基于流体传动理论的液压支架液压传动效率分析

利用流体传动的理论,对液压支架液压传动效率进行了分析。液压支架特殊的工作环境,会引起液压支架液压传动系统乳化液温度的升高,乳化液黏性降低,液压元件的泄漏量增加,导致液压支架液压容积效率降低,使得整个液压系统的效率下降。指出了提高液压支架液压传动效率的措施和应注意的问题。

Conditions of Ratio Changing Continuously for Multirange-Split-Transmission

According to the flow chart and the characteristics of components, the equation of ratio changing of multirange split transmission (MRST) was established. By mathematical analysis, both the relations among the ratios of the components and the condition for the ratio of MRST changing continuously were obtained. With the help of two examples, the correctness was proved.

Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

Velocity of a Liquid Drop with a Sorption-Controlled Surfactant

The terminal velocity of a liquid droplet settling in a sulfactant solution has been studied for the non-linear adsorption Langmuir frameworks accounting for monolayer saturation and non-ideal surfactant interactions. Most prior research uses a linear adsorption model which cannot capture these effects, The Maragoni migration of a liquid drop settling through a surfactant solution is examined by using Langmuir framework. The solution concentration Ceq is assumed large enough for the surfactant mass transfer to be adsorption-controlled. Langmuir model generates non-linear Marangoni stresses which diverge in the limit of approaching ∝, strongly retarding U'.

Effects of Shape and Quantity of Helical Baffle on the Shell-side Heat Transfer and Flow Performance of Heat Exchangers

Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisection, quadrant and sextant sector） were investigated. Numerical simulations were performed on HBHE at three helix an- gles （10°, 25° and 40°） by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.

Mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradation

The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line.

Flow characteristics of variable hydraulic transformer

A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow characteristics of VHT, such as its instantaneous flow rates, average flow rates, and flow pulsations in the ports, are investigated. Matlab software is used to simulate and calculate. There are five controlled angles of the port plate that can help to define the flow characteristics of VHT. The relationships between the flow characteristics and the structure in VHT are shown. Also, the plus-minus change of the average flow rates and the continuity of the instantaneous flow rates in the ports are presented. The results demonstrate the performance laws of VHT when the controlled angles of the port plate and of the swash plate change. The results also reveal that the special principle of the flow pulsation in the ports and the jump points of the instantaneous curves are the two basic causes of its loud noise, and that the control angles of the port plate and the swash plate and the pressures in the ports are the three key factors of the noise.

Study on shift schedule saving energy of automatic transmission of ground vehicles

To improve ground vehicle efficiency, shift schedule energy saving was proposed for the ground vehicle automatic transmission by studying the function of the torque converter and transmission in the vehicular drivetrain. The shift schedule can keep the torque converter working in the high efficiency range under all the working conditions except in the low efficiency range on the left when the transmission worked at the lowest shift, and in the low efficiency range on the right when the transmission worked at the highest shift. The shift quality key factors were analysed. The automatic trans-mission's bench-test adopting this shift schedule was made on the automatic transmission's test-bed. The experimental results showed that the shift schedule was correct and that the shift quality was controllable.

Separation of up-going and down-going wave fields of vertical cable data

The vertical cable method for acquiring and processing pre-stack 3-D marine seismic data is based on the technology developed by the US Navy for antisubmarine warfare. In order to achieve the maximum utili- zation of vertical cable field data, a new separation method of the up-going and down-going wave fields of the vertical cable data processing was developed in this paper, which is different from the separation of the down-going and up-going wave fields of normal VSP data processing. In tests with synthetic modeling data and actual field data, this newly developed method performs well and is also computationally simpler without pre-assumption conditions.

Numerical analysis of thermal fluid transport behavior during electron beam welding of 2219 aluminum alloy plate

A two-dimensional mathematical model based on volume-of-fluid method is proposed to investigate the heat transfer,fluidflow and keyhole dynamics during electron beam welding(EBW)on20mm-thick2219aluminum alloy plate.In the model,anadaptive heat source model tracking keyhole depth is employed to simulate the heating process of electron beam.Heat and masstransport of different vortexes induced by surface tension,thermo-capillary force,recoil pressure,hydrostatic pressure and thermalbuoyancy is coupled with keyhole evolution.A series of physical phenomena involving keyhole drilling,collapse,reopening,quasi-stability,backfilling and the coupled thermal field are analyzed systematically.The results indicate that the decreased heat fluxof beam in depth can decelerate the keyholing velocity of recoil pressure and promote the quasi-steady state.Before and close to thisstate,the keyhole collapses and complicates the fluid transport of vortexes.Finally,all simulation results are validated againstexperiments.

Hydraulic and thermal analysis of automatic transmission fluid in the presence of nano-particles and twisted tape:An experimental and numerical study

In the present study,hydraulic and thermal behavior of an automatic transmission nano-fluid(ATNF) inside a tube with a twisted tape has been investigated.The heat transfer improvement and pressure drop of transmission oil for each of case of using twisted tape and nano-particles were also examined separately and compared with each other.The Cu O nano-particles were used to prepare the ATNF.The effects of different Reynolds numbers and different mass fractions of nano-particle were investigated.The results showed that applying nano-particles and twisted tape simultaneously increases both the pressure drop and Nusselt number,on average by about 53% and 76%,respectively.By using a parameter,namely thermal performance index η,the effect of increasing heat transfer and pressure drop was studied simultaneously.The heat transfer improvement predominates the pressure drop increment in all cases.It was observed that the highest thermal performance of 1.9 was obtained at Re=634 and Φ=2%.Furthermore,regarding the increment of the Nu number,it was shown that the use of twisted tapes individually could increase the average Nu number by 41%,while the max increment arising from individual use of 2% nano-particles is 13%,so using twisted tape is a more effective-technique for this case study.

Peristaltic flow with convective mass condition and thermal radiation

The primary objective of present investigation is to introduce the novel aspects of convective mass condition and thermal radiation in the peristaltic transport of fluid. Magnetohydrodynamic(MHD) fluid was considered in a symmetric channel. Heat and mass transfer characteristics were analyzed in the presence of Soret and Dufour effects, and the results were presented via two forms of thermal radiation. The temperature, concentration and pressure rise per wavelength were examined. It is observed that the velocity slip and magnetic field parameters have opposite effects on the pressure rise per wavelength. Temperature of fluid is a decreasing function of the radiation parameter. Further, the temperature of fluid decreases by increasing the heat transfer Biot number. It is notified that the heat transfer rate at the wall is a decreasing function of radiation parameter.

Study on dryout point and heat transfer in subcooled flow boiling through vertical narrow annular channels

The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.

Research on the variable speed system of large power alternating current motor

The development status of the variable speed system of large power AC(alternating current)motor drive in China is introduced.The large power AC drive fed by AC-AC converters(cycloconverters)has developed greatly,and some innovations on the theory and engineering technique have been realized.They have been applied to rolling mills,mine hoists,and so on,and remarkable economic and social benefit has been achieved.The development of AC drive fed by large power IGCT(integrated gate commutated thyristors)AC-DC-AC converter is also introduced.It has excellent performance and reliable operation,and has been used in traction.

Analysis of 2D Flow and Heat Transfer Modeling in Fracture of Porous Media

Heat and mass transfer between porous media and fluid is a complex coupling process, which is widely used in various fields of engineering applications, especially for natural and artificial fractures in oil and gas extraction. In this study, a new method is proposed to deal with the flow and heat transfer problem of steady flow in a fracture. The fluid flow in a fracture was described using the same method as Mohais, who considered a fracture as a channel with porous wall, and the perturbation method was used to solve the mathematical model. Unlike previous studies, the shear jump boundary condition proposed by Ochoa-Tapia and Whitaker was used at the interface between the fluid and porous media. The main methods were perturbation analysis and the application of shear jump boundary conditions. The influence of permeability, channel width, shear jump degree and effective dynamic viscosity on the flow and heat transfer in the channel was studied by analysing the analytical solution. The distribution of axial velocity in the channel with the change of the typical parameters and the sensitivity of the heat transfer was obtained.

Effects of Pulsation on Separated Flow and Heat Transfer in Enlarged Channel

Numerical results of three-dimensional separated flow and heat transfer in an enlarged rectangular channel are presented in this paper.The expansion ratio and aspect ratio of the channel are 2.0 and 16.0,respectively.Reynolds number of the flow is 200 and it is over the critical Reynolds number.Over the critical Reynolds number,the flow in the symmetric channel becomes asymmetric and deflects to one side of the walls.Effects of the pulsating fluctuation at the inlet upon the flow in the channel are investigated.It is clarified that the inlet flow with a pulsating fluctuation of Strouhal number 0.05 and 0.10 strongly affects on the flow in the channel,and heat transfer on the walls is enhanced,especially on the wall surface covered with long separation bubble.On the other hand,the pulsation of St=0.0125 oscillates the shear layer more weakly than that of St=0.05,0.10 and the enhancement of heat transfer is smaller,though some vortices are shed from the vicinity of the side wall near the reattachment region.The oscillation of the main flow calms down gradually as the Strouhal number of the pulsation increases over 0.10.The influence of pulsation of St=0.20 on the flow is restricted in the near downstream of the step,and heat transfer on the walls is almost similar to that of the steady flow in the channel.

Effects of heat transfer on the peristaltic MHD flow of a Bingham fluid through a porous medium in a channel

In this paper, we study the effects of heat transfer on the peristaltic magneto- hydrodynamic （MHD） flow of a Bingham fluid through a porous medium in a channel. Long wavelength approximation （that is, the wavelength of the peristaltic wave is large in comparison with the radius of the channel） and low Reynolds number are used to linearize the governing equations. The velocity field for the model of interest is solved by Adomian decomposition method. The expressions for pressure rise, flow rate and frictional force are obtained. The effect of magnetic field, Darcy number, yield stress, amplitude ratio and the temperature on the axial pressure gradient, pumping charac- teristics and frictional force are discussed through graphs.

Hydrodynamic and Heat Transfer Characteristics of Magnetofluidized Beds

To investigate the flow and heat-transfer behaviors of magnetofluidized beds, an experimental facilitywas designed. A constant uniform magnetic field is produced by a Helmholtz electromagnet. The nature of fiuidization and heat-transfer characteristics of a horizontal electrically heated tube immersed in the bed were measured. The bed material is iron shots. Depending upon the intensity of magnetic field (weak, moderate and strong), the bed pressure drop and heat transfer coefficient are classified into three ranges of magnetic fields. The range of variation of maximum magnetic-field intensity is from 0 to about 20690 A/m.

Heat Transfer and Hydrodynamic Investigations of a Baffled Slurry Bubble Column

Heat transfer and hydrodynamic investigations have been conducted in a 0.108 m internal diameter bubble column at ambient conditions. The column is equipped with seven 19mm diameter tubes arranged in an equilateral triangular pitch of 36.5 mm. A Monsanto synthetic heat transfer fluid, Therminol-66 having a viscosity of 39.8 cP at 303 K, is used as a liquid medium. Magnetite powders, average diameters 27.7 and 36.6 μm, in five concentrations up to 50 weight percent in the slurry, are used. As a gas phase, industrial grade nitrogen of purity 99.6 percent is employed. Gas holdup in different operating modes and regimes have been measured for the two- and three-phase systems over a superficial gas velocity range up to 0.20 m/s in the semi-batch mode. Heat transfer coefficients are measured at different tube locations in the bundle at different radial and vertical locations over a range of operating conditions. All these data are compared with the existing literature correlations and models. New correlations are proposed.

Multipoint observations of Pi2 pulsations and correlation with dynamic processes in the near-Earth magnetotail on March 18,2009

Simultaneous measurements from THEMIS spacecraft, GOES11 and ground stations （Canadian Array for Realtime Investiga tions of Magnetic Activity or CARISMA, and 210 magnetic meridian or MM） on March 18, 2009 allow the study of dynamic processes in the nearEarth magnetotail and corresponding Pi2 pulsations on the ground in great detail. Fast earthward flows along with traveling Alfv6n waves and fast mode waves in the Pi2 band were observed by three Time History of Events and Macroscale Interactions during Substorms （THEM/S） probes （P3, P4 and P5） in the nearEarth plasmasbeet. At the mid to highlatitude nightside, the CARISMA stations located near the foot points of the three probes recorded Pi2s with two periods, about 80 s after the earthward fast flows observed by the P4 probe. The longperiod Pi2 （140-150 s） belongs to the transient response Pi2 （TR Pi2）, since the travel time of the Alfv6n waves between the plasma sheet and CARISMA stations is very close to half the period of the longperiod Pi2. The shortperiod Pi2 （60-80 s） has the same period band as the perpendicular velocity of the fast flows, which indicates that it may relate to the inertial current caused by periodic braking of the earthward fast flows. The 210 MM stations located at the lowlatitude duskside also observed Pi2s with the same start time, waveform and frequency, about 120 s after the earthward fast flows. Strong poloidal oscillations are shown by GOES11 （23 MLT） and the compressional component （Bb） is highly correlated with H components of the 210 MM stations, whereas the other two components （Br and Be） are not. These results confirm that the lowlatitude Pi2s are generated by cavity mode resonance, which is driven by an impulsive broadband source in the nearEarth magnetotail.