Sulfation in lead–acid batteries

Virtually, all military land vehicle systems use a lead–acid battery to initiate an engine start. The maintainability of these batteries and as a consequence, system readiness, has suffered from a lack of understanding of the reasons for battery failure. Often, the term most commonly heard for explaining the performance degradation of lead–acid batteries is the word, sulfation.Sulfation is a residual term that came into existence during the early days of lead–acid battery development. The usage is part of the legend that persists as a means for interpreting and justifying the eventual performance deterioration and failure of lead–acid batteries. The usage of this term is confined to the greater user community and, over time, has encouraged a myriad of remedies for solving sulfation problems. One can avoid the connotations associated with the all-inclusive word, sulfation by visualizing the general “sulfation” effect in terms of specific mechanistic models. Also, the mechanistic models are essential for properly understanding the operation and making proper use this battery system. It is evident that the better the model, the better the level of understanding.     

Factors influencing the crack–system compliance of a piping system

With regard to the overall integrity of a piping system containing a circumferential through-wall crack, the crack–system compliance affects the integrity in various ways: (a) the onset and stability of crack extension and (b) leakage through a crack. This paper shows how this compliance depends on various factors: the mode of loading (displacement versus load control), system geometry, flexibility of mounting at the built-in ends, and the presence of supports and restraints. More particularly the paper quantifies, for a simple model system, how the compliance is affected by changes in these parameters, and especially with regard to changes in the system geometry, for which some interesting effects have been found.     

Solar–hydrogen energy system for Egypt

A model for a solar–hydrogen energy system for Egypt has been developed by obtaining relationships for and between the main energy and energy related parameters. The magnitude and trends of the parameters, with and without hydrogen introduction, have been investigated over a period of time. The results indicate that the fossil fuel resources in Egypt could be exhausted within one to two decades. They also indicate that adopting the solar–hydrogen energy system would extend the availability of fossil fuel resources, reduce pollution, and establish a permanent energy system for Egypt. They show that Egypt could become an exporter of hydrogen. © 1999 International Association for Hydrogen Energy.     

New La–Fe–B ternary system hydrogen storage alloys

The new La₈Fe₂₈B₂₄-, La₁₅Fe₇₇B₈- and La₁₇Fe₇₆B₇-type alloys have multiphase structures including LaNi₅, La₃Ni₁₃B₂ and (Fe, Ni) phases. The amount of La₃Ni₁₃B₂ phase increased and that of (Fe, Ni) phase decreased with an increasing La/(Fe + B) atomic ratio. The measurement of P–C–I curves revealed that the maximum hydrogen capacity exceeded 1.12 wt% at 313 K in the pressure range of 10⁻³ MPa–2.0 MPa. The alloys exhibited good absorption/desorption kinetics at room temperature, and electrochemical experiments showed that all of the alloy electrodes exhibited good activation characteristics, high-rate dischargeability (HRD) and low-temperature (233 K) dischargeability (LTD).     

Superior electrochemical hydrogen storage properties of binary Mg–Y thin films

Mg–Y thin films capped with Pd have been prepared by direct current magnetron co-sputtering system. It is found that Mg alloyed with Y in film state forms ultrafine nanocrystalline intermetallic compounds. The structure together with the catalytic effect of Y gives rise to a high electrochemical hydrogen storage capacities and superior activation properties. It is worthy to note that Mg₇₈Y₂₂ film achieves a high discharge capacity of 1590 mAh g⁻¹ without requiring activation process. Moreover, Mg alloyed with Y effectively improves the cyclic stability of Mg-based films ascribing to the anti-corrosion role of Y. For Mg₃₇Y₆₃ film, more than 92％ of the maximum discharge capacity can be maintained after 100 charge–discharge cycles.     

Linear stability of Rayleigh–Benard–Poiseuille convection for electrochemical system

The effect of Poiseuille flow on the convective stability of electrochemical system is considered. It is found that the effect is destabilizing in the case of oscillatory instability in the system. It is shown that this effect is caused by the fact that the problem is not self-conjugate, because the system is multicomponent. In addition, it is found that the effect of Reynolds number on the stability of these systems is linear at small Reynolds number, in contrast to the self-conjugate Rayleigh–Benard problem, where the effect is quadratic.     

Porous microspheres as additives in lead–acid batteries

The theoretical specific energy of the lead/acid battery is 176 W h kg⁻¹. The specific energy actually achieved depends on the discharge rate but is typically only about 15–25% of this maximum value. The major reason for the lead acid battery's inability to obtain higher specific energies is that much of the active material in both the positive and negative electrode is not discharged. This is especially true at the higher discharge rates where the diffusion of sulfate ions into the positive plate limits the reaction. Porous, hollow, glass microspheres (PHGM) would allow for more electrolyte storage in the electrodes and enhance the high rate energy storage of lead acid batteries. In this paper, we present a method for making hollow, glass microspheres (HGMs) porous. Presently our process only produces small yields. We believe in the future that the yields with our process can be substantially increased. PHGMs could substantially improve the high rate performance of lead acid batteries and make these batteries more attractive for hybrid electric vehicle applications.     

Progress in polyethylene separators for lead–acid batteries

The types and properties of separators used for lead–acid batteries are reviewed. Attention is focused on the pocket-type polyethylene (PE) separator as this is widely used in present-day automotive batteries, i.e. in low-maintenance batteries with expanded lead–calcium grids. An improved PE separator has been developed by using a PE resin of high molecular weight. The resistance of the separator to attack by hot sulphuric acid is increased by a factor of 1.5. Batteries using the improved separator show a 40% increase in lifetime under the SAE 75 °C life-cycle test.     

Thermo-economical analysis between new absorption–ejector hybrid refrigeration system and small double-effect absorption system

The comparisons of coefficient of performance and the cyclic characteristics between the three-pressure absorption–ejector hybrid refrigeration system (AEHRS) and small double-effect absorption refrigeration system are carried out. The thermo-economical analysis models of the two systems in two cases of high-temperature heat resources: waste heat resources and natural gas fuel are presented. The thermo-economical performances of the two systems in two modes of the running hours per year (600 and 1000 h) are calculated and discussed to show the commercial perspective of the AEHRS.     

Reverse hydride transformations in the Pd–H system

In the present review, the development of notions about hydride transformations is described. It is shown that hydride transformations were classified as a special type of phase transition in a number of classic phase transformations. Then, the available information about reverse hydride transformations in the Pd–H system is summarized and it is shown that reverse hydride transformations in this system proceed by the mechanism of generation and growth. The C-shaped kinetic isothermal diagrams describe kinetics of direct α→β$\alpha \to \beta$ HT. Another type of kinetic diagram is typical for reverse β→α$\beta \to \alpha$ hydride transformations, and the rate of these hydride transformations just accelerates with temperature increase or hydrogen pressure decrease. Morphological peculiarities of reverse hydride transformations are described in detail. In the conclusion, a discussion of the unique role of hydrogen concentrational and hydrogen phase stresses in processes of hydride transformations is given. It has been found that these stresses are the most important thermodynamic and kinetic factors in the hydride transformation development.     

Brinkman–Forchheimer modeling for porous media thermoacoustic system

In this paper, analytical studies have been conducted on the flow and thermal fields of unsteady compressible viscous oscillating flow through channels filled with porous media representing stacks in thermoacoustic systems. The flow in the porous material is described by the Brinkman–Forchheimer–extended Darcy model. Analytical expressions for oscillating velocity, temperature, and energy flux density are obtained after linearizing and solving the governing differential equations with long wave, short stack, and small amplitude oscillation approximations. Experimental work is also conducted to verify the temperature difference obtained across the porous stack ends. To produce the experimental results, a thermoacoustic heat pump is designed and constructed where reticulated vitreous carbon (RVC) is used as the stack material. A very good agreement is obtained between the modeling and the experimental results. The expression of temperature difference across the stack ends obtained in the present study is also compared with the existing thermoacoustic literature. The proposed expression surpasses the existing expression available in the literature. The system of equations developed in the present study is a helpful tool for thermal engineers and physicist to design porous stacks for thermoacoustic devices.     

Synthesis and hydrogenation properties of Mg–La–Ni–H system by reactive mechanical alloying

We have synthesized Mg–30 mass%LaNi_2.28 composite material and investigated its hydrogenation behaviour. The reactive mechanical alloying process of the mixture of Mg and LaNi_2.28 was studied. It is found that a composite of _MgH2${\mathrm{MgH}}_2$, _La4H12.9${\mathrm{La}}_4{\mathrm{H}}_{12.9}$ and _Mg2NiH4${\mathrm{Mg}}_2{\mathrm{NiH}}_4$ formed after 80 h ball-milling under 3.0 MPa hydrogen. Scanning electron microscopic analysis indicated that these new phases are distributed homogeneously. This composite shows excellent hydriding properties even at moderate temperature. Under 3.0 MPa hydrogen pressure it absorbed more than 80% of its full capacity in the temperature range of 473–553 K within less than 1 min. The maximum hydrogen absorption capacity at 553 K is 5.4 mass%. The enhanced hydriding properties could be attributed to the fine and uniform particles and a synergeticly catalytic effect generated by mechanical milling.     

Essential characteristics for separators in valve-regulated lead–acid batteries

The absorptive separator plays an important role in the operation of valve-regulated lead–acid (VRLA) batteries. The composition and physical characteristics of recombinant-battery separator mats (RBSMs), also known as absorptive-glass mats (AGMs), directly affect three critical factors associated with the performance of VRLA batteries. The factors are: electrolyte supply, oxygen-transport, and constraint of positive active-material growth. This paper discusses the influence of the physical properties of RBSMs on the performance of VRLAs, explains how these properties are measured, and defines the characteristics of an ideal separator. Separators used presently in VRLAs meet some of these criteria, but development of advanced materials is required to improve battery life.     

Performance evaluation of photovoltaic/thermal–HDH desalination system

The efficiency of photovoltaic (PV) panel drops with increase in cell temperature. The temperature of the PV panel can be controlled with various cooling techniques. In the proposed work the PV panel is cooled by circulating water and the recovered heat energy is used to run a humidification and dehumidification desalination to produce distilled water from sea water (or) brackish water. This work deals with a detailed analysis of performance of combined power and desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system. A mathematical model of PV/thermal–humidification dehumidification plant was developed and simulations were carried out in MATLAB environment. The performance of photovoltaic/ thermal desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system was investigated under various solar radiation levels (800–1000 W/m²). For each solar radiation level the effect of mass flow rate of coolant water (30–110 kg/h) on water outlet temperature, PV efficiency, PVT thermal efficiency, distilled water production, and plant efficiency was studied. Results show that under each solar radiation level increasing coolant flow rate increases efficiency of PV panel and reduces the plant efficiency. The highest PV efficiency (16.598%) was reached under 800 W/m² at mass flow rate of 110 kg/h and the highest plant efficiency (43.15%) was reached under 800 W/m² at a mass flow rate of 30 kg/h. The maximum amount of distilled water production rate (0.82 L/h) was reached under 1000 W/m² at water mass flow rate of 30 kg/h.     

Electrochemical oxidation of alcohols on Pt–TiO2 binary electrodes

In this study Pt–TiO₂ binary electrodes were prepared by means of thermal decomposition of chloride precursors on Ti substrates, characterised by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), electrochemical techniques and CO stripping and used as anodes for alcohol oxidation. The minimization of the Pt loading without electrocatalytic activity losses was also explored. TiO₂ was chosen due to its chemical stability, low cost and excellent properties as substrate for Pt dispersion. It was found that TiO₂ loading up to 50% results in Electrochemically Active Surface (EAS) increase. The EAS of Pt(50%)-TiO₂(50%) was found to be almost one order of magnitude higher than that of pure Pt while the EAS of samples with Pt loading lower than 30% was negligible. The above conclusion has been confirmed both by following the charge of the reduction peak of platinum oxide and by CO stripping experiments. All samples have been evaluated during the electrochemical oxidation of methanol and ethanol. In both cases the Pt(50%)-TiO₂(50%) electrode had better electrocatalytic activity than the pure Pt anode. The observed higher performance of the binary electrodes was mainly attributed to the enhanced Pt dispersion as well as the formation of smaller Pt particles by the addition of TiO₂.     

Ternary compounds in the magnesium–titanium hydrogen storage system

Mg–Ti–H samples were mechano-chemically synthesized by ball milling in argon atmosphere or under elevated hydrogen pressure. The detailed reaction mechanism during hydrogen release and uptake during continuous cycling was investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) experiments. The thermal behaviour of the samples and hydrogen desorption properties were examined by simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry (MS) measurements. A ternary Ti–Mg–H compound with a fcc lattice form during mechano-chemical sample preparation in hydrogen atmosphere using metal powders, but not using metal hydrides as reactants. The amount of β-MgH₂ increases during the first hydrogen absorption cycle at 300 °C at the expense of the high-pressure polymorph, γ-MgH₂ and the amount of β-MgH₂ remain constant during the following hydrogenations. This study reveals that the ternary compound tends to absorb increasing amounts of magnesium in the dehydrogenated state during cycling. A strong coupling between the amounts of magnesium in the ternary Ti–Mg–H phase and the formation of magnesium and magnesium hydride during hydrogen release and uptake at 300 °C is observed. The composition and the amount of the Ti–Mg–H phase appear to be similar in the hydrogenated state. Fast absorption–desorption kinetics at 300 °C and lower onset temperatures for hydrogen release is observed for all investigated samples (lowest onset temperature of desorption T_on = 217 °C).     

Hydrogen storage properties of the Mg–Ti–H system prepared by high-energy–high-pressure reactive milling

Magnesium-based alloys are among the promising materials for hydrogen storage and fuel cell applications due to their high hydrogen content. In the present work, we investigated the hydrogen release/uptake properties of the Mg–Ti–H system. Samples were prepared from the mixtures of MgH₂ and TiH₂ in molar ratios of 7:1 and 4:1 using a high-energy-high-pressure (HEHP) mechanical ball-milling method under 13.8 MPa hydrogen pressure. Thermogravimetric analysis (TGA) showed that a relatively large amount of hydrogen (5.91 and 4.82 wt.%, respectively, for the above two samples) was released between 126 and 313 °C while temperature was increased at a heating rate of 5 °C min⁻¹ under an argon flow. The onset dehydrogenation temperature of these mixtures, which is 126 °C, is much lower than that of MgH₂ alone, which is 381 °C. The activation energy of dehydrogenation was 71 kJ mol⁻¹, which is much smaller than that of as-received MgH₂ (153 kJ mol⁻¹) or as-milled MgH₂ (96 kJ mol⁻¹). Furthermore, the hydrogen capacity and the dehydrogenation temperature remained largely unchanged over five dehydrogenation and rehydrogenation cycles.     

Study on optimal configuration of the grid-connected wind–solar–battery hybrid power system

The capacity allocation of each energy unit in the grid-connected wind–solar–battery hybrid power system is a significant segment in system design. In this paper, taking power grid dispatching into account, the research priorities are as follows: (1) We establish the mathematic models of each energy unit in the hybrid power system. (2) Based on dispatching of the power grid, energy surplus rate, system energy volatility and total cost, we establish the evaluation system for the wind–solar–battery power system and use a number of different devices as the constraint condition. (3) Based on an improved Genetic algorithm, we put forward a multi-objective optimisation algorithm to solve the optimal configuration problem in the hybrid power system, so we can achieve the high efficiency and economy of the grid-connected hybrid power system. The simulation result shows that the grid-connected wind–solar–battery hybrid power system has a higher comprehensive performance; the method of optimal configuration in this paper is useful and reasonable.