Effect Of Hydrogen Flow Rate Research Articles

Effect of hydrogen flow rate on microstructure and tribological properties of plasma-sprayed Cr2O3-65%TiO2 composite coatings

Atmospheric plasma spraying was used to deposit CT65 (Cr2O3-65 wt%TiO2) ceramic composite coatings on 304 stainless steel substrates. Coating structure, hardness, and compactness were evaluated by varying hydrogen flow rates (4, 6, and 8 L/min). The CT65 coating generated a slight phase change under different hydrogen flow rates, and the (Cr0.88, Ti0.12)2O3 solid solution phase was detected in the coating. The friction coefficients of these three coatings were maintained between 0.32 and 0.36. Increasing hydrogen flow rate reduced coating wear rate and transitioned wear mechanism from abrasive to adhesive. Friction film consisted of counterpart material transfer and coating solid solution. In addition, a wear behavior model diagram illustrated the friction-induced wear mechanism of CT65 composite coatings.

Analysis of polarization characteristics and optimal operating conditions for industrial-sized SOFC based on comparison with button cells

Although button solid oxide fuel cells (SOFCs) have been extensively used in fundamental research, practical commercial applications are developed on industrial-sized SOFCs. As the active area and fuel utilization increase, some issues that are not considered in button cells become essential. Therefore, it is necessary to focus on the differences between button cells and industrial-sized cells, including their polarization characteristics and performance evaluation. In this study, the polarization curves of both types of cells under different hydrogen flow rates are tested. Both types of cells experience a sudden increase in total area-specific resistance (Rtot) under high current density. However, the effects of hydrogen flow rate differs between cell types. Based on the equivalent circuit model (ECM) fitting of electrochemical impedance spectroscopy (EIS) measured under different DC biases and the theoretical calculation of gas diffusion and gas conversion resistances, it is demonstrated that the rapid increase in Rtot in button cells is primarily attributed to gas diffusion through the anode. In contrast, non-uniform gas distribution along the flow channel direction results in a dominant role of gas conversion resistance on Rtot in industrial-sized cells, especially at hydrogen flow rates below 0.4 L min−1. Although electrical efficiency is often overlooked in button cells, it is a crucial performance evaluation index in industrial-sized cells. The impact of operating parameters on power density and electrical efficiency is analyzed, revealing a trade-off between the two. With the critical Nernst electromotive force of Ni oxidation as the voltage lower limit, the optimal operating conditions with high electrical efficiency and prevention of Ni oxidation under different flow rates are obtained. It is investigated that operation should be carried out at a low flow rate below 0.3 L min−1 to achieve high electrical efficiency of over 50%. The selected operating parameters will change when the cell performance or load demand changes. However, the analysis method proposed in this paper can still provide a reference for selecting the operating parameters of a SOFC system.

Experimental evaluation of a 1 kW proton exchange membrane fuel cell with resistive, DC and AC loads

In this communication, an experimental investigation is carried out on a PEM (Proton Exchange Membrane) fuel cell. A small-scale standalone PEM fuel cell system of 1 kW capacity is demonstrated in the present study. The fuel cell is connected to the charge controller, and the charge controller is further connected to the DC and AC loads to study the fuel cell characteristics. A battery bank backup is also provided to account for the stable power output from the fuel cell. The purpose of the study is to determine the fuel cell's performance when operated with resistive, AC, and DC loads (home appliances within the rated power range). The effect of hydrogen flow rates on the power output is also presented in this paper. The DC and AC loads are connected to the fuel cell setup to study the characteristics of the fuel cell. From the study, it can be observed that the performance of the fuel cell is better at higher flow rates of hydrogen. The experimental results showed that the maximum power obtained was 986.8 W at a hydrogen supply rate of 15 LPM. The maximum fuel cell efficiency was found to be 44% at the flow rate of 8 LPM. The charge controller efficiency reported for DC and AC load connections is 94.97% and 96.98%, respectively. The inverter efficiency was observed to increase with the current value, with the maximum value reaching around 98.86%.

Effect of hydrogen flow rate on the synthesis of carbon nanofiber using microwave-assisted chemical vapour deposition with ferrocene as a catalyst

Carbon nanostructure materials are becoming of considerable commercial importance, with interest growing rapidly over the decade since the discovery of carbon nanofibers. In this study, a new novel method is introduced to synthesize the carbon nanofibers by gas-phase, where a single-stage microwave-assisted chemical vapour deposition approach is used with ferrocene as a catalyst and acetylene and hydrogen as precursor gases. Hydrogen flow rate plays a significant role in the formation of carbon nanofibers, as being the carrier and reactant gas in the floating catalyst method. The effect of process parameters such as microwave power, radiation time and gas ratio of C2H2/H2 was investigated statistically. The carbon nanofibers were characterized using scanning and transmission electron microscopy and thermogravimetric analysis. The analysis revealed that the optimized conditions for carbon nanofibers production were microwave power (1000 W), radiation time (35 min) and acetylene/hydrogen ratio (0.8). The field emission scanning electron microscope and transmission electron microscope analyses revealed that the vertical alignment of carbon nanofibers has tens of microns long with a uniform diameter ranging from 115 to 131 nm. High purity of 93% and a high yield of 12 g of CNFs were obtained. These outcomes indicate that identifying the optimal values for process parameters is important for synthesizing high quality and high CNF yield.

In-containment hydrogen behavior simulation and hydrogen concentration control under LBLOCA accidents

During a design basis accident in a pressurized water reactor (PWR), the released hydrogen through reactor breaks would induce the hydrogen detonation. The hydrogen passive autocatalytic recombiner (PAR) is widely used as a hydrogen elimination measure in nuclear power plants due to its passive capability, low starting threshold and easy installation. The present work aims to study the hydrogen risk after the occurrence of cold section double-end shear fracture large break loss coolant accident (LBLOCA) by using the 3D computational fluid dynamics program GASFLOW. A full containment model of CPR1000 is built. The hydrogen production rate inside the containment after LBLOCA is calculated from the related physicochemical reactions. The hydrogen transport, hydrogen concentration distribution and temperature distribution inside the containment are simulated. The effects of different roughness of the structure surface on the simulation are investigated, and it is proved that the operation of PAR can control the hydrogen concentration under the safety threshold of 4 vol%. The effects of hydrogen flow rate and PAR’s position on the hydrogen elimination efficiency are studied. Based on these studies, this paper makes some suggestions and theoretical references for the spatial arrangement scheme of PAR in the containment to optimize the hydrogen elimination efficiency.

Effect of hydrogen flow rate and particle diameter on coal-hydrogen-air rotating detonation engines

Rotating detonation engines having the advantages of high thermal efficiency theoretically, are being studied widely. Cheap solid fuels such as coals may decrease the cost. Experiments have proved the feasibility of gas-solid two-phase rotating detonation, but there is a lack of numerical simulations to fully show the flow field. In this study, numerical simulations of two-dimensional non-premixed coal-hydrogen-air rotating detonation engines were carried out to study the flow filed. Unsteady viscous two-phase model with volumetric reactions and kinetics/diffusion-limited rate model for the surface combustion were employed. Results show that the hydrogen-air reaction dominated the propagation of the rotating detonation wave. The instability occurred on the contact surface seriously when the hydrogen flow rate was 1.5 kg/s. As the particle diameter increased, the detonation velocity increased first and then kept almost constant.

Effect of hydrogen flow rates on the performance of two biodiesels fuelled dual fuel engine

In the present research work, effect of hydrogen (H₂) flow rate, on the performance of modified dual fuel (DF) engine powered with two biodiesels is studied. Biodiesels derived from Jack fruit seed (JKFSDOB) and Nigella Sativa oils (NLSTVAOB) and their B20 blends are used as pilot injected fuels while H₂ is used as the manifold inducted fuel in the modified DF engine. Further influence of H₂ gas flow rate on the modified DF engine by using conventional mechanical fuel injection (CMFIS) for optimal performance of engine is investigated. Increasing the hydrogen gas flow rates reduces brake thermal efficiency (BTE), smoke, CO (Carbon monoxide) and HC (Hydrocarbon) emissions while NOx (Nitric oxide) emissions from DF engine increased. The engine operated by renewable fuel combinations of biodiesels and H₂ in DF mode engine can facilitate partial as well as complete substitution for fossil fuels and reduce the greenhouse gas emissions.

Effects of hydrogen flow rate, injection pressure and EGR on performance of common rail direct injection (CRDi) engine in dual fuel mode

PurposeThe different performance tests were conducted on diesel engine compression ignition (CI) mode and CRDi engine.Design/methodology/approachThe CI engine was suitably modified to CRDi engine with Toroidal re-entrant combustion chamber (TRCC) and was run in dual-fuel (DF) mode. Hydrogen (H2) was supplied at different flow rates during the suction stroke, and 0.22 Kg/h of hydrogen fuel flow rate (HFFR) was found to be optimum. Diesel and biodiesel were used as pilot fuels. The CRDi engine with DF mode was run at various injection pressures, and 900 bar was found to be optimum injection pressure (IP) with 10o before top dead center (bTDC) as fuel injection timing (IT).FindingsThese operating engine conditions increased formation of oxides of nitrogen (NOx), which were reduced by exhaust gas recycle (EGR). With EGR of 15%, CRDi engine resulted in 12.6% lower brake thermal efficiency (BTE), 5.5% lower hydrocarbon (HC), 7.7% lower carbon monoxide (CO), 26% lower NOx at 80% load as compared to the unmodified diesel engine (CI mode).Originality/valueThe current research is an effort to study and evaluate the performance of CRDi engine in DF mode with diesel-H2 and BCPO-H2 fuel combinations with TRCC.

Experimental and modeling study on dynamic characteristics of a 65 kW dual-stack proton exchange membrane fuel cell system during start-up operation

Dynamic characteristics of multi-cell voltage in a non-loaded proton exchange membrane fuel cell (PEMFC) system during the start-up process are critical for the lifetime of a fuel cell stack. The effects of hydrogen flow rate and initial gas species in the anode compartment are experimentally studied with a 65 kW dual-stack PEMFC system. The individual cell voltages are measured using a cell voltage monitor (CVM) device and their statistic characteristics are analyzed. Furthermore, a model comprised of a hydrogen flow network model and an equivalent electrical circuit model is developed to simulate the individual cell voltage variation during start-up. Numerical and experimental results show excellent agreement. Finally, internal current and voltage distributions in a single cell model and multi-cell stack model are investigated and discussed. A large hydrogen flow rate is beneficial to reduce the serious local carbon corrosion caused by capacitance effect. The revealed dynamic characteristics of multi-cell voltage of the dual-stack are beneficial for the PEMFC system integration and optimization of control strategy during start-up operation.

The Effects of Hydrogen Flowrate during Pre-Annealing on Graphene Growth by Chemical Vapor Deposition Using Methanol as a Liquid Carbon Precursor

Studying an influence of several parameters on Chemical Vapor Deposition (CVD) used for graphene synthesis is crucial to optimizing the graphene quality to be Compatible with advanced devices. The effect of different hydrogen (H2) flow-rates (0, 50, 100, 150, 200, 250, and 300 sccm) during the pre-annealing process on CVD grown graphene have been reported. This study revealed that hydrogen flow rates during annealing changed the surface roughness/smoothness of the copper substrates. For high hydrogen flow rates, the smoothing effect was increased. Furthermore, the annealed graphene samples emerged a deferent number of layers because of morphological surface changes. According to Raman D- to G-band intensity ratios (ID/IG), the graphene quality was influenced by the annealing hydrogen flowrate. The visible light transmittance values of the grown graphene samples confirmed a few number of layers (mono to seven-layer). Mostly, the samples which annealed under moderate hydrogen flow rates showed less defects intensities and higher crystallite sizes.

Studying the effect of spraying parameters on the sintering of YSZ TBC using APS method

Plasma spray coatings 8YSZ (Zirconia stabilized with 8 wt% Yttria) are widely used for the protection of gas turbine parts against heat. Operating temperature of turbine engine causes sintering of the coating and this alters the microstructure of the coating. Sintering rate is dependent on the primary microstructure of the coating. The objective of this study is to compare the effect of spraying parameters on the sintering rate of YSZ TBC. Therefore, the effect of Hydrogen flow rate, powder feed rate and spray angle on sintering was studied. Sintering in constant temperature of 1100 °C for 10, 20, 50, 100 and 150 h was conducted in the environment atmosphere furnace. Microstructure studying was conducted using OM and FESEM and phase studying was conducted with XRD. Porosity and hardness measurement were considered as a measure of sintering. The results showed that the initial conditions of the coatings (the size and quantity of pores and residual stress) have a tremendous impact on the sintering behavior, such that a higher percent of the pores and smaller porosities increase sintering rate.

Development of Zhundong subbituminous coal char structure during hydrogasification under high pressure

In this study, the hydrogasification of Zhundong subbituminous coal char was performed in a pressurized fixed-bed reactor. The effects of hydrogen flow rate, char particle size, reaction temperature, hydrogen pressure, and char preparation temperature on hydrogasification reaction rate were investigated. Results showed hydrogasification was controlled by chemical reaction when hydrogen flow exceeded 1.5 L/min, particle size was less than 74 μm, and temperature was below 1123 K. The pore structural development of char during hydrogasification was studied using the nitrogen adsorption/desorption method. Two fractal dimensions were calculated based on fractal Frenkel–Halsey–Hill theory. Results indicated that the development of pore structure could be classified into three stages: the rapid formation of micropores in the initial stage, the increase in the amount of mesopores as a result of pore coalescence in the second stage, and the collapse of pores in the final stage. Fractal dimensions increased with carbon conversion in the beginning of hydrogasification, which indicated the well-developed pore structure and surface morphology of char. However, as reaction continued, the fractal dimensions decreased with carbon conversion due to the coalescence and collapse of pores, thereby reflecting a smoother surface of char. This finding was consistent with the result of scanning electron microscopy.

Deposition, nanostructure and phase composition of suspension plasma-sprayed hydroxyapatite coatings

Nanostructured hydroxyapatite (HA) coatings were successfully deposited on stainless steel substrates by suspension plasma spray (SPS) method. The suspension was prepared by a wet chemical method using Ca(NO3)2 and (NH4)2HPO4 as source materials. The TEM morphologies show that these HA particles are needle-like nanowires. The effect of hydrogen flow rate of plasma forming gas on the coating properties has been intensively studied. FE-SEM images confirm that coatings are nanostructured. X-ray diffraction pattern shows that as-sprayed coatings are HA phases and the crystal size is estimated to be less than twenty nanometers when low hydrogen flow rate is used. When high hydrogen flow rate is utilized, secondary phases appear in the as-sprayed HA coatings and the crystal size increases to dozens of nanometers. Fourier transform infrared spectroscopy and MicroRaman spectroscopy indicate the significant presence of OH− and CO32- ions in the coatings.

An experimental study of response surface methodology to optimise the operating parameters on PEM fuel cell

In this study, the effects of hydrogen flow rate, oxygen flow rate, cell and humidification temperature on power density were examined experimentally. The experiments have been carried out on a single proton exchange membrane (PEM) fuel cell with the active area of 25 cm². Response surface methodology (RSM) was used to determine the optimum conditions of PEM fuel cell by Design-Expert 8.0 (trial version). It was found that temperature had an important effect on the performance of PEM fuel cell by the results of experiments. Increasing both cell and humidification temperature increased the performance of the fuel cell system. Even cell performance decreases after exceeding a definite temperature. An increase occurred in performance at low cell potential with increasing the hydrogen flow rates. And, maximum power density, whose value was 0.5495 mW/m², was reached at these conditions of 0.4 V, 5 L/min hydrogen flow rate, 70°C humidification temperatures and 40°C cell temperatures.

Effect of hydrogen carrier gas on AlN and AlGaN growth in AMEC Prismo D-Blue® MOCVD platform

Effect of hydrogen flow rate on AlN and AlGaN growth is investigated in AMEC Prismo D-Blue® MOCVD platform. It is found that AlN growth rate increases with the increase of hydrogen flow rate. Al composition in AlGaN material increases initially with the increase of hydrogen flow rate at relatively low hydrogen flow rates (<120slm) and then saturates at high hydrogen flow rates. GaN partial growth rate shows a “U” shaped profile. Computational fluid dynamics (CFD) simulation of AlN growth is performed to understand the growth mechanism. The simulation results indicate that higher hydrogen flow rate could suppress the parasitic reaction and particle formation during AlN growth. Thus more source gases can be transported to the wafer surface, resulting in the increase of AlN growth rate.

Synthesis of Nitrogen‐Doped Carbon Nanotubes Using Injection‐Vertical Chemical Vapor Deposition: Effects of Synthesis Parameters on the Nitrogen Content

Nitrogen‐doped CNTs (N‐CNTs) were synthesized using an injection‐vertical chemical vapor deposition (IV‐CVD) reactor. This type of reactor is quite useful for the continuous mass production of CNTs. In this work, the optimum deposition conditions for maximizing the incorporation of nitrogen were identified. Ferrocene served as the source of the Fe catalyst and was dissolved in acetonitrile, which served as both the hydrocarbon and nitrogen sources. Different concentrations of ferrocene in acetonitrile were introduced into the top of a vertically aligned reactor at a constant flow rate with hydrogen serving as the carrier. The effects of hydrogen flow rate, growth temperature, and catalyst loading (Fe from the ferrocene) on the microstructure, elemental composition, and yield of N‐CNTs were investigated. The N‐CNTs possessed a bamboo‐like microstructure with a nitrogen doping level as high as 14 at.% when using 2.5 to 5 mg/mL of the ferrocene/acetonitrile mixture at 800°C under a 1000 sccm flow of hydrogen. A production rate of 100 mg/h was achieved under the optimized synthesis conditions.

Thermal Oxidation Kinetic of Carbon Nanotubes (CNTs)

Aligned multi-wall carbon nanotubes (CNTs) were synthesized by a catalytic cracking chemical vapor deposition (CC-CVD) method. The effects of hydrogen flow rates and hydrocarbon amounts were studied to selectively synthesize carbon nanomaterials at high yield, high purity, and high quantity. Iron nanoparticles that were produced from the thermal decomposition of iron oxide on the surface of aluminum oxide powder were used as a catalyst for the synthesis of the carbon structures. The effects of different hydrogen flow rates (10–700 ml/min) and the amount of ethylene gas (50–700 ml/min) on the morphology, quality and quantity of the product were investigated. The thermal oxidation kinetics of CNTs was investigated by dynamic thermogravimetry, in an air atmosphere, over the temperature range 25–800 °C and at constant nominal heating rate 10 °C/min. The corresponding activation energies, frequency factors, and reaction orders were determined.

Kinetics and Mechanism of Ni/Zeolite-Catalyzed Hydrocracking of Palm Oil into Bio-Fuel

Kinetics and mechanisms of Ni/zeolite-catalyzed cracking reaction of methyl ester palm oil (MEPO) were studied using a continuous flow-fixed bed reactor system at an atmospheric pressure. The catalyst was prepared by wet impregnation method with a solution of nickel nitrate hexahydrate as the precursor and zeolite as carrier. The characteristics of catalyst including active Ni metal content, crystallinity, total acidity, and porosity were evaluated. The reactions were performed with a varied hydrogen flow rate as a carrier gas as well as a reductant and reaction time. Liquid products were analyzed by GC. Analysis by GC-MS was only conducted on a product at hydrogen flow rate with the best conversion. It has been shown that the catalyst has a superior character for hydrocracking reactions of MEPO into green fuel. No considerable effect of hydrogen flow rate on the total conversion was observed. The tests showed that the kinetics of Ni/zeolite-catalyzed cracking reaction followed pseudo-first order kinetics. GC-MS analysis revealed the formation of light hydrocarbon products with C6-C8 of aliphatic and cyclic components without oxygenates. Distribution of the product indicated that the cracking reaction as well as the isomerization of the products of hydrocracking occurred. Thus, Ni/zeolite-catalyzed cracking involved cracking /hydrogenation, isomerization, cyclization, and deoxygenation.

Effects of hydrogen doping on surface and discharge properties of MgO thin films grown by ion plating

Magnesium oxide (MgO) thin films with a high crystallinity and a preferred (1 1 1) orientation were prepared by an ion plating technique and the effects of hydrogen flow rates on their structural, surface, optical and discharge properties were investigated. Dependence on hydrogen flow rates has a quadratic curve type characteristic with an inflection point at a hydrogen flow rate of 60 sccm. The results indicated that the controlled grain shape and the size of MgO film grown under an optimal hydrogen doping condition affect the surface, microstructure and defect states in the MgO films, resulting in a reduction in the discharge delay time of ac plasma display panels significantly.

Effects of hydrogen flow rate on the growth and field electron emission characteristics of diamond thin films synthesized through graphite etching

Diamond film deposition on silicon was explored using our newly developed graphite etching technology in a microwave plasma reactor. The effects of hydrogen flow rate on the growth rate, morphology and field electron emission properties of the synthesized diamond were investigated systematically. The growth rate and nucleation density of diamond films increased significantly with the decrease of hydrogen flow rate. Nanocrystalline diamond films were obtained with a low hydrogen flow rate (i.e. 3 sccm or lower). Diamond quality is improved and the growth rates are much higher in this graphite etching process, compared to conventional H 2 + 1% CH 4 gas mixture. The results suggest that diamond growth is enhanced by activated hydrocarbon radicals formed through in-situ etching of graphite by atomic hydrogen. The turn-on electric field decreased and the emission current increased with the decrease of the hydrogen flow rate. The enhanced field electron emission property of the diamond films synthesized at lower hydrogen flow rate is attributed to the decreased diamond grain size because the small diamond grains increase the electron conduction channels which facilitate the electron transport inside diamond films.