Interaction of hydrogen sulfide with Ni–Alprotective coatings prepared by vacuum deposition

A laboratory process for preparation of Ni–Al intermetallic layers withdefinite phase composition has been developed in order to obtain protective coatings for use inhydrogen containing or hydrogen producing gas mixtures. Magnetron sputtering and electronbeam evaporation, followed by heat treatment have been used for coating formation. Aluminumlayers deposited on nickel supports were annealed in vacuum for 1–5 hours at 573–973 K.Coatings on powder, granules and carbon fibers have been also obtained by magnetron sputteringusing composite Ni–Al targets. Structure and composition of layers have been investigated byXRD, XPS, electron and optical microscopy. The interaction of hydrogen sulfide with the coatedsamples have been studied. Coating surface structure and morphology depends on deposition andannealing conditions. These parameters also considerably influence the coated materials resistanceto a hydrogen-containing atmosphere.     

Time-dependent corrosion behavior of electroless Ni–P coating in H2S/Cl− environment

As a mature technology, electroless Ni–P alloy coating is widely applied in the protection of chemical equipment and pipelines owing to its excellent corrosion resistance, but its application and long-term service evaluation in the field of high-sulfur oil and gas are rare. Therefore, the time-dependent corrosion behavior of Ni–P coating, which was plated on the L360 steel surface, was investigated in a saturated H₂S medium by the method of surface analysis. The results indicate that Ni–P coating with a thickness of about 52.6 μm could significantly reduce the corrosion rate compared with uncoated pipeline steel. This is related to the structure of the dense, protective film on the surface. The uncoated pipeline steel suffered local corrosion during the immersion process, and then it developed into uniform corrosion with the formation of a large number of corrosion products. In comparison, Ni–P coatings corroded relatively mildly with only a thin corroded layer. However, during prolonged corrosion testing, the corrosive medium penetrated the coating/substrate interface at inherent defects, leading to severe local corrosion of the substrate.     

Hydrogen gas production with Ni,Ni–Co and Ni–Co–P electrodeposits as potential cathode catalyst by microbial electrolysis cells

The development of efficient and economical cathode, operating at ambient temperature and neutral pH is a crucial challenge for microbial electrolysis cell (MEC) to become commercialize hydrogen production technology. In the present work, eight different electrodes are prepared by the electroplating of Ni, Ni–Co and Ni–Co–P on two base metals i.e., Stainless Steel 316 and Copper separately to use as cathode in MEC. Electrodeposited cathode materials have been characterized by XRD, XPS, FESEM, EDX and linear voltammetry. The fabricated cathodes show higher corrosion stability with improved electro-catalytic performance for the hydrogen production in the MECs as compared to the bare cathodes (SS316 and Cu). Data obtained from linear voltammetry and MEC experiments show that developed cathode possess four times higher intrinsic catalytic activity in comparison to bare cathode. Electrodeposited cathodes are intensively examined in membrane-less MEC, operating under applied voltage of 0.6 V in batch mode at 30 ± 2 °C temperature, in neutral pH with acetate as substrate and activated sludge as inoculum. Ni–Co–P electrodeposit on Stainless Steel 316 cathode gives maximum hydrogen production rate of 4.2 ± 0.5 m³(H₂)m⁻³d⁻¹, columbic efficiencies 96.9 ± 2%, overall hydrogen recovery 90.3 ± 4%, overall energy efficiency 241.2 ± 5%, volumetric current density 310 ± 5 Am⁻³. The net energy recovery and COD removal are 4.25 kJ/gCOD and 61%, respectively. Prepared cathodes show stable performance for continuous 5 batch cycle operations in MEC.     

Experimental investigation of the silica gel–water adsorption isotherm characteristics

In designing adsorption chillers that employs silica gel–water as adsorbent-adsorbate pair, the overriding objective is to exploit low temperature waste-heat sources from industry. This paper describes an experimental approach for the determination of thermodynamic characteristics of silica gel–water working pair that is essential for the sizing of adsorption chillers. The experiments incorporated the moisture balance technique, a control-volume-variable-pressure (CVVP) apparatus and three types of silica gel have been investigated, namely the Fuji Davison Type A, Type 3A and Type RD. As evidenced by the experimental results, the Henry-type equation is found to be suitable for describing the isotherm characteristics of silica gel–water working pair at the conditions of adsorption chiller. The regeneration of adsorbent depends on the correct allocation of temperature as well as the amount of regeneration time. From the experiments, the isotherm characteristics of silica gel–water in the low- to high-pressure regimes and hence, its isosteric heat of adsorption will be determined. Key parameters for optimizing the amount of heat recovery such as the cycle and switching time of chiller can also be implied from the measured results.     

Experimental investigation on performance and emissions of a spark-ignition engine fuelled with natural gas–hydrogen blends combined with EGR

An experimental investigation on the influence of different hydrogen fractions and EGR rates on the performance and emissions of a spark-ignition engine was conducted. The results show that large EGR introduction decreases the engine power output. However, hydrogen addition can increase the power output at large EGR operation. Effective thermal efficiency shows an increasing trend at small EGR rate and a decreasing trend with further increase of EGR rate. In the case of small EGR rate, effective thermal efficiency is decreased with the increase of hydrogen fraction; while in the case of large EGR rate, thermal efficiency is increased with increasing of hydrogen fraction. For a specified hydrogen fraction, NO_x concentration is decreased with the increase of EGR rate and this effectiveness becomes more obviously at high hydrogen fraction. HC emission is increased with the increase of EGR rate and it decreases with the increase of hydrogen fraction. CO and CO₂ emissions show little variations with EGR rate, but they decrease with the increase of hydrogen fraction. The study shows that natural gas–hydrogen blend combining with EGR can realize high-efficiency and low-emission spark-ignition engine.     

Experimental investigation on the performance and emissions of a diesel engine fuelled with ethanol–diesel blends

An experimental investigation on the application of the blends of ethanol with diesel to a diesel engine was carried out. First, the solubility of ethanol and diesel was conducted with and without the additive of normal butanol (n-butanol). Furthermore, experimental tests were carried out to study the performance and emissions of the engine fuelled with the blends compared with those fuelled by diesel. The test results show that it is feasible and applicable for the blends with n-butanol to replace pure diesel as the fuel for diesel engine; the thermal efficiencies of the engine fuelled by the blends were comparable with that fuelled by diesel, with some increase of fuel consumptions, which is due to the lower heating value of ethanol. The characteristics of the emissions were also studied. Fuelled by the blends, it is found that the smoke emissions from the engine fuelled by the blends were all lower than that fuelled by diesel; the carbon monoxide (CO) were reduced when the engine ran at and above its half loads, but were increased at low loads and low speed; the hydrocarbon (HC) emissions were all higher except for the top loads at high speed; the nitrogen oxides (NO_x) emissions were different for different speeds, loads and blends.     

Experimental investigation of a natural zeolite–water adsorption cooling unit

In this study, a thermally driven adsorption cooling unit using natural zeolite–water as the adsorbent–refrigerant pair has been built and its performance investigated experimentally at various evaporator temperatures. The primary components of the cooling unit are a shell and tube adsorbent bed, an evaporator, a condenser, heating and cooling baths, measurement instruments and supplementary system components. The adsorbent bed is considered to enhance the bed’s heat and mass transfer characteristics; the bed consists of an inner vacuum tube filled with zeolite (zeolite tube) inserted into a larger tubular shell. Under the experimental conditions of 45 °C adsorption, 150 °C desorption, 30 °C condenser and 22.5 °C, 15 °C and 10 °C evaporator temperatures, the COP of the adsorption cooling unit is approximately 0.25 and the maximum average volumetric cooling power density (SCP_v) and mass specific cooling power density per kg adsorbent (SCP) of the cooling unit are 5.2 kW/m³ and 7 W/kg, respectively.     

Ni–P and Ni–Cu–P modified carbon catalysts for methanol electro-oxidation in KOH solution

The electrocatalytic oxidation of methanol was studied on Ni–P and Ni–Cu–P supported over commercial carbon electrodes in 0.1 M KOH solution. Cyclic voltammetry and chronoamperometry techniques were employed. Electroless deposition technique was adopted for the preparation of these catalysts. The effect of the electroless deposition parameters on the catalytic activity of the formed samples was examined. They involve the variation of the deposition time, pH and temperature. The scanning electron micrography showed a compact Ni–P surface with a smooth and low porous structure. A decreased amount of nickel and phosphorus was detected by EDX analysis in the formed catalyst after adding copper to the deposition solution. However, an improvement in the catalytic performance of Ni–Cu–P/C samples was noticed. This is attributed to the presence of copper hydroxide/nickel oxyhydroxide species. It suppresses the formation of γ-NiOOH phase and stabilizes β-NiOOH form. Linear dependence of the oxidation current density on the square root of the scan rate reveals the diffusion controlled behaviour.     

Experimental investigation of helical Savonius rotor with a twist of 180°

Conventional Savonius rotors have low performance such as low coefficient of power and low coefficient of torque. In order to increase this performance, a helical Savonius rotor with a twist of 180° is proposed. In this paper, we are interested in studying the aerodynamic behavior of the helical Savonius rotors installed in an open jet wind tunnel. Particularly we are interested in studying the influence of variation of Reynolds number and the overlap ratio on the performance of a modified Savonius rotor with aspect ratio of 1.57 at a Reynolds numbers equal to Re = 79,794, Re = 99,578, Re = 116,064 and Re = 147,059. Results conclude that the variation of Reynolds number and overlap ratio has an effect on the global characteristics of the helical Savonius rotor. A comparison between the helical one and the conventional one shows that the maximum power coefficient of the Savonius wind rotor is higher. This work is developed at Laboratory of Electro-Mechanical System (LASEM) of the National School of Engineers of Sfax (ENIS).     

Experimental investigation of energy separation in a counter-flow Ranque–Hilsch vortex tube with multiple inlet snail entries

The energy/temperature separation phenomenon and cooling efficiency characteristics in a counter-flow Ranque–Hilsch vortex tube (RHVT) are experimentally studied. The ascertainment focuses on the effects of the multiple inlet snail entries (N = 1 to 4 nozzles), cold orifice diameter ratios (d/D = 0.3 to 0.7) and inlet pressures (P_i = 2.0 and 3.0 bar). The experiments using the conventional tangential nozzles (N = 4), are also performed for comparison. The experimental results reveal that the RHVT with the snail entry provides greater cold air temperature reduction and cooling efficiency than those offered by the RHVT with the conventional tangential inlet nozzle under the same cold mass fraction and supply inlet pressure. The increase in the nozzle number and the supply pressure leads to the rise of the swirl/vortex intensity and thus the energy separation in the tube.     

Experimental investigation of heat transfer and friction factor with water–propylene glycol based CuO nanofluid in a tube with twisted tape inserts

Convective heat transfer and friction factor characteristics of water/propylene glycol (70:30% by volume) based CuO nanofluids flowing in a plain tube are investigated experimentally under constant heat flux boundary condition. Glycols are normally used as an anti-freezing heat transfer fluids in cold climatic regions. Nanofluids are prepared by dispersing 50 nm diameter of CuO nanoparticles in the base fluid. Experiments are conducted using CuO nanofluids with 0.025%, 0.1% and 0.5% volume concentration in the Reynolds numbers ranging from 1000 < Re < 10000 and considerable heat transfer enhancement in CuO nanofluids is observed. The effect of twisted tape inserts with twist ratios in the range of 0 < H/D < 15 on nanofluids is studied and further heat transfer augmentation is noticed. The increment in the pressure drop in the CuO nanofluids over the base fluid is negligible but the experimental results have shown a significant increment in the convective heat transfer coefficient of CuO nanofluids. The convective heat transfer coefficient increased up to 27.95% in the 0.5% CuO nanofluid in plain tube and with a twisted tape insert of H/D = 5 it is further increased to 76.06% over the base fluid at a particular Reynolds number. The friction factor enhancement of 10.08% is noticed and increased to 26.57% with the same twisted tape, when compared with the base fluid friction factor at the same Reynolds number. Based on the experimental data obtained, generalized regression equations are developed to predict Nusselt number and friction factor.     

Experimental investigation of reaction kinetics of gas–liquid–solid Bunsen reaction in iodine–sulfur process

Iodine–sulfur (IS) cycle is the most promising thermochemical water-splitting process for nuclear hydrogen production. The Bunsen reaction, which produces sulfuric and hydriodic acid for the two decomposition reactions, plays a crucial role for the continuous stable operation of the IS cycle. Insufficient kinetics studies on Bunsen reaction, particularly under the gas–liquid–solid heterogeneous conditions, have caused difficulties for the design of Bunsen reactor, as well as the optimization and improvement of the efficiency of the process. In this work, the reaction kinetics of gas–liquid–solid Bunsen reaction denoted in the pressure drop of SO₂ was experimentally investigated, and the effluences of the main factors, including the initial SO₂ pressure, molar ratio of I₂ to H₂O, temperature, and stirring rate, were studied. In addition, a kinetics model for simulating the heterogeneous reaction was proposed and verified by the experimental data obtained under the three-phase Bunsen reaction conditions.     

Electrocatalytic activity for the hydrogen evolution of the electrodeposited Co–Ni–Mo,Co–Ni and Co–Mo alloy coatings

The electrocatalytic activity for the HER of the ternary Co–Ni–Mo and the binary Co–Ni and Co–Mo alloy coatings is investigated in 1 M KOH solution. The surface morphology and the structure of the studied coatings is characterized by SEM and XRD analysis. The electrocatalytic activity for the HER is evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, cathodic polarization and chronopotentiometry techniques. XRD analysis reveals that all studied coatings are composed of the Co hcp structure. However, alloy deposits with Mo is characterized by more nanocrystalline structure. Electrochemical experiments reveal superior electrocatalytic activity of coatings with Mo in comparison to Co–Ni alloy. This is the results of larger real surface area of Co–Mo and Co–Ni–Mo alloys, which is confirmed by the higher surface roughness factors (R_f) calculated based on the EIS results. The ternary alloy coating is characterized by the highest R_f parameter and the highest catalytic activity for the HER.     

Experimental investigation on a MnCl2–CaCl2–NH3 thermal energy storage system

Thermal energy storage (TES) is regarded as one promising technology for renewable energy and waste heat recovery. Among TES technologies, sorption thermal energy storage (STES) has drawn burgeoning attention due to high energy storage density, long-term heat storage capability and flexible working modes. Originating from STES system, resorption thermal energy storage (RTES) system is established and investigated for recovering the heat in this paper. The system is mainly composed of three high temperature salt (HTS) unit beds; three low temperature salt (LTS) unit beds, valves and heat exchange pipes. Working pair of MnCl₂–CaCl₂–NH₃ is selected for the RTES system. 4.8 kg and 3.9 kg MnCl₂ and CaCl₂ composite adsorbents are filled in the adsorption bed. Results indicate that the highest thermal storage density is about 1836 kJ/kg when the heat charging and discharging temperature is 155 °C and 55 °C, respectively. Volume density of heat storage ranges from 144 to 304 kWh/m³. The highest ratio of latent heat to sensible heat is about 1.145 when the discharging temperature is 55 °C. The energy efficiency decreases from 97% to 73% when the discharging temperature increases from 55 to 75 °C.     

Effect of manufacturing conditions on properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution

The effects of the deposition time and coating bath with various pH and temperatures on the deposition rate, hydrogen generation rate per deposited catalyst of 1 g, surface morphology, catalyst particle distribution, and microstructure of electroless deposited Co–P/Ni foam catalysts were investigated. The degree of the effects of the parameters was in the following order: pH > temperature > deposition time. The effects of heat treatment temperature on the durability and catalytic activity were also investigated. Durability increased slightly in response to heat treatment, but hydrogen generation reduced owing to sodium sintering and oxide film formation. The optimum conditions were 12.0 (pH), 50 °C (temperature), and 30 min (deposition time) without heat treatment. The weight percent of the deposited catalyst and hydrogen generation rate per deposited catalyst of 1 g under the optimum conditions were 4.86 wt% and 1.49 L/min g (deposited catalyst), respectively. The apparent activation energy of the catalyst manufactured under the optimum conditions was 46.8 kJ/mol. The manufacturing conditions considerably affected the catalyst properties.     

Electroless deposition of Ni–Cu–P on a self-supporting graphene with enhanced hydrogen evolution reaction activity

With the increasing issues of the energy crisis and environmental pollution, the development of clean energy has become an urgent task. Herein, self-supporting graphene (SSG) that could serve as the three-dimensional catalyst support is developed by electrochemically intercalating the flexible graphite paper (FGP) in 1 M KOH. Then, the Ni-base alloy is deposited on the SSG by electroless plating. The resulting electrode (Ni–Cu–P/SSG) exhibits excellent hydrogen evolution reaction (HER) electrocatalytic performance in 1 M KOH. The Ni–Cu–P/SSG catalyst just requires the overpotentials of 75 and 219 mV to reach 10 and 100 mA cm⁻², respectively. Besides, the Ni–Cu–P/SSG still maintains superior HER catalytic activity after the stability test of 12 h. The Ni–Cu–P/SSG composite catalyst with high catalytic activity, remarkable stability and facile preparation method has a significant influence on the extension of renewable energy preparation and application.     

Effect of bath composition on properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution

The effect of bath composition on the properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution was investigated by varying the bath composition. The NaH₂PO₂/CoCl₂ and NH₂CH₂COOH/CoCl₂ concentration ratio had a strong effect on the catalyst properties. The effect of NH₂CH₂COOH/CoCl₂ was larger than that of NaH₂PO₂/CoCl₂ for the concentration ratio range with practical deposition rates. The optimum concentration ratio of the coating bath was CoCl₂:NH₂CH₂COOH:NaH₂PO₂ = 1:4:10. As the concentration of each component increased at the optimum concentration ratio, the coating bath decomposed on its own. As the amount of solute dissolved in the coating bath increased, the coating bath became unstable. The optimum composition of the stable coating bath to realize Co–P/Ni foam catalyst with good catalytic activity was 0.1 m (molality, mol/kg) CoCl₂, 0.4 m NH₂CH₂COOH, and 1.0 m NaH₂PO₂. The weight percent of the deposited catalyst and hydrogen generation rate per deposited catalyst of 1 g at optimum composition were 8.39 wt% and 0.93 L/min·g (deposited catalyst), respectively. The bath composition was found to have a great effect on the Co–P/Ni foam catalyst properties and coating bath stability.     

Hydrogen discharge on electrodeposited Ni–Mn–Fe coatings in 30 w⧸o koh

The hydrogen evolution reaction (HER) has been investigated on Ni–Mn–Fe electrocoated cathodes in 30 w⧸o KOH at 30°C. Ni–Mn–Fe alloys were electrodeposited on mild steel as thin coatings from sulphate baths with ammonium sulphate as additive. The effects of bath composition and deposition current density have been studied. The cathodes were pre-electrolysed at a cathodic current density i_c of 500 mAcm⁻² for 30 min before the kinetic parameters of the HER were determined. Ni–Mn–Fe coatings plated from Ni-rich electrolytes and at very high current densities showed improved activity towards the HER in 30 w⧸o KOH due to significant increase in the exchange current density. Microstructure examinations indicated that the superior electrocatalytic activity, seen in coatings obtained at high deposition current densities, is due to the presence of multi-textures. The coatings, in which formation of nanocrystalline grains and development of voids at grain interfaces occurs, exhibit the maximum electrocatalytic activity towards the HER.