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Abstract

In recent years, hydrogen molecule as therapeutic antioxidant was found to be useful for the treatment of a number of diseases. To supply hydrogen safely and reliably in the hospital, a patent-pending system was proposed by the authors, including a canister filled with metal hydride, a gas mixing chamber and some other components. The outlet flow of the canister must be controlled within certain accuracy to assure the medical effect of the hydrogen intake, thus was investigated in this work. The mathematical model of hydrogen release process, which couples porous flow, heat and mass transfer was solved using a commercial software package COMSOL Multiphysics 3.5a. The outlet flow dynamics are tested in the cases of convective heating and electrical heating, and great differences are found. For the case of electrical heating that provides constant heat flux, the mass flow rate of H2 showed little temporal variation after the initial transient. Moreover, under certain conditions a PI control strategy was successfully applied to regulate the valve openness for keeping a constant flow rate of H2.

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... It is evident that the predicted average reaction rates of metal hydride bed are agreement with the experimental data generally, which proves the mathematic models are reasonable and credible. In consideration of materials purity, thermal resistance and response time of thermocouples, a little deviation are found between simulated and experimental values, which can be readily [32] Specific heat of the metal (C p,s ) 419 J kg À1 K À1 [33] Specific heat of hydrogen gas (C p,g ) 14,283 J kg À1 K À1 [13] Thermal conductivity of metal (k) 2.5 W m À1 K À1 [7] Thermal conductivity of hydrogen gas (k g ) 0.1272 W m À1 K À1 [13] Saturated metal density (r sat ) 8428 kg m À3 [13] Particle size of the metal (d p ) 28.3 mm [13] Activation energy (E a ) 21,170 J mol À1 [13] The reaction enthalpy change (DH) 30 MJ kmol À1 [32] The reaction entropy change (DS) 108 J mol À1 K À1 [9] The ideal gas constant (R g ) 8.314 J mol À1 K À1 [32] Molar mass of the metal (M) 0.432 kg mol À1 [32] Molar mass of hydrogen gas (M g ) 0.002 kg mol À1 [32] Porosity of the metal (ε) 0.5 [19] Absorption rate constant (a) 7 5 s À1 [9] Heat transfer coefficient between hydride bed and fluid (h) 1000 W m À2 $K À1 [19] External heat transfer coefficient (h a ) 300 W m À2 $K À1 [13] Temperature of heat transfer fluid (Tw) 293 K [33] Fig. 3 e Validation of the predicted bed reacted fraction with experimental data. eliminated by improving the precision and accuracy of measurement devices. ...
... It is evident that the predicted average reaction rates of metal hydride bed are agreement with the experimental data generally, which proves the mathematic models are reasonable and credible. In consideration of materials purity, thermal resistance and response time of thermocouples, a little deviation are found between simulated and experimental values, which can be readily [32] Specific heat of the metal (C p,s ) 419 J kg À1 K À1 [33] Specific heat of hydrogen gas (C p,g ) 14,283 J kg À1 K À1 [13] Thermal conductivity of metal (k) 2.5 W m À1 K À1 [7] Thermal conductivity of hydrogen gas (k g ) 0.1272 W m À1 K À1 [13] Saturated metal density (r sat ) 8428 kg m À3 [13] Particle size of the metal (d p ) 28.3 mm [13] Activation energy (E a ) 21,170 J mol À1 [13] The reaction enthalpy change (DH) 30 MJ kmol À1 [32] The reaction entropy change (DS) 108 J mol À1 K À1 [9] The ideal gas constant (R g ) 8.314 J mol À1 K À1 [32] Molar mass of the metal (M) 0.432 kg mol À1 [32] Molar mass of hydrogen gas (M g ) 0.002 kg mol À1 [32] Porosity of the metal (ε) 0.5 [19] Absorption rate constant (a) 7 5 s À1 [9] Heat transfer coefficient between hydride bed and fluid (h) 1000 W m À2 $K À1 [19] External heat transfer coefficient (h a ) 300 W m À2 $K À1 [13] Temperature of heat transfer fluid (Tw) 293 K [33] Fig. 3 e Validation of the predicted bed reacted fraction with experimental data. eliminated by improving the precision and accuracy of measurement devices. ...
... It is evident that the predicted average reaction rates of metal hydride bed are agreement with the experimental data generally, which proves the mathematic models are reasonable and credible. In consideration of materials purity, thermal resistance and response time of thermocouples, a little deviation are found between simulated and experimental values, which can be readily [32] Specific heat of the metal (C p,s ) 419 J kg À1 K À1 [33] Specific heat of hydrogen gas (C p,g ) 14,283 J kg À1 K À1 [13] Thermal conductivity of metal (k) 2.5 W m À1 K À1 [7] Thermal conductivity of hydrogen gas (k g ) 0.1272 W m À1 K À1 [13] Saturated metal density (r sat ) 8428 kg m À3 [13] Particle size of the metal (d p ) 28.3 mm [13] Activation energy (E a ) 21,170 J mol À1 [13] The reaction enthalpy change (DH) 30 MJ kmol À1 [32] The reaction entropy change (DS) 108 J mol À1 K À1 [9] The ideal gas constant (R g ) 8.314 J mol À1 K À1 [32] Molar mass of the metal (M) 0.432 kg mol À1 [32] Molar mass of hydrogen gas (M g ) 0.002 kg mol À1 [32] Porosity of the metal (ε) 0.5 [19] Absorption rate constant (a) 7 5 s À1 [9] Heat transfer coefficient between hydride bed and fluid (h) 1000 W m À2 $K À1 [19] External heat transfer coefficient (h a ) 300 W m À2 $K À1 [13] Temperature of heat transfer fluid (Tw) 293 K [33] Fig. 3 e Validation of the predicted bed reacted fraction with experimental data. eliminated by improving the precision and accuracy of measurement devices. ...
Article
The metal hydrides have great potential for the storage and utilization of hydrogen. Because of the strong exothermic/endothermic effect of H2 absorption/desorption process, the structure development of metal hydride reactor should mainly focus on the heat transfer enhancement. The new spiral mini-channel reactor is proposed to increase the heat transfer efficiency and H2 absorption rate. The spiral tubes can not only eliminate the stress produced by temperature changes and volumetric expansions, but also improve the turbulent intensity and heat transfer rate. The numerical model of spiral mini-channel reactor is established, and the simulation results present that the new reactor shows high thermal efficiency and hydrogenation rate. The structure parameters of the reactor are optimized as minor radius of 2.2 mm, axial pitch of 5 mm, major radius of 5.5 mm and tube amount of 3. Furthermore, the operation conditions are investigated. The result indicates that superior performance is obtained for the packing fraction of 0.6 and H2 pressure over 10 atm during H2 absorption. With these promising features, this new spiral mini-channel reactor has broad prospects in the hydrogen energy field.
... Considering the reduction of the maximal heat transfer distance between heat exchange tubes and MH bed in the axial direction (Dd max ), a larger b can apparently make the bed temperature distribution uniform (Fig. 9(c) and (d)), and consequently accelerate the hydriding/dehydriding rate (Fig. 9(e)). The axial distance between the duplex tubes (Dd) and Dd max can be calculated using eqn (31) and (32). ...
... Some main thermal physical parameters in the model equations7,14,16,17,[32][33][34] ...
Article
Due to the strong exothermic/endothermic effect during the H2 absorption/desorption process, the design of metal hydride reactors has become a hot research topic to improve the rate of hydrogenation/dehydrogenation. Herein, based on bionic optimization and the constructal theory, a novel duplex helical elliptical tube reactor (DHER) is proposed for enhancing the heat transfer and reaction performances of metal hydride reactors. DHER displayed outstanding performances among 5 types of reactors, and the maximal temperature difference could be reduced by 5.1 K/5.6 K during the H2 absorption/desorption. The parameters of DHER were designed and optimized with the spiral diameter (Dc) = 10 mm, elliptical major axis (A) = 4 mm, elliptical minor axis (B) = 2 mm, pitch (Pt) = 13 mm, tilt angle (α) = 45°, and installation angle (β) = 180°. The sensitivity analysis for DHER is investigated, and the sequential effects of the structural parameters on the reaction performance followed the order of Dc > A > B > Pt > α. Through a comparative analysis of geometrical characteristics of the structural parameters and the reaction performance of the reactor, the results indicated that the radial projected area of the heat exchange tube is the dominant factor in the reaction performance of DHER. Moreover, the surface was calculated based on the sensitivity analysis data and fitted by the quadratic response surface regression model to predict the reaction time under different structural parameters, which may provide guidance for the design of reactors. In addition, the hydriding and dehydriding cyclic processes without preheating and precooling stages were confirmed to have prominent and reliable performances for DHER, attaining only 1227 s under its optimal cycle conditions during absorption (0.8 MPa, 273.15 K) and desorption (0.1 MPa, 373.15 K).
... The major thermal physical properties of calculated model [12,23,28,[40][41][42]. As can be seen from the Fig. 4 (a), the hydrogenation curves of DMCR were basically overlapped when d l ≤ 0.9 mm, and the hydriding rates were declined obviously when d l >0.9 mm. ...
Article
Metal hydride is one of highly efficient methods to storage H2 with the high density and mild operating conditions. As a reaction place for metal hydride, the reactor should have excellent heat transfer characteristics to deal with the strong thermal effect generated by the reaction. Novel disc mini-channel reactors without and with jacket (DMCR and DMCR-J) were proposed to improve the H2 storage efficiency greatly by increasing the uniformity of temperature distribution inside reactor. The reaction performances were investigated and optimized by 3D COMSOL models, and the results indicated the optimal performances of both reactors could be achieved when the heat transfer layer height was 0.9 mm and the metal hydride layer height was 5 mm, corresponding to the optimal H2 storage amount per unit height was 0.17 g mm⁻¹. Meanwhile, optimal operating conditions of both reactors were H2 pressure of 1 MPa for absorption and 0.1 MPa for desorption, heat exchange fluid temperature of 293 K for absorption and 353 K for desorption, flow velocity of 3 m s⁻¹ and metal hydride filling fraction of 0.7. Moreover, heat transfer jacket and reactor shape had little influence on the reaction performance. In addition, the five reactors with or without jacket were systematically investigated and compared, revealing the outstanding heat transfer and reaction performances of DMCR and DMCR-J, which only needed about 300 s for absorption and 200 s for desorption to reach 99.7% of maximal H2 storage capacity for 1.56 kg metal hydride, saving more than 80% reaction time compared with the straight tube reactor.
... Referring to the empirical rules [28], g and t i were set as 700% and 4 s, respectively, to ensure the numerical convergence. ...
Article
As the well-known solid hydrogen storage materials, metal hydrides (MHs) have been developed systematically for decades. During recent years, due to the development of thermal energy storage (TES) market, they have also received much attention gradually as the excellent TES materials because of the high energy density, low cost, and good reversibility. In this study, the stabilized discharging performance of an MH reactor for TES was investigated by numerical simulation. A mathematical model combining multi-physics and proportional-integral controller was established. Based on finite-time thermodynamics, gravimetric exergy-output rate (GEOR) considering the control requirement, finite-material, and finite-time constraints was defined. For a given reactor, the output temperature setting could be optimized based on GEOR. Besides, the effects of the reactor parameters on the optimum output temperature setting were systematically studied. The heat transfer analysis indicated the occurrence of the axial non-uniform reaction in the bed due to the inherent increase in the temperature of heat transfer fluid, resulting in the decrease of both GEOR and material availability. Accordingly, a new tapered bed structure (L/Do = 600/50 mm) was proposed to effectively improve the discharging efficiency from 76 to 90% and GEOR from 65 to 120 W kg⁻¹, which provides a helpful guidance for the advanced designing and construction of MH reactor for the practical TES applications.
... MHs are typically La-Ni-series alloys, which have many outstanding properties, including mild activation conditions, favor- able H 2 storage capacities, fast absorption/desorption kinetics, moderate plateau pressures, and low working temperatures and pressures. H 2 storage alloys can be widely used in applications including catalytic reactions (Anthuvan and Pandurangan, 2014), H 2 compressors ( Wang et al., 2010;Hopkins and Kim, 2010), heat pumps ( Anikina et al., 2017), thermochemical heat storage (Shen and Zhao, 2013), and the medical field ( Yang et al., 2014). To further investigate and develop these applications of gas-solid reactions, it is necessary to thoroughly understand the inherent laws of hydroge nation/dehydrogenation. ...
Article
Particle size often varies during gas–solid heterogeneous reactions. For example, metal hydrides (MH) can reversibly absorb and desorb H2, accompanied by the expansion and shrinkage of the alloy particles, respectively. Although the traditional shrinking-core model (SCM) can be used to describe the H2 absorption/desorption process, the calculation results from SCM show relatively large deviations from the experimental data without considering the factor of particle expansion/shrinkage. Therefore, we proposed a shrinking-core–varying-size model (SC-VSM, henceforth VSM) for MH particles that accurately determines the kinetics equation with particle deformation. Three types of control mechanism including H2 dissociative chemisorption, H internal diffusion, and surface reaction were studied extensively, and the rate-controlling step for both VSM and SCM was determined to be the internal diffusion of H. Hydriding experiments on the systems of LaNi5 and LaNi4.5Al0.5 were performed under quasi-isothermal and variable-pressure conditions. The simulation results indicated that the new VSM was highly consistent with the experimental data for both alloys, evidently providing higher precision than the traditional SCM. The simplified forms of the VSM diffusion equations for LaNi5 and LaNi4.5Al0.5 were also developed to facilitate their practicability during the hydriding process: LaNi5:1.426-1.419(1-X)23-0.046(1-X)53-0.95X+0.038(1-X)2=tτdiff′ LaNi4.5Al0.5:1.362-1.35(1-X)23-0.069(1-X)53-0.90X+0.057(1-X)2=tτdiff′
... Minko et al. [9,10] made additions to the basic mathematical model of a LaNi 5 eH 2 bed for the calculation of the effective thermal conductivity and the bed porosity. A correlation for the hydrogen outlet flow rate was used in the model by Yang et al. [11]. Some improvements, including introducing realistic geometry and using validated parameters in the model, were made by Xiao et al. [12]. ...
Article
An enhanced 3-D numerical model, described in Part 1 [1] of this two part work, has been employed to study a metal-hydrogen storage system. In this manuscript we investigate the effect of varying the hydrogen in-flow rate and total amount of hydrogen inserted on the time taken to absorb/store the hydrogen and the temperature excursions. In addition, the ability to vary the temperature of the thermal management fluid has been used to examine the relative effect of a fixed fluid temperature and one which is hotter for desorption and colder for absorption.
... l eff is the effective thermal conductivity of metal-hydride bed; As the thermal conductivity of a porous medium is pressure dependent due to the Knudsen effect, this should be implemented as a function of pressure in the calculations [35]. Previous models [27,36,37], have regarded this as a constant despite sensitivity to the bed pressure being shown in early research [32,35,38,39]. However, the effect of different values i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 1 ( 2 0 1 6 ) 3 5 3 7 e3 5 5 0 of the effective thermal conductivity on the performance of metal-hydride beds has been investigated [24]. ...
Article
The complexity of the metal-hydrogen interaction and the critical role of thermal management in a metal-hydride storage tank necessitate comprehensive mathematical modelling before a suitable design can be chosen and subsequently implemented. Existing models have been analysed and integrated into an enhanced model which incorporates several features more suited to practical applications using an intermetallic metal-hydride tank. These include matching initial conditions of the model to physically achievable experimental conditions, the ability to vary the cooling system fluid temperature and realistic modelling of hydrogen injection and extraction from the tank as well as incorporating the non-ideal gas equation and modifying the equilibrium pressure and effective thermal conducting equation based on experimental data.
... These correlations and values were used in the mathematical model of the MH storage tank. Yang et al. [106] proposed mass boundary conditions (flow coefficient) to determine hydrogen outlet flow and investigated the sensitivity to different parameters such as bed pressure, bed initial temperature and convective heat transfer coefficient. They also compared the effect of two types of internal heat exchange systems (electrical and convective heating) on the hydrogen outlet flow rate and found significant differences. ...
Article
Full-text available
Metal-hydrides have been of great interest as one of the most promising materials for hydrogen storage applications. For widespread use, the most appropriate container and thermal management systems to minimise the time of absorption and desorption and maximise the amount of stored hydrogen must be designed. In recent years, many attempts have been made to identify the relationship between different operating and design variables and the resultant performance of metal-hydride systems. In this review, features of mathematical models of metal-hydride reactors including the assumptions, different applied equations and solution methods which have been developed in previous studies are presented. The evolution of the reactor geometries and configurations of cooling systems as well as different effective factors of metal-hydride performance are also discussed.
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High entropy alloys (HEA) represent a kind of materials with unique structural and functional properties, and have attracted wide attentions in many fields including hydrogen storage. Due to the huge diversity in the composition of HEAs, novel hydrogen storage materials with superior comprehensive performance are expected to be developed following the concept, with some notable progress made in the past decade. In this study, the present research status in HEAs for hydrogen storage is summarized from the aspects of theoretical guide, composition and preparation, microstructure and hydrogen storage properties. Moreover, the key issues in future development and possible application scenarios are analyzed.
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The hydrogenation process usually accompanies with strong thermal effect, which may lead to the poor hydriding performance if the reaction heat cannot be removed promptly. The design and optimization of metal hydride reactor can significantly advance heat & mass transfer and H 2 storage efficiency. A novel radiation mini-channel reactor (RMCR) was proposed to improve the thermal efficiency, and a radiation mini-channel reactor with jacket (RMCR-J) was developed to eliminate the unfavorable heat transfer regions inside RMCR. The 7 reactors were extensively investigated and compared by 3D COMSOL models, revealing that radiation tube behaved the best reaction performance. The structural parameters of RMCR & RMCR-J were optimized as spread branch number of 3, main tube radius of 2 mm, branch tube radius of 2 mm, axial pitch of 5 mm, mounting distance of 8.5 mm and tilt angle of 0°. Moreover, the operation conditions were simulated and the optimal performance could be achieved at H 2 pressure of 1 MPa and initial fluid temperature of 293 K. The sensitivity analysis results indicated that axial pitch and mounting distance was the most sensitive structure factor for RMCR and RMCR-J, respectively. In addition, RMCR-J was confirmed to present a superior performance than RMCR.
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Hydriding/dehydriding reaction kinetics of metal hydrides (MH) is an important yet controversial issue. In the last few decades, numerous studies have been dedicated to elaborate the reaction phenomena for various hydride materials. Some crucial aspects sketching the physical picture of the reaction, e.g. the controlling mechanism, Avrami exponent as well as apparent activation energy, are frequently discussed using the solid-state kinetic models. It is noted, however, that the results show considerable disagreement even for the material prepared in a single batch. From the literature review, it appears that no consistent understanding on the reaction kinetics of hydride materials could ever be achieved, unless carefully selected models and appropriate statistical processing techniques are used to interpret data obtained from well-designed experiments.
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Acute oxidative stress induced by ischemia-reperfusion or inflammation causes serious damage to tissues, and persistent oxidative stress is accepted as one of the causes of many common diseases including cancer. We show here that hydrogen (H(2)) has potential as an antioxidant in preventive and therapeutic applications. We induced acute oxidative stress in cultured cells by three independent methods. H(2) selectively reduced the hydroxyl radical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H(2) did not react with other ROS, which possess physiological roles. We used an acute rat model in which oxidative stress damage was induced in the brain by focal ischemia and reperfusion. The inhalation of H(2) gas markedly suppressed brain injury by buffering the effects of oxidative stress. Thus H(2) can be used as an effective antioxidant therapy; owing to its ability to rapidly diffuse across membranes, it can reach and react with cytotoxic ROS and thus protect against oxidative damage.
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This paper presents a numerical investigation of two-dimensional coupled heat and mass transfer processes in MmNi4.6Fe0.4 and MmNi4.6Al0.4 based metal hydride beds of cylindrical configuration during desorption of hydrogen using a commercial software FLUENT 6.1.22. Temperature and concentration profiles at different radial locations, variation of average bed temperature and amount of hydrogen desorbed are presented at different hot fluid temperatures and bed thicknesses ranging from 30 to 50 °C and 5 to 15 mm, respectively. The numerical results show that the dehydriding process for both the alloys depends on the temperature distribution in the metal hydride bed. At a given hot fluid temperature of 50 °C, MmNi4.6Fe0.4 and MmNi4.6Al0.4 desorb the maximum hydrogen of about 1.11 and 1.28 wt%, respectively at the supply conditions of 30 bar and 25 °C. The present computational results are also compared with the experimental data reported in the literature and a good agreement was found between the two.
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A study of two-dimensional dynamic heat and mass transfer in a metal-hydrogen reactor during desorption is presented in this paper. A mathematical model has been established and solved numerically by the method of finite domains. The numerical simulation is used to present the time-space evolution of the temperature, the pressure and the hydride density in the reactor and to determine the sensitivity to some parameters (reactor geometry, outlet pressure, temperature of heating fluid and heat conductivity). This simulation allows us to study the effect of neglecting the term related to heat transport by convection in the model.
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The rate at which hydrogen can be drawn from a metal hydride tank is strongly influenced by the rate at which heat can be transferred to the reaction zone. In this work, the impacts of external convection resistance on thermodynamic behaviour inside the metal hydride tank are examined. A one-dimensional resistive analysis and two-dimensional transient model are used to determine the impact of external fins on the ability of a metal hydride tank to deliver hydrogen at a specified flow rate. For the particular metal hydride alloy (LaNi5) and tank geometry studied, it was found that the fins have a large impact on the pressure of the hydrogen gas within the tank when a periodic hydrogen demand is imposed. Model results suggest that the metal hydride alloy at the centre of the tank can be removed to reduce weight and cost, without detrimental effects to the performance of the system.
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We previously demonstrated that donor treatment with inhaled hydrogen protects lung grafts from cold ischemia/reperfusion (I/R) injury during lung transplantation. To elucidate the mechanisms underlying hydrogen's protective effects, we conducted a gene array analysis to identify changes in gene expression associated with hydrogen treatment. Donor rats were exposed to mechanical ventilation with 98% oxygen and 2% nitrogen or 2% hydrogen for 3h before harvest; lung grafts were stored for 4h in cold Perfadex. Affymetrix gene array analysis of mRNA transcripts was performed on the lung tissue prior to implantation. Pretreatment of donor lungs with hydrogen altered the expression of 229 genes represented on the array (182 upregulated; 47 downregulated). Hydrogen treatment induced several lung surfactant-related genes, ATP synthase genes and stress-response genes. The intracellular surfactant pool, tissue adenosine triphosphate (ATP) levels and heat shock protein 70 (HSP70) expression increased in the hydrogen-treated grafts. Hydrogen treatment also induced the transcription factors C/EBPα and C/EBPβ, which are known regulators of surfactant-related genes. Donor ventilation with hydrogen significantly increases expression of surfactant-related molecules, ATP synthases and stress-response molecules in lung grafts. The induction of these molecules may underlie hydrogen's protective effects against I/R injury during transplantation.
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Transport process affects the performance of a metal hydride reactor significantly. Therefore in a former paper presented by the same authors, two parameters, which are known as heat transfer controlled reaction rate and mass transfer controlled reaction rate, were defined to account for this effect and assist the design of the reactors. However, a few simplifications were adopted in that article, which may result in some errors. In order to achieve better accuracy and clarity, more factors such as the external convection heat transfer and propagation of reaction front were considered here in the formulation of the parameters. Then numerical simulations for the adsorption in a tubular reactor were carried out and the situation under which parameter analysis can be applied was discussed. More characteristics in the process were revealed by the newly formulated parameters, which could be seen from the comparison of the results by parameter analysis and numerical simulation.
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The performance of a metal hydride reactor is highly dependent on its transport process. It is important to know how the transport process affects the performance, therefore two key parameters—heat transfer controlled reaction rate and mass transfer controlled reaction rate were introduced to explain this kind of effect. Moreover, a brief discussion about how to use the new parameters was given. In order to analyze the reactor performance and heat/mass transfer characteristics, a non-local thermal equilibrium model describing the actual adsorption process was formulated, and numerical simulations were carried out. Then the two parameters were applied for the same purpose. The result of the parameter analysis coincided well with that of the numerical simulation, which approved the validity of the two parameters in identifying heat and mass transfer characteristics of the metal hydride reactor.
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In this paper, an experimental and numerical study of a closed metal-hydrogen reactor is presented. The temperature and the pressure temporal evolutions within the reactor, which thermally solicited at a constant temperature, are experimentally investigated and analysed. In addition, a test of the validity of a theoretical model describing the dynamic behaviour of a closed reactor, by comparing the experimental and numerical results, has been done and a reasonable agreement is obtained. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Article
The metal–hydrogen reactor is usually composed of a porous medium (hydride bed) and an expansion volume (gaseous phase). During the sorption process, the hydrogen flow and the heat transfer in the expansion part are badly known and can have some effects on the sorption phenomena in the hydride medium. At our knowledge, the hypothesis that neglects those effects is typically used. In this paper, a 2D study of heat and mass transfer has been carried out to investigate the transient transport processes of hydrogen in the two domains of a closed cylindrical reactor. A theoretical model is conducted and solved numerically by the control-volume-based finite element method (CVFEM). The result on temperature and hydride density distribution are presented and discussed. Moreover, this paper discusses in detail the effects of some governing operating conditions, such as dimensions of the expansion volume, height to the radius reactor ratio, and the initial hydrogen to metal atomic ratio, on the evolution of the pressure, fluid flow, temperature and the hydrogen mass desorbed.
Article
A 1-D model has been developed to evaluate various designs of metal hydride reactors with planar, cylindrical or spherical geometry. It simulates a cycling loop (absorption–desorption) focusing attention on the heat transfer inside the hydride bed, which is considered the rate-limiting factor. We have validated this model with experimental data collected on two reactors, respectively, containing 1 and 25 g of LaNi5, the second being equipped with aluminium foam. The simulation program reproduces accurately our experimental results. The impact of the foam cell size has been studied. According to our model, the use of aluminium foam allows the reactor diameter to be increased by 7.5 times, without losing its performance.
Article
Metal hydride heat pump (MHHP) can be utilized in a variety of applications and shows great potential in recovery of low-grade heat. Being its kernel component, the reactors should facilitate good heat and mass transfer to achieve satisfactory system performance. In this paper, the influences of certain heat transfer enhancement measures for the reactors were investigated by numerical simulation and thermodynamic analysis. Three types of reactors packed with metal hydride powder, metal hydride powder/Al foam and metal hydride compact were taken for discussion. As shown in the simulation results, for the MHHP adopting heat transfer enhancement, the coefficient of performance tends to reduce slightly while the specific heating power increases remarkably. Therefore, these measures work positively and are recommended for use in heat pump applications.
Article
Hairless albino mice with squamous cell carcinoma were exposed to a mixture of 2.5 percent oxygen and 97.5 percent hydrogen at a total pressure of 8 atmospheres for periods up to 2 weeks in order to see if a free radical decay catalyzer, such as hydrogen, would cause a regression of the skin tumors. Marked aggression of the tumors was found, leading to the possibility that hyperbaric hydrogen therapy might also prove to be of significance in the treatment of other types of cancer.
Molecular hydrogen reacts with the hydroxyl radical, a highly cytotoxic species produced in inflamed tissues. It has been suggested therefore to use gaseous hydrogen in a new anti-inflammatory strategy. We tested this idea, with the aid of the equipment and skills of COMEX SA in Marseille, a group who experiments with oxygen-hydrogen breathing mixtures for professional deep-sea diving. The model used was schistosomiasis-associated chronic liver inflammation. Infected animals stayed 2 weeks in an hyperbaric chamber in a normal atmosphere supplemented with 0.7 MPa hydrogen. The treatment had significant protective effects towards liver injury, namely decreased fibrosis, improvement of hemodynamics, increased NOSII activity, increased antioxidant enzyme activity, decreased lipid peroxide levels and decreased circulating TNF-alpha levels. Under the same conditions, helium exerted also some protective effects, indicating that hydroxyl radical scavenging is not the only protective mechanism. These findings indicate that the proposed anti-inflammatory strategy deserves further attention.
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Hydrogen gas debuts as a selective antioxidant with explosive potential as cytoprotective therapy for ischemia-reperfusion injury and stroke.
Controlling technique of process equipment and its applications
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Wang Y, Zhang ZX. Controlling technique of process equipment and its applications. Beijing: Chemical Industry Press; 2001.
A compact medical inhaling apparatus providing mixing gas with hydrogen as the effective component. Chinese patent, application number: CN
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Yang FS, Zhang ZX, Liu FF, Chen XY, Deng L. A compact medical inhaling apparatus providing mixing gas with hydrogen as the effective component. Chinese patent, application number: CN 201210437637.8; 2012.
Controlling technique of process equipment and its applications
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  • Z X Zhang
Wang Y, Zhang ZX. Controlling technique of process equipment and its applications. Beijing: Chemical Industry Press; 2001.