Feasibility study of hydrogen production for micro fuel cell from activated Al–In mixture in water

A safe and environmental-friendly method of hydrogen production from milled Al–In–Zn–salt mixture in water was proposed in this paper. The 10 h—milled Al–In–Zn–salt mixture had high reactivity and produced hydrogen in water at room temperature. Its improved reactivity came from that the additive Zn and salts facilitate to the negative shift of Al–In alloy and benefited the combination of Al, In and Zn in the milling process. Optimized the composition content, 1 g of 10 h—milled Al—5 wt%In—3 wt%Zn—2 wt%NaCl mixture had highest hydrogen yield of 1035 mL hydrogen/1 g Al in 4 min of hydrolysis reaction in water, corresponding to 9.21 wt% hydrogen (excluding water mass). Hydrogen supplying from milled Al–In–Zn–salt mixture was performed for micro fuel cell and 0.96 W was produced with the stable hydrogen supply rate. Therefore, the milled Al–In–Zn–salt mixture could be a feasible alternative for providing a source of CO₂ free hydrogen production to supply micro fuel cell.     

Natural convection of nanoparticle–water mixture near its density inversion in a rectangular enclosure

Natural convection of mixture of nanoparticles and water near its density maximum in a rectangular enclosure is studied numerically. A non-Boussinesq homogenous model is used in mathematical formulations of governing equations. The finite volume method is used to solve the governing equations. The results are presented graphically in the form of streamlines, isotherms and velocity vectors and are discussed for various nanoparticle volume fractions. It is observed that flow and temperature field is affected significantly in the presence of nanoparticles. The average heat transfer rate considering a non-Boussinesq temperature-dependent density (inversion of density) is lower than considering a Boussinesq temperature-dependent density. The average Nusselt number increases with an increase of nanoparticle volume fraction. It is observed that the density inversion of water leaves strong effects on fluid flow and heat transfer due to the formation of bi-cellular structure. The properties of nanoparticles also affect the fluid flow and heat transfer.     

Particle swarm optimization algorithm for ignition of hydrogen isotopes (deuterium–tritium) pellets

Recent improvements on high power lasers have made access to dense and hot plasmas possible realizing the inertial confinement fusion (ICF). Results from Osaka University experiments found that higher energy gains are reachable through ideal adiabatic shock-free volume ignition. Laser pulses limit the range of laser input energy. Thus, it becomes necessary to make efficient use of available energy to obtain the highest gain. The present paper aims to investigate the attainment of highest gain for D–T fuel using this energy with iteration model. It is shown that the maximum gain of 1.36 × 10⁶ is obtained only at input energy of 7.27 × 10¹⁰ J, volume of 0.586 cm³ and 8133times of solid state density.     

Heat recovery from molten CuCl in the Cu–Cl cycle of hydrogen production

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 0.13 m, and heights of 0.6 and 0.8 m, for a 1 and 0.5 mm droplet diameter, respectively. Additional results are presented and discussed for heat recovery from molten CuCl in the thermochemical Cu–Cl cycle.     

Hydrogen production for micro-fuel-cell from activated Al–Sn–Zn–X (X: hydride or halide) mixture in water

A systematic investigation of hydrogen production from milled Al–Sn–Zn–X (X: hydride or halide) mixtures in pure water was performed at room temperature. The hydrolysis mechanism of the mixtures was based on the work of micro-galvanic cell between aluminum and tin in water where aluminum reacted with water to generate AlOOH (Boehmite) and hydrogen. It was found that many effects such as milling time, temperature, additives and mass ratio had a significant role in the hydrogen production rate, especially that of the additives (hydride or halide) led to reduction of crystallite size and accumulation of uniform mixing. They also produced a lot of heat and the conductive ions which simulated the work of micro-galvanic cell. The milled Al–Sn–Zn–X (X: hydride or halide) mixtures had high reactivity and Al–Sn–Zn–MgH₂ mixture produced 790 mL g^?1 hydrogen in 5 min of the hydrolysis reaction with the activation energy of 17.570 kJ mol^?1, corresponding to 7.04 wt.% hydrogen excluding water mass. Therefore, a new method of CO₂ free and safe hydrogen production for micro-fuel-cell was obtained from the activated aluminum alloys in water.     

Self-compensating characteristic of steam–water mixture at low mass velocity in vertical upward parallel internally ribbed tubes

This paper presents an experimental investigation on Self-Compensating Characteristic (SCC) in vertical upward parallel tubes with low mass velocity of steam–water two-phase mixture. A physical model was built up using parallel internally ribbed tubes. A method called Differential Pressure Substitute was used to measure two-phase flow parameters. The results indicated that the SCC of vertical upward parallel tubes is caused by combined action of frictional pressure drop and gravitational pressure drop. The mass velocity in the tube with lower heat flux decreases first, and then increases with an increase in quality. The uneven heat fluxes among tubes are the main reasons that cause mass velocity differentials. Greater uneven heating ratio enhances the SCC in low quality region and weakens it in high quality region. The SCC has different variation rules in different pressure region. In the sub-critical pressure region, rising pressure weakens the SCC when quality is low and enhances it when quality is high. In near-critical pressure region, the mass velocity varies monotonically and slowly with the increase in quality because the difference between water and steam is minor in this pressure region. The results provide some instructive advices to improve the design and operation safety of once-through boiler.     

Hydrogen production from sodium borohydride in methanol–water mixtures

Hydrogen production systems based on the hydrolysis of sodium borohydride loose efficiency due to the excess water needed to account for the reaction and water capture by the by-product. Solubility of NaBH₄ and sodium borates in water is also a restricting factor together with the need for stabilizers necessary for reaction control in aqueous medium. In this work, methanol was used as an alternative to water. Literature data on this subject are scarce. Methanol lowers the freezing temperature of the reactant mixture with the advantage of providing short times for the initiation of the reaction and possibility of use at low temperatures. The effect of the water fraction on the efficiency of the reaction was studied at 45 °C. Results indicated increase in the reaction rates with decreasing water fraction. Sodium tetramethoxyborate was identified as the main by-product in methanol with no added water. When using methanol with no added water the reaction follows a first order rate kinetics with respect to sodium borohydride. Activation energy is reduced by a factor of 5 in the presence of methanol with no added water, when compared to values found in 100% water solutions. Methanol can be recovered by reaction of the by-product with water, offering increased storage and energy density to the system.     

Survey of experimental data and assessment of calculation methods of properties for the air–water mixture

Thermodynamic properties of the air–water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air–water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air–water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.     

Portable hydrogen generation from activated Al–Li–Bi alloys in water

A new process to obtain hydrogen from highly activated Al–Li–Bi alloys in water is described. The alloys had good hydrolytic properties at 298 K, and the optimized composite yielded 1340 mL hydrogen/g Al with 100% efficiency and achieved a maximum hydrogen generation rate of 988 mL/min g Al. These values are much higher than those obtained from hydrogen production with pure Al under the same conditions. The improvements were brought about by the increased amount of Li in the alloys; Al alloys with higher Li contents have larger surface areas and smaller grain sizes, allowing more hydrogen to be generated from Li hydrolysis in water. XRD and SEM analyses showed that the formation of BiLi₃ was helpful in improving the hydrolytic properties of the alloys via the work of the micro galvanic cell between Al and Bi, which was stimulated by the LiOH solution obtained from Li hydrolysis in water. Other effects, such as Bi content, global temperature, and annealing conditions, were also discussed. Al–Li–Bi alloys show promise as potential materials for supplying portable hydrogen to fuel cells.     

Comparative investigations of flame kernel development in a laser ignited hydrogen–air mixture and methane–air mixture

Concerns about energy availability and pollutant emissions, such as oxides of nitrogen and particulates have driven concerted efforts toward the design of next generation internal combustion engines, capable of using newer fuels, delivering higher efficiencies and lowering emissions. Among various new engine designs and concepts, laser ignition is one of the promising approaches to attain these objectives.     

Heat transfer of gas–liquid mixture in micro-channel heat sink

The main objective of the present investigation is to study heat transfer in parallel micro-channels of 0.1 mm in size. Comparison of the results of this study to the ones obtained for two-phase flow in “conventional” size channels provides information on the complex phenomena associated with heat transfer in micro-channel heat sinks. Two-phase flow in parallel micro-channels, feeding from a common manifold shows that different flow patterns occur simultaneously in the different micro-channels: liquid alone (or single-phase flow), bubbly flow, slug flow, and annular flow (gas core with a thin liquid film, and a gas core with a thick liquid film). Although the gas core may occupy almost the entire cross-section of the triangular channel, making the side walls partially dry, the liquid phase always remained continuous due to the liquid, which is drawn into the triangular corners by surface tension. With increasing superficial gas velocity, a gas core with a thin liquid film is observed. The visual observation showed that as the air velocity increased, the liquid droplets entrained in the gas core disappeared such that the flow became annular. The probability of appearance of different flow patterns should be taken into account for developing flow pattern maps. The dependence of the Nusselt number, on liquid and gas Reynolds numbers, based on liquid and gas superficial velocity, respectively, was determined in the range of Re_LS = 4–56 and Re_GS = 4.7–270. It was shown that an increase in the superficial liquid velocity involves an increase in heat transfer (Nu_L). This effect is reduced with increasing superficial gas velocity, in contrast to the results reported on two-phase heat transfer in “conventional size” channels.     

Transport properties of Ar–Kr binary mixture in nanochannel Poiseuille flow

Transport properties, including thermal conductivity and shear viscosity, of the Ar–Kr binary mixture confined in a nanochannel under Poiseuille flow are calculated by equilibrium molecular dynamics (EMD) simulation through Green–Kubo formula. An external force is applied in the x-direction to drive the Poiseuille flow. Thermal conductivity of the confined mixture in the x- and y-direction is obviously higher than that in macroscale, as a result of the strong interacting potential between the fluid atoms and the wall atoms. Thermal conductivity of the flowing binary mixture is obviously anisotropic. With increasing the external driving force, in the x-direction the thermal conductivity increases, whereas in the y-direction it keeps constant. The xz- and yz-component of the shear viscosity of the confined mixture are enhanced comparing with the xy-component owing to the collisions between the fluid atoms and the wall atoms in the z-direction. They are higher than the results in macroscale and decrease with the external driving force increasing. For the binary mixture, thermal conductivity and shear viscosity vary with the mole fraction of the Kr atoms. The interactions between the fluid atoms and the wall atoms play a key role in the transport properties of the binary mixture confined in the nanochannel.     

Optimization of flame stabilization methods in the premixed microcombustion of hydrogen–air mixture

The premixed combustion of a lean hydrogen–air mixture is analyzed in this study to examine various properties and flame stabilization. A two-dimensional (2D) analysis of a microscale combustor is performed with various shapes of bluff bodies (e.g., circular and triangular). Nine bluff bodies are placed at the entrance of the microscale combustor and solved with 2D governing equations. The analysis is performed with the three velocities of 10, 20, and 30 m/s, but the equivalence ratio is fixed in all cases. The various characteristics of the microscale combustor are studied such as the temperature of the wall, difference in peak temperature, the mean velocity at the outlet, and temperature of the exhaust gases. Flame stabilization depends on various factors such as bluff body shape and size, and the velocity of the fuel–air mixture at the inlet and recirculation zone. In comparison to all bluff body cases, we observe that the wall blade bluff body is the most efficient (low exhaust gas temperature, large recirculation zone, low mean velocity at the outlet of the microcombustor, and high wall temperature) compared with all eight other bluff body cases. Combustion efficiency is directly proportional to the wall temperature, meaning that the microcombustor with wall blade bluff bodies is more efficient with a stabilized flame. The simulation results are compared with published data on an L/D ratio of 15.     

A solar-powered adsorption cooling system using a silica gel–water mixture

Solar-powered adsorption cooling is an attractive solar energy application. Metallic solar collectors with fins have been used to increase the thermal conductivity in solar collectors. This approach has a negative effect due to solar energy loss by reflection and heat loss resulting from the sensible heat of the metal. For these reasons, a direct-radiation absorption collector is proposed here. The effects of the wavelength of the absorbed light, types of silica gel used and additives to improve the absorptivity have been investigated. We have verified that blue silica gel has a better absorptivity in the near-infrared region than white silica gel. The addition of activated carbon to the silica gel improves the desorption rate and regeneration temperature of the packed bed.     

Alkali catalyzed liquefaction of corncob in supercritical ethanol–water

Corncob liquefaction in supercritical ethanol–water was performed with and without the addition of an alkali catalyst by direct addition or biomass impregnation in a 250-cm³ batch reactor. The effects of temperature, solvent and alkali addition on the biomass conversion level and oil yield were investigated to find the optimum condition. For non-catalytic liquefaction using a 1:1 (v/v) ethanol: water ratio, a maximum oil yield and conversion level of 49.0% and 93.4%, respectively, were obtained at 340 °C. For alkali catalytic liquefaction, the oil yield with KOH addition (57.5%) was higher than that from KOH-impregnated corncob liquefaction (43.3%). The oil from liquefaction with KOH addition had higher heating value (26.7–35.3 MJ kg⁻¹) than the corncob (19.1 MJ kg⁻¹). The dominant components of the obtained oil were found by GC/MS analysis to be aldehyde, ester, phenol derivatives and aromatic compounds.     

Enhanced hydrogen generation from aluminum–water reactions

Hydrogen production from the reaction of aluminum powder with liquid water is investigated for nano- and micron-sized spherical aluminum powders over the 20–200 °C temperature range. The maximum hydrogen production rate increases with increasing temperature and decreasing particle size, consistent with a surface reaction controlled by Arrhenius kinetics. The maximum hydrogen production rate normalized by surface area is universal, and an expression is proposed that predicts the maximum rate for variable powder sizes and temperatures. The hydrogen yield increases with increasing temperature and decreasing particle size. Ultrasonic agitation of the mixture increases the hydrogen production rate and total hydrogen yield, and appears to be a promising reaction-enhancing technique. The finite hydrogen yield observed for larger particles and lower temperatures suggests that the reaction is inhibited after it progresses a certain depth into the particles, here termed the penetration thickness. The penetration thickness increases with temperature and is independent of particle size.     

Seasonal storage of electricity by hydrogen in benzene–water system

The use of hydrogen in benzene–water system which combines water electrolysis and hydrogenation in a polymer electrolyte cell was carried out as a means for seasonal storage of electricity. Gas diffusion electrodes were effective in improving coupled reactions of electrochemical benzene hydrogenation and water electrolysis. The reaction kinetics for the electrochemical hydrogenation process using gas diffusion electrodes was investigated by evaluating current efficiency and reaction rate. The results showed that the rate of hydrogen evolution was higher than the rate of benzene hydrogenation and the apparent activation energy of hydrogen evolution was lower than that of benzene hydrogenation. As the electrode potential increased, the hydrogen evolution rate increased. The benzene hydrogenation reaction rate reached a maximum at −0.8 V electrode potential, then decreased slightly. The current efficiency, however, reached its maximum at −0.7 V. Modifying electrodes by adding 0.2 wt% polyethylene glycol (PEG6000) reduced the mass transfer resistance of organic phase (cyclohexane/benzene) and improved the hydrogenation reaction rate.     

Study on the performance of hydrogen isotopes permeation sensor in liquid Li–Pb

Liquid Li–Pb alloy is served as neutron multiplier, tritium breeder, and coolant in Dual Coolant Lithium–Lead (DCLL) breeding blankets. In order to monitor the tritium transport continuously and measure the tritium production rate accurately, the concentration of hydrogen isotopes in liquid breeder is an essential factor for tritium measurement. The hydrogen isotopes permeation-based capsule seems to be the most reliable sensor and is simple from the fabrication point of view. To verify the stability and repeatability of hydrogen isotopes concentration measured by permeation capsule in Li–Pb, a system based on a Nb-capsule and a quadrupole mass spectrometry was devised. The sensor would be applied to determine the variation rate of total pressure while a quadrupole mass spectrometry to measure partial pressure values of different hydrogen isotopes. The response time of the sensor is less than 100 s in liquid Li–Pb alloy and the growth rate of pressure has good repeatability in dynamic mode. Besides, calculations based on numerical simulation of the hydrogen isotopes sensor are presented.     

Continuous detonation combustion of ternary “hydrogen–liquid propane–air” mixture in annular combustor

Experiments are performed on continuous detonation combustion of ternary hydrogen–liquid propane–air mixture in a large-scale annular combustor 406 mm in outer diameter with an annular gap of 25 mm. Liquid propane is fed into the combustor at the time when sustained continuous-detonation combustion of hydrogen–air mixture is attained therein. Mass flow rates of hydrogen, propane and air in the experiments ranged from 0.1 to 0.5 kg/s (hydrogen), 0.1 to 0.5 kg/s (propane), and 5 to 12 kg/s (air). Continuous-detonation combustion of liquid propane in air is obtained for the first time due to addition of hydrogen rather than due to enrichment of air with oxygen. Combustor operation with a single continuously rotating detonation wave (DW) for about 0.1 s has been obtained when the flow rates of propane and air remained constant while the flow rate of hydrogen was rapidly decreasing.     

Interphase heat transfer during bulk condensation in the flow of vapor–gas mixture

The investigation of heat transfer between a single droplet and a vapor–gas mixture at different Knudsen numbers of growing droplet is presented. The influence of the interphase heat transfer on the behavior of macroparameters and the distribution function of droplets was studied using the results obtained for bulk condensation of vapor–gas mixture flow in a nozzle. A comparison of results obtained within the frames of general formulation and ones following from the certain simplifying assumptions on the droplets temperature was carried out for the free molecular regime of droplets growth.