Thickening and Rheological Properties of Crystalline Polyester Used in Low Pressure Sheet Molding Compounds

Low pressure sheet molding compound （LPMC,1.0-3.0 MPa,95-103 ℃） is a new kind of thermosetting material with crystalline polyester as a physical thickenner.LPMC is different from conventional SMC using an earth oxide thickening agent （e.g.MgO） as chemical thickenner,it relies on the physical thickening of crystalline polyester.Crystalline polyester resin is the key material to mold LPMC parts.Currently there was no report about the thickening mechanism of crystalline polyester in LPMC.In this article,crystalline polyester resins,whose melting points were between 45 ℃ and 89 ℃,were synthesized by a two-step esterification.The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids.And by means of varying the content of crystalline polyester resin,the thickening effect on resin paste is investigated.In addition,the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis.The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied,too.Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%.And there exists three kinds of functions acting in the process of thickening：swelling,hydrogen bonds and induction crystallization.During the preparing process of resin paste in LPMC,the temperature of resin paste must be kept at 90 ℃.In addition,crystalline polyester make LPMC have a perfect fluid property.When the viscosity of LPMC sheet is beyond 1 kPa s,the fiber orientation is not obvious.But when the viscosity of LPMC sheet is about 500 Pa s,the fiber shows a certain degree of orientation.Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.

Gating system optimization of low pressure casting A356 aluminum alloy intake manifold based on numerical simulation

To eliminate the shrinkage porosity in low pressure casting of an A356 aluminum alloy intake manifold casting, numerical simulation on fi lling and solidifi cation processes of the casting was carried out using the ProCAST software. The gating system of the casting is optimized according to the simulation results. Results show that when the gating system consists of only one sprue, the fi lling of the molten metal is not stable; and the casting does not follow the sequence solidifi cation, and many shrinkage porosities are observed through the casting. After the gating system is improved by adding one runner and two in-gates, the fi lling time is prolonged from 4.0 s to 4.5 s, the fi lling of molten metal becomes stable, but this casting does not follow the sequence solidifi cation either. Some shrinkage porosity is also observed in the hot spots of the casting. When the gating system was further improved by adding risers and chill to the hot spots of the casting, the shrinkage porosity defects were eliminated completely. Finally, by using the optimized gating system the A356 aluminum alloy intake manifold casting with integrated shape and smooth surface as well as dense microstructure was successfully produced.

Effect of pressurizing speed on filling behavior of gradual expansion structure in low pressure casting of ZL205A alloy

The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get smooth mold filling process and provide a guide for the pressurizing speed design in the producing practice, the mathematical model with the pressurizing speed, expansion angle and height of the gradual expansion structure was established. For validation experiments, ZL205 A alloy castings were produced under two different pressurizing speeds. Weibull probability plots were used to assess the fracture mechanisms under different pressurizing speeds. Mechanical properties of ZL205 A alloy were applied to assess the entrainment of oxide film. The results show that the filling process of a gradual expansion structure in a low pressure casting can be divided into the spreading stage and filling stage by gate velocity. The gate velocity continues to increase in the gradual expansion structure, and increases with the increase of pressurizing speed or expansion angle. Under the effect of the falling fluid raised by the jet flow along the sidewall, the fluid velocity decreases in the jet zone from ingate to free surface. As such, oxide film entrainment does not occur when the gate velocity is greater than the critical velocity, andthe gate velocity no longer reflects the real state of the free surface. The scatter of the mechanical properties is strongly affected by the entrainment of oxide films.

Study of vortex in flow fields induced by surface dielectric barrier discharge actuator at low pressure based on Q criterion

Flow fields induced by a surface dielectric barrier discharge actuator at low pressure of 7 kPa are measured by particle image velocimetry. The distribution of local vortices in the flow field is revealed by the Q criterion. The reason for the generation of vortices is analyzed and the influence of pulse frequency and duty cycle on vortices is studied. The results show that the Q criterion can reveal the small-scale vortices, which cannot be indicated by the streamline. The direction transition zone where the induced jet moves from the vertical to the tangential and the shear layer between the jet and stationary air are prone to the generation of strong vortices. The influence of pulse frequency on vortices is not obvious, but the variation of duty cycle can significantly affect the strength and distribution of vortices.

Characteristics of long-gap AC streamer discharges under low pressure conditions

The generation and propagation of a streamer is a significant physical process of air gap discharge. Research on the mechanism of streamers under low-pressure conditions is helpful for understanding the process of long-gap discharge in a high-altitude area. This paper describes laboratory investigations of streamer discharge under alternating current（AC） voltage in a low pressure test platform for a 60 cm rod–plane gap at 30 kPa, and analyzes the characteristics of streamer generation and propagation. The results show that the partial streamer and breakdown streamer all occur in the positive half-cycle of AC voltage near the peak voltage at 30 kPa. The partial streamer could cause the distortion of current and voltage waveform, and it appears as the branching characteristic at the initial stage. With the extension of the streamer, the branching and tortuosity phenomena become gradually obvious, but the branching is suppressed when the streamer crosses the gap. The low-pressure condition has little influence on the tortuosity length and the tortuosity number of the streamer, but affect the diameter of streamer obviously.

Cure Reaction Kinetics of Low Pressure Sheet Molding Compound System Thickened by Crystalline Polymer

Several kinetic models for unsaturated polyester cure reaction and some existing parameter estimation techniques of these models were introduced. Correlated kinetic parameters and kinetic equations of the autocatalytic empirical kinetic model of LPSMC system were determined by using isothermal DSC to scan the system which was thickened by crystalline polymer （PEG-MAH）. Through using a serial curing degree of the system to validate the model, the experimental results were basically identical with the predictions of the autocatalytic empirical kinetic model. This model could provide a theoretical reference to the determination of molding techniques of low pressure SMC.

Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

A Monte Carlo simulation method with an instantaneous density dependent meanfree-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas.The ablated-particle density and velocity distributions are analyzed.The force distributions acting on the ablated particles are investigated.The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed.The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa.This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles.

Similarity principle of microwave argon plasma at low pressure

In order to validate the similarity principle of microwave breakdown, a two-dimensional （2D） fluid model of low- pressure microwave argon plasma is established and solved by the finite-element method. Proportional conditions are used in this model to build three different breakdown processes that meet the premise of a similarity principle, and these breakdown processes are called ＂similar cases＂ in this paper. Similar cases have proportionately sized breakdown regions, where the ratio of frequency of incident microwave f to gas pressure p （f/p）, and the reduced field E/p in them are kept the same. All the important physical parameters such as electron density, electron temperature, and reduced electric field can be obtained from the simulation of this model. The results show that the parameters between similar cases are in constant ratio without changing with time, which means that the similarity principle is also valid in microwave breakdown.

Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon

An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium （LTE）, the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.

Intelligent production optimization method for a low pressure and low productivity shale gas well

Shale gas wells frequently suffer from liquid loading and insufficient formation pressure in the late stage of production.To address this issue,an intelligent production optimization method for low pressure and low productivity shale gas well is proposed.Based on the artificial intelligence algorithms,this method realizes automatic production and monitoring of gas well.The method can forecast the production performance of a single well by using the long short-term memory neural network and then guide gas well production accordingly,to fulfill liquid loading warning and automatic intermittent production.Combined with adjustable nozzle,the method can keep production and pressure of gas wells stable automatically,extend normal production time of shale gas wells,enhance automatic level of well sites,and reach the goal of refined production management by making production regime for each well.Field tests show that wells with production regime optimized by this method increased 15%in estimated ultimate reserve(EUR).Compared with the development mode of drainage after depletion recovery,this method is more economical and can increase and stabilize production effectively,so it has a bright application prospect.

Ion property and electrical characteristics of 60MHz very-high-frequency magnetron discharge at low pressure

The pre-ionized 60 MHz very-high-frequency （VHF） magnetron discharge at low pressure, assisted by inductively coupled plasma （ICP） discharge, was developed. The measurement of ion flux density and ion energy to the substrate was carried out by a retarding field energy analyzer. The electric characteristics of discharge were also investigated by voltage-current probe technique. It was found that by reducing the discharge pressure of VHF magnetron discharge from 5 to 1 Pa, the ion flux density increased about four times, meanwhile the ion energy also increased doubly. The electric characteristics of discharge also showed that a little improvement of sputtering effectiveness was achieved by reducing discharge pressure. Therefore, the deposition property of VHF （60 MHz） magnetron sputtering can be improved by reducing the discharge pressure using the ICP-assisted pre-ionized discharge.

Investigation on the Effects and Mechanisms of PTFE Surface Modification by Low Pressure Plasma

Using argon as the work gas, the effects and mechanisms of poly（tetrafluoroethylene） （PTFE） film surface modification were investigated in a low pressure plasma reactor. Results show that higher hydrophilicity with little degradation, in terms of the scanning electron microscopy （SEM）, was obtained after treatment, especially when the sample was placed in the post-discharge area. More polar functional groups and higher surface free energy, especially the polar component, formed on the PTFE surface were responsible for the modification. For the relatively high purity radicals and rare discharge particles in the post-discharge area, the etching was restrained and the introducing reactions were enhanced, and thus, a better modification occurred there.

Application of Low Pressure Plasma Technology in the Field of Environmental Protection

The characteristics of low pressure plasma produced by a gas discharges lie in thatthe energy of the electrons are much higher than that of the heavy particles in the system. Inthis paperl the low-pressure plasma treatment technology for the environmental contaminantswas synthetically studied, and the reaction processing and mechanism between the low-pressureplasma and the environmental contaminants were theoretically analyzed. At last, the prospectsand existing problems on the application of low-pressure plasma in the field of environmentalprotection were discussed.

Retrofit on Low Pressure Cylinder Flow Path Succeeded

The retrofit on flow path of low pressure cylinder of domestic made 200 MW steam turbine undertaken by Longwei Power Generation Technology Service Company Ltd by using Westinghouse technology was successful for the first time on the No. 5 unit of Zhenhai Prover Plant. Zhejiang Province. The test carried out by the Xi’an Thermal Power Research Institute showed that the thermal efficiency after the retrofit

Effects of Freestream Turbulence,Reynolds Number and Mach Number on the Boundary Layer in a Low Pressure Turbine

In order to investigate the aerodynamics of a high speed low pressure turbine works in high Mach number and low Reynold number environment,the effect of freestream turbulence(FST)on the boundary layer development on the high speed low pressure turbine under different Reynolds numbers(Re)is numerically investigated.Large eddy simulation is adopted here with a subgrid scale model of Wall Adapting Local Eddy viscosity(WALE).Cases with Re ranging from 100000 to 400000 under an exit Mach number(Ma)of 0.87 have been considered at low and high FST levels.A low Ma case(0.17)under very low Re has also been studied under both low and high FST.It is found that higher Re or FST level leads to earlier transition.Re has a greater effect than FST on the development of boundary layer.The effect of FST on the boundary layer depends on the Re.The boundary layer development shows totally different behaviors under different Ma.A separation bubble could be formed under low Ma while no attachment could be detected under high Ma.The FST has a stronger effect on the separated boundary layer under low Ma,which could eliminate the separation in the present study.For all the cases under low FST,the Kelvin-Helmholtz instability is the dominate mechanism in the transition process.For the low Ma case with high FST,the streamwise streaks play a dominant role in the transition process.For the high Ma cases with high FST,both the streamwise streaks and Kelvin-Helmholtz instability work in the transition process.The streamwise streaks play a more important role when the Re increased.

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission.Pantograph-catenary arc vertical drift is more severe than the case under normal pressure,as it is easy to develop the rigid busbar,which may lead to the flashover occurring around the support insulators.We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment.Meanwhile,the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed.Moreover,arc drift characteristics and influencing factors are explored.The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized.In order to further explore the mechanism of the above physical process,a multi-field stress coupling model is built,as the multi-stress variation law of arc is quantitatively evaluated.The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored,as the physical mechanism of arc drifting under low pressure is theoretically explained.The research results provide theoretical support for arc suppression in high-altitude areas.

Oxidation of Fe-Cr-Ni Alloys in a Low Oxygen Partial Pressure Atmosphere to Mitigate Coke Formation

Anti-coking oxide films were prepared on a 25Cr35Ni and 35Cr45Ni alloy surface under the low oxygen partialpressure atmosphere of a H2-H2O mixture. The composition and phase structure of the oxide films were analyzed by energydispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-cokingperformance of a mini tube made of a HP40 (25Cr35Ni) alloy was evaluated on a bench scale pyrolysis and coking test unit.The results showed that the surface Fe and Ni content decreased after the oxidation of the two alloys in a low oxygen partialpressure atmosphere. The oxide films were mainly composed of MnCr_(2)O_(4) and Cr_(2)O_(3). The average mass of coke in the minitube with oxide film decreased by 87% relative to that of a tube without an oxide film when the cracking temperature was 900℃. The ethylene, propylene, and butadiene yields in the pyrolysis tests were almost the same for the mini tubes withand without an oxide film. The oxide film on the alloy surface effectively inhibited catalytic filamentous coke formation.An industrial test showed that the run length of the cracking furnace with the in-situ coating technology was significantlyextended.

Application of a macromolecular chelating agent in chemical mechanical polishing of copper film under the condition of low pressure and low abrasive concentration

The mechanism of the FA/O chelating agent in the process of chemical mechanical polishing （CMP） is introduced. CMP is carried on a φ300 mm copper film. The higher polishing rate and lower surface roughness are acquired due to the action of an FA/O chelating agent with an extremely strong chelating ability under the condition of low pressure and low abrasive concentration during the CMP process. According to the results of several kinds of additive interaction curves when the pressure is 13.78 kPa, flow rate is 150 mL/min, and the rotating speed is 55/60 rpm, it can be demonstrated that the FA/O chelating agent plays important role during the CMP process.

EXPERIMENTAL RESEARCH ON AERODYNAMIC PERFORMANCE AND EXIT FLOW FIELD OF LOW PRESSURE AXIAL FLOW FAN WITH CIRCUMFERENTIAL SKEWED BLADES

In this article, the low pressure axial flow fan with circumferential skewed rotor blade, including the radial blade, the forward-skewed blade and the backward-skewed blade, was studied with experimental methods. The aerodynamic performance of the rotors was measured. At the design condition at outlet of the rotors, detailed flow measurements were performed with a five-hole probe and a Hot-Wire Anemometer （HWA）. The results show that compared to the radial rotor, the forward-skewed rotor demonstrates a wider Stable Operating Range （SOR）, is able to reduce the total pressure loss in the hub region and make main loading of blade accumulating in the mid-span region. There is a wider wake in the upper mid-span region of the forward-skewed rotor. Compared to the radial rotor, in the backward-skewed rotor there is higher total pressure loss near the hub and shroud regions and lower loss in the mid-span region. In addition, the velocity deficit in the wake is lower at mid-span of the backward-skewed rotor than the forward-skewed rotor.

INTERNAL FLOW MECHANISM AND EXPERIMENTAL RESEARCH OF LOW PRESSURE AXIAL FAN WITH FORWARD-SKEWED BLADES

This article presents the flow mechanism analysis and experimental study of a forward-skewed impeller and a radial impeller in low pressure axial fan. The forward-skewed blade was obtained by the optimization design of the radial blade and CFD technique. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the forward-skewed blade has demonstrated the improvements in efficiency, total pressure ratio, Stable Operating Range （SOR） and less aerodynamic noise. Detailed flow measurement and computation were performed for outlet flow field for investigating the responsible flow mechanisms. The results show the forward-skewed blade can cause a spanwise redistribution of flow toward the blade mid-span and reduce tip loading. This results in reduced significantly total pressure loss near hub and shroud endwall region, despite the slight increase of total pressure loss at mid-span.