Investigation of single-walled carbon nanotubes-titanium metal composite as a possible hydrogen storage medium

The present experimental work deals with the investigation of hydrogen uptake study of single-walled carbon nanotubes (SWCNTs-Ti)-titanium metal composite. The mixture containing SWCNTs and Ti powder is made into tablet by cold pressing. The composite has been prepared and hydrogenated by evaporating the tablet in hydrogen ambient on glass substrates using electron beam (EB) evaporation technique. Efficient hydrogen uptake of 4.74 wt.% is achieved with the composite and the adsorbed hydrogen posses the average hydrogen binding energy of 0.4 eV. The obtained hydrogen uptake is due to the cumulative adsorption of hydrogen by CNTs and Ti nanostructured materials. The physical properties are characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction study (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analysis. Hydrogenation and dehydrogenation behavior of the composite are studied using CHN-elemental analysis and thermo gravimetric/thermal desorption spectroscopy (TG/TDS) studies, respectively. The stored hydrogen is found to be 100% reversible in the temperature range of 160–310 °C.     

Chemical and isotopic compositions of water and dissolved sulfate from shallow wells on Vulcano Island,Aeolian Archipelago,Italy

Twenty-two cold and thermal waters from shallow wells sampled in June 1995 in the Vulcano Porto area, Vulcano Island, were analyzed for major and minor chemical constituents, oxygen and hydrogen isotopes and tritium contents, and sulfur isotopes in the dissolved sulfate. The sulfur isotopic composition of the dissolved sulfate ranges between +0.6 and +6.5‰ (mean +3.7±1.7‰), and is interpreted as deriving mainly from fumarolic SO₂ undergoing oxidation in deep and shallow aquifers, with possible minor contributions from oxidation of H₂S. Dissolution of secondary anhydrite may have been a minor source of the isotopically heavy aqueous sulfate in the cold groundwaters. The chemical and isotopic features of the waters support previous interpretative hydrologic models of Vulcano Porto, which comprise a number of aquifers fed basically by two major end-members, i.e. meteoric water and crater-type fumarolic inputs, the latter in the form of absorbed emissions or condensate. These data, along with the sulfur isotopes of aqueous sulfate, exclude involvement of seawater in the recharge of the groundwater system of the island.     

Thermal cycle testing of calcium chloride hexahydrate as a possible PCM for latent heat storage

In order to study the changes in latent heat of fusion and melting temperature of calcium chloride hexahydrate (CaCl₂·6H₂O) inorganic salt as a latent heat storage material, a thousand accelerated thermal cycle tests have been conducted. The effect of thermal cycling and the reliability in terms of the changing of the melting temperature using a differential scanning calorimeter (DSC) is determined. It has been noticed that the CaCl₂·6H₂O melts between a stable range of temperature and has shown small variations in the latent heat of fusion during the thermal cycling process. Thus, it can be a promising phase change material (PCM) for heating and cooling applications for various building/storage systems.     

Sodium sulfate as an efficient additive of negative paste for lead-acid batteries

This paper is devoted to the effect of sodium sulfate as negative paste additive on the performance of the lead-acid battery. Six different percentages of sodium sulfate were added to negative paste. The effect of sodium sulfate on discharge capacity, cycle life and cold cranking ability of the sealed lead-acid batteries were investigated. Batteries containing sodium sulfate in negative plates at low amount (0.1 wt%) showed a remarkable electrical behavior during the test. Results indicate that negative electrodes containing 0.1 wt% sodium sulfate exhibit discharge capacity of the more than 3% and 12% with respect to negative electrodes without sodium sulfate before and after cycling test, respectively. Addition of sodium sulfate also increases the time of reaching to cut off voltage of 6 V at cold cranking test more than 17%. The main effect of sodium sulfate is to increase the cycle life of the lead-acid batteries to more than 18%. Scanning electron microscopy (SEM) was used for the investigation of paste morphology.     

Oxygen vacancy-based ultrathin Co3O4 nanosheets as a high-efficiency electrocatalyst for oxygen evolution reaction

Enhancing the catalytic activity of Co₃O₄ electrocatalysts featuring abundant oxygen vacancies is required to enable their application in oxygen evolution reaction (OER). However, developing a harmless defect engineering strategy based on mild conditions to realize such an enhancement remains a challenge. Here, ultrathin Co₃O₄ nanosheets with abundant oxygen vacancies were prepared through a simple two-step method comprising a hydrothermal process and pre-oxidation to study the catalytic activity of the nanosheets toward OER. The ultrathin sheet structure and the Co₃O₄ nanosheets surface provide abundant active sites. The oxygen vacancy not only improves the catalyst activity, but also improves the electron transfer efficiency. These advantages make ultrathin Co₃O₄ nanosheets with abundant oxygen vacancies an excellent electrocatalyst for oxygen evolution. In an alkaline medium, ultrathin Co₃O₄ nanosheets exhibited excellent OER catalytic activity, with a small overpotential (367 mV for 10 mA/cm²) and faster reaction kinetics (65 mV/dec).Moreover, the electrocatalyst still maintained 68% of its original catalytic activity after 24 h operation. This work provides an extensive and reliable method for the preparation of low-cost and highly efficient OER electrocatalysts.     

基于铁矿石载氧体加压煤化学链燃烧的试验研究

在反应温度为970℃、压力范围为0.1～0.6 MPa的条件下,以铁矿石为载氧体,采用固定床反应器,对煤化学链燃烧进行了试验研究,考察了加压对燃料反应器内水蒸气气氛下煤化学链燃烧的反应特性.结果表明:加压能加快煤水蒸气气化速率,加强水气转换反应,并对煤气组分产生影响,使CO浓度降低,CO2和H2浓度升高;加压后还原反应烟气中不再含有H2,CO和CH4的浓度也变得很低,说明加压可提高还原反应中煤气的转化率;随着压力的升高,碳转化率先升高后又降低,存在着一个中间压力值,使碳转化率最高.     

Decreasing the initial irreversible capacity loss by addition of cyclic sulfate as electrolyte additives

Initial irreversible capacity loss in graphite electrodes was suppressed by 1,3,2-dioxathiolane-2,2-dioxide and its derivatives (cyclic sulfates) in propylene carbonate (PC) containing electrolyte. Cyclic voltammetry (CV) showed that cyclic sulfates were decomposed at higher potentials than that for electrolyte solvents. In galvanostatic charge and discharge measurement, first cycle efficiency was increased from 58.2% to 90.5% by the addition of 1,3,2-dioxathiolane-2,2-dioxide. Passivation films formed by cyclic sulfates were observed by X-ray photoelectron spectroscopy (XPS), FT-IR, and pyrolysis/GC/MS (pyro/GC/MS). These results indicate that the surface was covered by a PEO like polymer with the inner layer comprised of Li₂S like compounds.     

氧化铁作为氧载体在无烟燃烧技术中反应活化能的确定

以氧化铁作为熔融盐循环热载体无烟燃烧技术中的氧载体,在CH4气氛下进行了热重实验,并根据TG曲线进行了动力学分析,最后判断反应过程在550～670℃温度段为扩散控制的G-B模型,而在810～970℃温度段则为收缩球体模型,并依据模型分别计算出了活化能和频率因子。     

La substituted Sr2MnO4 as a possible cathode material in SOFC

Sr_2−xLa_xMnO_4+δ (x = 0.4, 0.5, 0.6) oxides were studied as the cathode material for solid oxide fuel cells (SOFC). The reactivity tests indicated that no reaction occurred between Sr_2−xLa_xMnO_4+δ and CGO at annealing temperature of 1000 °C, and the electrode formed good contact with the electrolyte after being sintered at 1000 °C for 4 h. The total electrical conductivity, which has strong effect on the electrode properties, was determined in a temperature range from 100 to 800 °C. The maximum value of 5.7 S cm⁻¹ was found for the x = 0.6 phase at 800 °C in air. The cathode polarization and AC impedance results showed that Sr_1.4La_0.6MnO_4+δ exhibited the lowest cathode overpotential. The area specific resistance (ASR) was 0.39 Ω cm² at 800 °C in air. The charge transfer process is the rate-limiting step for oxygen reduction reaction on Sr_1.4La_0.6MnO_4+δ electrode.     

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO₂ and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.     

Hydrology of the Greater Tongonan geothermal system, Philippines, as deduced from geochemical and isotopic data

Fluids in the Greater Tongonan geothermal system exhibit a large positive ¹⁸ O shift from the Leyte meteoric water line. However, there is also a significant shift in ²H. The δ²H−δ¹⁸O plot shows that the geothermal fluids may be derived by the mixing of meteoric water (δ¹⁸O = −7‰ and δ²H = −41‰) with local magmatic water (δ¹⁸O = 10 ± 2‰ and δ²H = −20 ± 10‰). The most enriched water in the Greater Tongonan system, in terms of δ¹⁸O, δ²H and Cl, is comprised of approximately 40% magmatic water. Baseline isotope results support a hydrogeochemical model in which there is increasing meteoric water dilution to the southeast, from Mahiao to Sambaloran and towards Malitbog. The Cl−δ¹⁸O plot confirms that the geothermal fluid in Mahanagdong, further southeast, is distinct from that of the Mahiao-Sambaloran-Malitbog system.     

基于Fe_3O_4的化学链制氢动力学特性

针对Fe3O4化学链制氢和CO2分离过程,研究了Fe3O4在CO气氛下还原以及铁在水蒸气下氧化的动力学特性.用Coats-Redfen单升温速率积分法、Ozawa组合升温速率法和lnln恒温分析法对反应机理进行了探讨,并计算了动力学参数.热重数据计算结果表明:在CO和N2体积分数分别为5%和95%时,还原反应属于一级反应,750～900,℃时反应活化能为112,kJ/mol;在CO、CO2和N2体积分数分别为42.9%、14.3%和42.8%时,还原反应可用Jander扩散模型描述,750,～950,℃时反应活化能为49.828,kJ/mol;经Ozawa法验证,加入CO2后的还原反应活化能明显降低.铁与水蒸气的氧化反应接近二维核生长模型,反应活化能较低,为29.633,kJ/mol,且随着温度升高,反应速率常数增大.     

Natural convection of water-CuO nanofluid in a cavity with two pairs of heat source-sink

Natural convection in a two-dimensional square cavity filled with a water-CuO nanofluid is numerically studied. Two pairs of heat source-sink are considered to cover the entire length of the bottom wall of the cavity while the other walls are thermally insulated. The nanofluid is assumed to be homogenous and Newtonian. The governing differential equations are discretised by the control volume approach and the coupling between velocity and pressure is solved using the SIMPLE algorithm. A comparison study is presented between two cases with different arrangements of the two pairs on the bottom wall. The effects of Rayleigh number and solid volume fraction of the nanofluid on the heat transfer rate have also been examined. The results show that regardless of the position of the pairs of source-sink, the heat transfer rate increases with an increase of the Rayleigh number and the solid volume fraction.     

高温氧气发生器在W火焰锅炉中的点火特性

针对燃用无烟煤的W火焰锅炉在冷态启动过程中要消耗大量燃油的问题,提出了一种高温氧气直接点火技术:用少量燃油将氧气加热至高温状态,然后用高温氧气直接点燃无烟煤煤粉气流.利用热态点火实验和数值计算方法证明了该技术的可行性和有效性.结果表明:利用高温氧气发生器可将氧气安全可靠地加热至最高可达1 450℃的高温状态;在纯氧氛围的作用下,燃油具有瞬间燃尽的特点;高温氧气发生器出口处的温度场和氧气质量分数呈现均匀分布;当高温氧气发生器的点火热功率为700kW时,无烟煤煤粉气流的火焰温度达到1 250℃,火焰长度超过8m.     

某舰用冷凝器凝结水含氧量的测试

通过一种新型水中氧分析系统,对某舰用冷凝器在不同工况下的凝结水出口的含氧量进行动态测试,从而掌握冷凝器的热力性能,并为以后改型设计提供必要的依据。     

NiFe2O4为载氧体的生物质半焦化学链燃烧热力学模拟研究

本文建立了以铁酸镍（NiFe2O4）为载氧体的生物质半焦化学链燃烧模型,利用HSC Chemistry 5.0软件对生物质半焦和NiFe2O4载氧体之间的化学链燃烧反应进行了热力学计算,模拟载氧体被半焦还原以及载氧体被空气氧化两个步骤的氧化还原过程,得到燃料反应器的优化操作参数为：载氧体和生物质半焦的摩尔比（O/BC）为1.5,燃料反应器的温度为800℃。热力学分析显示,NiFe2O4在化学链燃烧反应中是按照NiFe2O4→Ni-Fe2O3→ Ni-Fe3O4→Ni-FeO→Ni-Fe的顺序逐级被还原的。氧化过程的模拟说明,在空气气氛中,失去的晶格氧可以恢复到初始的程度,而实验手段得到的氧化产物的X射线衍射图则证明,通过氧化,被还原的载氧体可以大部分恢复到NiFe2O4尖晶石结构。     

Effect of the pore size distribution on the separation factor of membranes used as barriers for isotopic separation by gaseous diffusion

The standard way of evaluating the separation factor for the isotopic separation of U235/238 in the conventional uranium enrichment process by gaseous diffusion through membranes, considers only an average value for the pore radius. This is equivalent to assuming a membrane with all pores of the same size. In this work we discuss the influence of a realistic pore size distribution on the indicated factor and the physical interpretation of these results.     

Optimal ratios of the piston speeds for a finite speed irreversible Carnot heat engine cycle

The performance of an irreversible Carnot heat engine cycle is analysed and optimized by using the theory of finite time thermodynamics based on Agrawal's [2009. A finite speed Curzon-Ahlborn engine. European Journal of Physics, 30 (3), 587–592] model of finite piston speed on the four branches and Petrescu et al.’s [2002b. Optimization of the irreversible Carnot cycle engine for maximum efficiency and maximum power through use of finite speed thermodynamic analysis. In: Proceedings of ECOS’2002, 3–5 July, Berlin, Germany, Vol. II, 1361–1368] model of a Carnot cycle engine with the finite rate of heat transfer, heat leakage from heat source to heat sink and irreversibilities caused by finite speed, friction and throttling through the valves. The finite piston speeds on the four branches are further assumed to be different, which is different from the model of constant speed of the piston on the four branches. Expressions of power output and thermal efficiency of the cycle are derived for a fixed cycle period and internal entropy generation rate. Numerical examples show that the curve of power output versus thermal efficiency is loop shaped, and there exist optimal finite piston speeds on the four branches which lead to the maximum power output and maximum thermal efficiency, respectively. The effects of the heat leakage coefficient and internal entropy generation rate on the optimal finite piston speed ratios are discussed.     

Is a direct numerical simulation of chaos possible? A study of a model nonlinearity

There are many subtle issues associated with solving the Navier–Stokes equations. In this paper, several of these issues, which have been observed previously in research involving the Navier–Stokes equations, are studied within the framework of the one-dimensional Kuramoto–Sivashinsky (KS) equation, a model nonlinear partial–differential equation. This alternative approach is expected to more easily expose major points and hopefully identify open questions that are related to the Navier–Stokes equations. In particular, four interesting issues are discussed. The first is related to the difficulty in defining regions of linear stability and instability for a time-dependent governing parameter; this is equivalent to a time-dependent base flow for the Navier–Stokes equations. The next two issues are consequences of nonlinear interactions. These include the evolution of the solution by exciting its harmonics or sub-harmonics (Fourier components) simultaneously in the presence of a constant or a time-dependent governing parameter; and the sensitivity of the long-time solution to initial conditions. The final issue is concerned with the lack of convergent numerical chaotic solutions, an issue that has not been previously studied for the Navier–Stokes equations. The last two issues, consequences of nonlinear interactions, are not commonly known. Conclusions and questions uncovered by the numerical results are discussed. The reasons behind each issue are provided with the expectation that they will stimulate interest in further study.