metal hydride alloys in a cylindrical reactor. Numerical simulations are performed based on a multiple-physics modeling to analyze the transient heat transfer during the hydrogen absorption process. The objective is to minimize the time elapsed for the process and to reduce the hotspot temperature by determining the number and shape of rectangular fins while the total volume of fins used are fixed. The simulation results show that the more fins are applied the better heat transfer is achieved and that there exists an optimal length of the fins.

Metal hydride alloys are considered as a promising alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas tank, metal hydride alloys can store hydrogen at nearly room pressure and use less volume to store the same amount of hydrogen. However, this hydrogen storage method necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, a finned conductive insert is adopted to improve the heat transfer in the cylindrical reactor. The fins collect the heat that is volumetrically generated in LaNi5 metal hydride alloys and deliver it to the channel located in the center, through which a refrigerant flows. A multiple-physics modeling is performed to analyze the transient heat and mass transfer during the hydrogen absorption process. Fin design is made to identify the optimum shape of the finned insert for the best heat rejection. For the shape optimization, use of a predefined transient heat generation function is proposed. Simulations show that there exists an optimal length for the fin geometry.

We conducted a phased electromagnetic forming process analysis (EFPA) over time through a coupling of electromagnetic analysis and structural analysis. The analysis is conducted through a direct linkage between electromagnetic analysis and structural analysis. The analysis process is repeated until the electric current is completely discharged by a formed coil. We calculate the forming force that affects the workpiece using MAXWELL, a commercial electromagnetic finite element analysis program. Then, we simulate plastic behavior by using the calculated forming force data as the forming force input to ANSYS, a commercial structure finite element analysis program. We calculate the forming force data by using the model shape in MAXWELL, a commercial electromagnetic finite element analysis program. We repeat the process until the current is fully discharged by the formed coil. Our results can be used to reduce the error in data transformation with a reduced number of data transformations, because the proposed approach directly links the electromagnetic analysis and the structural analysis after removing the step of the numerical analysis of a graph describing the forming force, unlike the existing electromagnetic forming process. Second, it is possible to simulate a more realistic forming force by keeping a certain distance between nodes using the re-mesh function during the repeated analysis until the current is completely discharged by the formed coil, based on the MAXWELL results. We compare and review the results of the EFPA using the peak value of the forming force that acts on the workpiece (which is the existing analysis method), and the proposed phased EFPA over time approach.

Many researches have been focused on internal condensation with machined microstructure patterns on internal surfaces that can improve heat transfer performance up to 400% comparing to smooth surfaces. However, microstructure patterns are not effective for all geometries such as micro-channels and other complicated shapes. This study uses a dropwise condensation (DWC) promoter that can be easily applied to different geometries to improve internal condensation heat transfer. The main objectives of this study are to investigate internal condensation heat transfer by the dropwise condensation promoter via (i) developing an internal dropwise condensation model and (ii) conducting internal condensation experiments with the dropwise condensation promoter. The dropwise condensation model was modified to the available internal condensation model. The experiments for internal steam condensation were conducted for aluminum and copper tubes with external fins and an internal coating for dropwise condensation. The experimental results are compared to the results from several correlations in the literature and the model developed in this study. It is found that most correlations in the literature overestimate internal condensation heat transfer coefficients at low mass fluxes. The dropwise condensation model shows that dropwise condensation promoters can enhance internal condensation heat transfer coefficients. This conclusion is verified by experimental results demonstrating that the hydrophobic dropwise condensation promoter used in this study can enhance internal condensation heat transfer coefficients by 50%.

Nowadays, due to the development of information industry and technologies, the objective of cellular phone is not only to communicate, but also to give people various functions such as e-banking, web surfing and even excitement and fun. Because of increased usage of the cellular phone, the available time of the phone rechargeable battery is getting shorter. Therefore, in order to extend the serviceable time of the rechargeable battery, we propose self-generation system using a tubular type of permanent magnet linear self-generator (TPMLG) which can be embedded in cellular phone. The vibrational model is studied utilizing the mechanical resonance and the magnetic circuit such as permanent magnet, steel yoke and coil is designed to improve electricity generation. To investigate the electric characteristics of designed generation system, the transient finite element analysis using commercial software "MAXWELL" is performed.

Thermal conduction capability of metal hydrides can be enhanced by 400 ~ 500% through pelletizing the metal hydride powder after a well-controlled copper-coating treatment. In this paper, pelletized LaNi5 metal hydride is studied to evaluate its heat transfer performance and hydrogen absorption rate. In order to analyze the transient heat transfer and hydriding reaction, numerical simulations are carried out based on a multiple-physics modeling. The reactor temperature variation and the dimensionless mass of absorbed hydrogen are plotted for different hydrogen gas supply pressures. The results are compared with the conventional powder-type metal hydride reactor.

Renewable energy systems operated by a thermal energy resource such as geothermal power plants and solar thermal power systems are demanding improvement in their condensation performance [Kutscher & Costenaro, 2009]. While their energy resources are naturally obtained at almost no cost, heat rejecting components become relatively expensive to maintain and operate. In this research, a heterogeneous condensing surface is proposed to enhance the condensation heat transfer coefficient in vapor-to-liquid heat exchangers. On its surface, parallel stripes with hydrophobic feature and ones without it alternate. The effect of the partially hydrophobic condensing surface on the dropwise condensation heat transfer of saturated steam on the flat plate copper surface is experimentally investigated. A vertical flat plat condenser is constructed to evaluate the performance of the heterogeneous condensing surface in comparison with a plain copper sample and a homogeneous hydrophobic-treated copper sample. Experimental results show that condensation heat transfer of steam on the homogeneous hydrophobic-treated sample is superior to that on the plain copper surface despite the fact that both the surfaces stably promote dropwise condensation. The heat transfer coefficients for the heterogeneous surface at lower subcooling temperatures, when its stripes situate horizontally, are as high as the heat transfer coefficients for the homogeneous hydrophobic-treated surface. The enhancement for the horizontal heterogeneous sample over the plain copper sample is approximately 100%. The heat transfer coefficient for the heterogeneous sample with its stripes being vertical at 4 K subcooling is 25% greater than that of the plain copper sample. Higher heat transfer coefficients are observed at lower subcooling temperatures for all the samples. The results and observations of this project suggest that the heterogeneous surface has the potential to enhance the heat transfer coefficients.

In this paper, a dropwise condensation model using innovative “nano-scale, pin structured surfaces” is presented. The surfaces are porous surfaces oriented with nano- or sub micro-scale pins randomly designed or structurally arranged on extended and/or porous surfaces. These surfaces can promote a dropwise condensation showing a higher heat transfer rate than that of “filmwise” condensation by increasing the number of nucleation sites on the condenser surface and providing tunable surface properties such as surface wetting conditions. The developed model is consisted of a heat flux estimation of a single condensate drop based on thermal resistance analysis and a population theory for small and large condensate drops. The results of heat flux of a single condensate drop indicate that a smaller condensate drop with higher contact angle has a higher condensation heat flux; however, when it combined with population theory, a hemispherical shape of condensate with Wenzel surface wetting mode and a higher pin density can increase dropwise condensation heat transfer rates. In addition, a thinner nano- or sub micro-scale pins surfaces is required to increase condensation heat fluxes, when it is applied.