Effect of melt-to-solid volume ratio and preheating temperature on Mg/Al bimetals interface by centrifugal casting

Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.

Electronically Controlling the System of Preheating Intake Air by Flame for Diesel Engine Cold-Start

In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.

Performance of Ti6Al4V fabricated by electron beam and laser hybrid preheating and selective melting strategy

Electron beam selective melting(EBM)and selective laser melting(SLM)are regarded as significant manufacturing processes for near-net-shaped Ti6Al4V components.Generally,in the conventional EBM process,preheating is necessitated to avoid"smoke"caused by the charging of electrons.In the conventional SLM process,laser as an energy source without the risk of"smoke"can be employed to melt metal powder at low temperatures.However,because of the low absorption rate of laser,the powder bed temperature cannot reach a high level.It is difficult to obtain as-built TiAl4V with favorable comprehensive properties via conventional EBM or SLM.Hence,two types of electron beam and laser hybrid preheating(EB-LHP)combined with selective melting strategies are proposed.Using laser to preheat powder allows EBM to be performed at a low powder bed temperature(EBM-LT),whereas using an electron beam to preheat powder allows SLM to be performed at a high powder bed temperature(SLM-HT).Ti6Al4V samples are fabricated using two different manufacturing strategies(i.e.,EBM-LT and SLM-HT)and two conventional processes,i.e.,EBM at a high powder bed temperature(EBM-HT)and SLM at a low powder bed temperature(SLM-LT).The temperature-dependent surface quality,microstructure,density,and mechanical properties of the as-built Ti6Al4V samples are characterized and compared.Results show that EBM-LT Ti6Al4V exhibits a higher ultimate tensile strength(981±43 MPa)and a lower elongation(12.2%±2.3%)than EBM-HT Ti6Al4V owing to the presence ofα′martensite.The SLM-HT Ti6Al4V possesses the highest ultimate tensile strength(1,059±62 MPa)and an elongation(14.8%±4.0%)comparable to that of the EBM-HT Ti6Al4V(16.6%±1.2%).

Nonlinear Evolution of Jet-Like Spikes from the Single-Mode Ablative Rayleigh-Taylor Instability with Preheating

In this research, the nonlinear evolution of jet-like spikes in the single-mode ablative Rayleigh-Taylor instability （ARTI） in the presence of preheating, is studied numerically. It is demonstrated that the preheating plays an essential role in the formation of jet-like spikes in the nonlinear ARTI. The evolution of jet-like spikes in the ARTI with preheating consists of three stages with distinctly different distinguishing features. In the early stage, the preheating contributes to significantly increase the density-gradient scale length and broaden the velocity profile of the ablation surface, where the former can reduce the linear growth of the ARTI and mitigate the growth of its harmonics. In the middle stage, the ablative Kelvin-Helmholtz instability is dramatically suppressed due to the ablation effects. In the late stage, the jet＇s length （i.e. bubble-spike amplitude） is further increased by the bubble acceleration in the highly nonlinear ARTI, resulting eventually in the formation of jet-like spikes.

Effect of ECAE Preheating on Grain Refining of Nickel-Titanium Alloy

The influence of equal channel angular extrusion preheating on the microstructure of NiTi was examined. Temperatures under non-isothermal condition is 750, 850 and 950 ℃, and ram speed was 25 mm·s^(-1). The micrographs showed that processing by each of the three temperatures via ECAE can refine the initial coarse grains of NiTi (as-received) after the first pass, and the developments of microstructure were quite different under different hot-working conditions. The influence of ECAE preheating (including temperature and time) on the microstructure of nickel-titanium was analyzed.

Nanosecond laser preheating effect on ablation morphology and plasma emission in collinear dual-pulse laser-induced breakdown spectroscopy

Focus-offset collinear dual-pulse laser-induced breakdown spectroscopy is designed and used to investigate the laser ablation and spectral intensity with an aluminum alloy sample.The laser crater morphologies and ablation volumes were measured.An inter-pulse time delay dependent ablation efficiency on a nanosecond laser-heated sample was observed,which was similar to the trend of spectral intensity versus inter-pulse time delay in the delay time less than 3μs.Based on the observation,the nanosecond pulse laser preheating effect on subsequent second laser ablation and signal enhancement is discussed,which will be helpful for understanding the ablation and signal enhancement mechanism in the standard collinear DP-LIBS technique.

Investigation on preheating process in SLS machine

Selective laser sintering (SLS) is an important Rapid Prototyping method because its wide range of materials. The powder is fused and processed into a part because it is heated in the process. Preheating of powder on the surface of powder bed is a one important process which is a guarantee by which parts can be successfully fabricated and influences accuracy of parts fabricated in SLS technology. The uniformity of temperature on powder bed influences accuracy and performance of parts. It is necessary to understand the influences of the parameters of preheating set on uniformity of temperature on surface of powder bed. This paper analyzes general preheating process of irradiator for the preheating of powder on the surface of powder bed during SLS processing, and investigates influences of the flux density on the temperature field on the top surface of powder bed. The models of distribution of flux density and the distribution of surface temperature of powder bed are presented. The result predicted according to the models is reasonably consistent with experimental result. This model plays important role in design of preheating set and control of SLS processing. It is concluded that the uniformity of temperature field on the powder bed is determined mostly by the geometry of heating component and its fix location and the flux density is inverse proportional to the highness.

Effect of groove angle and preheating temperature on temperature profile and fluid velocity in weld pool

The three dimensiotud transient weld pool dynamics are numerically analyzed ,for Forcearc welding, which is a new gas metal arc welding technology to get deep fusion penetration with smaller angle sf V groove to enhance welding efficiency significantly. The influence of groove angle and preheatin,g temperature on heat and .fluid .flow is studied and compared to get an optimal welding parameter. Good agreement is shown between the predicted and experimental results, such as weld bead cross-section and thermal cycles. It can he seen that an apprpriate groove angle could be used to replace high preheating temperature to get inproced penetration and thermal cycles.

The influence of preheating on microstructure and properties of the cladding layer with plasma arc powder surfacing

In this paper, the influence of preheating on the layer microstructure and properties is analyzed in the layer metal microstructure. The influence of preheating temperature on the shape and amount of primary carbides and borides little, but on initial γ-dendrites is large. With the increasing of preheating temperature, little by little the γ-dendrites , which grown from parent material to layer, are flourishing to disappearing, and the microhardness at the center of the layer is increasing.

Studying the Preheating Effect on Certain Mechanical Properties of the Coating Layer by Vacuum Ion Plasma Coating

The present paper is concerned with the study of two main points: clarifying the effect of preheating on the surface microscopic shape of coating layer by vacuum ion plasma coating technology and on the amount of micro-hardness besides studying the properties of the surfaces that concern the parts of the mechanical system because of their direct and active effect on the machine efficient performance and machine life in general and their important effect on the product efficiency. As known, the instruments that measure the traditional roughness give us numbers and charts that, to a certain extent, describe the actual state of the surface shape within limited range of accuracy, but it has become necessary to find more accurate methods that suit the development obtained in industry, namely, the important applications like aircraft missiles and others. One of the suggested solutions for this is to get benefit of average fractal dimension for the surface by the help of the new technologies which, in return, help in the possibility to determine the surface state with high accuracy that matches the importance of application.

Effect of Preheating Temperature on the Mechanical and Fracture Properties of Welded Pearlitic Rail Steels

The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 300℃, 350℃ and 400℃?before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200℃ preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness KI for the parent rail was 127 MPa.m0.5, while that for the optimum welded joint (200℃ preheat) was 116.5 MPa.m0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200℃ preheat.

Constraints on real scalar inflation from preheating using LATTICEEASY

In this paper,we undertake a detailed study of real scalar inflation using LATTICEEASY simulations to investigate preheating phenomena.Generally,the scalar inflation potential with non-minimal coupling can be approximated using a quartic potential.We observe that the evolutionary behavior of this potential remains unaffected by the coupling coefficient.Furthermore,the theoretical predictions for the scalar spectral index(n_(s))and tensor-toscalar power ratio(r)are independent of this coefficient.Consequently,the coefficients of this model are not constrained by Planck observations.Fortunately,the properties of preheating after inflation provide a viable approach to examining these coefficients.Through LATTICEEASY simulations,we trace the evolution of particle number density,scale factor,and energy density during the preheating process.Subsequently,we derive the parameters,such as the energy ratio(γ)and the e-folding number of preheating(N_(pre)),which facilitate further predictions of n s and r.We successfully validate real scalar inflation model using preheating in LATTICEEASY simulations based on the analytical relationship between preheating and inflation models.

A novel preheating method for the Li-ion battery using supercooled phase change materials

The Li-ion battery is widely used in power tools, energy storage systems, and electric vehicles. In reality, battery thermal management is essential to control the battery temperature within a specific temperature range. Although research has shown that preheating the battery at low temperatures on cold days can improve output performance significantly, few efforts have been made to study the preheating method in-depth. As a result, this research proposes two preheating designs for cylindrical batteries with supercooled phase change materials: Single-and dual-phase change material(PCM) designs. A mathematical model is developed to analyze the effect of the PCM layer’s height, thickness, and mass on the preheating effect for seven candidate PCMs with high supercooling degrees. Furthermore, the economic efficiency of the single-PCM design with different PCMs is compared. In addition, the optimal ratio of the PCMs’ height for the dual-PCM design is investigated. Eventually, the improvement of the battery’s output performance is discussed. The results reveal that the proposed designs can effectively preheat the battery with a temperature rise higher than 10°C. The single-PCM design using Li NO3·3H2O shows the best preheating ability, while CH3COONa·3H2O is the most economical. Although the dual-PCM design cannot outperform the single-PCM design, it can preheat the battery twice and show better flexibility. Compared with the battery without preheating, a 26650-format battery with the single-PCM design can prolong the operating time by 38.8 min and save the electric quantity by 2.1 A h;while they are by 42.8 min and 2.3 A h with the dual-PCM design.

Coal-Biomass Preheating Combustion Characteristics in Cement Precalciner.Part 1:Preheating of Coal/Biomass

The co-combustion of biomass and coal can positively impact the environment and reduce the cost of power generation.However,biomass fuels have many limitations.Circulating fluidized bed(CFB)preheating combustion is suitable for co-combusting coal and biomass because of better fuel adaptability.In the cement industry,fuel combustion and raw meal decomposition in precalciners affect cement quality and cause pollutant emissions.The preheating combustion method used in precalciners can improve combustion performance and reduce NO_(x)emissions.This study investigated the preheating characteristics of a coal-biomass mixed fuel in a cement precalciner.The effects of load,biomass type,and biomass proportion on the preheated fuel and the conditions of the CFB were investigated.The results indicated that a lower load reduces the combustible components in gaseous and solid preheated fuels.However,due to the gas volume remains constant under different loads,a lower load also increases temperature and intensifies the reaction.The carbon chain and microscopic structural activities of preheated fuels are considerably enhanced,facilitating their combustion in precalciners and reducing nitrogen oxides in rotary kilns.Furthermore,adding biomass can improve the reactivity of a fuel subjected to preheating.Thus,biomass fuels(e.g.,rice husks)exhibit high combustion efficiency,and thus high energy utilization.The present study achieved better pore structure and molecular activity using preheated fuel from a CFB preheater.In addition,the improvement of pore structure and molecular activity increases with the proportion of the biomass.

Experimental investigation and optimization of the gasification parameters of macadamia nutshells in a batch-fed bubbling fluidized bed gasifier with air preheating

Gasification of biomass waste has a significant potential to reduce environmental impact and promote sustainability by producing syngas,which is considered as renewable energy.This work investigated the gasification of macadamia nutshells in air-preheated,batch-fed fluidized bed gasifier.The study conducted a parametric analysis to assess the effect of equivalence ratio(ER)and air temperature on the gasifier temperature profile and its performance based on gas composition,higher heating value(HHV),and gas yield.The research was conducted within the range of 0.15-0.35 for the ER and 25-825℃ for the air temperature.Multi-objective numerical optimization was conducted using response surface methodology(RSM).From the parametric study,a distinct temperature profile was observed along the gasifier height,with the peak temperature near the top of the fluidized bed section and the lowest temperature at the top of the gasifier.Air preheating mostly favored gasification temperature at the lower part of the gasifier and showed rare significance at the top.No improvement in gasifier performance was observed beyond an air temperature of 620℃,which was identified as the ideal air-preheating temperature.Analysis of variance(ANOVA)revealed that the ER was the most influential parameter in the production of combustible gasses,syngas HHV and gas yield.Air preheating did not have a significant effect on methane production and gas yield.The most optimal values for ER and air temperature were obtained as 0.195℃ and 620℃,respectively,producing optimal values of 9.54,14.65%,2.03,4.02 MJ⋅Nm^(-3),and 1.82 Nm^(3)⋅kg^(-1) for hydrogen,carbon monoxide,methane,HHV,and gas yield,respectively.

Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

Preheating Combustion Characteristics of Ultra-Low Volatile Carbon-Based Fuel

Pulverized coal combustion technology with preheating solid fuel in a circulating fluidized bed was used for the combustion test of ultra-low volatile carbon-based fuel.This paper first validated the feasibility and advantages of applying the combustion technology to this kind of fuel.The carbon-based fuel could achieve a stable preheating process in this test system.After the preheating,the apparent sensible heat of the fuel was significantly increased.This provided a necessary condition for the stable ignition and efficient combustion of the carbon-based fuel in the post-combustion chamber.The relative proportions of CO,H2,and CH4 in preheated coal gas were very low,and the effect of high-temperature coal gas at the entrance of the post-combustion chamber was greatly impaired,indicating that the combustion process in post-combustion chamber was mainly the combustion of preheated char.At the same time,the strong reducing atmosphere in the circulating fluidized bed also facilitated the reduction of fuel-nitrogen into N2,which resulted in low NOx emissions.On this basis,with the combination of preheating combustion technology and air-staging combustion technology,the NOx emissions had drastically decreased when the burnout air distribution position moved down or varied from a single-layer distribution to a multi-layer distribution system.The lowest original NOx emissions were 90.6 mg/m3(at 6%O2),and the combustion efficiency exceeded 97%,which ultimately achieved efficient and clean combustion of ultra-low volatile carbon-based fuel.

Experimental Investigation of Cutting Nitrogen Oxides Emission from Cement Kilns using Coal Preheating Method

The large consumption of coal in cement industry leads to a significant nitrogen oxide(NO_(x))emission,which has caused severe atmospheric pollution due to the existing low-efficiency denitration technologies.In this research,a fuel pretreatment method on the concept of coal preheating was proposed to reduce NO_(x)emission from cement kilns.A special bench-scale experiment was designed to verify the feasibility of the proposed method.Experimental results showed that the proposed method could achieve high combustion efficiency,steady operation and low NO_(x)emission.The maximum reduction efficiency of primary NO in kiln gas reached 91.4%while the lowest NO_(x)emission was 145 mg/m^(3)(@10%O_2)during the experiment.The effects of key parameters on NO_(x)emission and primary NO_(x)reduction efficiency were comprehensively investigated.It was found that primary and secondary air ratios determined the oxygen content in the flue gas and the reaction temperature,which multiply affected the fuel-NO_(x)formation and activity of reductants.Increasing the length of the reducing zone could not only enhance the primary NO_(x)reduction efficiency,but also lower the combustion efficiency.In addition,cement raw material could greatly accelerate the formation of fuel-NO_(x)while its catalytic action on NO_(x)reduction was limited.