Fluid Dynamics & Materials Processing

3D Numerical Fluid Flow Modelling In Multiple Fractured Porous Reservoirs

2020-05-11T07:09:53+08:00

This paper compares the fluid flow phenomena occurring within a fractured reservoir for three different fracture models using computational fluid dynamics. The effect of fracture-matrix interface condition is studied on the pressure and velocity distribution. The fracture models were compared based on the variation in pressure and permeability conditions. The model was developed for isotropic and anisotropic permeability conditions.

The results suggest that fracture aperture can have a drastic effect on fluid flow. The porous jump fracture-matrix interface condition produces more realistic transport of fluids. By increasing the permeability in the isotropic porous matrix, the pressure drop was significantly higher in both the fracture and reservoir region. Under anisotropic conditions in the 3D fractured reservoir, the effect of the higher longitudinal permeability was found to lower the pressure in the fractured reservoir. Depending on the properties of the fractured reservoir, this study can enhance the understanding of fracture-matrix fluid interaction and provide a method for production optimisation.

Heat and mass transfer characteristics of alkali metals in a combined wick

2020-05-11T07:09:54+08:00

To study the heat and mass transfer characteristics of alkali metals in a combined porous wick in high-temperature heat pipes, a three-dimensional (3-d) numerical model is constructed by using the finite volume method, Darcy‘s theory, and the theory of local thermal equilibrium. The research finds that the pressure drop of fluids flowing through a combined porous wick exhibits an increasing trend with increasing flow velocity at the inlet and with decreasing permeability of the porous media; a combined porous wick of lower porosity and permeability and larger fluid velocity at the inlet is found to have a less uniformly distributed fluid velocity; the different temperatures of the fluid at the inlet mainly influence the inlet section of the computational model, while having negligible effect thereon in the axial direction (this embodies the thermal homogeneity of such heat pipes). The result reveals that the temperature change in fluids at the inlet does not significantly affect the overall temperature distribution in a combined wick.

Numerical simulation of fluid and heat transfer in biological tissue containing the exact structure of microvascular network using immersed boundary method

2020-05-11T07:09:56+08:00

The aim of this study is to develop a model of fluid and heat transfer in biological tissue containing the exact structure of microvascular network, and to analyze the influence of structural changes of the network in diabetes on flow and heat transfer. A cubic region representing local skin tissue is selected as the computational domain, which is composed of two sub-domains of intravascular and extravascular parts. To save computing resources, the capillary network is reduced to a 1D pipeline model and embedded into the extravascular part. According to the concept of immersed boundary method (IBM), fluid and heat fluxes across capillary wall are distributed to surrounding tissue nodes by delta function.

The steady and periodic blood pressure conditions were set respectively at the entrances of capillary network. Under steady blood pressure condition, both the interstitial fluid pressure and tissue temperature around the capillary network are larger than those in other places. Under the periodic blood pressure condition, tissue temperature shows the trend of fluctuating with the same frequency, but the amplitude attenuation and time delay of the fluctuation waveform occur with the propagation of thermal wave. When the connectivity of capillary network is impaired, the capacity of blood redistribution through the capillary network becomes weaker and a part of the vessel branches lose blood flow, which further aggravates the amplitude attenuation and time delay of skin temperature fluctuation.

Numerical modelling of proppant transport in hydraulic fractures

2020-05-11T07:09:57+08:00

The distribution of proppant injected in hydraulic fractures significantly affects the fracture conductivity and well performance. The proppant transport in thin fracturing fluid used during hydraulic fracturing in the unconventional reservoirs is considerably different from fracturing fluids in the conventional reservoir due to the very low viscosity and quick deposition of the proppants. This paper presents the development of a three-dimensional Computational Fluid Dynamics (CFD) modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures. The proposed model also simulates the fluid leak-off behaviour from the fracture wall. The Euler-Granular and CFD-Discrete Element Method (CFD-DEM) multiphase modelling approach has been applied, and the equations defining the fluid-proppant and inter-proppant interaction have been solved using the finite volume technique. The proppant transport in hydraulic fractures has been studied comprehensively, and the computational modelling results of proppant distribution and other flow properties are in good agreement with the published experimental study. The parametric study is performed to investigate the effect of variation in proppant size, fluid viscosity and fracture width on the proppant transport. Smaller proppants can be injected early, followed by larger proppants to maintain high propping efficiency. This study has enhanced the understanding of the complex flow phenomenon between proppant and fracturing fluid and can play a vital role in hydraulic fracturing design.

Study on Dynamic Prediction of Two-Phase Pipe Flow in Inclined Wellbore with Middle and High Yield

2020-05-11T07:09:59+08:00

Gas-liquid two-phase flow is ubiquitous in the process of oil and gas exploitation, gathering and transportation. Flow pattern, liquid holdup and pressure drop are important parameters in the process of gas-liquid two-phase flow, which are closely related to the smooth passage of the two-phase fluid in the pipe section. Although Mukherjee, Barnea and others have studied the conventional viscous gas-liquid two-phase flow for a long time at home and abroad, the overall experimental scope is not comprehensive enough and the early experimental conditions are limited. Therefore, there is still a lack of systematic experimental research and wellbore pressure for gas-liquid two-phase flow under the conditions of middle and high yield and high gas-liquid ratio in conventional viscosity, and the prediction accuracy is low. In view of this, this study carried out targeted systematic research, and from the flow pattern, liquid holdup and pressure drop aspects, established the relevant model, obtained a set of inclined wellbore gas-liquid two-phase pipe flow dynamic prediction method. At the same time, firstly, the model is tested by experimental data, and then the model is compared and verified by a number of field measured wells, which proves that the model is reliable and the prediction accuracy of wellbore pressure is high.

On the Liquid-Vapor Phase-Change Interface Conditions for Numerical Simulation of Violent Separated Flows

2020-05-11T07:10:01+08:00

Numerous models have been proposed in the literature to include phase change into numerical simulations of two-phase flows. This review paper presents the modeling options that have been taken in order to obtain a model for violent separated flows with application to sloshing wave impacts. A relaxation model based on linear non-equilibrium thermodynamics is used to compute the rate of phase change. The integration in the system of partial differential equations is done through a non-conservative advection term. At each stage some alternative models from the literature are presented and discussed. The theoretical framework for all phase change model (conservation equations and entropy growth) is also summarized.

Linear and Nonlinear Stability Analysis in Microfluidic Systems

2020-05-11T07:10:02+08:00

In this article we use analytical and numerical modeling to describe parallel viscous two-phase flows in microchannels. The focus is on idealized two-dimensional geometries, with a view to validating the various methodologies for future work in three dimensions. In the first instance, we use analytical Orr--Sommerfeld theory to describe the linear instability which governs the formation of small-amplitude waves in such systems. We then compare the results of this analysis with an in-house Computational Fluid Dynamics (CFD) solver called TPLS. Excellent agreement between the theoretical analysis and TPLS is obtained in the regime of small-amplitude waves. We continue the numerical simulations beyond the point of validity of the Orr--Sommerfeld theory. In this way, we illustrate the generation of nonlinear interfacial waves and reverse entrainment of one fluid phase into the other. We justify our simulations further by comparing the numerical results with corresponding results from a commercial CFD code. This comparison is again extremely favourable -- this rigorous validation paves the way for future work using TPLS or commercial codes to perform extremely detailed three-dimensional simulations of flow in microchannels.

Melting Heat Transfer of Prandtl Fluid over a Stretching Surface in The Presence of Fluid Particles Suspension

2020-05-11T07:09:52+08:00

Boundary layer flow and melting heat transfer of a Prandtl fluid over a convective surface in the presence of fluid particles suspensions has been investigated. The converted set of boundary layer equations are solved numerically by RKF-45 method. Obtained numerical results for flow and heat transfer characteristics are deliberated for various physical parameters. Furthermore, the skin friction coefficient and Nusselt number are also presented. It is found that, the heat transfer rates are advanced in occurrence of nonlinear radiation camper to linear radiation. Also it is noticed that, velocity profile increases by increasing Prandtl parameter but establishes opposite results for temperature profile.

Pressure-Driven Gas Flows in Micro Channels with a slip boundary: A numerical investigation

2020-05-11T07:09:54+08:00

In this paper, the numerical investigation of low Reynolds and Mach numbers of compressible nitrogen gas flow with slight rarefaction in microchannels is presented. The model equations have been solved using Comsol Multiphysics software; a solver for partial differential Navier–Stokes equations based on a two-dimensional Finite Element Method, with first-order slip boundary conditions. It is demonstrated that both compressibility and rarefaction effects are present in the microchannels. This study evaluates the pressure-driven and velocity of isothermal flow along micro-filters. The simulated results have been validated and compared with other numerical data from the literature, which indicate that our model can accurately predict the pressure driven flow distributions in microchannels

INFLUENCE OF TIP CLEARANCE ON UNSTEADY FLOW IN AUTOMOBILE ENGINE PUMP

2020-05-11T07:09:55+08:00

汽车发动机泵是汽车冷却系统的重要组成部分，对发动机性能有直接影响。基于SST k-ω湍流模型，Fluent实现了不同叶尖间隙的汽车发动机泵的非定常数值模拟。为了研究流场和压力波动，还分析了蜗壳中二次流分布的特征。结果表明，泵的流场压力波动特征在不同水平的叶尖间隙处表现出明显的周期性变化。每个监测点的压力波动峰值取决于叶片频率。同时，随着叶尖间隙的增加，叶片和蜗壳的压力波动逐渐增大，而顶端间隙处的压力波动逐渐减小。泵中的压力梯度也随着叶轮旋转而周期性地变化。随着叶尖间隙的增加，叶轮，蜗壳和叶尖间隙的压力逐渐减小。在叶轮内部，蜗壳出口和蜗壳部分具有二次流动涡流。随着叶尖间隙的增大，叶轮转轮内的涡流强度减弱，蜗壳出口处的涡流强度增强。在蜗壳的横截面上，大多数涡旋形态变化很小，但涡旋强度减小。蜗壳和叶尖间隙逐渐减小。在叶轮内部，蜗壳出口和蜗壳部分具有二次流动涡流。随着叶尖间隙的增大，叶轮转轮内的涡流强度减弱，蜗壳出口处的涡流强度增强。在蜗壳的横截面上，大多数涡旋形态变化很小，但涡旋强度减小。蜗壳和叶尖间隙逐渐减小。在叶轮内部，蜗壳出口和蜗壳部分具有二次流动涡流。随着叶尖间隙的增大，叶轮转轮内的涡流强度减弱，蜗壳出口处的涡流强度增强。在蜗壳的横截面上，大多数涡旋形态变化很小，但涡旋强度减小。

Convection the Water on a Chemical Condenser

2020-05-11T07:09:57+08:00

A detailed investigation of the convection of the water in a chemical condenser is carried out. Two openings are fixed on the plates of the cavity, the inlet opening and the outlet one. The Navier-Stokes equations are solved using a control volume method and the SIMPLEC algorithm is used for the execution of pressure-velocity coupling. Special emphasis is given to detail the effect of the Reynolds number, the tilt of the channel and Rayleigh number on the heat transfer created by convection. The results are presented for the parameters of control as, Rayleigh number ( ), Prandtl number ( ), the inclination of the channel ( ) and Reynolds number ( ). The results show that the flow structure and the heat transfer depend significantly on the Reynolds number, Rayleigh number, and the inclination of the channel. Two ranges of studies were raised.

Design and research of large-flow pilot operated check valves

2020-05-11T07:09:58+08:00

Reversing impact load conditions may cause severe vibration in large-flow pilot operated check valves. Cavitation erosion may also occur in valve ports after long-term operation. To prevent cavitation erosion, improve the performance of pilot operated check valves, enhance working reliability, and performance stability thereof, firstly, the cavitation index and working principles of large-flow pilot operated check valves are introduced. Then, the structural parameters of a pilot poppet, main poppet, and through-flow section of flow channels are designed to explore reverse impact characteristics and cavitation characteristics thereof. The results showed that the variation of controlling pressure had a minor effect on cavitation. With increasing controlling pressure, the vibration of the poppet decreased and the valve unloading capacities also decreased. The cavitation index showed a linear relationship with impact pressure, but is non-linear with hydraulic flow under different impact parameters. And the stepped throttling structure could effectively reduce the pressure oscillation, as well as improve the response speed, enhance the impact characteristics, and reduce the cavitation. Meanwhile, the larger the orifice, the shorter the unloading time. Cavitation mainly appeared while the pilot poppet of pilot operated check valves is fully opened, and the stepped main poppet throttling structure is an optimal result. Moreover, the matching of structural parameters is optimised. The cavitation index is reduced while the work reliability and service life of the structure are improved. The experimental result verified the rationality of the cavitation index.

Determination of a Safe Distance for Atomic Hydrogen Depositions in Hot-Wire Chemical Vapour Deposition by Means of CFD Heat Transfer Simulations

2020-05-11T07:10:00+08:00

A heat transfer study was conducted, in the framework of Computational Fluid Dynamics (CFD), on a Hot-Wire Chemical Vapour Deposition (HWCVD) reactor chamber to determine a safe deposition distance for atomic hydrogen produced by HWCVD. The objective of this study was to show the feasibility of using heat transfer simulations in determining a safe deposition distance for deposition of this kind. All CFD simulations were set-up and solved within the framework of the CFD packages of OpenFOAM namely; snappyHexMesh for mesh generation, buoyantSimpleFoam and rhoSimpleFoam as the solvers and paraView as the post-processing tool. Using a standard set of deposition parameters for the production of atomic hydrogen by HWCVD, plots of the gas temperature in the deposition region were produced. From these plots, we were able to determine a safe deposition distance in the HWCVD reactor to be in the range between 3 and 4 cm from the filament.

Experimental Investigation of PM2.5 and Formaldehyde Pollutants of an Office

2020-05-11T07:09:52+08:00

PM_2.5and formaldehyde are two main indoor pollutants threatening the health of human beings. In this paper, the concentrations of PM_2.5 and formaldehyde in an office were measured under different conditions. The effects of temperature on the release of the decoration materials including flooring, gypsum powder, joint mixture and corestock were also carried out. The results show that window ventilation can achieve the same PM_2.5 purification effect as an air cleaner. The concentration of released formaldehyde from the decoration materials is highly correlated with indoor temperature and has little correlation with humidity. The formaldehyde release from the decoration materials increases approximately linearly with the increase of the heating temperature. The order in which the formaldehyde concentration is released is joint mixture, gypsum powder, corestock and flooring. The concentration of released formaldehyde from the four decoration materials varies from 0.08 ppm to 0.4 ppm when the heating temperature increaeses from 16 ℃ to 30 ℃.