ERT成像算法在管道泥浆浓度测量中的应用

电阻层析成像(ERT)技术的非侵入性和可视化特点在管道泥浆浓度检测中具有独特的优势,作为ERT技术的核心,成像算法的选择对于检测水平有很大影响。采用LBP算法、Newton-Raphson迭代算法和Landweber迭代算法对3种管道泥浆流型进行反演成像,并从成像精度、成像速度和抗噪声能力3个指标定量评价了3种算法的适用性。计算结果表明,LBP算法具有最快的成像速度和最强的抗噪声能力;Newton-Raphson算法具有最高的成像精度。根据成像实时性的要求确定选用何种算法。

Characteristics of turbulent flow distribution in branch piping system

Flow distribution in branch piping system is affected by flow characteristics and different geometric variations. Most of the flow distribution studies are performed with one-dimensional analysis to yield overall information only. However, detailed analysis is required to find effects of design parameters on the flow distribution. For this aspect, three-dimensional turbulent flow analysis was performed to assess turbulence model performance and effects of upstream pressure and branch pipe geometry. Three different turbulence models of standard k-e model, realizable k-e model and standard k-co yield similar results, indicating small effects of turbulence models on flow characteristics analysis. Geometric variations include area ratio of main and branch pipes, branch pipe diameter, and connection shape of main and branch pipes. Among these parameters, area ratio and branch diameter and shape show strong effect on flow distribution due to high friction and minor loss. Uniform flow distribution is one of common requirements in the branch piping system and this can be achieved with rather high total loss design.

Numerical Research on the Fiber Suspensions in a Turbulent T-shaped Branching Channel Flow

The concentration and orientation of fiber in a turbulent T-shaped branching channel flow are investi-gated numerically. The Reynolds averaged Navier-Stokes equations together with the Reynolds stress turbulent model are solved for the mean flow field and the turbulent kinetic energy. The fluctuating velocities of the fluid are assumed as a random variable with Gaussian distribution whose variance is related to the turbulent kinetic energy. The slender-body theory is used to simulate the fiber motion based on the known mean and fluctuating velocities of the fluid. The results show that at low Reynolds number, fiber concentration is high in the flow separation regions, and fiber orientation throughout the channel is widely distributed with a slight preference of aligning along the horizontal axis. With increasing of Re, the high concentration region disappears, and fiber orientation becomes ho-mogeneous without any preferred direction. At high Reynolds number, fiber concentration increases gradually along the flow direction. The differences in the distribution of concentration and orientation between different fiber aspect ratio are evident only at low Re. Both Re and fiber aspect ratio have small effect on the variance of orientation angle.

Numerical Modeling and Analysis of Gas Entrainment for the Ventilated Cavity in Vertical Pipe

A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to predict the multiscale flow field created by ventilated cavity. Model predictions were validated against experimental measurements on void fraction and bubble size distributions. Simulations were carried out to explore the effect of ventilation rate and inlet turbulence intensity on the macroscale cavity shape and the bubbly flow downstream of the ventilated cavity. As the ventilation rate increasing, a reverse trend was observed for the void fraction and bub-ble size distributions. It is concluded that the average void fraction in the pipe flow region is determined by the vo-lumetric ratio between liquid and gas. However, the bubble size evolution is dominated by the breakage effect induced by turbulence in the vortex region. Furthermore, simulations were conducted to analyze geometric scale effect based upon Froude similitude. The results imply that the velocity distributions were properly scaled. Slight scale effect was seen for the void fraction caused by faster dispersion of bubbles in the larger size model. The comparatively greater bubble size was predicted in the smaller model, implying significant scale effects in terms of tur-bulence and surface tension effect. It reveals that empirical correlations valid in wide range are required for the extrapolation from small-size laboratory models.

Three-phase flow of submarine gas hydrate pipe transport

In the hydraulic transporting process of cutter-suction mining natural gas hydrate, when the temperature-pressure equilibrium of gas hydrate is broken, gas hydrates dissociate into gas. As a result, solid-liquid two-phase flow(hydrate and water) transforms into gas-solid-liquid three-phase flow(methane, hydrate and water) inside the pipeline. The Euler model and CFD-PBM model were used to simulate gas-solid-liquid three-phase flow. Numerical simulation results show that the gas and solid phase gradually accumulate to the center of the pipe. Flow velocity decreases from center to boundary of the pipe along the radial direction. Comparison of numerical simulation results of two models reveals that the flow state simulated by CFD-PBM model is more uniform than that simulated by Euler model, and the main behavior of the bubble is small bubbles coalescence to large one. Comparison of numerical simulation and experimental investigation shows that the values of flow velocity and gas fraction in CFD-PBM model agree with experimental data better than those in Euler model. The proposed PBM model provides a more accurate and effective way to estimate three-phase flow state of transporting gas hydrate within the submarine pipeline.

Numerical Prediction of Flow Patterns after Various Pipe Fittings

An accurate prediction of flows using CFD depends on a large number of factors. In addition to discretizing the flow region, the correct definition of boundary or initial conditions and the choice of suitable numerical methods, the applied turbulence model influences the results of the flow simulation to a great extent. Therefore, a validation of the results with the experimental data is of great importance for a correct selection of a turbulence model. It is the scope of this paper to assess different turbulence models for the simulation of pipe flows. The calculation results of pipe flows through a combination of 90~ elbows and a 1/3 segmental orifice are compared with experimental measurement results. This has the advantage that the suitability of the turbulence models for simulating both shear and swirl flows can be investigated. Thus, the k-ω, k-ε model and the Launder Reece Rodi Reynolds stress model are compared with each other and experimental results. Furthermore, this investigation is extended through including a much more c detached-eddy simulation. This model provides better prediction of the flow by resolving the large eddies and modeling the small ones. The experimental results originate from LDV measurements over the entire pipe cross-section. This measuring method provides velocity vectors over the measured surface.

The urban unsteady and non-pressure rain pipe flow routing by the dynamical-wave method

The dynamical-wave routing model of the urban unsteady and non-pressure rain pipe flow was established by conservation of mass, momentum and energy, and it was solved by applying the four point implicit difference method and the pursuit method. It was obtained from the experiment checking and comparative analysis that the dynamical-wave muting model can reflect influence like attenuate and backwater when flood peak propagate in pipeline with high calculation precision and vast application scope, and it can be applied in routing of urban rain pipe flow of different slopes and inflow conditions. The routing model supplies a scientific foundation for the town rainfall piping design or checking, disaster administration of storm runoff, and so on.

Thermal Performance of a Single-row Fin-and-tube Heat Exchanger

Experiments were carried out to study the heat transfer characteristics of a single-row aluminum fin-and-tube crossflow heat exchanger with an emphasis in the regime of low flow rate of the in-tube fluid. The Chilton-Colburn analogy, in conjunction with the least-squares power-law technique, was used to correlate experimental data. Both air- and water-side heat transfer correlations were developed in the form of the Nusselt numbers as a function of Reynolds and Prandtl numbers. The experimental observations are quantitatively compared to the predictions of correlations available in the published literature. Different transfer mechanisms were found to be operative in the ranges of water-side Reynolds numbers based on the hydraulic diameter. In a range of Reynolds number from 1,200 to 6,000, the water-side thermal resistance accounts for less than ten percent of the overall thermal resistance. The dominant thermal resistance is always on the air-side. On the other hand, the thermal resistance of water-side is nearly equal to that of air-side in a Reynolds number range from 500 to 1,200.

Experimental investigation of vortex-induced vibrations of long free spans near seabed

There are many experimental studies dedicated to determining the effect of the proximity of a plane boundary on the vortex-induced vibration (VIV) of submarine pipeline spans, but they all only concerned the first mode VIV motion of the pipe. In this paper, a pipe model, 16 mm in diameter, 2.6 m in length and with a mass ratio (mass/displaced mass) of 4.30, was tested in a current tank. The reduced velocity was in the range of 0-16.7 and gap ratios at the pipe ends were 4.0, 6.0 and 8.0. The response of the model was measured using optical fiber strain gauges. Results of response amplitude and frequency were presented and the transition from the first dominant mode to the second one was shown. In the tests, it was found that the response amplitude experienced a continuous transition between the two modes, but the dramatic increase in the response frequency appeared with the shift in dominant mode from the first mode to the second one as the flow velocity increased. As the gap ratio decreased, the shift in the dominant mode took place at a higher reduced velocity.

Examples of Boundary Layers Associated with the Incompressible Navier-Stokes Equations

The author surveys a few examples of boundary layers for which the Prandtl boundary layer theory can be rigorously validated.All of them are associated with the incompressible Navier-Stokes equations for Newtonian fluids equipped with various Dirichlet boundary conditions(specified velocity).These examples include a family of(nonlinear 3D) plane parallel flows,a family of(nonlinear) parallel pipe flows,as well as flows with uniform injection and suction at the boundary.We also identify a key ingredient in establishing the validity of the Prandtl type theory,i.e.,a spectral constraint on the approximate solution to the Navier-Stokes system constructed by combining the inviscid solution and the solution to the Prandtl type system.This is an additional difficulty besides the wellknown issue related to the well-posedness of the Prandtl type system.It seems that the main obstruction to the verification of the spectral constraint condition is the possible separation of boundary layers.A common theme of these examples is the inhibition of separation of boundary layers either via suppressing the velocity normal to the boundary or by injection and suction at the boundary so that the spectral constraint can be verified.A meta theorem is then presented which covers all the cases considered here.

A mathematical model in closed for unsteady mixed flows water pipes Dedicated to the NSFC-CNRS Chinese-French summer institute on fluid mechanics in 2010

We present the formal derivation of a new unidirectional model for unsteady mixed flows in nonuniform closed water pipes. In the case of free surface incompressible flows, the FS-model is formally obtained, using formal asymptotic analysis, which is an extension to more classical shallow water models. In the same way, when the pipe is full, we propose the P-model, which describes the evolution of a compressible inviscid flow, close to gas dynamics equations in a nozzle. In order to cope with the transition between a free surface state and a pressured （i.e., compressible） state, we propose a mixed model, the PFS-model, taking into account changes of section and slope variation.

An Approximate Model of Microchannel Cooling

Forced convective heat transfer in micro-rectangular channels can be described by a group of twodimensional differential equations. These equations take the conduction in microchannel wb along the direction of flow of coolants into account, which are more generalized than those which neglect the conduction. For the same reason, they are suitable particularly for gases-cooled microchannels.With only numerical solution to the equations till today, an approximate analytic solution is derived here. From this solution, a rather simple formula can be introduced bober, by which the differences between considering the conduction and neglecting it are easily found. In addition, the rcasonableness of the classical fin method is also discussed. An experimental example of air-cooled microchannels is illustrated.

Theoretical and Computational Analyses of LNG Evaporator

Theoretical and numerical analysis on the fluid flow and heat transfer inside a LNG evaporator is conducted in this work. Methane is used instead of LNG as the operating fluid. This is because; methane constitutes over 80% of natural gas. The analytical calculations are performed using simple mass and energy balance equations. The analytical calculations are made to assess the pressure and temperature variations in the steam tube. Multiphase numerical simulations are performed by solving the governing equations(basic flow equations of continuity, momentum and energy equations) in a portion of the evaporator domain consisting of a single steam pipe. The flow equations are solved along with equations of species transport. Multiphase modeling is incorporated using VOF method. Liquid methane is the primary phase. It vaporizes into the secondary phase gaseous methane. Steam is another secondary phase which flows through the heating coils. Turbulence is modeled by a two equation turbulence model. Both the theoretical and numerical predictions are seen to match well with each other. Further parametric studies are planned based on the current research.