分子间作用力对制备含有机废弃之水泥浆体影响研究(英文)

研究以水泥处理固体有机物时,有机物对水泥水化的影响。以膜流模式说明水份在水泥浆体内传输的现象。水膜存在半干之水泥浆体,其厚度小于100 nm,膜流由离分压所驱动,而离分压来自分子间作用力。膜拟结果发现,水泥浆体内局部位置可用以进行水化之水量为Q=-Aslv/6vπ。当有机物添加在水泥浆体内时,会影响Hamaker常数,Aslv,因此可能使膜流不稳定或完全抑制膜流,因而使水泥浆体内局部缺水,影响水化进行,造成成品强度降低,影响品质。

废轮胎橡胶粒在水泥浆体内之接口问题(英文)

探讨粉碎后之废轮胎橡胶颗粒表面改质方法,以强化其与水泥浆间作用力的问题。使用之改质剂有氢氧化钠溶液、含硫量较高之润滑油与甲苯。粉碎之橡胶颗粒依其粒径大小分为三群。试体除做抗压、抗拉与抗剪等强度测试以了解物理及机械性质外,并以金相显微镜实时观测水化过程中橡胶与水泥结合情况。实验结果发现,以氢氧化钠处理过之橡胶颗粒与水泥泥之结合最好,此乃因强化其表面亲水性,有利于与水泥作用。反之以甲苯处理之橡胶结果最差,因其表面之亲水性较小。以润滑油处理之橡胶所得试体之性质较不稳定,此与含硫量与处理过程有关。文中并提出以显微镜做线上实时观测试体表面水化变化以做为试体制作改进之参考依据。此方法可降低试体制作之庞大人力与材料费用。

EXPERIMENTAL STUDY OF FORCED SHOCK TRAIN OSCILLATION IN ISOLATOR UNDER ASYMMETRIC INCOMING FLOW

To analyze the response of the wall pressure fluctuation in an isolator when the shock train is subjected to a periodic motion at a low frequency,the isolator experiment is conducted in a blow-down supersonic wind tunnel at free stream Mach number of 1.98 under asymmetric incoming flow.Experimental results show that：The isolator effectively isolates the periodic back pressure fluctuation from affecting upstream undisturbed flow;The wall pressure fluctuations are due to the propagation of wave fronts with the second acoustic mode,but they are subjected to an oscillating shock train in the most part of the shock oscillation region;The attenuation of wall pressure fluctuations on the lower wall with thick boundary layer accords with the exponential law,but it fluctuates on the upper wall with thin boundary layer in the shock oscillation region.

Static and dynamic tensile failure characteristics of rock based on splitting test of circular ring

Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius （ρ） under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough （ρ〈0.3）, specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs’ formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.

A Capacitor-Free CMOS Low-Dropout Regulator for System-on-Chip Application

A stable CMOS low drop-out regulator without an off-chip capacitor for system-on-chip application is presen- ted. By using an on-chip pole splitting technique and an on-chip pole-zero canceling technique, high stability is achieved without an off-chip capacitor. The chip was implemented in CSMC＇s 0.5μm CMOS technology and the die area is 600μm×480μm. The error of the output voltage due to line variation is less than -＋ 0.21% ,and the quiescent current is 39.8μA. The power supply rejection ratio at 100kHz is -33.9dB, and the output noise spectral densities at 100Hz and 100kHz are 1.65 and 0.89μV √Hz, respectively.

HYBRID SCHEME FOR COMPRESSIBLE TURBULENT FLOW AROUND CURVED SURFACE BODY

A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.

Numerical Simulation and Experimental Study on the Performance of Gas/liquid Spiral Separator

The gas/liquid spiral separator, a key component in the compressed air system, was used to remove liquid and oil from gas stream by centrifugal and gravitational forces. To optimize the design of the separator,the relationship between the performance and structural parameters of separators is studied. Computational fluid dynamics (CFD) method is employed to simulate the flow fields and calculate the pressure drop and separation efficiency of air-liquid spiral separators with different structural parameters. The RSM (Reynolds stress model)turbulence model is used to analyze the highly swirling flow fields while the stochastic trajectory model is used to simulate the traces of liquid droplets in the flow field. A simplified calculation formula of pressure drop in spiral structures is obtained by modifying Darcy's equation and verified by experiment.

Test and application of hydraulic expansion bolts in a roadway under goaf with ultra-close separation

The roof of a roadway under goal with ultra-close separation consists of thin rock strata and rocks caving in upper goal. Influenced by the mining of the upper coal seam, the roof is loose and broken, and its integ- rity is poor. Resin anchored bolts cannot provide an effective anchoring force in such roof conditions. By conducting free expansion tests and field pull-out tests on a hydraulic expansion bolt, this study has ana- lyzed the influencing factors and laws of radial expansion and anchoring force changes in the rod body. This has revealed the anchoring mechanism of such bolts, and has obtained reasonable water injection pressures and suitable drilling diameters （which are 20-25 MPa and 32-35 mm respectively） for the hydraulic expansion bolt （cR28 mm） used in these tests. Based on pull-out tests at different interlayer spacing, the applicability of hydraulic expansion bolts had been verified for controlling the roof of road- ways under goal with ultra-close distance. Combined with the deformation and failure characteristics of the test roadway roof, this paper proposes a united roof-control technology based on the use of hydraulic expansion bolts and advancing intubation for the roof. Engineering practice indicated that the roof of the test roadway did not generate leaking and caving phenomenon, and the amount of roof deformation was controlled to within 150 mm. Maintenance of the roadway roof has been improved significantly, which ensures safe mining in coal seams with ultra-close separation.

Prediction of Pressure Gradient and Holdup in Small Eoetvoes Number Liquid-Liquid Segregated Flow

The segregated flow pattern, which occurs in a 26.1 mm diameter, horizontal, stainless steel test section, is investigated. Pressure gradient and in situ phase distribution data were obtained for different combinations of phase superficial velocities ranging from 0.05 m.s^-1 to 0,96 m.s^-1. For the current small Eoetvoes number liquid-liquid system （EOD=4.77）, the dominant effect of interfacial tension and wall-wetting properties of the liquids over the gravity is considered. The approach introduces the closure relationship for the case of turbulent flow m a rough pipe, and attempts to modify the two-fluid model to account for the curved interface. In present flow rates range, wave amplitudes were found small, while interfacial mixing was observed. An adjustable definition for hydraulic diame- ters of two fluids and interfacial friction factor is adopted. The predicted pressure gradient and in situ phase distribution data have been compared with present experimental data and those reported in the literature.

Energy consumption in rock fragmentation at intermediate strain rate

In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s- 1. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity.

Stress evolution and failure process of Brazilian disc under impact

To reveal stress distribution and crack propagation of Brazilian discs under impact loads, dynamic tests were conducted with SHPB （split Hopkinson pressure bar） device. Stress states of specimens were monitored with strain gauges on specimen surface and SHPB bars. The failure process of specimen was recorded by ultra speed camera FASTCAM SAI.1 （675 000 fps）. Stress histories from strain gauges offer comprehensive information to evaluate the stress equilibrium of specimen in time and space. When a slowly rising load （with loading rates less than 1 200 N/s for d 50 mm bar） is applied, there is usually good stress equilibrium in specimen. The stress distribution after equilibrium is similar to its static counterpart. And the first crack initiates at the disc center and propagates along the load direction. But with the front of incident wave becoming steep, it is hard for specimens to get to stress equilibrium. The first crack may appear anywhere on the specimen together with multiple randomly distributed secondary cracks. For a valid dynamic Brazil test with stress equilibrium, the specimen will break into two halves neatly. While for tests with stress disequilibrium, missing strap may be found when broken halves of specimens are put together. For those specimens broken up neatly at center but having missing wedges at the loading areas, it is usually subjected to local buckling from SHPB bars.

Characteristics of supersonic flow in new type externally pressurized spherical air bearings

In order to predict accurately the characteristics of supersonic flow in new type externally pressurized spherical air bearings under large bearing clearance and high air supply pressure, which could decrease their load carrying capacity and stability, a CFD-based analysis was introduced to solve the three-dimensional turbulent complete compressible air flow governing equations. The realizable κ-ε model was used as a turbulent closure illustrate that the interaction exists between shock waves The supersonic flow field near air inlets was analyzed. The flow structures and boundary layer, and the flow separation is formed at the lower comer and the lower wall around the point of a maximum velocity. The numerical results show that the conversion from supersonic flow to subsonic flow in spherical air bearing occurs through a shock region （pseudo-shock）, and the viscous boundary layer results in the flow separation and reverse flow near the shock. The calculation results basically agree with the corresponding experimental data.

Dynamic compressive strength and failure mechanisms of microwave damaged sandstone subjected to intermediate loading rate

To investigate the influence of microwave heating on the dynamic behavior and failure mechanisms of rock,dynamic compression tests were conducted on microwave-irradiated sandstone specimens using a modified split Hopkinson pressure bar(SHPB)system.Experimental results show that microwave radiation can effectively weaken the compressive strength of sandstone.Rock specimens show three different failure modes under impact load:tensile failure,tensile−shear composite failure and compressive−shear failure.The dynamic Poisson’s ratio,calculated using the measured P-and S-wave velocities,is introduced to describe the deformation characteristics of sandstone.With the increase in microwave power and heating time,the Poisson’s ratio declines first and then increases slightly,and the turning point occurs at 244.6℃.Moreover,the microstructural characteristics reveal that microwave radiation produces dehydration,pore expansion,and cracking of the rock.The damage mechanisms caused by microwave radiation are discussed based on thermal stress and steam pressure inside the rock,which provides a reasonable explanation for the experimental results.

Strain rate sensitivity of closed cell aluminium fly ash foam

With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress--strain behaviour at different strain rates ranging from 700 s^-1 to 1950 s^-1. The numerical model of split Hopkinson pressure bar （SHPB） was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress--strain curves wez＇e developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate.

Selective recovery of lithium from spent lithium iron phosphate batteries using oxidation pressure sulfuric acid leaching system

Oxidation pressure leaching was proposed to selectively dissolve Li from spent LiFePO_(4) batteries in a stoichiometric sulfuric acid solution.Using O_(2) as an oxidant and stoichiometric sulfuric acid as leaching agent,above 97% of Li was leached into the solution,whereas more than 99% of Fe remained in the leaching residue,enabling a relatively low cost for one-step separation of Li and Fe.And then,by adjusting the pH of leachate,above 95% of Li was recovered in the form of the Li_(3)PO_(4) product through iron removal and chemical precipitation of phosphate.

Effect of specimen size on energy dissipation characteristics of red sandstone under high strain rate

In this experiment, red sandstone specimens, having slenderness ratios of 0.5, 0.7, 0.9 and 1.1 respectively, were subjected to blow tests using a Split Hopkinson Pressure Bar(SHPB) system at a pressure of 0.4 atmospheres. In this paper, we have analyzed the effect of slenderness ratio on the mechanical properties and energy dissipation characteristics of red sandstone under high strain rates. The processes of compaction, elastic deformation and stress softening deformation of specimens contract with an increase in slenderness ratio, whilst the nonlinear deformation process extends correspondingly. In addition, degrees of damage of specimens reduced gradually and the type of destruction showed a transformation trend from stretching failure towards shear failure when the slenderness ratio increased. A model of dynamic damage evolution in red sandstone was established and the parameters of the constitutive model at different ratios of length to diameter were determined. By comparison with the experimental curve, the accuracy of the model, which could reflect the stress–strain dynamic characteristics of red sandstone, was verified. From the view of energy dissipation, an increase in slenderness ratio of a specimen decreased the proportion of energy dissipation and caused a gradual fall in the capability of energy dissipation during the specimen failure process. To some extent, the study indicated the effects of slenderness ratios on the mechanical properties and energy dissipation characteristics of red sandstone under the high strain rate, which provides valuable references to related engineering designs and academic researches.

Experimental study on mechanical properties of modified polytetrafluoroethylene

In order to study the mechanical properties of modified low-density polytetrafluoroethylene （PTFE）, universal testing machine is used for quasi-static tension and compression tests and Hopkinson bar test is for mechanical property under impact load. The mechanical properties of the samples with different length-diameter ratios under different impact loads are analyzed and dynamic response characteristics of the modified PTFE at different impact speeds are studied. The results show that, adding the copper powder in PTFE material can increase not only the tensile strength and elongation of the PTFE material sig- nificantly, but also the compressive strength; with the increase of strain rate, the yield strength of modified PTFE increases.

Separation process of butanol-butyl acetate-methyl isobutyl ketone system by the analysis to residual curve and the double effect pressure-swing distillation

The separation of ternary mixture of butanol, butyl acetate, and methyl isobutyl ketone(MIBK) was initially analyzed by the residual curve. In this process, MIBK was chosen as the azeotropic agent during the first step of separation. The optimum mass ratio of extra MIBK was 1.6 in the modified feed stream according to the residual curve. Thus on this condition the top product was butanol-MIBK azeotrope while the bottom product was butyl acetate in the preliminary separation of the mixture. Then the butanol and MIBK azeotrope was separated by the double effect pressureswing distillation with the low pressure column performing at 30 kPa and the atmospheric pressure column at 101 kPa. The optimal operating conditions were then obtained by using Aspen Plus to simulate and optimize the process. The results showed that the mass purities of butanol, butyl acetate, and MIBK were all more than 99% and reached the design requirements. Additionally, compared with the traditional distillation with outside heating, the double effect pressure swing distillation saved the reboiler duty by 48.6% and the condenser duty by 44.6%.

Combined effects of temperature and axial pressure on dynamic mechanical properties of granite

In order to get the dynamic mechanical properties of deep rock mass suffered both high temperature and high pressure,impact loading experiments on granite subjected to temperature and axial pressure were carried out. Furthermore, the internalstructure characteristics of granite under different temperatures were observed by scanning electron microscopy (SEM). The results show that the longitudinal wave velocity assumes a downward trend which shows a rapid drop before falling slowly as the temperature increases. The uniaxial compressive strength of the specimen decreases significantly at temperatures of 25?100 °C compared to that at temperatures of 100?300 °C. The peak strain rises rapidly before the dividing point of 100 °C, but increases slowly after the dividing point. The internal structure of the rock changes substantially as the temperature increases, such as the extension and transfixion of primary and newborn cracks. In addition, the thermal damage under axial pressure is greater than that described by the longitudinal wave velocity and the phenomenon shows obviously when the temperature increases.

Pressure characteristics of a hydrocyclone for fine particle separation

Solid-liquid hydrocyclones are mainly used to separate large particles, such as the particles of drilling fluid in petroleum industry, and large mineral particles. Till now the hydrocyclonic separation for fine particles is still a big problem. Basic separation principle of hydrocyclones and experimental research facility are simply introduced. The difficulty of separating fine particle is analyzed. Based on a solid-liquid hydrocyclone used for separating fine particles, relationships of dimensionless pressure characteristic parameters, i.e. Euler number and pressure drop ratio, with several main dimensionless parameters, such as split ratio, swirl number and gas-liquid ratio, were experimentally studied in detail. The research was carried out by using the hydrocyclonic separation experimental rig at the University of Bradford. It is shown that the less the size of particle, the less the value of radius of the balance orbit occupied by the particle, and then the more difficult for the particle to be separated. Experiments indicate that Euler number of the tested hydrocyclone increases with the rise of Reynolds number, split ratio, swirl number and gas-liquid ratio respectively, and the pressure drop ratio falls with the increase of Reynolds number, split ratio and swirl number respectively. It is concluded that the most effective way to decrease the unit energy dissipation of hydrocyclone is to reduce swirl number or gas-liquid ratio of the mixed media.