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Ceramic materials have good temperature and corrosion resistance, which is one of the ideal materials used in microchannel catalyst support for medium and high temperature catalytic reaction. Three-dimensional (3D) flow field structure is the most potential microchannel structure due to its high efficiency of mass and heat transfer. However, ceramic materials are hard and brittle, and the size of microchannel structures are small. It is a great challenge to construct a ceramic based microchannel catalyst support with a complex 3D flow field by traditional processing methods. In this paper, a 3D staggered flow field microchannel with the width of 450 μm and the depth of 1500 μm was designed and processed by diamond wire sawing. The mass and heat transfer properties of straight microchannel (SM), micro-column array (MA) and 3D staggered microchannel (3DSM) were compared by simulation. The effects of different windward angles (60°, 90° and 120°) on the performance of mass and heat transfer in 3D flow field were analyzed. The simulation results showed that the performance evaluation criteria (PEC) of 3DSM120° was 1.37, which meant better performance of heat and mass transfer than SM and MA. And the PEC of 3DSM structure was increased from 1.25 to 1.37 with the windward angle increasing from 60° to 120°. The pressure drop characteristics and hydrogen production performance of the microchannel catalyst support with different structures (SM, MA, 3DSM) were tested. The experimental results showed that the 3DSM had a good hydrogen production performance of methanol steam reforming (MSR) with the inlet flow rate of 1.5 ml/h at 300 °C. The methanol conversion rate was 99.43%, which was 15.41% and 6.20% higher than that of SM and MA, respectively, due to its better performance of mass and heat transfer. • A 3D staggered microchannel catalyst support with 3D flow field is designed and fabricated by diamond wire sawing. • The influences of 3D flow field structure on improving the heat and mass transfer performance are analyzed. • The PEC of 3D flow field structure is increased from 1 to 1.37, higher than other general flow field structure. • A methanol conversion of 99.43% is obtained by MSR microreactor with 3DSM120° structure at 300 °C, 1.5 ml/h feeding rate. [ABSTRACT FROM AUTHOR]

Hydrogen production by steam thermal reforming with waste heat of industrial particle material is of good prospects. But the insufficient research on the heat extraction traits of particulate matter has set up obstacles to its application. This paper focused on the effect of contact number, as it has not yet been fully studied. A series of steady-state numerical models based on a face-centered cubic packing was established to simulate the effect of contact number by removing selected particles. The results show that the contact number has a marked influence on the thermal resistance. As the contact number decreases by 12, the thermal resistance increases by 13.9∼31.9%. The removal of particles causes redistribution of heat transfer in different heat transfer modes. The heat transfer from the solid layer to the next layer decreases by 57.8% at most, and the radiation heat transfer between them is strengthened (36% at most). The effect of heat redistribution due to the removal of particles is significantly weakened after the heat flows through the first particle layer without removal operation. With these results, a better interpret of particulate matter heat extraction may be established. [Display omitted] • Effect of contact number on the heat transfer of the packed bed is studied. • The physical model is constructed by removing selected particles. • Temperature, heat flow characteristics and the heat transfer ratio are analyzed. • The reduction in the contact number increases the overall thermal resistance. • Removing particles causes redistribution of heat transfer modes. [ABSTRACT FROM AUTHOR]

Gasification for hydrogen production by the H-type finned tube embedded in the packed bed is considered to be more economical. Based on the thermal flow reversal reactor, the heat transfer characteristics of H-type finned tube embedded on the both sides of high-temperature zone of the packed bed under the quasi-steady were researched. The contribution of radiation heat transfer rate on the H-type finned tube is about 60.5% at most and radiation mainly occurs on the central tube. Within the range of inlet temperature and Re, the fin-assisted degree is both decreased gradually and the maximum is 48.9%. When the temperature is above 906 K or within the range of Re, the heat transfer rate of the fin is mainly from the radiation heat transfer rate. Under the condition of high inlet temperature and high Re, the fin-assisted degree is minimum, which indicates the operation stability of the H-type finned tube is better. • The contribution of radiation heat transfer on H-type finned tube is ~60.5%. • Radiation mainly occurs on the central tube in this paper. • The fin-assisted degree in this paper is ~48.9%. • When T in > 906 K or Re > 652.3, heat transfer rate of fins is mainly from radiation. • In high inlet temperature and Re condition, the finned tube works more steadily. [ABSTRACT FROM AUTHOR]

Methanol microreactors are of much application value in mobile hydrogen production (HP) thanks to their tiny volume, flexibility and safety and all that. Microchannels, the core of a reactor, provide a site and heat supply for the reaction. In this paper, a microchannel with multi-scale structures, i.e. submicro structure, corrugated structure, fin structure and matrix structure, is designed. Then the influence mechanism of these structures on the hydrogen production of methanol reforming is studied. Specifically, the influences of microstructures like submicro and corrugated structures on the performance of the catalyst in the microchannel as well as the influence of fin structure and matrix structure on the heat and mass transfer performance of the channel are studied. From the experimental research on the methanol conversion rate and H 2 flow rate of the microchannel with multi-scale structures, the influence rule of different structures on the HP performance of the channel is summarized. The experimental results show that these multi-scale structures not only improve the loading of the catalyst of the microchannel, but also its heat and mass transfer, which increases the methanol conversion rate of the microchannel with multi-scale structures by 33% and its H 2 flow rate by 0.266 mol/h. [Display omitted] • Multi-scale microchannel with submicron, corrugated and fin structures is designed. • Effect of structures at various scales on microchannel's HP performance is studied. • Multi-scale structure enhances catalyst loading ability, heat and mass transfer. • Methanol conversion rate of multi-scales microchannels can increase by 33%. [ABSTRACT FROM AUTHOR]

A microchannel reactor with a porous surface catalyst support has been applied to methanol steam reforming (MSR) for hydrogen production. The fluid flow, heat transfer, and hydrogen production efficiency of the microchannel reactor are significantly affected by the fabricated porous surface support, such as the pore sizes and their distributions. This paper presents a novel microchannel reactor with a gradient porous surface as the reaction substrate to enhance the performance of the microreactor for hydrogen production. Numerical modeling of the gradient porous surface is developed based on fractal geometry, and three different types of porous surfaces as the catalyst supports (two gradient porous surfaces and one uniform pore-size surface) are investigated. The fluid flow and heat transfer characteristics of these three types of microchannel reactors are studied numerically, and the results showed that the microreactor with a positive gradient pore sized surface exhibited relatively better overall performance. Experimental setups and tests were performed and the results validate that the microchannel reactor with a positive gradient porous surface can increase the heat transfer performance by up to 18% and can decrease the pressure drop by up to 8% when compared to a microreactor with a uniform pore sized surface. Hydrogen production experiments demonstrated that the microreactor with positive gradient pore sizes has the highest methanol conversion rate of 56.3%, and this rate is determined to be 6% and 9% higher than that of microreactors with reverse gradient porous surfaces and uniform pore sized surface, respectively. • A novel microreactor with gradient porous surface was proposed. • A numerical model based on fractal geometry was proposed. • The gradient porous surface can boost the flow and heat transfer performance. • The microreactor proposed has better methanol conversion performance. [ABSTRACT FROM AUTHOR]

We propose a theoretical method based on experience and inference and improved the temperature formula for the fluid flow in a porous structure in order to improve the efficiency of porous catalytic carrier of methanol hydrogen production. The comparison between linear gradient porous structure and fixed gradient porous structure is the purpose of this paper. The present work deals mainly with some impact factors which include porosity, Reynolds number, Fluid velocity, Fluid pressure, Nusselt number, Plante number, heat transfer coefficient of fluid convection and Fluid temperature. There are three major findings. First, wet-cycle proportional factor control equations were introduced to further improve the temperature formula. Second, fluid mixing of the gradient porous structure is more sufficient, relative to the fixed gradient porous structure. Third, the fluid temperature of the gradient porous structure drops more rapidly relative to the fixed gradient porous structure. These findings contribute to improved aspects of porous catalytic carriers. • Wet-cycle proportional factor control equations were introduced to further improve the temperature formula. • Gradient-changing models had a much greater change in velocity than the fixed-gradient model. • The pressure in the fixed-gradient model was less than that in the gradient-changing models. • The convective heat transfer coefficient of the gradient-changing models was larger than that of the fixed-gradient model. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen-fueled internal combustion engines (H2ICEs) have been the topic of research for many decades, and contemporary reviews have surveyed the relevant literature. Because of a number of relatively large R&D projects that have been ongoing recently, much progress has been made that is worth reporting. Specifically, this paper reviews the advancements made in plotting the possibilities offered by direct injection of hydrogen, in-cylinder heat transfer, modeling and combustion strategies (on an engine as well as vehicle level). These efforts have resulted in impressive efficiency numbers, both at peak and part load operation, while keeping emissions far below regulatory limits and reaching satisfactory specific power outputs. New demonstration vehicles have been put on the road showing the relatively low barriers (on a vehicle level) to introduce hydrogen engined transportation and these are briefly described. The paper discusses the merits of H2ICEs but also what makes them potentially unfit as a realistic alternative. Finally, the paper concludes with the main areas of research that require further efforts. [Copyright &y& Elsevier]

An integrated lab-scale copper-chlorine (Cu-Cl) thermochemical cycle for hydrogen production at the University of Ontario Institute of Technology (UOIT) is presented and analyzed in this paper. In a practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the oxidized anolyte (consumed anolyte at the electrolyzer cell) needs to be recycled to be concentrated sufficiently for the electro-chemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation and CuCl 2 concentrator. This study examines the thermodynamic performance of all unit operations in the lab-scale Cu-Cl cycle. A process simulation model with Aspen Plus is used to assess the system by energy and exergy analyses. For the specific system design characteristics, the cycle is capable of producing 100 L/h of hydrogen. From the simulation results, the overall energy and exergy efficiencies of the lab-scale Cu-Cl cycle are determined to be 11.6% and 34.9%, respectively. Furthermore, after the thermolysis and hydrolysis reactors, the quench cell and CuCl 2 concentrator have the highest exergy losses with thermal energy transferred through CuCl solidification and water vaporization phase-change processes at relatively high temperature. Additional results of the processes are presented and discussed. • A lab-scale study of an integrated Cu-Cl cycle at UOIT for hydrogen production is presented. • Recycling of oxidized anolyte is achieved through a sequence of separation processes. • A thermodynamic assessment is conducted through simulations in Aspen Plus. • The unit thermal energy, exergy and exergy destruction rates are evaluated for all system modules. [ABSTRACT FROM AUTHOR]

Abstract With the steam obtained by the energy released from ventilation air methane oxidation, the hydrogen production through gasification method is considered more commercial. In order to constrain the steam parameter fluctuation, the shunt honeycomb ceramics are adopted to fill between the heat exchange tubes. However, transient heat transfer characteristics of this kind of heat exchanger have not been fully studied. This paper carried out a numerical simulation study on the transient heat transfer characteristics of H finned tube under periodic reverse-flow conditions. Results show that the existence of shunt honeycomb ceramics enhances the effect of radiation. Gas flow direction reversing destructs the original boundary layer, achieving a sudden rise of the convective heat flux in the new upstream. It takes about 12s to form a new relative stable boundary layer. The apparent heat transfer coefficient achieves a maximum of 108.77 W m−2 K−1 and an average of 99.1 W m−2 K−1. Highlights • Temperature and heat flux distribution on the fins and ceramics wall facing tube were studied. • Trait of flow field and heat flux on the fin before and after gas reversing was revealed. • Variation characteristics of the apparent heat transfer coefficient was obtained. • Radiation contribution rate of the finned tube was researched. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat. The unsteady model was set up, which has been applied to investigate the effects of particle sizes (1.77 mm–14.60 mm) on particle temperature, heat transfer quantity, overall coefficient of heat-transfer, etc. The heat transfer performance of waste heat recovery heat exchanger is improved when the particle size increases, which is conducive to increase hydrogen production. The particle temperature change rate, the specific enthalpy change rate, the moving velocity of the maximum heat release rate particle, the contribution rate of solid phases, the heat release rate and the overall coefficient of heat-transfer increase, but the effective time of heat transfer decreases. When the particle size increases from 1.77 mm to 14.60 mm, the solid phase average contribution rate increases from 89.43% to 94.03%, the overall coefficient of heat-transfer increases from 1.39 W m−2 K−1 to 13.41 W m−2 K−1, the heat release rate increases from 48.9% to 99.9% and the effective time of heat transfer reduces from 48 h to 6.7 h. Highlights • A method for hydrogen production using solid particle waste heat was proposed. • The effects of particle sizes on methanol steam reforming were studied. • The one time heat transfer method of particles waste heat recovery was proposed. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a comparative review of different options for recovering heat from molten CuCl in the Cu–Cl cycle of hydrogen production. Various technologies exist for recovering heat from the molten CuCl in the cycle, but each has its advantages and challenges. In this paper, different parameters such as heat transfer rate, additional materials in the cycle, energy efficiency, temperature retention, economics, material issues, and design feasibility are considered in the evaluation of methods. It is shown that casting/extrusion, atomization methods, with a separate vessel using water as a coolant and rotary/spinning atomization using air as a coolant, can be considered as the most efficient and reliable methods for heat recovery from molten CuCl. [Copyright &y& Elsevier]

Abstract: The copper–chlorine (Cu–Cl) cycle of thermochemical hydrogen production requires heat recovery from molten CuCl at various points within the cycle. This paper examines the convective heat transfer between molten CuCl droplets and air in a counter-current spray flow heat exchanger. This direct contact heat exchanger is analyzed as a proposed new method of recovering heat from the solidified molten CuCl. Effective thermal management within the Cu–Cl cycle is crucial for achieving high thermal efficiency. The cycle’s efficiency is improved drastically when all heat released by the products of reactions is recycled internally. Recovering heat from molten CuCl is very challenging due to the phase transformations of molten CuCl, as it cools from liquid to different solid states. In this paper, a spray column direct contact heat exchanger is analyzed for the heat recovery process. A predictive model of heat transfer and droplet flow is developed and then solved numerically. The results indicate that full heat recovery is achieved with a heat exchanger diameter of 0.13m, and heights of 0.6 and 0.8m, for a 1 and 0.5mm droplet diameter, respectively. Additional results are presented and discussed for heat recovery from molten CuCl in the thermochemical Cu–Cl cycle. [Copyright &y& Elsevier]

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature. [ABSTRACT FROM AUTHOR]

Hydrogen production by the two-step solar thermochemical cycle has high cycle efficiency, low cost, and a great development space. Of special interest is the solar thermochemical cycle based on ZnO/Zn redox reactions since its high theoretical hydrogen yield and relatively low endothermic reaction temperature. In this paper, a steady heat transfer model for thermal ZnO dissociation in a solar thermochemical reactor is developed, coupling conduction, convection and radiation with chemical reaction. Accuracy was evaluated by comparison of results obtained from other references. Based on the new proposed reactor, the model is adopted to analyze the operating parameter effect on the conversion rate and fluid feature inside the solar reactor. The results show that the mass flow rate of ZnO and aperture gas temperature have a positive relation with ZnO conversion rate, however, the diameter of particles and aperture gas velocity has an inverse relation with ZnO conversion rate under specific condition. The results will provide useful foundation for improving the solar-to-fuel conversion rate in the near future. [ABSTRACT FROM AUTHOR]

Photo-fermentative bio-hydrogen production process is a complicated bio-chemical reaction process, its performance has a closely relationship with the configuration of photo-bioreactor, light distribution and density, generated heat from the bio-chemical reaction, and light-heat-mass transfer properties in the bio-hydrogen production system. Light and temperature have significant influence on the bacteria growth and enzyme activity, which further affects the performance of the photosynthetic bacteria and its hydrogen production potential. Current research status of the design of the photo-bioreactor, and transfer characteristics in the process of photo-fermentative bio-hydrogen production were reviewed in this paper. The design requirement, light distribution scheme, and heat-mass transfer enhancement approaches were all discussed. The in-depth understanding and grasp of the factors affecting light-heat-mass transfer performance in the hydrogen production process, effective regulation mechanism of photosynthetic hydrogen production can be put forward, and fundamentally optimized photo-fermentative bio-hydrogen production process, promoted the industrialization of biological hydrogen production process. [ABSTRACT FROM AUTHOR]

As a crucial step in nuclear-based hydrogen production Cu Cl cycle, the performance analysis of the heat transfer processes is of paramount importance. However, as a newly built system, the major obstacle of applying standard performance analysis methods to the heat transfer process is the sparse data, i.e., there is not sufficient experimental data available for a systematic performance analysis. In this research, a Monte-Carlo-Simulation-based (MCS-based) performance analysis method is developed, and it is demonstrated that this method can be used effectively to tackle the problems caused by sparse data in the heat transfer processes. In this paper, the details of the heat transfer process in a nuclear-based hydrogen production based on a four-step Cu Cl cycle are discussed first. Afterwards, modeling of the heat transfer process for MCS-based performance analysis is provided. Finally, the confidence interval of the simulation results is obtained. This method forms the basis for the future study of reliability of nuclear-based hydrogen production. [ABSTRACT FROM AUTHOR]

In the heat transfer process of nuclear hydrogen production system based on a 4-step Cu–Cl cycle, there are three major varying temperatures, namely room temperature, hydrolysis temperature and oxygen decomposition temperature. The heat requirement of the system will change with the temperatures. Therefore, it is important to identify the optimal ranges of the varying temperatures to make sure the heat requirement will be satisfied by the heat from a nuclear power plant, when the temperatures fluctuating in the optimal ranges. Genetic-algorithm-based Monte Carlo simulation method is developed in this paper to identify the optimal ranges. This method is able to obtain the optimal ranges through random sampling. The final result indicates that GA-based MCS method can be applied to identify the optimal ranges of the varying temperatures in the heat transfer process, and the ranges are highly trustable. [ABSTRACT FROM AUTHOR]

A new predictive model is developed in this paper to analyze the height of the reactor for continuous production of copper oxy-chloride in the thermochemical Cu–Cl cycle for hydrogen production. The volumetric phase fraction is used to develop an energy balance and integrated spatially to determine the inlet temperature of nitrogen and steam mixtures for continuous production of copper oxy-chloride. The effects of the ratio of mixing power to mass of the suspended particle, the ratio of interfacial surface area of the gas film to the volume of liquid, and diameter of the steam/nitrogen bubble in the reactor, on the height of the reactor are reported for a production capacity of 3 kg of hydrogen per day. Results indicate that a smaller ratio of interfacial surface area to volume of liquid significantly reduces the height of the reactor. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a three-dimensional (3D) hydrogen desorption model is applied to the thin double layered annulus ZrCo based hydrogen storage bed to precisely study the hydrogen desorption reaction and resultant heat and mass transport phenomena inside the bed. The 3D hydrogen desorption simulations are carried out and calculated results are compared with the experimental data measured by Kang et al. [1]. The present model reasonably captures the bed temperature evolution behavior and the hydrogen discharging time for 90% desorption. In addition, the thin double layered annulus metal hydride bed (MHB) design is numerically evaluated by comparing with a simple cylindrical MHB. More uniform distributions in the bed temperature and H/M atomic ratio and resultant superior hydrogen desorption performance are achieved with the thin double layered annulus bed owing to its high external surface to volume ratio and thus more efficient heating. This numerical study indicates that efficient design of the metal hydride bed is key to achieve rapid hydrogen discharging performance and the present 3D hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions. [Copyright &y& Elsevier]

Abstract: This paper presents the development of a new heat-transfer correlation for the flow of SuperCritical Water (SCW) in bare circular tubes, and its applicability to thermalhydraulic analysis for Heat eXchanger (HX) designs, linking a SuperCritical Water-cooled nuclear Reactor (SCWR) and a Copper-Chlorine (Cu–Cl) cycle-based hydrogen co-generation facility. A large set of experimental data, obtained in SCW flowing upwards in a 4-m long vertical bare tube with a 10-mm Internal Diameter (ID), was analyzed. The data were collected at pressures of about 24 MPa, inlet temperatures from 320 to 350 °C, values of mass flux ranging from 200 to 1500 kg/m2·s and heat fluxes up to 1250 kW/m2, for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. A dimensional analysis was conducted, using the Buckingham Π-theorem, to derive a general form of the empirical SCW heat-transfer correlation for the Nusselt number, which was finalized based on the experimental data obtained within the Normal Heat-Transfer (NHT) and Improved Heat-Transfer (IHT) regimes. The derived correlation showed the best fit for the experimental data within a wide range of flow conditions. This correlation has an uncertainty of about ±25% for Heat Transfer Coefficient (HTC) values and approximately ±15% for calculated wall temperatures. Subsequently, this correlation was used to calculate HTCs in support of preliminary thermalhydraulic calculations for HXs with SCW and SuperHeated Steam (SHS) as the operating fluids. The HXs are to be designed for integration into the No-Reheat or Single Reheat SCW Nuclear Power Plant (NPP) cycles and provide a link to support hydrogen production through the Cu–Cl cycle. Thermal energy will be transferred from the SCWR to an intermediate SHS loop operating at 5 MPa and delivered to the hydrolysis and oxygen-production process steps of the Cu–Cl cycle facility, which operates at temperatures of up to 530 °C. The analyzed HXs are of a double-pipe, counter-flow design. Calculations involved numerical solutions to identify HX outlet flow temperatures, required pipe lengths, number of pipes for each HX unit, mass flow rates and other relevant heat transfer parameters. Various test conditions have been assessed in support of a database to determine feasible configurations for an HX design. [Copyright &y& Elsevier]

Abstract: The metal hydride heat transformer shows great potential for the low-grade heat recovery. However, the heat output is variable, and these dynamics have to be taken into account in realistic applications. In this paper, a new index called true temperature boost is introduced together with conventional indices to assess the performance of the heat transformer system. Detailed analyses are carried out using a mathematical model that authors developed, investigating effects of key design and operating factors on the system’s performance. The amount of hydrogen transferred between coupled reactors is found to be crucial to obtain a high coefficient of performance, while specific heating power is very sensitive to the cycle time. On the true temperature boost, the driving force of reaction and the heat transfer conditions exert the most significant effects. [Copyright &y& Elsevier]

Abstract: This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100°C to 220°C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60°C to 165°C. [Copyright &y& Elsevier]

Abstract: In this paper, fluid flow characteristics through a packed bed reactor are investigated. The packed bed is utilized in the hydrogen production step of the copper–chlorine (Cu–Cl) thermochemical cycle. The hydrogen reaction is given by 2Cu(s) + 2HCl(g) = 2CuCl(molten) + H2(g) at 450 °C. Effectively controlling the pressure drop through the packed bed is important for increasing the system efficiency, since auxiliary pumps and other parasitic losses are affected by the pressure drop. Also, the chemical processes in the packed bed are affected by changes in pressure, temperature and heat transfer rates. Experimental results from a laboratory scale packed bed reactor, operating at ambient conditions, are presented and compared with analytical predictions, in terms of the pressure drop caused by fluid flow through the packing material. Three different packing materials, with various sphericities, are investigated with diameters of 450 μm, 4 mm, and 1 cm. The Ergun equation is shown to provide good agreement for flow conditions in the upper region of Reynolds numbers investigated (20 < Rep < 150); however, lack of agreement is observed at lower Reynolds numbers (Rep < 20). An analytical formulation for micro scale particles in a packed bed is developed based on the Stokes law for creeping flow. Good agreement is achieved with the corresponding experimental data. A new correction is also developed to connect the two flow regimes, as well as predict trends in the transition region. The results successfully demonstrate close agreement between the predictions and measured data. [Copyright &y& Elsevier]

Abstract: The advantages of a flat-tube solid oxide fuel cell (FT-SOFC) include easy sealing, low stack volume and low resistance to current collection. Because the performance of the FT-SOFC is closely linked to the interior hydrogen channel design, this paper studied various channel designs using a numerical approach. Ordinary FT-SOFCs have many channels with small cross-sectional areas. Unfortunately, this design makes it possible for the sealing material to block the channel entrance. Furthermore, it is difficult for the hydrogen to be evenly distributed under this type of design. To overcome these problems, a new design was developed to reduce the number of channels and increase the cross-sectional area. Contrary to expectations, the numerical approach applied here revealed that new design resulted in poor hydrogen transport into the support region and an average current density of 2846.7 A/m2, lower than that of the traditional design. Another design with a gradually increasing width from inlet to outlet was applied to increase the performance, maintain the mechanical strength and reduce the pressure drop of SOFCs. This design improved the average current density to 3135.4 A/m2. However, the cell performance with this channel design decreased significantly when the channel inlet became too narrow or when the outlet became too wide. [Copyright &y& Elsevier]

Abstract: In this paper, a novel bayonet tube high temperature heat exchanger (HTHE) with inner and outer fins is presented. It can be used in the ultra high temperature environment, such as hydrogen production, very high temperature reactor and externally fired combined cycle. Numerical investigation of heat transfer performance on the inside of bayonet element has been conducted for structure design. The numerical results suggest that the inner fin and inner tube should not be welded together. It is recommended that the air enters from the inner tube and exits from the annular space in the high temperature zone. A high temperature experimental system has been established to test the heat transfer and pressure drop characteristics of the HTHE. The surface area density of the tested HTHE is 6 times higher than that of the bare bayonet tube heat exchanger. The experimental results indicate that the mass flow rate on both sides and inlet temperature on the fuel gas side have a significant effect on the heat transfer rate and effectiveness, while the pressure drop ratios are mainly affected by the mass flow rate rather than the inlet temperature. Comparison between the tested HTHE and the similar HTHE without fins indicates that the proposed HTHE has a significant potential to improve the comprehensive heat transfer performance. [Copyright &y& Elsevier]

Abstract: Solar thermal cracking of natural gas is a promising technology, which has attracted researchers in recent years for its potential to lead to the development of CO2 free hydrogen production process. However, experimental access to the reaction chamber of solar cracking reactors is a challenge due to the high temperature process as the instruments capable of measuring fluid flow cannot survive the medium inside the reactor. However, computational fluid dynamics (CFD) can provide an insight into the flow, where experimental access is limited or not possible. This paper presents a CFD analysis for directly irradiated solar thermochemical reactor to characterize the influence of flow behavior on the heat transfer and solar cracking process. The heat transfer by radiation from carbon particles is considered by providing global absorption and scattering coefficients in the computational domain obtained from Mie code. The flow field is based on RNG k–ɛ model derived using renormalization group theory. This technique accounts for the effect of swirl on turbulence thereby enhancing accuracy for the swirl flows. Validation of the numerical results is carried out by making a comparison with the experimental results. Highlighting the effects of carving on the solar reactor walls, this study presents numerical analyses of solar reactor geometry for two cases; namely, when there is no vortex forming carving in the cavity, and when there is vortex forming helical carving. The results show that carving has significant influence on the flow behavior, however, it has very little effect on the outlet temperature. The numerical results also show that the radiative heat transfer mechanism is the dominant means of heat transfer compared to the effects of conduction and convection. [Copyright &y& Elsevier]

Abstract: This paper presents a two-dimensional mathematical model to evaluate transient heat and mass transfer in a metal hydride tank (hereinafter MHT) with metal foam heat exchanger. The model is validated by comparison with experimental data. A good agreement is obtained. A study of the geometric and the operating parameters of the metal foam (such as base material, pore size and relative density) has been carried out to identify their influence on the performance of the charging process of the MHT. After that, the model was used as a tool to predict the performance of the hydrogen-charging process of two configurations of MHTs with metal foam heat exchangers. The obtained results showed that the reduction of the storage time due to the metal foam heat exchanger can be more important when the MHT is equipped with a concentric heat exchanger tube. [Copyright &y& Elsevier]

Abstract: A 2D computational fluid dynamics (CFD) model was developed to study the performance of a planar solid oxide electrolyzer cell (SOEC) for hydrogen production. The governing equations for mass continuity, momentum conservation, energy conservation and species conservation were discretized with the finite volume method (FVM). The coupling of velocity and pressure was treated with the SIMPLEC (Semi-Implicit Method for Pressure Linked Equations – Consistent) algorithm. Simulations were performed to investigate the effects of operating/structural parameters on heat/mass transfer and the electric characteristics of a planar SOEC. It is found that the gas velocity at the cathode increases significantly along the main flow channel, as the increase in H2 molar fraction decreases the density and viscosity of the gas mixture at the cathode. It is also found that increasing the inlet gas velocity can enhance the SOEC performance. Another important finding is that the electrode porosity has small effect on SOEC performance. The results of this paper provide better understanding on the coupled heat/mass transfer and electrochemical reaction phenomena in an SOEC. The model developed can serve as a useful tool for SOEC design optimization. [Copyright &y& Elsevier]

Abstract: Although alane (AlH3) has many interesting properties as a hydrogen storage material, it cannot be regenerated on-board a vehicle. One way of overcoming this limitation is to formulate an alane slurry that can be easily loaded into a fuel tank and removed for off-board regeneration. In this paper, we analyze the performance of an on-board hydrogen storage system that uses alane slurry as the hydrogen carrier. A model for the on-board storage system was developed to analyze the AlH3 decomposition kinetics, heat transfer requirements, stability, startup energy and time, H2 buffer requirements, storage efficiency, and hydrogen storage capacities. The results from the model indicate that reactor temperatures higher than 200°C are needed to decompose alane at reasonable liquid hourly space velocities, i.e.,>60h−1. At the system level, a gravimetric capacity of 4.2wt% usable hydrogen and a volumetric capacity of 50gH2/L may be achievable with a 70% solids slurry. Under optimum conditions, ∼80% of the H2 stored in the slurry may be available for the fuel cell engine. The model indicates that H2 loss is limited by the decomposition kinetics rather than by the rate of heat transfer from the ambient to the slurry tank. [Copyright &y& Elsevier]

Abstract: The main focus of this paper is the modeling, simulation, and analysis of the calcium bromide hydrolysis reactor stage in the calcium–bromine thermochemical water-splitting cycle for nuclear hydrogen production. One reactor concept is to use a spray of calcium bromide into steam, in which the heat of fusion supplies the heat of reaction. Droplet models were built up in a series of steps incorporating various physical phenomena, including droplet flow, heat transfer, phase change, and reaction, separately. Given the large heat reservoir contained in a pool of molten calcium bromide that allows bubbles to rise easily, using a bubble column reactor for the hydrolysis appears to be a feasible and promising alternative to the spray reactor concept. The two limiting cases of bubble geometry, spherical and spherical-cap, are considered in the modeling. Results for both droplet and bubble modeling with COMSOL MULTIPHYSICS™ are presented, with recommendations for the path forward. [Copyright &y& Elsevier]

Abstract: By means of steam reforming, natural gas is converted to carbon dioxide and hydrogen. The reactions take place in reactor tubes which are covered with catalyst at the inside, where the reactive mixture flows. At the outside they are heated by combustion of natural gas with air. In this paper the conversion process is modeled for a single reactor tube by both chemical reaction models and heat transfer models. The model yields data of temperature, heat transfer and concentrations of hydrogen, carbon monoxide and natural gas along a reactor tube. Simulated temperatures have been validated with measured data from a prototype reformer. Next, the model was used to evaluate the performance of the reformer for six design modifications. It was found that the most promising improvements are created by increasing the air fraction in the burner and the thickness of the insulation shield. [Copyright &y& Elsevier]

Abstract: This paper deals with a two-dimensional model of a preferential oxidation (PROX) reactor to be used in a beta 5kWe hydrogen generator, named HYGen II, to integrate with polymer electrolyte fuel cells (PEFCs) for residential applications. The reactor geometrical configuration developed is a single-stage multi-tube configuration, in which a cocurrent air flow in the interspace is aimed at improving heat transfer and consequently controlling the temperature of the reactor. The aim of the model is to investigate the process performance of the reactor in order to enhance optimization and control of the PROX unit. The model concerns chemical kinetics and heat and mass transfer phenomena in the reactor. The model plays a key role in overcoming the issues of system design, by evaluating the temperature and the gas concentration profiles in the reactor. The CO removal from simulated reformate was examined with varying inlet temperature. Simulation results showed the strong dependence of the overall performance upon the reactor geometrical configuration. [Copyright &y& Elsevier]