基于板式换热器的天然气冷却模拟与实验研究

结合实际工程项目,针对某新型天然气冷箱液化流程中的三台钎焊板式换热器,采用双通道耦合换热模型,以分段线性插值法计算天然气物性,基于FLUENT软件进行了天然气冷却换热过程的CFD数值模拟仿真,并开展了该新型冷箱的实验测试研究。将数值模拟计算结果与HSYSY工艺流程设计值以及实验测试结果进行对比。结果表明,数值模拟计算结果与HSYSY设计值平均误差为4.94%,证明了采用CFD数值模拟方法对HYSYS工艺流程设计与设备选型进行校核具有一定的参考价值。数值模拟计算结果与实验测试结果平均误差为7.78%,证明了数值模拟仿真所采用的简化假设、换热模型以及求解方法对于板式换热器天然气冷却换热过程是合理的。     

Numerical and experimental investigation of laser propulsion

Aiming at the application of laser propulsion to stratospheric flight, we propose here a repetitive propulsion system, friction-less environment and metal-free ablation in a water cannon target. A special reservoir of water is proposed to supply a definite amount of water only at the time of laser irradiation. This system is tested for the object levitated on the airflow, which is called air-slider in order to simulate friction-less environment. In order to avoid the evaporation and freezing of water in lower atmospheric pressures, we propose here an air curtain system. We have performed simulations and experiments and confirmed that a small amount of air flow can sustain the high pressure inside the water reservoir. PACS 42.62.Cf; 52.38.Mf; 07.87.+v     

Numerical and experimental investigation of long-period gratings in photonic crystal fiber for refractive index sensing of gas media

We have used the finite-difference frequency-domain (FDFD) method to simulate the core mode to cladding mode couplings in long-period gratings (LPGs) in photonic crystal fiber (PCF). Four sets of LPG-PCF have been fabricated with respective periodicities of 590, 540, 515, and 490 μm, resulting in corresponding resonance wavelengths (RWs) of 1241, 1399, 1494, and 1579 nm. We show both theoretically and experimentally that the longer the RW, the more sensitive the LPG-PCF is to the index change in Ar. We demonstrate a robust sensitivity of 517 nm per refractive index unit using the LPG-PCF at 1579 nm RW.     

气体靶密度的数值计算与实验研究

 采用了1维简单模型来模拟气体靶的空间密度分布情况,并且该计算值得到了实验的验证。使用M-Z干涉仪诊断锥型喷嘴喷射的气体靶密度分布,得到了不同压力和不同延时下的干涉图样。自行编写了实验数据处理程序,得到了不同情况下气体密度的空间分布。在相互作用实验中,由气体分子密度随压力的变化,可以确定合适的压力,以获得预期的气体靶密度;由气体分子密度随时间的变化,可以确定激光与气体的作用时刻。     

气体靶密度的数值计算与实验研究

采用了1维简单模型来模拟气体靶的空间密度分布情况,并且该计算值得到了实验的验证。使用M-Z干涉仪诊断锥型喷嘴喷射的气体靶密度分布,得到了不同压力和不同延时下的干涉图样。自行编写了实验数据处理程序,得到了不同情况下气体密度的空间分布。在相互作用实验中,由气体分子密度随压力的变化,可以确定合适的压力,以获得预期的气体靶密度;由气体分子密度随时间的变化,可以确定激光与气体的作用时刻。     

磁力提升装置样机的数值分析与实验研究

研制的磁力提升装置实现了对加速器驱动次临界系统(ADS)新型钨基合金球靶材的电磁提升。其基本原理是通过控制一组螺线管的加电时序,实现磁场的移动,移动磁场作用于靶材完成其输运。螺线管作为该装置的主要部件,其结构影响电磁提升的效率。为优化其结构,采用Ansys Maxwell分析螺线管的磁场分布,确定螺线管结构。同时利用Ansys Maxwell给每个螺线管加不同宽度的脉冲进行数值模拟,通过调节每个螺线管的通断电时间和同时工作的螺线管单元数,模拟计算合金球的受力。在数值模拟的基础上完成了磁力提升装置样机的加工和实验研究,实现了钨基合金球输运的预期效果。     

磁力提升装置样机的数值分析与实验研究

研制的磁力提升装置实现了对加速器驱动次临界系统(ADS)新型钨基合金球靶材的电磁提升。其基本原理是通过控制一组螺线管的加电时序,实现磁场的移动,移动磁场作用于靶材完成其输运。螺线管作为该装置的主要部件,其结构影响电磁提升的效率。为优化其结构,采用Ansys Maxwell分析螺线管的磁场分布,确定螺线管结构。同时利用Ansys Maxwell给每个螺线管加不同宽度的脉冲进行数值模拟,通过调节每个螺线管的通断电时间和同时工作的螺线管单元数,模拟计算合金球的受力。在数值模拟的基础上完成了磁力提升装置样机的加工和实验研究,实现了钨基合金球输运的预期效果。     

A new dual matrix burner for one-dimensional investigation of aerosol flames

In spray-flame synthesis of nanoparticles, a precise understanding of the reaction processes is necessary to find optimal process parameters for the formation of the desired products. Coupling the chemistries of flame, solvent, and gas-phase species initially formed from the particle precursor in combination with the complex flow geometry of the spray flame means a special challenge for the modeling of the reaction processes. A new burner has been developed that is capable to observe the reaction of precursor solutions frequently used in spray-flame synthesis. The burner provides an almost flat, laminar, and steady flame with homogeneous addition of a fine aerosol and thus enables detailed investigation and modeling of the coupled reactions independent of spray formation and turbulent mixing. With its two separate supply channel matrices, the burner also enables the use of reactants that would otherwise react with each other already before reaching the flame. These features enable the investigation of a wide range of flame-based synthesis methods for nanoparticles and, due to the flat-flame geometry, kinetics models for these processes can be developed and validated. This work describes the matrix burner development and its gas flow optimization by simulation. Droplet-size distributions generated by ultrasonic nebulization and their interaction with the burner structure are investigated by phase-Doppler anemometry. As an example for nanoparticle-forming flames from solutions, iron-oxide nanoparticle-generating flames using iron(III) nitrate nonahydrate dissolved in 1-butanol were investigated. This effort includes measurements of two-dimensional maps of the flame temperature by a thermocouple and height-dependent concentration profiles of the main species by time-of-flight mass spectrometry. Experimental data are compared with 1D simulations using a reduced reaction mechanism. The results show that the new burner is well suited for the development of reaction models for precursors supplied in the liquid phase usually applied in spray-flame synthesis configurations.     

Numerical and experimental investigation of seam welding with a pulsed laser

The present work develops two numerical models to compute thermal phenomena during pulsed laser welding. The first one which is based on finite difference model calculates the welding width and its penetration by utilizing heat transfer equations. Parametric design capabilities of the finite element code ANSYS were also employed for the simulation of the second model. The transient temperature profiles, the fusion dimensions and the heat affected zones (HAZ) have been calculated here. The thermo-physical properties are dependent on temperature and so a nonlinear solution is employed. It is found that the temperature profile and penetration depth are strongly dependent on the pulse parameters of laser beam. Finally, the results of the two models and the experimental outcomes are compared.     

Numerical investigation of subcritical microwave discharges in a high-pressure gas

Subcritical microwave streamer discharges are investigated using a two-dimensional model that describes gas-dynamic processes in the ideal gas approximation and a self-consistent electromagnetic field in the wave approximation and takes into account the minimum required number of kinetic processes (such as ionization, attachment, recombination, diffusion, and electric conduction). The initial conditions imitate the initiation of a discharge from a small cavity with a reduced gas density and an arbitrarily small degree of gas ionization. The possibility of describing streamer discharges without reference to ionizing hard radiation is confirmed.     

Border collision route to quasiperiodicity: Numerical investigation and experimental confirmation

Numerical studies of higher-dimensional piecewise-smooth systems have recently shown how a torus can arise from a periodic cycle through a special type of border-collision bifurcation. The present article investigates this new route to quasiperiodicity in the two-dimensional piecewise-linear normal form map. We have obtained the chart of the dynamical modes for this map and showed that border-collision bifurcations can lead to the birth of a stable closed invariant curve associated with quasiperiodic or periodic dynamics. In the parameter regions leading to the existence of an invariant closed curve, there may be transitions between an ergodic torus and a resonance torus, but the mechanism of creation for the resonance tongues is distinctly different from that observed in smooth maps. The transition from a stable focus point to a resonance torus may lead directly to a new focus of higher periodicity, e.g., a period-5 focus. This article also contains a discussion of torus destruction via a homoclinic bifurcation in the piecewise-linear normal map. Using a dc-dc converter with two-level control as an example, we report the first experimental verification of the direct transition to quasiperiodicity through a border-collision bifurcation.     

Numerical and experimental investigation on ASE effects in high-power slab amplifiers

A three-dimensional calculation of the amplified spontaneous emission (ASE) is presented that allows rapid determination (with suitable approximation techniques) of the gain-length product (GLP) in high-power slab amplifiers. These calculations include non-saturable absorption, ASE line-narrowing effects, and total internal reflections (TIR) at the pumping surfaces. A parametric study of the slab geometry is presented and compared with experimental results. A good qualitative agreement between theory and experiment is achieved.     

Numerical and experimental investigation of the fracture behavior of shock loaded alumina

Plate impact expeiments are conducted to investigate the dynamic behavior of alumina by using one stage light gas gun. A ve-locity interferometer system for reflectors (VISAR) is used to obtain Hugoniot elastic limit and the free surface velocity profile,which consists of an elastic wave followed immediately by a dispersive inelastic wave. The stress histories under different impact velocities are measured by in-material manganin gauges. Based on the experimental data a Hugoniot curve is fitted,which shows ...     

A theoretical and experimental investigation of long-pulse,electron-beam-produced rare gas plasmas

Visible emission spectroscopy (380-650 nm) has been performed on intense, electron beam (1 kA, 300 ns, 300 kV) produced Ar, Kr, and Xe plasmas at pressures ranging from 10 to 750 torr. Singly ionized and neutral lines dominated the spectra in all cases except argon, where only singly ionized lines occurred. The temperature of the plasma as determined by comparing line intensities was between 1 and 2 eV. A computer model for chemical kinetics of the electron-beam-produced plasmas in Ar, Kr, and Xe was formulated. The model predicts time, pressure, and temperature trends of the ions, neutrals, and electrons, which agree with trends found experimentally     

Numerical and experimental investigation of the effect of filtering on chaotic symbolic dynamics

Motivated by the practical consideration of the measurement of chaotic signals in experiments or the transmission of these signals through a physical medium, we investigate the effect of filtering on chaotic symbolic dynamics. We focus on the linear, time-invariant filters that are used frequently in many applications, and on the two quantities characterizing chaotic symbolic dynamics: topological entropy and bit-error rate. Theoretical consideration suggests that the topological entropy is invariant under filtering. Since computation of this entropy requires that the generating partition for defining the symbolic dynamics be known, in practical situations the computed entropy may change as a filtering parameter is changed. We find, through numerical computations and experiments with a chaotic electronic circuit, that with reasonable care the computed or measured entropy values can be preserved for a wide range of the filtering parameter.     

Numerical and experimental investigation of temperature effects on the surface plasmon resonance sensor

The effects of temperature on a surface plasmon studied experimentally and theoretically. SPR resonance （SPR） sensor in Kretschmann configuration are experiments are carried out over a temperature range of 278- 313 K in steps of 5 K. A detailed theoretical model is provided to analyze the variation of performance with varying temperature of the sensing environment. The temperature dependence of the properties of the metal, dielectric, and analyte are studied, respectively. The numerical results indicate that the predictions of the theoretical model are well consistent with the experiment data.     

Numerical and experimental investigation of kerf depth effect on high-frequency phased array transducer

Background

High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the structure design and fabrication of the kerfed ultrasonic array is quite challenging when very high frequency (?100 MHz) is required.

Objective and method

Here we investigate the effect of kerf depth on the performances of array transducers. A finite element tool, COMSOL, is employed to simulate the properties of acoustic field and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. Furthermore, Inductively Coupled Plasma (ICP) deep etching process is used to etch 36°/Y-cut lithium niobate (LiNbO₃) crystals and the limitation of etching aspect ratio is studied. Several arrays with different profiles are realized under optimized processes. At last, arrays with a pitch of 25 μm and 40 μm are fabricated and characterized by a network analyzer.

Results

Kerf depth plays an important role in the performance of the transducer array. The crosstalk is proportional to kerf depth. When kerf depth is more than 13 μm, the array with crosstalk less than −20 dB, which is acceptable for the real application, could provide a desired resolution. Compared to beam focusing, kerf depth exhibits more effect on the beam steering/focusing. The lateral pressure distribution is quantitatively summarized for four types of arrays with different kerf depth. The results of half-cut array are similar to those of the full-cut one in both cases of focusing and steering/focusing. The Full-Width-at-Half-Maximum (FWHM) is 55 μm for the half-cut array, and is 42 μm for the full-cut one. The 5-μm-cut array, suffering from severe undesired lobes, demonstrates similar behaviors with the no-cut one. ICP process is used to etch the 36°/Y-cut LiNbO₃ film. The aspect ratio of etching profile increases with the kerf width decreasing till it stops by forming a V-shaped groove, and the positive tapered profile angle ranges between 62° and 80°. If the mask selectivity does not limit the process in terms of achievable depth, the aspect ratio is limited to values around 1.3. The measurement shows the electrical impedance and crosstalk are consistent with the numerical calculation.

Conclusion

The numerical results indicate that half-cut array is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays. In fact, the minimum pitch that could be obtained is around 25 μm, equivalent to a pitch of 1.6λ, with a kerf depth of 16 μm under the optimized ICP parameters.     

An electrochemical and structural investigation of porous composite anode materials for LIB

A porous composite anode for lithium ion battery (LIB) was investigated. The composite anode was prepared by electrodepositing Sn?CSb alloy on a template-like electrode and then annealing it in the atmosphere of N₂, whereas the porous template-like electrode was obtained by forming a sponge-like porous membrane on a copper foil via a mixed phase inversion process, followed by pre-plating Cu through membrane pores in it. SEM and XRD results showed that composite structure of the anode consisted of electrodeposited Sn?CSb alloy dispersed in a PAN-pyrolyzed conjugated conducting polymer gridding, which was tightly connected with the Cu foil through transition alloy layer formed by heat treatment. Due to its relatively reasonable microcosmic structure, the composite anode presented better cycling performance and specific capacity retention during charging and discharging at diverse rates. When cycled between 0 and 2.0?V (vs Li/Li⁺) at 0.5?C rate, the reversible charge/discharge capacity of the composite material remained 415 and 414.8?mAh?g^?1, respectively, after 30 cycles, corresponding to 82.9% of the capacity retention. When charging and discharging at 2?C rate, the composite material electrode showed 71.7% capacity retention at the 30th cycle.