Modeling of multiphase flow in low permeability porous media:Effect of wettability and pore structure properties

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications.However,a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability.To address this issue,based on the digital rock of low permeability sandstone,a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process.In addition,a dual-porosity pore network model(PNM)is constructed to obtain the water-oil relative permeability of the sample.The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties.Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability.The injected water breaks through the outlet earlier with a large mass flow,while thick oil films exist in rough hydrophobic surfaces and poorly connected pores.The variation of water-oil relative permeability is significant,and residual oil saturation is high in the oil-wet system.The flooding is extensive,and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces;thus,water relative permeability is lower in the water-wet system.While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity.Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance,and a large microporosity corresponds to low residual oil saturation.This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

Numerical Simulation of Oil-Water Two-Phase Flow in Low Permeability Tight Reservoirs Based on Weighted Least Squares Meshless Method

In response to the complex characteristics of actual low-permeability tight reservoirs,this study develops a meshless-based numerical simulation method for oil-water two-phase flow in these reservoirs,considering complex boundary shapes.Utilizing radial basis function point interpolation,the method approximates shape functions for unknown functions within the nodal influence domain.The shape functions constructed by the aforementioned meshless interpolation method haveδ-function properties,which facilitate the handling of essential aspects like the controlled bottom-hole flow pressure in horizontal wells.Moreover,the meshless method offers greater flexibility and freedom compared to grid cell discretization,making it simpler to discretize complex geometries.A variational principle for the flow control equation group is introduced using a weighted least squares meshless method,and the pressure distribution is solved implicitly.Example results demonstrate that the computational outcomes of the meshless point cloud model,which has a relatively small degree of freedom,are in close agreement with those of the Discrete Fracture Model(DFM)employing refined grid partitioning,with pressure calculation accuracy exceeding 98.2%.Compared to high-resolution grid-based computational methods,the meshless method can achieve a better balance between computational efficiency and accuracy.Additionally,the impact of fracture half-length on the productivity of horizontal wells is discussed.The results indicate that increasing the fracture half-length is an effective strategy for enhancing production from the perspective of cumulative oil production.

Base Flow Index Evaluation for Yom River,Thailand

The most controversial river in Thailand is the Yom River.It has not been modified by large dam because of several valuable natural resources.Therefore,the river is flooded in rainy season and very low flow in dry season.The low flow causes drought which is much more serious than flooding.The Yom River Basin management is only way to circumvent the low flow problem by studying base flow index(BFI).Base flow analyses for 8 gauging stations along the river were performed by 2 techniques i.e.graphical and modified U.K.Institute of Hydrology(MIH).The mean BFI results from graphical and MIH are 0.37(0.05)and 0.45(0.12).The result from graphical is more reasonable due to its lower standard deviation.BFI values from MIH vary with watershed area which may result from the using of fixing value of N-day at 10.Solution for this problem is ongoing in this study.

INNOFLOW匀流染色机的应用实践

阐述了匀流染色机的染色工作原理、结构特征以及染色时主要工艺条件的控制。实践表明,匀流染色机与常规染色机相比,染色时间缩短14%~16%,节省染料10%左右,节省助剂（盐、碱）30%左右;耗水量减少50%以上,蒸汽节省50%左右,电能节省25%左右;排污也相应减少50%以上,符合节能减排、生态环保的要求。

A NOVEL SLIGHTLY COMPRESSIBLE MODEL FOR LOW MACH NUMBER PERFECT GAS FLOW CALCULATION

By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perect gas flows is derived. In view of numerical calculations, this model is proved very efficient, for it is kept within thep-v frame but does not have to satisfy the time consuming divergence-free condition in order to get the incompressible Navier-Stokes equation solution. Writing the equations in the form of conservation laws, we have derived the characteristic systems which are necessary for numerical calculations. A cell-centered finite-volume method with flux difference upwind-biased schemes is used for the equation solutions and a new Exact Newton Relaxation (ENR) implicit method is developed. Various computed results are presented to validate the present model. Laminar flow solutions over a circular cylinder with wake developing and vortex shedding are presented. Results for inviscid flow over a sphere are compared in excellent agreement with the exact analytic incompressible solution. Three-dimensional viscous flow solutions over sphere and prolate spheroid are also calculated and compared well with experiments and other incompressible solutions. Finally, good convergent performances are shown for sphere viscous flows.

Multiphase fluid dynamics and transport processes of low capillary number cavitating flows

To better understand the multiphase fluid dynamics and associated transport processes of cavitating flows at the capillary number of 0.74 and 0.54, and to validate the numerical results, a combined computational and experimental investigation of flows around a hydrofoil is studied based on flow visualizations and time-resolved interface movement. The computational model is based on a modified RNG k-ε model as turbulence closure, along with a vapor-liquid mass transfer model for treating the cavitation process. Overall, favorable agreement between the numerical and experimental results is observed. It is shown that the cavi- tation structure depends on the interaction of the water-vapor mixture and the vapor among the whole cavitation stage, the interface between the vapor and the two-phase mixture exhibits substantial unsteadiness. And, the adverse motion of the interface relates to pressure and velocity fluctuations inside the cavity. In particular, the velocity in the vapor region is lower than that in the two-phase region.

An overview on nonlinear porous flow in low permeability porous media

This paper gives an overview on nonlinear porous flow in low permeability porous media, reveals the microscopic mechanisms of flows, and clarifies properties of porous flow fluids. It shows that, deviating from Darcy＇s linear law, the porous flow characteristics obey a nonlinear law in a low-permeability porous medium, and the viscosity of the porous flow fluid and the permeability values of water and oil are not constants. Based on these characters, a new porous flow model, which can better describe low permeability reservoir~ is established. This model can describe various patterns of porous flow, as Darcy＇s linear law does. All the parameters involved in the model, having definite physical meanings, can be obtained directly from the experiments.

Flow patterns and boundary conditions for inlet and outlet conduits of large pump system with low head

The flow patterns in the inlet and outlet conduits have a decisive effect on the safe, stable, and highly efficient operation of the pump in a large pumping station with low head. The numerical simulation of three-dimensional （3D） turbulence flow in conduits is an important method to study the hydraulic performance and conduct an optimum hydraulic design for the conduits. With the analyses of the flow patterns in the inlet and outlet conduits, the boundary conditions of the numerical simulation for them can be determined. The main obtained conclusions are as follows： （i） Under normal operation conditions, there is essentially no pre-swirl flow at the impeller chamber inlet of an axial-flow pump system, based on which the boundary condition at the inlet conduit may be defined. （ii） The circulation at the guide vane outlet of an axial-flow pump system has a great effect on the hydraulic performance of the outlet conduit, and there is optimum circulation for the performance. Therefore, it is strongly suggested to design the guide vane according to the optimum circulation. （iii） The residual circulation at the guide vane outlet needs to be considered for the inlet boundary condition of the outlet conduit, and the value of the circulation may be measured in a specially designed test model.

Analytical solution of a double moving boundary problem for nonlinear flows in one-dimensional semi-infinite long porous media with low permeability

Based on Huang＇s accurate tri-sectional nonlin- ear kinematic equation （1997）, a dimensionless simplified mathematical model for nonlinear flow in one-dimensional semi-infinite long porous media with low permeability is presented for the case of a constant flow rate on the inner boundary. This model contains double moving boundaries, including an internal moving boundary and an external mov- ing boundary, which are different from the classical Stefan problem in heat conduction： The velocity of the external moving boundary is proportional to the second derivative of the unknown pressure function with respect to the distance parameter on this boundary. Through a similarity transfor- mation, the nonlinear partial differential equation （PDE） sys- tem is transformed into a linear PDE system. Then an ana- lytical solution is obtained for the dimensionless simplified mathematical model. This solution can be used for strictly checking the validity of numerical methods in solving such nonlinear mathematical models for flows in low-permeable porous media for petroleum engineering applications. Finally, through plotted comparison curves from the exact an- alytical solution, the sensitive effects of three characteristic parameters are discussed. It is concluded that with a decrease in the dimensionless critical pressure gradient, the sensi- tive effects of the dimensionless variable on the dimension- less pressure distribution and dimensionless pressure gradi- ent distribution become more serious; with an increase in the dimensionless pseudo threshold pressure gradient, the sensi- tive effects of the dimensionless variable become more serious; the dimensionless threshold pressure gradient （TPG） has a great effect on the external moving boundary but has little effect on the internal moving boundary.

Numerical Simulation on Flow Past Two Side-by-Side Inclined Circular Cylinders at Low Reynolds Number

A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.

Analysis and management strategies for the low voltage problems of rural power grid based on the distribution network flow calculation method

For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low voltage problems were highlighted in the rural power grid due to the characteristics of rural power grid. Using the distribution network flow calculation method, we evaluated the low voltage problems of the rural power grid which belongs to Chongqing Jiangbei Power Company. In addition, we collected the data of distribution transformers in electricity consumption peak period. Some practical management strategies were proposed by the analysis and evaluation of potential and appeared low voltage problems.

The effects of drainage basin geomorphometry on minimum low flow discharge: the study of small watershed in Kelang River Valley in Peninsular Malaysia

This study investigate the relationships between geomorphometric properties and the minimum low flow discharge of undisturbed drainage basins in the Taman Bukit Cahaya Seri Alam Forest Reserve, Peninsular Malaysia. The drainage basins selected were third-order basins so as to facilitate a common base for sampling and performing an unbiased statistical analyses. Three levels of relationships were observed in the study. Significant relationships existed between the geomorphometric properties as shown by the correlation network analysis; secondly, individual geomorphometric properties were observed to influence minimum flow discharge; and finally, the multiple regression model set up showed that minimum flow discharge(Q min) was dependent of basin area(AU), stream length(LS), maximum relief(Hmax), average relief(HAV) and stream frequency(SF). These findings further enforced other studies of this nature that drainage basins were dynamic and functional entities whose operations were governed by complex interrelationships occurring within the basins. Changes to any of the geomorphometric properties would influence their role as basin regulators thus influencing a change in basin response. In the case of the basin's minimum low flow, a change in any of the properties considered in the regression model influenced the “time to peak' of flow. A shorter time period would mean higher discharge, which is generally considered the prerequisite to flooding. This research also conclude that the role of geomorphometric properties to control the water supply within the stream through out the year even though during the drought and less precipitations months. Drainage basins are sensitive entities and any deteriorations involve will generate reciprocals and response to the water supply as well as the habitat within the areas.

A phosphotungstic acid coupled silica-Nafion composite membrane with significantly enhanced ion selectivity for vanadium redox flow battery

An ultra-high ion-selective Nafion composite membrane modified by phosphotungstic acid(PWA)coupled silica for vanadium redox flow battery(VRB)was constructed and prepared through solution casting.The composite membrane exhibits excellent proton conductivity and vanadium ions blocking property by incorporating the nanohybrid composed of silica and PWA into the Nafion ionomer.Simple tuning for the filling amount of the nanohybrid endows the obtained membranes preeminent vanadium barrier property including a minimum vanadium permeability of 3.13×10-7cm2min-1and a maximum proton conductivity of 0.081 S cm-1at 25°C.These indicate an ion selectivity of 2.59×105S min cm-3,which is 6.8times higher than that of recast Nafion(0.33×105S min cm-3).As a result,the VRB with the composite membrane shows superior battery performance containing a lower self-discharge rate,higher capacity retention and more robust cyclic stability compared with recast Nafion over a range of current densities from 40 to 100 m A cm-2.

Mechanisms for non-ideal flow in low-power arc-heated supersonic nozzles

The flow in a low-powered arc gas heater com- bined with a supersonic nozzle of throat diameter less than 1 mm is quite complicated and difficult to describe in quan- titative detail. Experiments on arc-heated supersonic jet thrusters of monatomic gases argon and helium have been carried out and their performance measured. The flow charac- teristics are analyzed with the help of numerical simulation. Results show that the viscous effect is the most important factor causing the large difference between ideal and real performance. A large outer section of the exit flow is slow- moving. This is especially pronounced in helium, where 70 % of the exit area of the nozzle might be in subsonic flow. Fric- tion forces can be much larger than the net thrust, reaching several times higher in helium, resulting in very low efficien- cies. Other factors causing the differences between ideal and real flow include： complex flow in the throat region, electric arc extending to the nozzle expansion section, heat transfer to the inlet gas and from the hot plasma, and environmen- tal pressure in the vacuum chamber. It is recognized that the ordinary concepts of supersonic nozzle flow must be greatly modified when dealing with such complicated situations. The general concepts presented in this paper could be helpful in guiding the design and operation of this equipment.

PROMOTER FLOW ACTION OF SOLID-STATE LOW MELT POINT METAL ON THE POLYPROPYLENE

With the aid of a slip-disentanglemnt theory, a rheological equation has been deduced about the composite system of solid-state low melting point metal and polymer. By measuring some rheological properties of the composite system composed of low melt point metal and polypropylene (LMPM/PP), the results show that LMPM has a promoter flow action upon PP when using a small amount of LMPM and, if some coupled agents are added, the promoter flow action will be remarkable. Moreover, while LMPM being added into the composite, the temperature sensitivity of system will go rip. This indicates that the system's viscosity will drop further if its temperature is increased.

基于Solidworks Flow Simulation的微流阻微开启压力止回阀设计

针对传统止回阀存在高开启压力和高流阻的问题,设计了一种微流阻、微开启压力的止回阀。依据CAD设计图,对阀门开启压力和流阻进行了理论计算。利用Solidworks Flow Simulation软件,分析阀门分别处于75°、40°、10°工况时的压力云图,计算出每个工况下的流量系数。结果表明,设计的阀门开启压力小、流阻系数小、流量系数大、通流能力好,能有效减小流体系统中总输送泵的能耗,达到了设计的目标。

Numerical Simulation of Stall Flow Control Using a DBD Plasma Actuator in Pulse Mode

A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions. The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations. The governing equations are solved using an efficient implicit finitevolume method. The responses of the separated flow field to the effects of an unsteady body force in various inter- pulses and duty cycles as well as different locations and magnitudes are studied. It is shown that the duty cycle and inter-pulse are key parameters for flow separation control. Additionally, it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.

Mathematical Modeling,Field Calibration and Numerical Simulation of Low-Speed Mixed Traffic Flow in Cities

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Solid Transfer in Low Flow Sewers, the Distance Travelled So Far Is Not Enough

Sewer blockages are on the increase whilst water closet (WC) flush volumes are on the decrease. Furthermore, Water UK reported figures show that the actual number of properties affected by sewer flooding is on the rise. Sewer blockages can lead to sewer flooding of homes and collapse of sewers which impact negatively on social, economic and environmental factors, and therefore, they are not sustainable. Water conservation is required due to water stress but reduced water use results in less water to waste, which in turn reduces solids’ transfer in sewers. When considering reducing water usage through water conservation, these savings could be cancelled out by an increased population and the situation exacerbated by the impacts of climate change. There are issues in relation to varying design methods, a reliance on engineering judgement in sewer design, uncertainty relating to future water stress, and a lack of cross disciplinary design decision-making. Public health engineering solutions are needed to reduce the number of sewer blockages and the environmental impact of sewer flooding. This paper examines the fundamental research that have been carried out in the area of “solid transfer in sewers” resulting from “less water to waste” since the mid-20th Century. Contrary to existing literature, this paper identifies that, now more than ever, this type of research is needed to deal with the increased need for water conservation. To judge that solid transfer research is complete can be compared to supporting a statement that “water conservation is complete”.

VISUALIZATION OF FLOW STRUCTURES IN A TURBULENT BOUNDARY LAYER USING A NEW TECHNIQUE

In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.