Simulation of the fluidic features for diffuser/nozzle involved in a PZT-based valveless micropump

PZT-based valveless micropump is a microactuator that can be used for controlling and delivering tiny amounts of fluids,and diffuser/nozzle plays an important role when this type of micropump drives the fluid flowing along a specific direction.In this paper,a numerical model of micropump has been proposed,and the fluidic properties of diffuser/nozzle have been simulated with ANSYS.With the method of finite-element analysis,the increased pressure drop between inlet and outlet of diffuser/nozzle induces the increment of flow rate in both diffuser and nozzle simultaneously,but the increasing rate of diffuser is faster than that of nozzle.The L/R,ratio of L(length of cone pipe) and R(radius of minimal cross section of cone pipe) plays an important role in fluidic performance of diffuser and nozzle as well,and the mean flow rate will decrease with increment of L/R.The mean flow rate reaches its peak value when L/R with the value of 10 regardless the divergence angle of diffuser or nozzle.The simulation results indicate that the fluidic properties of diffuser/nozzle can be defined by its geometric structure,and accordingly determine the efficiency of micropump.

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

EXPERIMENTAL STUDY ON THE MACRO-AND MICRO- CHARACTERISTICS OF THE SPRAY FROM A PRESSURE SWIRL NOZZLE

The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The effects of injection pressure,nozzle geometry and liquid properties on these characteristics are also discussed.The results are helpful to understand the underlying physics of the pressure swirl nozzle and serve as the basis for the practical design,usage and improvement of the nozzle.

The effect of nozzle layout on droplet ejection of a piezo-electrically actuated micro-atomizer

We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.

Microstructure and Properties of SemisolidA356 Alloy Strip Affected by Nozzle Temperature of a Novel Micro Fused-Casting

The semisolid A356 alloy strip was prepared by a novel continuous micro fused-casting process. The microstructure evolution and mechanical property of A356 aluminum alloy strip with different nozzle temperatures were investigated. The nozzle temperature had great influences on the microstructure and property primarily accompanied with the crystal change in the fused-casting area through the cooling conditions. The results showed that the semisolid A356 alloy strip samples fabricated by micro fused-casting demonstrated good performances and uniform structures with the nozzle temperature at 593 ℃ and the stirring velocity at 700 r/min. The fine grains of the primary α-Al phase with average grain size of 51 μm and shape factor up to 0.71 were obtained under the micro fused-casting process, and the ultimate average vickers hardness came up to 83.39±0.89 HV, and the tensile strength and elongation of the A356 alloy strip reached 245.32 MPa and 7.85%, respectively.

Diffusion-weighted magnetic resonance imaging and micro-RNA in the diagnosis of hepatic fibrosis in chronic hepatitis C virus

BACKGROUND Diffusion-weighted magnetic resonance imaging has shown promise in the detection and quantification of hepatic fibrosis. In addition, the liver has numerous endogenous micro-RNAs(miRs) that play important roles in the regulation of biological processes such as cell proliferation and hepatic fibrosis.AIM To assess diffusion-weighted magnetic resonance imaging and miRs in diagnosing and staging hepatic fibrosis in patients with chronic hepatitis C.METHODS This prospective study included 208 patients and 82 age-and sex-matched controls who underwent diffusion-weighted magnetic resonance imaging of the abdomen, miR profiling, and liver biopsy. Pathological scoring was classified according to the METAVIR scoring system. The apparent diffusion coefficient (ADC) and miR were calculated and correlated with pathological scoring.RESULTS The ADC value decreased significantly with the progression of fibrosis, from controls(F0) to patients with early fibrosis(F1 and F2) to those with late fibrosis(F3 and F4)(median 1.92, 1.53, and 1.25 × 10^(-3) mm^2/s, respectively)(P = 0.001).The cut-off ADC value used to differentiate patients from controls was 1.83 × 10^(-3) mm^2/s with an area under the curve(AUC) of 0.992. Combining ADC and miR-200 b revealed the highest AUC(0.995) for differentiating patients from controls with an accuracy of 96.9%. The cut-off ADC used to differentiate early fibrosis from late fibrosis was 1.54 × 10^(-3) mm^2/s with an AUC of 0.866. The combination of ADC and miR-200 b revealed the best AUC(0.925) for differentiating early fibrosis from late fibrosis with an accuracy of 80.2%. The ADC correlated with miR-200 b(r =-0.61, P = 0.001), miR-21(r =-0.62, P = 0.001), and miR-29(r = 0.52,P = 0.001).CONCLUSION Combining ADC and miRs offers an alternative surrogate non-invasive diagnostic tool for diagnosing and staging hepatic fibrosis in patients with chronic hepatitis C.

RESEARCH ON DIFFUSION IN MICRO-CHANNEL FLOW DRIVEN BY ELECTROOSMOSIS

Numerical simulation using the finite differential method was carried out to analyze the diffusion of an impulse sample in the micro-channel driven by electroosmosis. The results show that the electrical field strength applied externally and the concentration of buffer solution play a significant role in the diffusion of sample, however, hydraulic diameter and aspect ratio of height to width of channel play a small role in it. Weakening the electrical field strength applied externally and the concentration of buffer solution properly can prevent the sample band from broadening effectively, and promote the efficiency of testing and separation as well as keep a faster speed of transport. The conclusions are helpful to the optimal design for micro-channel.

Nozzle Spray Diffusivity Changing Law for Ultra Fast Cooling in Hot Strip Mill

Slot nozzle and intensive nozzle can be used in ultra fast cooling equipment. The spray cooling method with higher water pressure can be taken in order to achieve ultra fast cooling for hot rolled strip. Water will be diffused after it is sprayed out from ultra fast cooling nozzle. Spray diffusivity will affect water velocity and penetrability of water into residual water layer on top of the strip,and then it will affect strip cooling effect. Water spraying process can be simulated by Fluent and some conclusions were obtained. Slot nozzle width and outlet velocity within setting range could not affect the length of potential core zone and the spray diffusivity. Intensive nozzle diameter and outlet velocity will affect the length of potential core zone and the spray diffusivity with different extent. These conclusions will provide referenced role for confirming ultra fast cooling nozzle size and distance between ultra fast cooling nozzle and hot rolled strip.

Diffusive healing of internal fatigue micro-cracks in pure titanium

The internal micro cracks with the critical length about 30?μm and thickness less than 1?μm were introduced into the pure titanium samples by uniaxial tension compression low cycle fatigue method. The experimental results indicate that the internal fatigue micro crack clearly evolves from the original penny shaped crack into a string of spherical voids in the longitudinal section plane of the fatigue sample after the vacuum diffusive healing at the high temperature. The quantitative relationship between the radius and the spacing of spherical voids depends on the crack position (within grains, on grain boundaries or transgranular sites) and its orientations within the grain. The diffusive healing, the related thermodynamics and mechanism, and the effect of the surface tension anisotropy on the relationship between void diameter and void spacing are also discussed.

Experimental Study on the Influence of Fracturing Fluid Retention on Shale Gas Diffusion Law

Shale gas reservoirs have poor physical properties and a large number of micro-nano pores have been developed.Shale gas wells have no natural productivity and need fracturing reconstruction measures to put into production.However,the fracturing fluid will enter the reservoir space of shale matrix after fracturing and affect the production of shale gas.At present,there is no consensus on the influence of fracturing fluid retention on gas well production.Based on this,the paper adopts gas molecular transport analyzer to carry out experimental research on the influence of fracturing fluid on shale gas diffusion law after entering matrix pores.The results show that:(1)Compared with the diffusion capacity of single-phase shale gas,the diffusion capacity of shale gas decreases significantly when fracturing fluid is present in the reservoir;(2)In the process of fracturing fluid flowback,when the water saturation in the reservoir decreases from 50%to 0,the gas well productivity increases by about 60%.(3)When fracturing fluid exists in the reservoir,the pore diameter has an exponential relationship with the shale gas diffusion coefficient,and the diffusion coefficient increases exponentially with the increase of pore diameter.The research of this paper provides theoretical basis for guiding the efficient development of shale gas wells.

A numerical investigation in buoyancy effects on micro jet diffusion flame

The buoyancy effect on micro hydrogen jet flames in still air was numerially studied.The results show that when the jet velocity is relatively large(V≥0.2 m/s),the flame height,width and temperature decrease,whereas the peak OH mass fraction increases significantly under normal gravity(g=9.8 m/s^2).For a very low jet velocity(e.g.,V=0.1 m/s),both the peak OH mass fraction and flame temperature under g=9.8 m/s^2 are lower than the counterparts under g=0 m/s^2.Analysis reveals that when V≥0.2 m/s,fuel/air mixing will be promoted and combustion will be intensified due to radial flow caused by the buoyancy effect.However,the flame temperature will be slightly decreased owing to the large amount of entrainment of cold air into the reaction zone.For V=0.1 m/s,since the heat release rate is very low,the entrainment of cold air and fuel leakage from the rim of tube exit lead to a significant drop of flame temperature.Meanwhile,the heat loss rate from fuel to inner tube wall is larger under g=9.8 m/s^2 compared to that under g=0 m/s^2.Therefore,the buoyancy effect is overall negative at very low jet velocities.

Optical Measurements of Shock Waves in Critical Nozzles at Low Reynolds Numbers

Two-dimensional critical nozzle flows at low Reynolds numbers are visualized by the rainbow schlieren deflectometry. Experiments have been performed in a region of overexpanded nozzle flow. The variation of the shock structure against the back pressure ratio can be clearly visible with color gradation. Static pressure rises due to the shock-induced flow separation are compared with the previous theories. The unsteady characteristics of overexpanded critical nozzle flows at low Reynolds numbers are quantitatively and qualitatively visualized using laser schlieren and Mach-Zehnder interferometer systems combined with a high-speed digital camera. It was found that an oscillating normal shock wave appears inside the nozzle, and that the shock wave has a specified dominant frequency. Also the time-history of the oscillating shock wave is obtained from both the systems and compared with each other.

Computational Analysis of Flow Field on the Propulsion Nozzle of a Micro-Turbojet Engine

The purpose of this paper is to analyze the flow field on the propulsion nozzle of a micro-turbojet engine in function of the velocity. The 2D axisymmetric numerical simulation was made by using commercial software FLUENT?. A micro-turbojet engine was also employed for this study and it has the following characteristics: 100 N thrust, 130,000 rpm, mass flow rate 0.2650 kg/s, weight 1.2 kg. This engine is operating in Mexico city under the following conditions: P0, 78,000 Pa T0, 300 K, πc, 2.1 and a turbine entry temperature of 1000 K;it is considered that the nozzle is not choked. For this study, the viscous standard k- model, a semi-empirical model based on transport model equations for the turbulent kinetic energy (k) and its dissipation rate, is used. The transport model equation for k is derived from the ex-act equation, while the transport model equation for is obtained by using physical reasoning and bears resemblance to its mathematically exact counterpart. The employed grids are structured and the boundary conditions are obtained from a thermodynamic analysis. The results that are obtained show an increment of the velocity of 6.25% to the exit propulsion nozzle.

Scanning Electron Microscopy (SEM) Analysis and Hardness of Diffusion Bonded Titanium-Titanium and Titanium-Copper Plates with Static Force and without Interlayers

In the present research, commercially pure Ti (grade-2) has been diffusion bonded with Ti and Cu plate under static force without any interlayers. The diffusion bonded samples were tested for micro hardness and micro structural analysis through optical microscopy and SEM. It is found from the present investigation that the bonded zone is affected by the processing variables such as bonding time (1 - 2 h), bonding force (250 N), bonding temperature (973 - 1073 K) and surface roughness. Results of the investigation revealed that temperature range of ?973 - 1073 K along with time duration of 1 - 2 hours in vacuum has resulted in a joint having high hardness with minimum pores. Hardness of the bond depends on the grain boundary diffusion at the interface and maximum hardness was achieved in the case of Ti-Cu joints. When Ti-Cu plates were used for bonding at 973 K for 2 hours, Cu-Ti solid solution along with a zone of different intermetallics was formed in the bonded zone. However, at higher temperatures, no continuous zone of intermetallics was found in the bonded region but instead Ti-Cu solid solution appeared.

NUMERICAL SIMULATION FOR CONVECTION-DIFFUSION PROBLEM WITH PERIODIC MICRO-STRUCTURE

In this article, the convection dominated convection-diffusion problems with the periodic micro-structure are discussed. A two-scale finite element scheme based on the homogenization technique for this kind of problems is provided. The error estimates between the exact solution and the approximation solution, of the homogenized equation or the two-scale finite element scheme are analyzed. It is shown that the scheme provided in this article is convergent for any fixed diffusion coefficient 5, and it may be convergent independent of δ under some conditions. The numerical results demonstrating the theoretical results are presented in this article.

Preparation of Hydrophobic Surface on Titanium by Micro-Rolling and Laser Diffusion Carbonitriding

The application of rolling for fabricating grate on titanium stripe has been explored in this paper. Then the mechanically robust Ti（C,N） diffusion layer was synthetized directly on the grates by laser carbonitriding in the mixture gas of nitrogen and methane. The results shows that the carbonitriding process is accelerated by temperature enhancement with decreasing scanning speed, The Ti（C,N） diffusion layer is kept at 2 ~nn in thickness, when the scanning speed is smaller than 4 mm/s. The contact angle increases from 20~ to 143.6~ by designing an appropriate grate size and surface roughness. Meanwhile, the relationship between hydrophobicity, hardness performance and scanning speed is also discussed. The hardness of diffusion layer increases with decreasing laser scanning speed, and is up to 11.2 GPa. The surface structure and hydrophobic state are maintained after three cycles of sandpaper abrasion, which has improved the robustness of surface grate.

Understanding micro-diffusion bonding from the fabrication of B_4C/Ni composites

A Ni-B_4C macroscopic diffusion welding couple and a Ni-15 wt% B_4C composite fabricated by spark plasma sintering(SPS) were used to understand the micro-scale diffusion bonding between metals and ceramics. In the Ni-B_4C macroscopic diffusion welding couple a perfect diffusion welding joint was achieved. In the Ni-15 wt% B_4C sample, microstructure analyses demonstrated that loose structures occurred around the B_4C particles. Energy dispersive X-ray spectroscopy analyses revealed that during the SPS process, the process of diffusion bonding between Ni and B_4C particles can be divided into three stages. By employing a nano-indentation test, the room-temperature fracture toughness of the Ni matrix was found to be higher than that of the interface. The micro-diffusion bonding between Ni and B_4C particles is quite different from the Ni-B_4C reaction couple.

Application of radioanalysis to the transport of micro-constituents by diffusion

Predictions on the leaching behaviour of microconstituents from dumped, stored, or immobilised wastes are based on estimates of the effective diffusion coefficients involved, which usually range from ～10^-6 to ～10-12 cm^2.s^- 1. Radioanalysis, especially radiotracer procedures, can be applied to determine these parameters on small (field) samples of granular material and test specimens of immobilised wastes. A summary of standard experiments for both types of material under non-steady state and steady state conditions is

折射式微喷头水力性能试验及工作参数优选

为探究折射式微喷头水力性能并确定其适宜的工作参数,开展微喷头水力性能测试,明晰不同工况下单个微喷头水量分布特征,分析其流量、射程、喷灌强度随工作压力和喷嘴直径的变化趋势。探究在正方形和正三角形组合方式下,工作压力和组合间距变化对喷灌均匀系数CU的影响,基于主成分分析方法,统一相关评价指标,建立折射式微喷头工作参数综合评价模型。结果表明:单喷头的流量、喷灌强度均与工作压力呈正相关,而射程随压力的变化并不明显;正方形和正三角形两种组合方式下,组合间距变化对CU产生的影响明显大于工作压力和组合方式;依据各工况评分高低,对微喷头最优工况做出合理选择,实例应用的结果表明:折射式微喷头最优工况为正三角形组合,工作压力0.25 MPa,组合间距0.4 m。

Three-dimensional flow field simulation of steady flow in the serrated diffusers and nozzles of valveless micro-pumps

This paper presents a three-dimensional flow field simulation of the steady flows through diffusers and nozzles with straight or serrated-sided walls to analyze the effect of the channel structure on the flow characteristics.The pressure and velocity profiles in the diffusers and the nozzles as well as the net volumetric flow rate are determined.Our simulation demonstrates that the pressure and velocity profiles in the serrated diffuser/nozzles are more complicated than those with the straight-sided wall,while the net steady flow rate with the straight-sided wall increases monotonically with the increase of the pressure difference,the steady flow rate with serrated sided walls increases gradually to reach a maximum and then decreases with the increase of the pressure difference.The results suggest that the number of the sawteeth plays a significant role in optimizing the design of serrated diffusers and nozzles for improving the transport efficiency of valveless micro-pumps.