Transient flow behavior in serpentine curved microchannel of inertial microfluidic devices

2020 ◽  
Vol 30 (2) ◽  
pp. 025005
Author(s):  
Teng Shen ◽  
Zhanggen Zhu ◽  
Liu Huang ◽  
Jiaqing Chang
Keyword(s):  
Transient Flow ◽  
Flow Behavior ◽  
Microfluidic Devices

New benchmark solutions for transient natural convection in partially porous annuli

2016 ◽  
Vol 26 (3/4) ◽  
pp. 1187-1225 ◽  
Author(s):  
Nicola Massarotti ◽  
Michela Ciccolella ◽  
Gino Cortellessa ◽  
Alessandro Mauro
Keyword(s):  
Natural Convection ◽  
Free Convection ◽  
Transient Flow ◽  
Flow Behavior ◽  
Outer Radius ◽  
Temperature Fields ◽  
Content Type ◽  
Transient Natural Convection ◽  
Velocity And Temperature Fields ◽  
Benchmark Solutions

Purpose – The purpose of this paper is to focus on the numerical analysis of transient free convection heat transfer in partially porous cylindrical domains. The authors analyze the dependence of velocity and temperature fields on the geometry, by analyzing transient flow behavior for different values of cavity aspect ratio and radii ratio; both inner and outer radius are assumed variable in order to not change the difference ro-ri. Moreover, several Darcy numbers have been considered. Design/methodology/approach – A dual time-stepping procedure based on the transient artificial compressibility version of the characteristic-based split algorithm has been adopted in order to solve the transient equations of the generalized model for heat and fluid flow through porous media. The present model has been validated against experimental data available in the scientific literature for two different problems, steady-state free convection in a porous annulus and transient natural convection in a porous cylinder, showing an excellent agreement. Findings – For vertically divided half porous cavities, with Rayleigh numbers equal to 3.4×106 for the 4:1 cavity and 3.4×105 for the 8:1 cavity, the numerical results show that transient oscillations tend to disappear in presence of cylindrical geometry, differently from what happens for rectangular one. The magnitude of this phenomenon increases with radii ratio; the porous layer also affects the stability of velocity and temperature fields, as oscillations tend to decrease in presence of a porous matrix with lower value of the Darcy number. Research limitations/implications – A proper analysis of partially porous annular cavities is fundamental for the correct estimation of Nusselt numbers, as the formulas provided for rectangular domains are not able to describe these problems. Practical implications – The proposed model represents a useful tool for the study of transient natural convection problems in porous and partially porous cylindrical and annular cavities, typical of many engineering applications. Moreover, a fully explicit scheme reduces the computational costs and ensures flexibility. Originality/value – This is the first time that a fully explicit finite element scheme is employed for the solution of transient natural convection in partially porous tall annular cavities.

scholarly journals FLOW BEHAVIOUR OF OIL BLOB THROUGH A CAPILLARY TUBE CONSTRICTION DURING PULSED INJECTION

2018 ◽  
Vol 81 (1) ◽  
Author(s):  
Shiferaw Regassa Jufar ◽  
Tareq M Al-Shami ◽  
Ulugbek Djuraev ◽  
Berihun Mamo Negash ◽  
Mohammed Mahbubur Rahman
Keyword(s):  
Pressure Gradient ◽  
Transient Flow ◽  
Capillary Tube ◽  
Reverse Flow ◽  
Flow Behavior ◽  
Adverse Pressure Gradient ◽  
Gradient Zone ◽  
Pulsed Injection ◽  
Time Required ◽  
Continuous Injection

A numerical simulation of flow of oil blob through a capillary tube constriction is presented. The simulation was run in a 2D axisymmetric model. Water is injected at the inlet to mobilize oil blob placed near the capillary tube constriction. Transient flow images were used to understand the flow evolution process. Results from the study show that pulsed injection effectively assisted to squeeze out the oil blob through the capillary tube constriction with shorter time compared to continuous injection.  Pulsed injection reduced the time required for the first droplet to cross the capillary tube constriction by about 3 folds compared to continuous injection. In addition, the droplet that crossed the constriction is larger when the flow was pulsed. In both cases, there is a reverse flow in the opposite direction of the injection. However, the severity of the reverse flow is stronger in the case of continuous injection. Immediately downstream the constriction, there is an adverse pressure gradient zone during continuous injection which limits the mobility of droplet that crossed the constriction. However, in the case of pulsed injection, there is a favorable pressure gradient zone immediately downstream the constriction. This zone expedites mobility of droplets that cross the constriction by transporting them further downstream through suction effect. Apparently, pulsed injection eases off the adverse pressure gradient and allowed more volume of oil to pass through the constriction. Within about two periods of pulsation, 84% of original oil placed at the beginning crossed the constriction compared to only 35% in the case of continuous injection. Even though the same amount of water was injected in both cases, pulsed injection clearly altered the flow behavior. The observation from this study may be extended to more complex flows in order to tailor the method for certain specific applications, such as flow of residual oil through a reservoir.

scholarly journals Analysis of Flow Behavior for Acid Fracturing Wells in Fractured-Vuggy Carbonate Reservoirs

2018 ◽  
Vol 2018 ◽  
pp. 1-20 ◽  
Author(s):  
Mingxian Wang ◽  
Zifei Fan ◽  
Xuyang Dong ◽  
Heng Song ◽  
Wenqi Zhao ◽  
...  
Keyword(s):  
Composite System ◽  
Numerical Solutions ◽  
Transient Flow ◽  
Flow Behavior ◽  
Outer Region ◽  
Carbonate Reservoirs ◽  
Single Fracture ◽  
Specific Flow ◽  
Type Curves ◽  
Acid Fracturing

This study develops a mathematical model for transient flow analysis of acid fracturing wells in fractured-vuggy carbonate reservoirs. This model considers a composite system with the inner region containing finite number of artificial fractures and wormholes and the outer region showing a triple-porosity medium. Both analytical and numerical solutions are derived in this work, and the comparison between two solutions verifies the model accurately. Flow behavior is analyzed thoroughly by examining the standard log-log type curves. Flow in this composite system can be divided into six or eight main flow regimes comprehensively. Three or two characteristic V-shaped segments can be observed on pressure derivative curves. Each V-shaped segment corresponds to a specific flow regime. One or two of the V-shaped segments may be absent in particular cases. Effects of interregional diffusivity ratio and interregional conductivity ratio on transient responses are strong in the early-flow period. The shape and position of type curves are also influenced by interporosity coefficients, storativity ratios, and reservoir radius significantly. Finally, we show the differences between our model and the similar model with single fracture or without acid fracturing and further investigate the pseudo-skin factor caused by acid fracturing.

QPG-dominated transient flow behavior of a well in a subsurface formation

2020 ◽  
pp. 125939
Author(s):  
Ren-Shi Nie ◽  
Xiaohui Fan ◽  
Min Li ◽  
Zhangxin Chen ◽  
Chuan-Lei Fan ◽  
...  
Keyword(s):  
Transient Flow ◽  
Flow Behavior ◽  
Subsurface Formation

Prototype and numerical studies of interference characteristics of two ski-jump jets from opening spillway gates

2015 ◽  
Vol 32 (2) ◽  
pp. 289-307 ◽  
Author(s):  
Yexiang Xiao ◽  
Zhengwei Wang ◽  
Jidi Zeng ◽  
jintai Zheng ◽  
Jiayang Lin ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Field Test ◽  
Transient Flow ◽  
Scale Effects ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Dynamic Mesh ◽  
Content Type ◽  
Transient Simulations ◽  
Large Dam

Purpose – The purpose of this paper is to experimentally and numerically investigate the interference characteristics between two ski-jump jets on the flip bucket in a large dam spillway when two floodgates are running. Design/methodology/approach – The volume of fluid (VOF) method together with the Realizable k-ε turbulence model were used to predict the flow in two ski-jump jets and the free surface motion in a large dam spillway. The movements of the two gates were simulated using a dynamic mesh controlled by a User Defined Function (UDF). The simulations were run using the prototype dam as the field test to minimize errors due to scale effects. The simulation results are compared with field test observations. Findings – The transient flow calculations, accurately predict the two gate discharges compared to field data with the predicted ski-jump jet interference flow pattern similar to the observed shapes. The transient simulations indicate that the main reason for the deflected nappe is the larger opening difference between the two gates as the buttress side gate closes. When both gates are running, the two ski-jump jets interfere in the flip bucket and raise the jet nappe to near the buttress to form a secondary flow on this jet nappe surface. As the gate continues to close, the nappe surface continues to rise and the surface secondary flow become stronger, which deflects the nappe over the side buttress. Originality/value – A dynamic mesh is used to simulate the transient flow behavior of two prototype running gates. The transient flow simulation clarifies the hydraulics mechanism for how the two ski-jump jets interfere and deflect the nappe.

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