Reheat effect on the improvement in efficiency of the turbine driven by pulse detonation

Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine efficiency.Taking this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was used.The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine.The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was improved.At a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.

Investigation of system parameters towards safer impact based shock-to-detonation transition in a novel laser driven flyer plate prototype

Laser driven flyer plate technology offers improved safety and reliability for detonation of explosives in industrial applications ranging from mining and stone quarrying to the aerospace and defense industries.This study is based on developing a safer laser driven flyer plate prototype comprised of a laser initiator and a flyer plate subsystem that can be used with secondary explosives.System parameters were optimized to initiate the shock-to-detonation transition(SDT)of a secondary explosive based on the impact created by the flyer plate on the explosive surface.Rupture of the flyer was investigated at the mechanically weakened region located on the interface of these subsystems,where the product gases from the deflagration of the explosive provide the required energy.A bilayer energetic material was used,where the first layer consisted of a pyrotechnic component,zirconium potassium perchlorate(ZPP),for sustaining the ignition by the laser beam and the second layer consisted of an insensitive explosive,cyclotetramethylene-tetranitramine(HMX),for deflagration.A plexiglass interface was used to enfold the energetic material.The focal length of the laser beam from the diode was optimized to provide a homogeneous beam profile with maximum power at the surface of the ZPP.Closed bomb experiments were conducted in an internal volume of 10 cm^(3) for evaluation of performance.Dependency of the laser driven flyer plate system output on confinement,explosive density,and laser beam power were analyzed.Measurements using a high-speed camera resulted in a flyer velocity of 670±20 m/s that renders the prototype suitable as a laser detonator in applications,where controlled employment of explosives is critical.

Assessing the energy release characteristics during the middle detonation reaction stage of aluminized explosives

Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale,which prolong the release of detonation energy and the energy release at different stages also shows significant differences.However,at present,there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives,which can have a duration of tens to hundreds of microseconds.The present work demonstrates an approach to assessing the midstage of an aluminized explosive detonation based on a water push test employing a high degree of confinement.In this method,the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank.Upon detonation,the gaseous products expand in one direction while forcing water ahead of them.The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera.The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction.During the middle stage of the detonation process of these aluminized explosives,the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products.A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate.This work demonstrates an effective means of evaluating the performance of aluminized explosives.

Study on concentration distribution and detonation characteristics for non-axisymmetric fuel dispersal

The study of non-axisymmetric fuel dispersal and detonation can provide reference for the prevention of industrial cloud explosion accidents and the design of fuel air explosive(FAE).The concentration and detonation fields of 85 kg cylindrical and fan-shaped fuel are investigated by experiments and numerical simulations.A dynamic model of the whole process for fuel dispersal and detonation is built.The concentration distribution of fuel is used as the initial condition to calculate the detonation stage,thus solving the initial value problem of detonation field.The phase and component changes of fuel cloud at different locations are compared.The fuel cloud is divided into directions of 0°,90°,135°and 180°.The results show that the maximum cloud radius is 20.94 m in 135°and the minimum is 12.04 m in 0°.The diameter of the detonation fireball is 53.6 m,and the peak temperature is 3455 K.The highest peak overpressure is 3.44 MPa in 0°and the lowest is 2.97 MPa in 135°.The proportion of liquid phase in 0°is22.90%,and the fuel loss is 11.8% and 9% higher than that in 135°and cylindrical charge,respectively.The stable propagation distance of blast wave in 135°is 42.50% longer than 0°and 28.37% longer than cylindrical charge.

Current optimization-based control of dual three-phase PMSM for low-frequency temperature swing reduction

In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.

Atmospheric transmission algorithm for pulsed X-rays from high-altitude nuclear detonations based on scattering correction

In high-altitude nuclear detonations,the proportion of pulsed X-ray energy can exceed 70%,making it a specific monitoring signal for such events.These pulsed X-rays can be captured using a satellite-borne X-ray detector following atmospheric transmission.To quantitatively analyze the effects of different satellite detection altitudes,burst heights,and transmission angles on the physical processes of X-ray transport and energy fluence,we developed an atmospheric transmission algorithm for pulsed X-rays from high-altitude nuclear detonations based on scattering correction.The proposed method is an improvement over the traditional analytical method that only computes direct-transmission X-rays.The traditional analytical method exhibits a maximum relative error of 67.79% compared with the Monte Carlo method.Our improved method reduces this error to within 10% under the same conditions,even reaching 1% in certain scenarios.Moreover,its computation time is 48,000 times faster than that of the Monte Carlo method.These results have important theoretical significance and engineering application value for designing satellite-borne nuclear detonation pulsed X-ray detectors,inverting nuclear detonation source terms,and assessing ionospheric effects.

Deciphering engineering principle of three-phase interface for advanced gas-involved electrochemical reactions

As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER),have become an emerging research direction and have gained increasing attention due to their advantages of environmental friendliness and sustainability.Various studies have been designed to accelerate sluggish kinetics but with limited results.Most of them promote the reaction by modulating the intrinsic properties of the catalyst,ignoring the synergistic effect of the reaction as a whole.Due to the introduction of gas,traditional liquid-solid two-phase reactions are no longer applicable to future research.Since gas-involved electrochemical reactions mostly occur at the junctions of gaseous reactants,liquid electrolytes and solid catalysts,the focus of future research on reaction kinetics should gradually shift to three-phase reaction interfaces.In this review,we briefly introduce the formation and constraints of the three-phase interface and propose three criteria to judge its merit,namely,the active site,mass diffusion and electron mass transfer.Subsequently,a series of modulation methods and relevant works are discussed in detail from the three improvement directions of‘exposing more active sites,promoting mass diffusion and accelerating electron transfer’.Definitively,we provide farsighted insights into the understanding and research of three-phase interfaces in the future and point out the possible development direction of future regulatory methods,hoping that this review can broaden the future applications of the three-phase interface,including but not limited to gas-involved electrochemical reactions.

Research of detonation products of RDX/Al from the perspective of composition

Aluminized explosives exhibit excellent performance because the oxidation of aluminum(Al)powders enhances the pressure and temperature of detonation products.However,the equation of state(EOS)of detonation products has not been understood well.In the present study,we conducted long-time tests(approximately 1 ms)of a metal rod driven by detonation products of RDX,RDX/Li F,and RDX/Al.In addition,we used laser velocimetry(PDV)to measure the freesurface velocity of the rod.Thermochemical code DLCHEQ was successfully applied to the hydrodynamic program SSS to perform the roddriven test,and a novel method was established to study the EOS of detonation products from the perspective of composition.The reliability of DLCEHQ was validated by a small deviation(<10%)between the experimental rod free-surface velocity of RDX and the calculated results;the deviation was considerably less than that from the results obtained using the JWL EOS and ideal-gas EOS.The endothermic process and the reaction of Al powders(Al+H_(2)O+NO+CO_(2)→CO+H_(2)+N_(2)+Al_(2)O_(3))were analyzed by calculating the rod free-surface velocity of RDX/Li F and RDX/Al,respectively.The results of the present study demonstrated that the thermodynamic state of Al powders has notable influence on the EOS of aluminized detonation products,and the findings were compared with those of previous studies.First,the temperature equilibrium between Al powders and CHNO products is not always achieved,and the disequilibrium is more obvious when the reaction of Al powders is stronger.Second,the reaction rate of Al powders depends on pressure and Al content.Finally,the endothermic process of Al powders has a high contribution to the decrease in the work ability of RDX/Al instead of the gasconsumption mechanism of the Al reaction.More than half of the reaction heat of Al powders is used to heat itself,whereas the gas consumption during the reaction is negligible.

High-Order Bound-Preserving Finite Difference Methods for Multispecies and Multireaction Detonations

In this paper,we apply high-order finite difference(FD)schemes for multispecies and multireaction detonations(MMD).In MMD,the density and pressure are positive and the mass fraction of the ith species in the chemical reaction,say zi,is between 0 and 1,withΣz_(i)=1.Due to the lack of maximum-principle,most of the previous bound-preserving technique cannot be applied directly.To preserve those bounds,we will use the positivity-preserving technique to all the zi'is and enforceΣz_(i)=1 by constructing conservative schemes,thanks to conservative time integrations and consistent numerical fluxes in the system.Moreover,detonation is an extreme singular mode of flame propagation in premixed gas,and the model contains a significant stiff source.It is well known that for hyperbolic equations with stiff source,the transition points in the numerical approximations near the shocks may trigger spurious shock speed,leading to wrong shock position.Intuitively,the high-order weighted essentially non-oscillatory(WENO)scheme,which can suppress oscillations near the discontinuities,would be a good choice for spatial discretization.However,with the nonlinear weights,the numerical fluxes are no longer“consistent”,leading to nonconservative numerical schemes and the bound-preserving technique does not work.Numerical experiments demonstrate that,without further numerical techniques such as subcell resolutions,the conservative FD method with linear weights can yield better numerical approximations than the nonconservative WENO scheme.

Deflagration to detonation transition in weakly confined conditions for a type of potentially novel green primary explosive:Al/Fe_(2)O_(3)/RDX hybrid nanocomposites

The properties of the combustion and deflagration to detonation transition(DDT)of Al/Fe_(2)O_(3)/RDX hybrid nanocomposites,a type of potentially novel lead-free primary explosives,were tested in weakly confined conditions,and the interaction of Al/Fe_(2)O_(3)nanothermite and RDX in the DDT process was studied in detail.Results show that the amount of the Al/Fe_(2)O_(3)nanothermite has a great effect on the DDT properties of Al/Fe_(2)O_(3)/RDX nanocomposites.The addition of Al/Fe_(2)O_(3)nanothermite to RDX apparently improves the firing properties of RDX.A small amount of Al/Fe_(2)O_(3)nanothermite greatly increases the initial combustion velocity of Al/Fe_(2)O_(3)/RDX nanocomposites,accelerating their DDT process.When the contents of Al/Fe_(2)O_(3)nanothermite are less than 20 wt%,the DDT mechanisms of Al/Fe_(2)O_(3)/RDX nanocomposites follow the distinct abrupt mode,and are consistent with that of RDX,though their DDT processes are different.The RDX added into the Al/Fe_(2)O_(3)nanothermite increases the latter's peak combustion velocity and makes it generate the DDT when the RDX content is at least 10 wt%.RDX plays a key role in the shock compressive combustion,the formation and the properties of the DDT in the flame propagation of nanocomposites.Compared with RDX,the fast DDT of Al/Fe_(2)O_(3)/RDX nanocomposites could be obtained by adjusting the chemical constituents of nanocomposites.

Electrical characteristics of new three-phase traction power supply system for rail transit

A novel three-phase traction power supply system is proposed to eliminate the adverse effects caused by electric phase separation in catenary and accomplish a unifying manner of traction power supply for rail transit.With the application of two-stage three-phase continuous power supply structure,the electrical characteristics exhibit new features differing from the existing traction system.In this work,the principle for voltage levels determining two-stage network is dissected in accordance with the requirements of traction network and electric locomotive.The equivalent model of three-phase traction system is built for deducing the formula of current distribution and voltage losses.Based on the chain network model of the traction network,a simulation model is established to analyze the electrical characteristics such as traction current distribution,voltage losses,system equivalent impedance,voltage distribution,voltage unbalance and regenerative energy utilization.In a few words,quite a lot traction current of about 99%is undertaken by long-section cable network.The proportion of system voltage losses is small attributed to the two-stage three-phase power supply structure,and the voltage unbal-ance caused by impedance asymmetry of traction network is less than 1‰.In addition,the utilization rate of regenerative energy for locomotive achieves a significant promotion of over 97%.

Speed Regulation Method Using Genetic Algorithm for Dual Three-phase Permanent Magnet Synchronous Motors

Dual three-phase Permanent Magnet Synchronous Motor(DTP-PMSM)is a nonlinear,strongly coupled,high-order multivariable system.In today’s application scenarios,it is difficult for traditional PI controllers to meet the requirements of fast response,high accuracy and good robustness.In order to improve the performance of DTP-PMSM speed regulation system,a control strategy of PI controller based on genetic algorithm is proposed.Firstly,the basic mathematical model of DTP-PMSM is established,and the PI parameters of DTP-PMSM speed regulation system are optimized by genetic algorithm,and the modeling and simulation experiments of DTP-PMSM control system are carried out by MATLAB/SIMULINK.The simulation results show that,compared with the traditional PI control,the proposed algorithm significantly improves the performance of the control system,and the speed output overshoot of the GA-PI speed control system is smaller.The anti-interference ability is stronger,and the torque and double three-phase current output fluctuations are smaller.

Numerical simulation of flow field characteristics and the improvement of pressure oscillation of rotating detonation engine

Due to the inherent working mode of rotating detonation engine(RDE),the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss,which makes it difficult to design nozzle and improve propulsion performance.Therefore,in order to improve the characteristics of detonation flow field,the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper,and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field,which is a new method to regulate the detonation flow field.The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber,which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy.In the external flow field of combined chamber,the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed,which results in Mach disk structure.Moreover,the pressure monitoring points are set at the external flow field.The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened.Compared to the annular chamber,the relative standard deviation(RSD) has been reduced from 14.6% to5.6%.The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field,and is of great significance to promote the potential of RDE and nozzle design.

Dynamic analysis of buried pipeline with and without barrier system subjected to underground detonation

Failure of pipe networks due to blast loads resulting from terrorist attacks or construction facilities, may cause economic loss, environmental pollution, source of firing or even it may lead to a disaster. The present work develops a closed-form solution of buried pipe with barrier system subjected to subsurface detonation. The solution is derived based on the concept of double-beam system. Euler Bernoulli's beams are used to simulate the buried pipe and the barrier system. Soil is idealized as viscoelastic foundation along with shear interaction between discrete Winkler springs(advanced soil model). The finite SineFourier transform is employed to solve the coupled partial differential equations. The solution is validated with past studies. A parametric study is conducted to investigate the influence of TNT charge weight, pipe material, damping ratio and TNT offset on the response of buried pipe with and without barrier system. Further a statistical analysis is carried out to get the significant soil and pipe input parameters. It is perceived that peak pipe displacements for both the cases(with and without barrier) are increases with increasing the weight of TNT charge and decreases with increasing the damping ratio and TNT offset. The deformation of pipe also varies with pipe material. Pipe safety against blast loads can be ensured by providing suitable barrier layer. The present study can be utilized in preliminary design stage as an alternative to expensive numerical analysis or field study.

Optimization of Control Loops and Operating Parameters for Three-Phase Separators Used in Oilfield Central Processing Facilities

In this study,the Stokes formula is used to analyze the separation effect of three-phase separators used in a Oilfield Central Processing Facility.The considered main influencing factors include(but are not limited to)the typical size of oil and water droplets,the residence time and temperature of fluid and the dosage of demulsifier.Using the“Specification for Oil and Gas Separators”as a basis,the control loops and operating parameters of each separator are optimized Considering the Halfaya Oilfield as a testbed,it is shown that the proposed approach can lead to good results in the production stage.

Purification of Moringa oleifera Leaves Protease by Three-Phase Partitioning and Investigation of Its Potential Antibacterial Activity

One of plant-based products for dental care is plant-based proteolytic enzymes which are principally proteases. In order not to damage the protein and bioactive content, an efficient method should be employed for their purifications. As such, three-phase partitioning (TPP) was used to purify protease from moringa (Moringa oleifera). TPP is an emerging, promising, non-chromatographic and economical technology which is simple, quick, efficient and often one-step process for the separation and purification of bioactive molecules from natural sources. It involves the addition of salt (ammonium sulphate) to the crude extract followed by the addition of an organic solvent (butanol). The protein appears as an interfacial precipitate between upper organic solvent and lower aqueous phases. The various conditions such as ammonium sulphate, ratio of crude extract to t-butanol and pH which are required for attaining efficient purification of the protease fractions were optimized. Under optimized conditions, it was seen that, 35% of ammonium sulphate saturation with 1:0.75 ratio of crude extract to t-butanol at pH 7 gave 4.94-fold purification with 96.20% activity yield of protease in the middle phase of the TPP system. The purified enzyme from Moringa oleifera has no antimicrobial effect on the pathogenic bacteria tested. However, this purified enzyme, can be considered as a promising agent, cheap, and safe source which is suitable for using in various industries.

Vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers under blast load

In this article,vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers subjected to blast load are studied.Higher-order ES-MITC3 element based on higher-order shear deformation theory(HSDT)to achieve the governing equations.The sandwich plates with the ultra-light feature of the auxetic honeycomb core layer(negative Poisson’s ratio)and reinforced by two laminated three-phase skin layers.The obtained results in our work are compared with other previously published to confirm accuracy and reliability.In addition,the effects of parameters such as geometrical and material parameters on the vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers are fully investigated.

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N_(2) reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N_(2) molecules and the limited supply of N_(2) to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N_(2) molecules.The eNRR system is further modified using a gas diffusion electrode(GDE) coated with polytetrafluoroethylene(PTFE) to form an effective three-phase boundary of liquid water-gas N_(2)-solid catalyst to facilitate easy access of N_(2) to the catalytic sites.As a result,the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH_(3) production rate of 7.69 μg h^(-1) cm^(-2) at-0.2 V_(RHE),which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell.This work represents a successful demonstration of dual modification strategies;catalyst modification and N_(2) supplying system engineering,and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.

Automatic measurement of three-phase contact angles in pore throats based on digital images

With the help of digital image processing technology, an automatic measurement method for the three-phase contact angles in the pore throats of the microfluidic model was established using the microfluidic water flooding experiment videos as the data source. The results of the new method were verified through comparing with the manual measurement data.On this basis, the dynamic changes of the three-phase contact angles under flow conditions were clarified by the contact angles probability density curve and mean value change curve. The results show that, for water-wetting rocks, the mean value of the contact angles is acute angle during the early stage of the water flooding process, and it increases with the displacement time and becomes obtuse angle in the middle-late stage of displacement as the dominant force of oil phase gradually changes from viscous force to capillary force. The droplet flow in the remaining oil occurs in the central part of the pore throats, without three-phase contact angle. The contact angles for the porous flow and the columnar flow change slightly during the displacement and present as obtuse angles in view of mean values, which makes the remaining oil poorly movable and thus hard to be recovered. The mean value of the contact angle for the cluster flow tends to increase in the flooding process, which makes the remaining oil more difficult to be recovered. The contact angles for the membrane flow are mainly obtuse angles and reach the highest mean value in the late stage of displacement, which makes the remaining oil most difficult to be recovered. After displacement, the remaining oils under different flow regimes are just subjected to capillary force, with obtuse contact angles, and the wettability of the pore throat walls in the microfluidic model tends to be oil-wet under the action of crude oil.

Study on the prediction and inverse prediction of detonation properties based on deep learning

The accurate and efficient prediction of explosive detonation properties has important engineering significance for weapon design.Traditional methods for predicting detonation performance include empirical formulas,equations of state,and quantum chemical calculation methods.In recent years,with the development of computer performance and deep learning methods,researchers have begun to apply deep learning methods to the prediction of explosive detonation performance.The deep learning method has the advantage of simple and rapid prediction of explosive detonation properties.However,some problems remain in the study of detonation properties based on deep learning.For example,there are few studies on the prediction of mixed explosives,on the prediction of the parameters of the equation of state of explosives,and on the application of explosive properties to predict the formulation of explosives.Based on an artificial neural network model and a one-dimensional convolutional neural network model,three improved deep learning models were established in this work with the aim of solving these problems.The training data for these models,called the detonation parameters prediction model,JWL equation of state(EOS)prediction model,and inverse prediction model,was obtained through the KHT thermochemical code.After training,the model was tested for overfitting using the validation-set test.Through the model-accuracy test,the prediction accuracy of the model for real explosive formulations was tested by comparing the predicted value with the reference value.The results show that the model errors were within 10%and 3%for the prediction of detonation pressure and detonation velocity,respectively.The accuracy refers to the prediction of tested explosive formulations which consist of TNT,RDX and HMX.For the prediction of the equation of state for explosives,the correlation coefficient between the prediction and the reference curves was above 0.99.For the prediction of the inverse prediction model,the prediction error of the explosive equation was within 9%.This indicates that the models have utility in engineering.