利用红外温度测量方式预测微管内流动沸腾流型

本文利用红外热成像仪对不锈钢微管内水的流动沸腾的壁面瞬态温度场进行了测量。结果表明,相比传统的热电偶测量方式,在微尺度实验中采用红外温度测量瞬态温度场具有更高的可靠性。利用红外温度测量的显示特点,预测不锈钢微管内流动沸腾的流型变化情况,在本文的实验条件下,不锈钢微管内水的流动沸腾流型变化基本上是以单相流、汽塞流和环状流的交替产生为主。

GC低流型流动树脂与玻璃离子修复楔状缺损疗效比较

目的:比较GC低流型流动树脂和玻璃离子修复楔状缺损的疗效。方法:随机将80例患有楔状缺损的前磨牙分成观察组和对照组,每组各40例,分别采用GC低流型流动树脂和GC Fuji II型玻璃离子水门汀充填修复,修复后3个月和1年分别对患牙的修复进行临床效果评价。结果:随访3个月,2组成功率差异无统计学意义(P>0.05)。随访1年,GC低流型流动树脂组疗效优于GC Fuji II型玻璃离子组,差异有统计学意义(P<0.05)。结论:GC低流型流动树脂是一种修复楔状缺损的理想材料。

油-水乳状液流过弯管的局部阻力特性研究

以油-水为工质 ,对进口水平、出口垂直向上的 90°弯管内油 水乳状液局部阻力特性进行了实验研究 ,弯管内径 4 5mm ,弯曲半径 3 0 0mm .在实验数据分析的基础上 ,较为准确地判别出了油 水乳状液在整个实验范围内的流动流型 ,提出了油 水乳状液流过弯管的局部阻力计算公式 .结果表明 ,计算值和实验值符合良好 .

润滑油对管内沸腾换热影响研究综述

润滑油的存在会对管内流动沸腾换热产生影响,不同粘度、浓度的润滑油影响效果不同,不同的换热条件,如干度、质量流量、热流密度的变化也会改变润滑油对换热的影响。因此,本文对相关文献的研究成果进行了回顾,分析和总结了润滑油对管内流动沸腾换热的影响。

Application of jet main region specification model in CFD simulation for room air movement analysis

This paper analyzes the applications of four air terminal device（ATD）models（i.e.,the basic model,the box model,the N-point momentum model,the jet main region specification model）in computational fluid dynamics（CFD）simulation and their performance in case study.A full-scale experiment is performed in an environment chamber,and the measured air velocity and temperature fields are compared with the simulation results by using four ATD models.The velocity and temperature fields are measured by an omni-directional thermo-anemometer system.It demonstrates that the basic model and the box model are not applicable to complicated air terminal devices.At the occupant area,the relative errors between simulated and measured air velocities are less than 20% based on the N-point momentum model and the jet main region specification model.Around the ATD zone,the relative error between the numerical and measured air velocity based on the jet main region specification model is less than 15%.The jet main region specification model is proved to be an applicable approach and a more accurate way to study the airflow pattern around the ATD with complicated geometry.

Flow pattern and pressure drop of gas-liquid two-phase swirl flow in a horizontal pipe

The gas-liquid two-phase swirl flow can increase the gas-liquid two-phase contact area and enhance the heat and mass transfer efficiency between gas and liquid.The swirl flow has important practical application value for promoting gas hydrate formation and ensuring the flow safe of natural gas hydrate slurry.The experimental section was made of plexiglass pipe and the experimental medium was air and water.The flow pattern of the gas-liquid two-phase swirl flow in the horizontal pipe was divided,according to a high-definition camera and the overall characteristics of the gas-liquid interface.The flow pattern map of the gas-liquid two-phase swirl flow in a horizontal pipe was studied.The influence of the flow velocity and vane parameters on pressure drop was investigated.Two types of gas-liquid two-phase swirl flow pressure drop models was established.The homogeneous-phase and split-phase pressure drop models have good prediction on swirl bubble flow,swirl dispersed flow,swirl annular flow and swirl stratified flow,and the predictive error band is not more than 20%.

Structure and production fluid flow pattern of post-fracturing high-rank coal reservoir in Southern Qinshui Basin

Field geological work, field engineering monitoring, laboratory experiments and numerical simulation were used to study the development characteristics of pore-fracture system and hydraulic fracture of No.3 coal reservoir in Southern Qinshui Basin. Flow patterns of methane and water in pore-fracture system and hydraulic fracture were discussed by using limit method and average method. Based on the structure model and flow pattern of post-fracturing high-rank coal reservoir, flow patterns of methane and water were established. Results show that seepage pattern of methane in pore-fracture system is linked with pore diameter, fracture width, coal bed pressure and flow velocity. While in hydraulic fracture, it is controlled by fracture height, pressure and flow velocity. Seepage pattern of water in pore-fracture system is linked with pore diameter, fracture width and flow velocity. While in hydraulic fracture, it is controlled by fracture height and flow velocity. Pores and fractures in different sizes are linked up by ultramicroscopic fissures, micro-fissures and hydraulic fracture. In post-fracturing high-rank coal reservoir, methane has level-three flow and gets through triple medium to the wellbore; and water passes mainly through double medium to the wellbore which is level-two flow.

Effects of Orifice Orientation and Gas-Liquid Flow Pattern on Initial Bubble Size

In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat terns have been developed based on force balance. The effects of the orientation of gasliquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient airwater system, thesultable gasllquid flow pattern is important to obtain smaller bubbles under the low velocity liquid crossflow con ditions with stainless steel spargers. Among the four types of gasliquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found tobe insgnifican whenliq.uid velocity is.higher than. 3.2 m;sa or theorifice diameter is small enough.

Application of time–frequency entropy from wake oscillation to gas–liquid flow pattern identification

Gas–liquid two-phase flow abounds in industrial processes and facilities. Identification of its flow pattern plays an essential role in the field of multiphase flow measurement. A bluff body was introduced in this study to recognize gas–liquid flow patterns by inducing fluid oscillation that enlarged differences between each flow pattern. Experiments with air–water mixtures were carried out in horizontal pipelines at ambient temperature and atmospheric pressure. Differential pressure signals from the bluff-body wake were obtained in bubble, bubble/plug transitional, plug, slug, and annular flows. Utilizing the adaptive ensemble empirical mode decomposition method and the Hilbert transform, the time–frequency entropy S of the differential pressure signals was obtained. By combining S and other flow parameters, such as the volumetric void fraction β, the dryness x, the ratio of density φ and the modified fluid coefficient ψ, a new flow pattern map was constructed which adopted S（1–x）φ and （1–β）ψ as the vertical and horizontal coordinates, respectively. The overall rate of classification of the map was verified to be 92.9% by the experimental data. It provides an effective and simple solution to the gas–liquid flow pattern identification problems.

Droplet Pattern Formation and Translation in New Microfluidic Flow- Focusing Devices

We conducted experiments on specially designed microfluidic chips that generate droplets through a microfluidic ow-focusing approach. The fluid flow in the microfluidic channel produced a shear flow field at low Reynolds numbers. The droplets in the microfluidic system exhibited special droplet pattern formations similar to periodic crystal-like lattices because of the competition between shear forces and surface tension. By adjusting the flow rate ratio of the water （droplet phase） to oil （continuous phase） phases and changing the outlet channel widths, the droplets formed monolayer dispersion to double-layer formation to monolayer squeezing when the outlet channel widths were 250 or 300 μm. We also obtained droplets with monolayer dispersion, three-layer arrangements, double-layer squeezing, and monolayer squeezing when the outlet channel width was 350 μm. The outlet channel width was increased to 400 μm, and four-layer arrangements were observed. We also studied the translation of droplet formation, which resulted in a detailed strategy to control drop size and droplet pattern formation for emulsi cation in microfluidic devices. We expect that our strategy can provide theoretical guidance to synthesize dispersion or polydisperse colloid particles.

Simulation of electromagnetic-flow fields in Mg melt under pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of pure Mg were investigated.The results show that microstructure of pure Mg is considerably refined via columnar-to-equiaxed growth under the pulsed magnetic field and the average grain size is refined to 260？？ under the optimal processing conditions.A mathematical model was built to describe the interaction of the electromagnetic-flow fields during solidification with ANSYS software.The pulsed electric circuit was first solved and then it is substituted into the magnetic field model.The fluid flow model was solved with the acquired electromagnetic force.The effects of pulse voltage frequency on the current wave and on the distribution of magnetic and flow fields were numerically studied.The pulsed magnetic field increases melt convection,which stirs and fractures the dendritic arms into pieces.These broken pieces are transported into the bulk liquid by the liquid flow and act as nuclei to enhance grain refinement.The Joule heat effect produced by the electric current also participates in the microstructural refinement.

Characterizing and Analyzing the Airflow Field inside the Nozzle Block of Murata Vortex Spinning

A three-dimensional computational fluid dynamics model is developed by software Fluent 6.2, to simulate the flow field inside the nozzle block of the Murata vortex spinning. The flowing state and the distribution law of static pressure and velocity are characterized and analyzed. The relationship between the flowing state and the structure of the vortex spun yarn is also discussed. The research results can enhance the understanding of the yarn formation principle from viewpoint of the airflow field law inside the nozzle block of Murata vortex spinning.

Simulation and analysis of airflow stability during fire in mine belt roadway

According to fluid dynamics analysis during the fire, the criteria k-ε two-equation model for solving three-dimensional turbulence was determined, the pollutants generated in the fire disaster were set by adopting Mixture multiphase flow, and the SIMPLE algorithm was used for solving on the basis of comprehensive consideration on the heat radia- tion and components transmission during fire. By simulating the airflow flowing state inside the tunnel during fire disaster of downward ventilation, drift ventilation, and ascensional ventilation, respectively, with regard to the actual situation of No.l, No.3, and No.5 belt roadway in Kongzhuang Coal Mine, the velocity vector distributions of pollutants under different inlet air volumes were obtained, and the damage degree and influential factors of disaster were also clear, which is helpful to control and avoid disaster during belt roadway fire.

Two Approaches of Substance Flow Analysis—An Inspiration from Fluid Mechanics

That flow is the common feature of substance flow and fluid flow is the viewpoint emphasized in the paper. Some notes on fluid mechanics, including the two approaches of fluid flow description, were given. The concepts of the chain and the chain group of product life cycles, which are essential for understanding the specific features of substance flow, were advanced. Taking the specific feature of substance flow into consideration, on the analogy of the two approaches in fluid mechanics, two approaches of substance flow analysis, i.e. L method and E model, were formulated. Illustrative models of steady and unsteady substance flow were sketched by both methods, and comparison between them was made in general.

Computation of flow through the oesophagogastric junction

Whilst methods exist to indirectly measure the effects of increased flow or gastro-oesophageal refluxing, they cannot quantitatively measure the amount of acid travelling back up into the oesophagus during reflux, nor can they indicate the flow rate through the oesophagogastric junction (OGJ). Since OGJ dysfunction affects flow it seems most appropriate to describe the geometry of the OGJ and its effect on the flow. A device known as the functional lumen imaging probe (FLIP) has been shown to reliably measure the geometry of and pressure changes in the OGJ. FLIP cannot directly measure flow but the data gathered from the probe can be used to model flow through the junction by using computational flow dynamics (CFD). CFD uses a set of equations known as the Navier-Stokes equations to predict flow patterns and is a technique widely used in engineering. These equations are complex and require appropriate assumptions to provide simplifications before useful data can be obtained. With the assumption that the cross-sectional areas obtained via FLIP are circular, the radii of these circles can be obtained. A cubic interpolation scheme can then be applied to give a high-resolution geometry for the OGJ. In the case of modelling a reflux scenario, it can be seen that at the narrowest section a jet of fluid squirts into the oesophagus at a higher velocity than the fluid surrounding it. This jet has a maximum velocity of almost 2 ms-1 that occurs where the OGJ is at its narrowest. This simple prediction of acid ‘squirting’ into the oesophagusillustrates how the use of numerical methods can be used to develop a better understanding of the OGJ. This initial work using CFD shows some considerable promise for the future.

Turbulence Model Investigations on the Boundary Layer Flow with Adverse Pressure Gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients （APGs） is conducted by using Reynolds-averaged Navier-Stokes （RANS） equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox （2006） k-co are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.

Simulation of Variable Viscosity and Jeffrey Fluid Model for Blood Flow Through a Tapered Artery with a Stenosis

Non-Newtonian fluid model for blood flow through a tapered artery with a stenosis and variable viscosity by modeling blood as Jeffrey fluid has been studied in this paper. The Jeffrey fluid has two parameters, the relaxation time A1 and retardation time A2. The governing equations are simplified using the case of mild stenosis. Perturbation method is used to solve the resulting equations. The effects of non-Newtonian nature of blood on velocity profile, temperature profile, wall shear stress, shearing stress at the stenotsis throat and impedance of the artery are discussed. The results for Newtonian fluid are obtained as special case from this model.

Three-Dimensional Numerical Investigation of the Separation Process in a Vortex Tube at Different Operating Conditions

Air separators provide safe, clean, and appropriate air flow to engines and are widely used in vehicles with large engines such as ships and submarines. In this operational study, the separation process in a Ranque-Hilsch vortex tube cleaning （cooling） system is investigated to analyze the impact of the operating gas type on the vortex tube performance; the operating gases used are air, nitrogen, oxygen, carbon dioxide and nitrogen dioxide. The computational fluid dynamic model used is equipped with a three-dimensional structure, and the steady-state condition is applied during computations. The standard k-c turbulence model is employed to resolve nonlinear flow equations, and various key parameters, such as hot and cold exhaust thermal drops, and power separation rates, are described numerically. The results show that nitrogen dioxide creates the greatest separation power out of all gases tested, and the numerical results are validated by good agreement with available experimental data. In addition, a comparison is made between the use of two different boundary conditions, the pressure-far-field and the pressure-outlet, when analyzing complex turbulent flows in the air separators. Results present a comprehensive and practical solution for use in future numerical studies.

Comparison of the Reynolds-averaged Turbulence Models on Single Phase Flow Simulation in Agitated Extraction Columns

The flow field of liquid phase (water) of agitated extraction columns is simulated with the help of computational fluid dynamics (CFD). Four kinds of Reynolds-averaged turbulence models, i.e. the standard k-ε model, the RNG (renormalization group) k-s model, the realizable k-ε model and the Reynolds stress model, are compared in detail in order to judge which is the best model in terms of the accuracy, less CPU time and memory required. The performance of the realizable k-s model is obviously improved by reducing the model constant from C2 = 1.90 to C2 = 1.61. It is concluded that the improved realizable k-e model is the optimal model.

Comparison of a Full Second-Order Moment Model and an Algebraic Stress Two-Phase Turbulence Model for Simulating Bubble-Liquid Flows in a Bubble Column

A full second-order moment (FSM) model and an algebraic stress (ASM) two-phase turbulence modelare proposed and applied to predict turbulent bubble-liquid flows in a 2D rectangular bubble column. Predictiongives the bubble and liquid velocities, bubble volume fraction, bubble and liquid Reynolds stresses and bubble-liquidvelocity correlation. For predicted two-phase velocities and bubble volume fraction there is only slight differencebetween these two models, and the simulation results using both two models are in good agreement with the particleimage velocimetry (PIV) measurements. Although the predicted two-phase Reynolds stresses using the FSM are insomewhat better agreement with the PIV measurements than those predicted using the ASM, the Reynolds stressespredicted using both two models are in general agreement with the experiments. Therefore, it is suggested to usethe ASM two-phase turbulence model in engineering application for saving the computation time.