Oil shale pyrolysis kinetics and variable activation energy principle

A modified first order kinetic equation with variable activation energy is employed to model the total weight loss of Ellajjun oil shale samples. Fixed bed retort with 400 g of oil shale sample size is used in this study in 350–550 °C temperature range. Variable heating rate, h, in the range 2.6–5 °C min⁻¹ are tested.     

Radiative flow of Maxwell nanofluid containing gyrotactic microorganism and energy activation with convective Nield conditions

On the account of industrial and technological applications, the enhancement of energy by inserting nanoparticles is a hot topic in the present century. Therefore, the current analysis presents a theoretical analysis regarding the flow of electrically conducted Maxwell nanofluid over a stretching surface in the presence of the gyrotactic microorganism. In addition, the influence of thermal conductivity and Arrhenius activation energy are considered. By using the apposite transformation, the system of contemporary partial differential expressions is first converted into nonlinear ordinary differential system. The set of these transmuted equations is solved with the help of the shooting method. Reliable results are obtained for the velocity profile, temperature, motile microorganism density and concentration. It is evaluated that by increasing the value of bioconvection Peclet and Lewis numbers, the microorganism distribution exhibited diminishing behavior. These results may be useful in improving the efficiency of heat transfer devices and microbial fuel cells.     

Minimum ignition energy of hydrogen-air mixtures at ambient and cryogenic temperatures

The ignition and combustion of hydrogen in air is considered more hazardous compared to other fuels due to the lower minimum ignition energy (MIE) and the wider flammability range. Spark discharge is the most common type of electrostatic ignition hazard. There is a need in validated safety engineering tools to accurately calculate MIE in a wide range of temperatures from atmospheric to cryogenic which are characteristic for hydrogen systems and infrastructure. Current MIE assessment methodologies rely on the availability of experimental data on quenching distance and/or laminar burning velocity and thus are mostly empirical correlations. This prevents their application beyond the limited number of experimental data, i.e. to arbitrary composition of the hydrogen-air mixture at arbitrary temperatures including cryogenic. This work aims at the development of a model able to accurately predict MIE for hydrogen-air mixtures with arbitrary initial composition and temperature. Cantera and Chemkin software are used to calculate the properties and unstretched laminar burning velocity of hydrogen-air mixtures. The flame thickness is found to well represent the critical flame kernel in the suggested model. The model is validated against experimental data on MIE for mixtures at ambient and cryogenic (down to 123 K) temperatures. Results show that the effect of flame stretch and preferential diffusion shall be considered to accurately predict MIE for lean hydrogen-air mixtures, which was not possible for previous models.     

Binary chemical reaction with activation energy in radiative rotating disk flow of Bingham plastic fluid

This article presents flow, heat and mass transfer phenomena in Bingham plastic fluid. The flow channel is considered to be a rotating disk with a slip which is different in span and streamwise directions, and heat transfer is investigated using dissipation term of the fluid. Arrhenius activation energy and binary chemical reaction are the imperative features of the study of mass transfer. Bingham plastic fluid and anisotropic slip are the key factors of the study due to their numerous applications in manufacturing industries. On the other hand, the radiative heat transfer phenomenon is considered which is widely used in nuclear and power generating systems. The partial differential equations that govern the flow, and heat and mass transfer are converted into ordinary differential equations by utilizing von Kármán's similarity transformation for rotating disk flows. The velocity, temperature, and concentration profiles and some important physical quantities are examined against important flow parameters. It is observed that the thermal radiation showed an increasing effect on temperature profile and the activation energy enhanced the mass transfer rate. The radial slip increased the volumetric flow rate and reduced the boundary layer thickness. The tangential slip reduced the volumetric flow rate and increased the boundary layer thickness.     

Variable thermal conductivity influence on micropolar nanofluid flow triggered by a stretchable disk with Arrhenius activation energy

The analysis of magnetized micro–nanoliquid flows generated by the movable disk is executed in this study. The disk is contained under the porous zone influence. The heat generation, heat sink, and temperature-dependent conductance analysis are reported through the energy equation. The activation energy in terms of a chemical reaction is incorporated through the mass equation. The flow model is normalized through the implementation of similarity transformations. The numerical algorithm Runge–Kutta–Fehlberg is used to solve the reduced system. Results are plotted graphically and in tabular format to investigate the velocity, thermal, and concentration fields. Numeric benchmarks of couple and shear stresses, thermal and concentration rates are also computed. The temperature is augmented against the incremented thermophoretic, variable conductivity, and Brownian movement parameters. The presence of variable conductivity parameter resulted in a weaker rate of heat transportation. The heat transportation rate is boosted with an incremented Prandtl number.     

Nonlinear mixed convection flow of a tangent hyperbolic fluid with activation energy

In this communication, the dynamics of a non‐Newtonian tangent hyperbolic fluid with nanoparticles past a nonuniformly thickened stretching surface is discussed. We examine the impact of nonlinear mixed convection flow of a hyperbolic tangent fluid with the Cattaneo‐Christov heat and mass diffusion model past a bidirectional stretching surface. The effects of activation energy and magnetic field are incorporated in the analysis. The variables of transformations are used to change the nonlinear partial differential equations into ordinary differential equations (ODEs). Then, these ODEs are numerically solved using the Matlab routine of the bvp4c algorithm. The derailed analysis of the influences of the governing parameters on velocities along the x‐ and y‐axes, temperature and concentration profiles are presented using tables and figures. The outcomes of these parameters reveal that the velocities along the x‐ and y‐axes are decreased for the values of We increasing but the opposite behavior is observed as the value of $A$ increases. The results also show that the values of $e$ and $Nb$ rise as the temperature profiles increase. Similar influences are observed on the profile of concentration as the values of $F$ and $f$ rise. As the values of $N1$ go from 0.27 to 0.25, the skin‐friction coefficient increases, and similarly, as $Nb$ goes from 0.3 to 0.1, $?\theta \prime (0)$ is enhanced.     

变热流条件下木材点燃时间与热流变化率关系的实验研究

实验研究了外加线性变化热流条件下木材点燃时间与热流变化率之间的关系,测量了不同种类木材在不同热流变化率下的点燃时间。通过分析实验数据发现,点燃时间和热流变化率之间符合很好的幂函数关系,而密度是影响木材着火的一个关键因素。     

Experimental studies on explosive limits and minimum ignition energy of syngas: A comparative review

Syngas, as one cleaner and efficient approach to coal utilization, has been widely regarded as one promising alternative fuel. Owing to the existence of hydrogen molecule, syngas has a great potential to explosion which would be favoured by thermo-power devices but be worried by safety issues on the processes of production, storage, and delivery. Explosive limits and minimum ignition energy are two essential but crucial aspects for the initiation of explosion, and thus a well understanding on those issues should be a prerequisite for massive utilizations. This paper has presented a comprehensive review on the recent progress in the experimental studies on the explosive limits and minimum ignition energy for syngas. Some essential conclusions and some interesting observations have been remarked, and the potential of further studies have been prospected.     

Flash ignition of Al nanoparticles: Mechanism and applications

Aluminum nanoparticles (Al NPs), due to their high energy density, are important materials for propulsion systems, material synthesis and hydrogen generation. However, the oxidation mechanism of Al NPs at large heating rate remains inconclusive due to the lack of direct experimental evidence. Here, we studied the oxidation mechanism of Al NPs under large heating rate (on the order of 10⁶ K/s or higher) by a simple flash ignition method, which uses a camera flash to ignite Al NPs. The flash ignition occurs when the Al NPs have suitable diameters and sufficient packing density to cause a temperature rise above their ignition temperatures. Importantly, transmission electron microscopy analysis reveals that the Al NPs are oxidized via the melt-dispersion mechanism, providing the first direct experimental evidence thereof. Finally, flash ignition is also applicable to the ignition of flammable gaseous, liquid and solid materials by the addition of Al NPs in lieu of sparks and hotwire igniters.     

Measurements of minimum ignition energy in premixed laminar methane/air flow by using laser induced spark

Reducing engine pollutant emissions and fuel consumption is an important challenge. Lean-burning engines are a promising development; however, such engines require high-energy ignition systems for typical working conditions (equivalence ratio, Φ < 0.7). Laser-induced ignition is envisaged as a way to obtain high-energy ignition as a result of progress that has been made in laser beam technology in terms of stability, size, and energy. This study investigated the minimum energy necessary to ignite a laminar premixed methane air mixture experimentally. A parametrical study was performed to characterize the effects of the flow velocity, equivalence ratio, and lens focal length on the minimum energy required for ignition. Experiments were conducted using a premixed laminar CH₄/air burner. Laser-induced breakdown was achieved by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser with an anti-reflection-coated lens. Mixture ignition and the early stages of flame propagation were studied using a high speed Schlieren technique. Despite the stochastic characteristic of the laser breakdown phenomena, good reproducibility in the minimum energy required for the ignition measurements was observed. The cases in which the CH₄/Air mixture flow ignites are defined as those with a laminar flame front propagation visible in the Schlieren images 10 ms after the energy deposition. The same minimum ignition energy (MIE) versus equivalence ratio (Φ) type of curves were obtained with a laser-induced spark and with a spark plug. Due to the threshold of energy required to obtain breakdown and the stochastic character of the energy absorption by the spark, a constant value was obtained (corresponding to the breakdown threshold) when the minimum ignition energy was lower than the breakdown threshold. As already noticed by several authors, MIE values higher than those observed using spark plugs were obtained. However, these differences tended to disappear at the lean and rich fuel limits.     

Coupled effect of multislips and activation energy in a micropolar nanoliquid on a convectively heated elongated surface

This research communication explores the impact of wall slips along with the suspension of nanomaterials in a chemically reactive micropolar liquid stream on a stretched surface with convective heating. Activation of energy is analyzed through the modified Arrhenius function. Radiative heat flux with nonlinearity and temperature-dependent thermal source (sink) are considered in the heat transmission process. The Cattaneo–Christov approach featuring the time of thermal relaxation is employed. Successive application of scaling analysis followed by the Runge–Kutta–Fehlberg numerical approach delivered computational solutions for the partial differential equations delineating the problem under study. The response of flow variables for different values of various emerged physical variables is elaborated in detail via graphical and numerical presentations. Comparison of the outcome of the current analysis for certain cases is in accordance with the outcomes available in the literature. The findings reveal that pairs of velocity, microrotation, temperature, and species concentration oppositely reacted to both parameters of slip. The temperature of the nanofluid is improved by 18.5%, for specified values of radiation and temperature ratio parameters over that of the pure base liquid. Activation energy augments concentration. The drag coefficient declines with growing thermal and solutal Grashof numbers. Sherwood number is enhanced for higher values of the temperature difference and chemical reaction parameters.     

Heat transfer analysis of inclined magnetic field and activation energy in Maxwell nanofluid with thermophoresis effects

Numerical analysis is performed for incompressible Maxwell nanofluid model flow under the implications of thermophoresis and inclined magnetic field over a convectively stretched surface. The system that comprises differential equations of partial derivatives is remodeled into the system of ordinary differential equations via similarity transformations and then solved through by Runge–Kutta–Fehlberg with shooting technique. The physical parameters, which emerge from the derived system, are discussed in graphical formats. Excellent proficiency in the numerical process is analyzed by comparing the results with available literature in limiting scenarios. The significant outcomes of the current investigation are that the velocity field decays for higher fluid parameters while that peter out the fluid temperature. Further, the heat transfer rate is reduced with the incremental values of fluid and thermophoresis parameters while it uplifts with Biot and Prandtl numbers.     

Modelling auto ignition of hydrogen in a jet ignition pre-chamber

Spark-less jet ignition pre-chambers are enablers of high efficiencies and load control by quantity of fuel injected when coupled with direct injection of main chamber fuel, thus permitting always lean burn bulk stratified combustion. Towards the end of the compression stroke, a small quantity of hydrogen is injected within the pre-chamber, where it mixes with the air entering from the main chamber. Combustion of the air and fuel mixture then starts within the pre-chamber because of the high temperature of the hot glow plug, and then jets of partially combusted hot gases enter the main chamber igniting there in the bulk, over multiple ignition points, lean stratified mixtures of air and fuel. The paper describes the operation of the spark-less jet ignition pre-chamber coupling CFD and CAE engine simulations to allow component selection and engine performance evaluation.     

Experimental and numerical investigation of a direct injection spark ignition hydrogen engine for heavy-duty applications

The H₂ internal combustion engine is gaining increasing interest especially for commercial vehicles. Regarding the optimization of the combustion process, results of experimental investigations on a H₂ heavy-duty single-cylinder engine in combination with numerical 3D-CFD investigations are presented. In addition to a Direct Injection (DI) Spark Ignited (SI) configuration, Port Fuel Injection (PFI) is explored to provide a reference with near homogeneous cylinder charge. The main objective is to assess a 3D-CFD-RANS framework based on ECFM and state-of-the art sub-models to describe the most important phenomena occurring in H₂ spark ignition engines and to support the experimental analysis. Experimental results show that the PFI configuration provides efficiency and emissions benefits at the expense of volumetric efficiency. The proposed CFD model demonstrates the ability to successfully simulate different engine operating conditions for both PFI and DI systems. In particular, it is shown that the charge stratification typical for DI systems is not beneficial for the studied configuration as it increases wall heat losses and NOx formation.     

浅析循环流化床锅炉的三种点火方式

通过对利用燃油点火方式、木柴点火方式、热渣点火方式点燃循环流化床锅炉的经验总结,对利用这三种方式点燃循环流化床锅炉的方法进行了简述,剖析了这三种点火方式的优缺点,并指出了较佳的点火方式。     

空调冷冻水泵变频能耗特性的研究

通过分析冷冻水管路特性随空调负荷变化的特点 ,得出了计算空调冷冻水泵变频调速运行总能耗的一般关系式。研究表明 ,在中央空调系统中 ,由于冷冻水管路特性曲线随空调负荷而变化 ,在确定水泵变频调速运行的能耗时已不能直接应用泵的相似定律 ;变频冷冻水泵的能耗并不与转速或流量的三次方成正比 ,而是与空调负荷、空调用户的流量分配及空调用户的位置等有关。     

Spark ignition transitions in premixed turbulent combustion

Recent discoveries and developments on the dynamic process of premixed turbulent spark ignition are reviewed. The focus here is on the variation of turbulent minimum ignition energies (MIE_T) against laminar MIE (MIE_L) over a wide range of r.m.s. turbulence fluctuation velocity (uʹ) alongside effects of the spark gap between electrodes, Lewis number, and some other parameters on MIE. Two distinguishable spark ignition transitions are discussed. (1) A monotonic MIE transition, where MIE_L sets the lower bound, marks a critical uʹ_c between linear and exponential increase in MIE_T with uʹ increased. (2) A non-monotonic MIE transition, where the lower bound is to be set by a MIE_T at some uʹ_c, stems from a great influence of Lewis number and spark gap despite turbulence. At sufficiently large Lewis number >> 1 and small spark gap (typically less than 1 mm), turbulence facilitated ignition (TFI), where MIE_T < MIE_L, occurs; then MIE_T increases rapidly at larger uʹ > uʹ_c because turbulence re-asserts its dominating role. Both phenomena are explained by the coupling effects of differential diffusion, heat losses to electrodes, and turbulence on the spark kernel. In particular, the ratio of small-scale turbulence diffusivity to reaction zone thermal diffusivity, a reaction zone Péclet number, captures the similarity of monotonic MIE transition, regardless of different ignition sources (conventional electrodes versus laser), turbulent flows, pressure, and fuel types. Furthermore, TFI does and/or does not occur when conventional spark is replaced by nanosecond-repetitively-pulsed-discharge and/or laser spark. The latter is attributed to the third lobe formation of laser kernel with some negative curvature segments that enhance reaction rate through differential diffusion, where MIE_L < MIE_T (no TFI). Finally, the implications of MIE transitions relevant to lean-burn spark ignition engines are briefly mentioned, and future studies are suggested.     

液粘调速装置在节能减排中的应用

针对水泵风机采用恒速节流调节运行时存在浪费大量电能的问题,吉林油田水厂选用液粘调速装置改造水泵机组后,通过改变水泵和风机转速调整水量、风量,使轴功率大幅度降低,节约大量电能,经济效益可观。     

Mathematical modeling and study of MHD flow of Williamson nanofluid over a nonlinear stretching plate with activation energy

This study investigates the Williamson nanofluid flow through a nonlinear stretching plate. It aims to analze the global influence of Williamson parameter (λ) rather than local, which is researched for a linear stretching case in the literature. In addition, the features of activation energy are also taken into account in the current review. The developed model with the consequent similarity transformation has still not been perceived. The transformed partial differential equations are solved analytically. The consequences of embedded parameters on the velocity, temperature, and concentration profiles are displayed through figures. Also, the consequences of embedded parameters on skin friction, heat transfer, and mass transfer are demonstrated through tables.     

潜油电泵变频节能分析

本文根据潜油电泵的特性曲线分析电潜泵变频调速的节能机理以及理论节能量,最后通过现场测试的电参数数据给出了潜油电泵变频调节的实际节电量。