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AbstractThe design of heat exchangers plays an important role in the performance of solid-state hydrogen storage devices. In this study, three different designs of hydrogen storage devices were investigated, incorporating phase change material (PCM), specifically, RT25HC into their walls in various shapes. A mathematical model, validated using previous experimental data, was employed to calculate heat and mass transfer and determine the reaction time period. The calculations were conducted using ANSYS Fluent, with a constant hydrogen supply pressure of 10 bars and a temperature of 295 K. The absorption properties of the storage reactor were investigated through various parameters such as liquid fraction, hydrogen concentration, and natural convection heat transfer coefficients. Results showed that the geometric structure and PCM distribution significantly impacted the performance of the hydrogen storage devices. Design 1, with a centralized PCM distribution, demonstrated moderate heat transfer rates and a longer reaction time. Design 2, featuring a more distributed PCM layout, improved heat transfer rates and reduced hydrogen kinetics time by 40%. Design 3, which optimized the geometric structure with advanced PCM shapes, achieved the highest heat transfer rates and improved hydrogen kinetics time by 50%. This design also enabled the storage of thermal energy at a high density, ranging from 10.2 J/g to approximately 190.5 J/g. The study provides critical information on the design of efficient solid hydrogen storage processes. The findings suggest significant potential for improved performance in industrial applications such as electric vehicles and domestic energy supply. The high efficiency of the large-scale reactor is due to its well-designed system, which effectively converts chemical energy into thermal energy. Optimizing the reactor geometry and PCM distribution is crucial for achieving superior hydrogen storage and retrieval performance. [ABSTRACT FROM AUTHOR]

This study investigates the influence of different reactors incorporating copper circular fins within the hydride, along with variations in the reactor coolant—specifically water, oil, and nitrogen. Employing user-defined functions in the commercial software Ansys Fluent 15, a 2D numerical model was developed to assess thermal characteristics (temperature, heat flux, etc.) and kinetics of MH-hydrogenation, with a focus on the cooling fluid type. The reactor experiences diverse pressures (5–15 bar), an initial temperature of 298 K, and a coolant speed of 1 m/s. Validation of numerical results was performed against experimental data. The study delves into absorption properties of the storage reactor, examining crucial parameters such as hydrogen concentration, heat transfer coefficient of forced convection, and average temperature within the reactor. The findings reveal that coupling internal fins with water or oil as a coolant yields optimal performance, especially on an industrial scale. Nitrogen, on the other hand, exhibited the least favorable thermal performance, while the addition of fins significantly improved the cooling performance of the storage unit. Results were quantitatively analyzed across various scenarios to enhance understanding of the synergistic role of fins and cooling fluids in the storage performance of H 2 within LaNi 5 alloy. • The use of copper fins enhances the hydrogenation proces. • Reactor design has their role in hydrogen storage. • The cooling fluid in hydrogen storage reactors has an essential role. [ABSTRACT FROM AUTHOR]

Strengthening the thermal transfer of hot bodies is one of the topics that the old and new researches aim at due to its wide use in the fields of applied engineering. This research includes a study of thermal activity of five hot objects placed inside a cold chamber and rotating at constant speed. An equilateral triangular shape is the cross-sectional shape of the bodies. A rheologically complex fluid is poured into the chamber completely. A magnetic field of constant strength is applied to the x-direction of the chamber. The items studied here are: the rheological nature of the fluid by changing the value of power-law index (n = 0.8, 1 and 1.2), the rotational speed of the chamber is in terms of the Reynolds number (Re = 5 to 40), the magnetic field strength expressed in terms of the Hartmann number (Ha = 0 to 100) and finally buoyancy force (Ri = 0 to 50). The investigation was carried out using a numerical method adopted by a digital simulator with very high characteristics. The results showed that the thermal activity varies from one body to another. The effect of magnetic field on Nusselt number of the bodies decreases as the value of power-law increases. [ABSTRACT FROM AUTHOR]

In a cylindrical shell and multi-tube heat exchanger (of large configuration), the incorporation of four distinct nanoparticles (Al2O3, MgO, SiO2, and SnO2) at various concentrations (0%-5%, v/v) into PCM (RT82) was investigated during the solidification process. A numerical model was developed and validated through experimental and theoretical findings found in literature. Whatever the metal oxides' concentration, a clear enhancement of the freezing rate of PCM was observed over its solidification period, where this improvement was boosted proportionally with the rise of metal oxides concentration. However, the worst performance of the nano-PCM system was obtained using SnO2 nanoparticles, where a total solidification of PCM is observed after 26000 s for 5% (v/v) SnO2. In contrast, the best performance was resulted using SiO2, for which a total hardening of PCM was reached after 21000 s for 5% (v/v) silicon dioxide. This means that a reduction of 19.23% of the freezing period was obtained using SiO2 compared to SnO2 system at the same volume fraction (5%). It was found that in presence of nanoparticles (nano-PCM system), the solidification rate of PCM is in the order: SiO2>MgO> Al2O3>SnO2. According to the thermophysical properties of metal oxides, it was found that the enhancing role of nanoparticles (toward PCM solidification) is density-dependent. Therefore, the effect of heat capacity may be overlooked. [ABSTRACT FROM AUTHOR]

Metal foam (MF) and nano-sized particles (NSP) are regarded as patent tools for enhancing the thermal performance of phase change materials (PCM)-based latent thermal energy storage unit (LTES), but data on this issue for large-scale installations is very scarce. This study provides a comprehensive computational analysis of the effects of MF and NSP on the solidification process of RT82 paraffin (PCM matrix) in a large-scale shell-and-tube latent thermal energy storage unit (of heat exchanger form). The developed 2D transient model developed on Ansys Fluent 15.0 software was initially verified using available literature experimental data. The process performance was tested for 5% Al2O3 nanoparticles and various MFs [i.e. aluminum (Al), copper (Cu), nickel (Ni) and titanium (Ti)] with varied porosity (96–100%). The computed mean and spatial temperature and solidified degree of the PCM block showed a drastic acceleration of the solidification process with the b MF technique rather than with the nanoparticles system. The solidification performance increased in the direction of MF-thermal conductivity increase, i.e. Cu > Al > Ni > Ti, and material porosity decrease. These conditions allow rapid HTF heat recovery and then stocking considerable thermal energy. However, the MF porosity could not decrease below 95% to avoid a huge loss of material storage (PCM), thereby diminishing the thermal storage capacity of the LTES unit. [ABSTRACT FROM AUTHOR]

The solar flux distribution on the Parabolic Trough Collector (PTC) absorber tube is extremely non-uniform, which causes non-uniform temperature distribution outside the absorber tube. Therefore, it generates high thermal stress which causes creep and fatigue damage. This presents a challenge to the efficiency and reliability of parabolic trough receivers. To override this problem, we have to homogenize the heat flux distribution and enhance the heat transfer in the receiver's absorber tube to improve the performance of the PTC. In this work, 3D thermal and thermal stress analyses of PTC receiver performance were investigated with a combination of Monte Carlo Ray-Trace (MCRT), Computational Fluid Dynamics (CFD) analysis, and thermal stress analysis using the static structural module of ANSYS. At first, we studied the effect of the receiver tube material (aluminium, copper, and stainless steel) on heat transfer. The temperature gradients and the thermal stresses were compared. Second, we studied the effect of the addition of nanoparticles on the working Heat Transfer Fluid (HTF), employing an Al2O3-H2O based nanofluid at various volume concentrations. To improve the thermal performance of the PTC, a nanoparticle volume concentration ratio of 1%-6% is required. The results show that the temperature gradients and thermal stresses of stainless steel are significantly higher than those of aluminium and copper. From the standpoint of thermal stress, copper is recommended as the tube receiver material. Using Al2O3 in water as an HTF increases the average output temperature by 2%, 6%, and 10% under volume concentrations of 0%, 2%, and 6% respectively. The study concluded that the thermal efficiency increases from 3% to 14% for nanoparticle volume fractions ranging from 2% to 6%. [ABSTRACT FROM AUTHOR]