Initial Axial Velocity Research Articles

Photocatalytic degradation of ethylene in tubular microreactor coated with thin-film of TiO2: Mathematical modeling with experimental validation and geometry analysis using computational fluid dynamics simulations

The study aimed to establish a comprehensive understanding of the photocatalytic process and optimize the reactor design for efficient ethylene regulation to improve the shelf-life of fruits and vegetables. For this, it was performed 2D computational fluid dynamics modeling at two different reactor geometry (conventional cylindric reactor and annular cylindric reactor) using the conservation equations combined with Langmuir-Hinshelwood mechanism. A continuous single-phase multicomponent fluid flow with the reactor surface supported with a thin-film catalyst under UV-A light irradiation was simulated for initial ethylene concentration at 0.479–4.234 × 10−3 molC2H4 m−3 and inlet axial velocity at 0.0085–0.1019 m s−1. In the 2D CFD results, it was observed that the difference in ethylene concentration between the microreactor bulk and surface is only significant for high initial concentrations and axial velocities. Furthermore, it was found that the parabolic conversion profile remains unchanged for lengths greater than 10% of the reactor length across all geometries studied. The variation in reactor diameters resulted in a substantial reduction in ethylene conversion; however, the incorporation of an annular cylinder coated with a catalyst led to an enhancement in conversion rates, with improvements of approximately 28%, 17%, and 6% observed for diameters of 5 mm, 10 mm, and 20 mm, respectively. This reduction in improvement as diameter increase can be attributed to the laminar flow dynamics that impede the diffusion of ethylene molecules from the bulk to the catalytic surface. Consequently, the simulated data highlight the potential of employing a catalyst-doped annular cylinder as a promising strategy to increase ethylene conversion and extend the shelf life of fruits. However, it should be noted that the addition of an annular cylinder, while enhancing conversion, also introduces operational complexities and cost implications due to the significant increase in pressure drop associated with lower diameters.

Study on W-Band Sheet Beam Metallic Grating Amplifier Based on Combined Cherenkov and Cyclotron Resonances

In principle, if the beam is with initial transverse and axial velocity as well as propagating in period slow wave circuits, the combined Cherenkov and cyclotron resonances will exist, and the interaction will be enhanced. To illustrate and understand the influence of the combined resonance on the performance of devices intuitively, W-band sheet beam amplifiers with single-grating and staggered double-grating slow wave structures based on combined resonance and Cherenkov resonance are all designed and simulated, respectively. The results show that gain, bandwidth, and efficiency can be improved by utilizing multiresonances compared with Cherenkov resonance, which shows the attractive performance of the combined resonance. For the single-grating amplifier (SGA), the gain, bandwidth, and efficiency are improved by 1.68 dB, 2 GHz, and 0.45%, respectively. For the staggered double-grating amplifier (SDGA), the gain, bandwidth, and efficiency are improved by 0.85 dB, 5 GHz, and 0.42%, respectively. Besides, the comparisons of SGA and SDGA based on combined resonance are also presented and analyzed to provide a reference for the project implementation.

The Behavior of Supersonic Jets Generated by Combination Gas in the Steelmaking Process.

In the duplex steelmaking process, the oxygen flow rate is suppressed to reduce the increasing rate of the temperature in the molten bath, resulting in severe dynamic conditions. To improve the mixing effect of the molten bath, a Laval nozzle structure designed for combination gas has been proposed. In this research, five types of Laval nozzle structure have been built based on the combination gas content, and both numerical simulations and experiments are performed to analyze the flow field of the supersonic jet. The axial velocity and oxygen concentration were measured in the experiment, which agreed well with the numerically simulated data. The results show that both initial axial velocity and potential core length increase with the flow rate of combination gas. Further, applying a higher N2 flow rate could improve the oxygen utilization rate at different ambient temperatures, but this issue increases the oxygen utilization rate; however, the latter can be reduced at higher ambient temperatures.

Analysis of the Combined Cyclotron and Cherenkov Resonances in Metallic Grating Structures

The metallic grating structure is usually used in the Cherenkov maser. In order to further improve the gain and bandwidth of the sheet beam metallic grating waveguide system, the beam can be with initial transverse and axial velocity instead of pure axial velocity. In this situation, the sheet helical beam will interact with several space harmonics waves simultaneously, and then, the combined cyclotron and Cherenkov resonances can be utilized. Based on the linear theory, the “hot” dispersion equation of the sheet beam metallic grating cyclotron maser is derived and calculated. Through the numerical calculations, the contribution of each resonance, and the influence of beam voltage, the magnetic field and transverse to axial velocity ratio on the gain and bandwidth are analyzed. Besides, the effects of the beam voltage and magnetic field on the growth rate are also simulated, which can further verify the accuracy of the theoretical calculations. This analysis shows the potential of the sheet helical beam with a metallic grating waveguide system, which can be further studied and applied in the future.

Characteristics of Flow Field for Supersonic Oxygen Multijets with Various Laval Nozzle Structures

The Laval nozzle is used widely in steelmaking processes to increase the velocity of an oxygen jet up to approximately 2 Mach numbers. The present research is aimed at determining the effect of the Laval nozzle structure on a supersonic oxygen jet flow field. Both one-dimensional isoentropic flow theory and a characteristic-line method were used to design five-hole oxygen lances of two types and, applicable to oxygen multijets, to analyze their flow field characteristics by a series of numerical simulations and experimental studies. When compared to the conventional oxygen lance designed according to the one-dimensional isoentropic flow theory, the new oxygen lance designed with employment of the characteristic-line method is more effective in both suppressing the shock wave generation and improving the initial axial velocity of oxygen jets under the same test conditions. As a result, a larger impaction cavity was generated by the new oxygen lance and the mass transfer within oxygen, liquid slag, and molten steel was enhanced.

Motion law and density influence of a submersible aerial vehicle in the water-exit process

The water-exit process is a key step in connecting underwater navigation and air flight of a submersible aerial vehicle. In order to study motion law and density influence of the vehicle in the water-exit process, and taking into account the limitations of the experiment and numerical simulation in the study of the whole water-exit process, a theoretical modeling method is proposed. First, the vehicle’s shape is presented, and the water-exit dynamic model is established by mechanics and motion analysis. Then, numerical simulation and theoretical modeling are used to calculate the water-exit motion under same conditions, and the validity of the water-exit model is verified by the calculation results. Finally, on basis of the established model, the water-exit motion of the vehicle with three different densities is calculated under different initial water-exit angles, axial velocities and thrusts, and the water-exit motion law and vehicle’s density influence on the water-exit motion are obtained. The proposed method and obtained results can be used as effective guidance for the vehicle finishes the water-exit motion successfully.

Investigation of supersonic separation mechanism of CO2 in natural gas applying the Discrete Particle Method

In order to study the separation mechanism of CO2 droplets and natural gas in a supersonic separator, different structure of cyclones were designed and the flow characteristics of natural gas in the supersonic separator were numerically calculated. The mathematical model of the continuous phase (methane gas) and the dispersed phase (CO2 droplets) was established, the distribution of the gas flow field and the droplets paths in the supersonic separator were obtained using Discrete Particle Method, the droplet separation efficiency was defined, and the effect of the droplet sizes and speed on the separation efficiency were analyzed. The results show that there is an obvious restriction relation between the pressure and tangential velocity distribution caused by the swirl blade, a balanced point (optimized structure) is necessary to achieve the purpose of condensation and separation of CO2 droplets. And the separation efficiency increases with the increase of droplet size and the CO2 droplets can be separated completely when the droplet size is greater than 1.5μm. The initial axial velocity has no obvious effect on the separation efficiency of the supersonic separator.

Expansion characteristics of multiple wall jets in cylindrical observation chamber

The objective of this study is to investigate the drag reduction effect of a new launch technology by utilizing propellant gases to drain off water in the front of the projectile inside the gunbarrel for submerged launch process of underwater gun. A static analogue visualized device was designed and the high-speed digital photographic system was adopted to investigate expansion processes of multiple wall jets in cylindrical observation chamber. The evolution laws of Taylor cavities can be obtained by dealing with the expansion sequence maps. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the interaction process between the multiple wall jets and liquid medium, which can achieve the detailed distribution characteristics of phase, pressure, temperature and velocity in flow field. Results show that, by increasing four wall jets to eight wall jets, the decrease of the inlet turbulent kinetic energy of each jet leads to a decline in the initial axial velocity. However, the Taylor cavities achieve to converge more quickly for the case with more numbers of combustion-gas jets due to less nozzle interval distance. In addition, the convergence of Taylor cavities can enhance the drainage effect of the multiple wall jets and achieve excellent drag reduction effect for the underwater launching process, wherein the drainage effect for the case of six wall jets is the most outstanding.

Electron energy and electron trajectories in an inverse free-electron laser accelerator based on a novel electrostatic wiggler

We expand here a theory of a high-gradient laser-excited electron accelerator based on an inverse free-electron laser (inverse-FEL), but with innovations in the structure and design. The electrostatic wiggler used in our scheme, namely termed the Paul wiggler, is generated by segmented cylindrical electrodes with applied oscillatory voltages over segments. The inverse-FEL interaction can be described by the equations that govern the electron motion in the combined fields of both the laser pulse and Paul wiggler field. A numerical study of electron energy and electron trajectories has been made using the fourth-order Runge–Kutta method. The results indicate that the electron attains a considerable energy at short distances in this device. It is found that if the electron has got sufficient suitable wiggler amplitude intensities, it can not only gain higher energy in longer distances, but also can retain it even after the passing of the laser pulse. In addition, the results reveal that the electron energy gains different peaks for different initial axial velocities, so that a suitable small initial axial velocity of e-beam produces substantially high energy gain. With regard to the transverse confinement of the electron beam in a Paul wiggler, there is no applied axial guide magnetic field in this device.

Cross-flow-induced instability and nonlinear dynamics of cylinder arrays with consideration of initial axial load

The instability and nonlinear dynamics of planar motions of a cylinder array subjected to cross-flow have been studied via a five-mode discretization of the governing partial differential equation, focusing on the effect of initial axial load externally imposed on the cylinder. Theoretical results based on a stability analysis have indicated that, with increasing initial axial load and flow velocity, the system may lose stability either via flutter or via buckling. The boundaries of these two forms of instability are predicted analytically. To explore the post-instability dynamics of the system, a Runge–Kutta scheme is used to solve the nonlinear governing equation of motion. Three typical behaviors, including limit cycle motions of the system, are obtained. It is shown that, for relatively low flow velocity, with increasing initial axial load, just beyond the pitchfork bifurcation the cylinder would settle in a buckled equilibrium position; and for high flow velocity, however, this phenomenon only occurs when the initial axial load becomes sufficiently large.

Sensitivity and amplitude calibration of a Fourier transform 3D quadrupole ion trap mass spectrometer

With a three-dimensional (3D) quadrupole ion trap running in a Fourier transform operating mode, the detected signal is an image of the collective motion of the confined ions. Consequently, it is assumed that the image signal is the sum of the axial trajectories of the simultaneously confined ions. The resulting frequency spectrum after Fourier transformation comprises frequency peaks at the axial secular frequencies of the confined species according to their mass/charge ratio. With a singly confined species, the maximal amplitude of the image signal is proportional to the amplitude of the secular axial frequency peak. The matrix method is employed to express the axial trajectory sampled at the confinement field period. In that case, the expression of the image signal, as well as its maximal amplitude, is calculated as a function of the trap operating conditions and initial axial positions and axial velocities of the ions. The initial position and velocity distributions are connected to the injection mode. With the steady ion flow injection mode (SIFIM) and an initial phase of the confinement field equal to kπ, the maximal amplitude of the image signal is proportional to either the sum of the initial axial positions or the number of confined ions and the mean value of the initial axial positions. By simulation, amplitude fluctuation of the frequency peak is then calculated for a number of ions ranging between some tens to some thousands of ions injected by SIFIM. The peak amplitude fluctuations induced by the fluctuations of the number of ions are seven times greater than those induced by the fluctuations of the distribution of the initial axial positions.

In-Source Fragmentation of Very Labile Peptides in Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Synthetic acidic proline-rich peptides devoid of basic chemical groups were studied by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). Their ion mass spectra recorded in reflector positive ion mode have shown unusual features, i.e., absence or very weak presence of protonated peptide together with a major peak associated with fragmentation at a site that corresponds to the amide bond N-terminal to the first proline of the XPP motif. In contrast, arginine-containing analogues were stable in MALDI-TOF, whereas peptides sharing a free N-terminal amino group were moderately subject to the same fragmentation. Effects of extraction delay time suggest that this process takes place very early (nanoseconds) at the beginning of the plume expansion. The effect of the nature of the matrix on the survival yield indicates a better correlation with the initial axial velocity than with the matrix proton affinity. All the data show some strong differences with the classical in-source decay (ISD). Our results suggest the role of the available protons in the close neighborhood of the peptide during the crystallization process and the prompt fragmentation induced by collisions in the first step of ablation. Undoubtedly, our study highlights that the MALDI-TOF analysis of peptides containing proline and no basic group should be carried out with extreme caution.

Particle Trajectory in a Bidirectional Vortex Flow

In this research particle trajectory in a bidirectional vortex flow has been numerically predicted and the results experimentally validated. Scale analyses of forces show their order of magnitudes and give a criterion to recognize the order of magnitude of exerting forces on the particle. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, density, and position of entering particle are assumed to be known. If the particle length scale is considered not to be comparable with the chamber length and if particle number density is low, then influence of particle on the flow field is negligible and a one-way solution is applicable. The governing equation is converted to a set of nonlinear, coupled, second-order ODE and solved by a numerical scheme. Results show that higher density, larger diameter, and higher initial axial velocity tend to move the particles further in the axial direction. Also, the maximum axial movement of the particle occurs when the initial radial velocity is zero and there is an optimum entrance position that provides a maximum traveling trajectory for particles. Increasing initial z-direction velocity component and density will result in increasing traveling trajectory.

Optimized simultaneous transverse and longitudinal focusing of intense ion beam pulses for warm dense matter applications

Intense, space-charge-dominated ion beam pulses for warm dense matter and heavy ion fusion applications must undergo simultaneous transverse and longitudinal bunch compression in order to meet the requisite beam intensities desired at the target. The longitudinal compression of an ion bunch is achieved by imposing an initial axial velocity tilt on the drifting beam and subsequently neutralizing its space-charge and current in a drift region filled with high-density plasma. The Neutralized Drift Compression Experiment (NDCX) at Lawrence Berkeley National Laboratory has measured a sixty-fold longitudinal current compression of an intense ion beam with pulse duration of a few nanoseconds, in agreement with simulations and theory. A strong solenoid is modeled near the end of the drift region in order to transversely focus the beam to a sub-millimeter spot size coincident with the longitudinal focal plane. The charge and current neutralization provided by the background plasma is critical in determining the total achievable transverse and longitudinal compression of the beam pulse. Numerical simulations show that the current density of an NDCX ion beam can be compressed over a few meters by factors greater than 10 5 with peak beam density in excess of 10 14 cm −3. The peak beam density sets a lower bound on the local plasma density required near the focal plane for optimal beam compression, since the simulations show stagnation of the compression when n beam> n plasma. Beam–plasma interactions can also have a deleterious effect on the compression physics and lead to the formation of nonlinear wave excitations in the plasma. Simulations that optimize designs for the simultaneous transverse and longitudinal focusing of an NDCX ion beam for future warm dense matter experiments are discussed.

Matrix–analyte-interaction in MALDI-MS: Pellet and nano-electrospray preparations

The incorporation of analytes into matrix crystals and even more so its mechanistic aspects as a prerequisite for a successful MALDI-MS has been discussed controversially in the literature. Solventless sample preparation techniques can shed new light on this question. In order to investigate some crucial aspects of these preparation techniques, lyophylized peptides and proteins were ground or milled with the powder of two different matrices, 2,5-DHB as incorporating matrix and 2,6-DHB for which protein incorporation was definitely excluded in a prior study, and pressed into pellets. The dependence of the quality of the UV-MALDI-spectra on the mass (up to 12,360 Da) and the milling time in a ball mill is reported. For mellitin different initial axial ion velocities were found, when desorbed from 2,5-DHB-pellets as prepared and after wetting and re-drying. Velocities of 150 and 580 m s −1 for dry and wetted pellets are taken as representative for hard desorption from a surface and soft desorption of matrix-incorporated analytes, respectively. Proteins labeled with either fluorescein isothiocyanate (FITC) or Texas Red (TR) were nano-electrosprayed onto a bed of ferulic acid in a ‘dry’ or ‘wet’ mode. All ‘dry’ deposits exhibit strong fluorescence but do not yield MALDI-ion signals. All ‘wet’ deposits yield MALDI-signals of the proteins; the fluorescence of FITC is quenched in ‘wet’ deposits because of the low matrix pH.

Delayed extraction experiments using a repulsing potential before ion extraction: evidence of non‐covalent clusters as ion precursor in UV matrix‐assisted laser desorption/ionization. Part II—Dynamic effects with α‐cyano‐4‐hydroxycinnamic acid matrix

Delayed extraction experiments were undertaken to gain a better insight into the dynamic effects involved in the ion formation in UV matrix-assisted laser desorption/ionization. Part I1 was devoted to a 2,5-dihydroxybenzoic (2,5-DHB) matrix. The results clearly demonstrated the existence and the role of high-mass precursors corresponding to a non-covalent matrix-analyte association in ion formation. In this complementary study, ion flight time and abundance were studied as a function of the delay extraction time using the matrix alpha-cyano-4-hydroxycinnamic acid (HCCA). Under our instrumental conditions, where ejected ions experienced a low repulsing electric field before extraction, two main results were obtained: (i) two ion components are observed in the peak profiles depending on the repulsing field, a first, major component (I) similar to that observed for 2,5-DHB and a second, minor component (II) apparently triggered by the delayed extraction pulse, and (ii) ion time-of-flight variation vs delay time remained lower than that noted with 2,5-DHB matrix, indicating that the initial axial velocity is smaller. The initial kinetic energy of matrix and low molecular mass peptide ions for the component I is not high enough to overcome the repulsing potential in the delay time range (200-2200 ns) and we have to assume that ions have non-covalent clusters as precursors. Complete desolvation of these clusters-aggregates would be achieved through the extraction step. Simulations of the ion time-of-flight as a function of the delay time allow the determination of the average size of the precursors, typically 4500, 40000 and 50000 u for HCCA, ACTH 7-38 and bovine insulin quasi-molecular ion, respectively, assuming that the precursors are singly charged. The size of these ion precursors is greater than that of those generated for 2,5-DHB. For component II, ions are probably not solvated and they are directly desorbed from the target. Taking into account the results on HCCA and 2,5-DHB matrices and other results from the literature, a general model for ion formation based on clusters as ion precursors is proposed and discussed.

The velocity-scalar cross spectrum of stretched spiral vortices

The stretched-spiral vortex model is used to calculate the velocity-scalar cross spectrum for homogeneous, isotropic turbulence in the presence of a mean scalar gradient. The only nonzero component of the cospectrum is that contributed by the velocity component in the direction of the imposed scalar gradient while the quadrature spectrum is identically zero, in agreement with experiment. For the velocity field provided by the stretched-spiral vortex, the velocity-scalar spectrum can be divided into two additive components contributed by the velocity components along the vortex axis, and in the plane normal to this axis, respectively. For the axial velocity field, a new exact solution of the scalar convection-diffusion equation is found exhibiting scalar variation in the direction of the vortex tube axis. An asymptotic expression was found for the cospectrum contributed by this solution and the axial velocity, with the leading order term showing a k−5/3 range. This term is produced by the winding of the initial axial velocity field by the axisymmetric vortex core. The next order term gives a k−7/3 range, and arises from the lowest order effect of the nonaxisymmetric vorticity on the evolution of the axial velocity. Its coefficient can be of either sign or zero depending on the initial conditions. The contribution to the cospectrum from the velocity in the plane of the vortex is also calculated, but no universal high wave number asymptotic form is found. The integrals are evaluated numerically and it is found that the resulting cospectrum does not remain of one sign. Its form depends on the choice of the vortex core velocity profile and time cutoff in the spectral integrals. The one-dimensional cospectrum contributed by the axial velocity is compared with the experimental data of Mydlarski and Warhaft [J. Fluid Mech. 358, 135–175 (1998)].

Influence of the magnitude of the two initial velocities on the flow field of a coaxial turbulent jet

The present investigation is a continuation of a program to study the effects of various parameters on the flow field of a coaxial turbulent jet. In the present study the effect of varying the absolute value of the two initial axial mean velocities of the jet is investigated experimentally, while keeping their ratio constant. The effect of absolute value of each stream velocity, on the flow field, was investigated by means of achieving the velocity ratio, λ= U i/ U o=2, three times with two different velocities each time. Moreover, The similarity of the axial mean velocity profiles was investigated, for two other values of λ=3.3 and 4.5, and compared with the results of the single jet. The results show that the reduction in the absolute values of the velocities of both streams while keeping the same velocity ratio constant made the coaxial jet decay faster along the centerline. In addition, similarity of the radial profiles of the axial mean velocity was obtained in the fully merged region.

A modal and damping analysis of viscoelastic Timoshenko tubes conveying fluid

This paper presents a viscoelastic finite element approach to the vibration analysis of viscoelastic Timoshenko tubes conveying inviscid incompressible fluid, within which the temperature-dependent functions of material properties are assumed known. The derivation of a viscoelastic finite element model, applied to a time-domain solution, is detailed. The dynamic behaviour of viscoelastic tubes conveying fluid is investigated for several initial axial tensions and fluid velocities. Numerical results are presented and discussed. Copyright © 2001 John Wiley & Sons, Ltd.

A modal and damping analysis of viscoelastic Timoshenko tubes conveying fluid

This paper presents a viscoelastic finite element approach to the vibration analysis of viscoelastic Timoshenko tubes conveying inviscid incompressible fluid, within which the temperature-dependent functions of material properties are assumed known. The derivation of a viscoelastic finite element model, applied to a time-domain solution, is detailed. The dynamic behaviour of viscoelastic tubes conveying fluid is investigated for several initial axial tensions and fluid velocities. Numerical results are presented and discussed. Copyright © 2001 John Wiley & Sons, Ltd.