Bubble Generation in the Micro-Channel With a Barrier

2007 ◽  
Author(s):  
Renqiang Xiong ◽  
Mo Bai ◽  
Yun Whan Na ◽  
Jacob N. Chung
Keyword(s):  
Experimental Data ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Flow Behavior ◽  
Operating Conditions ◽  
Channel Width ◽  
Tween 20 ◽  
Micro Channel ◽  
Bubble Generation ◽  
Bubble Length

Micro-bubble generation in a rectangular co-flowing micro-channel with a cross-section area of 1.69 × 0.07mm2 was experimentally and numerically investigated. Air and water were used to be the gas and liquid, respectively. Mixtures of water-glycerol and water-Tween 20 were also used to obtain the effect of viscosity and surface tension. The experimental data shows that the break-up process is periodic under certain operating conditions. The bubble dynamics are also examined using a computational fluid dynamics (CFD) simulation. The CFD model successfully simulates the flow behavior and provides a closer examination of the bubble shape. The bubble length L to the channel width w is a function of the ratio of gas flow rate Qg and liquid flow rate Ql which is the same as that used in the T-junction. Bubble frequency f is found to be related with channel width w, channel depth h, and QlQg/(Qg + Ql · π/4). The formulation shows good agreement with the experimental data at the low frequency region. Different bubble shapes can be obtained at different liquid viscosities and surface tensions. The dimensionless bubble length L/w can still be predicted by a modified equation which uses the real bubble width wb or an equivalent bubble length Le.

CFD Simulation of Wall-Bounded Laminar Flow Through Screens: Part II — Mixing Characterization

2020 ◽  
Author(s):  
W. Abou Hweij ◽  
F. Azizi
Keyword(s):  
Cfd Simulation ◽  
Flow Behavior ◽  
Particle Method ◽  
Immiscible Fluids ◽  
Laminar Flows ◽  
Operating Conditions ◽  
Static Mixers ◽  
Flow Through ◽  
Dispersive Mixing ◽  
Lagrangian Particle Method

Abstract This paper characterizes the mixing behavior of laminar flows within a circular pipe equipped with plain woven meshes or screens, acting as static mixers. In this quest, their performance was numerically investigated using the Lagrangian particle method in a commercial CFD solver, whereby the effect of changing the screen geometry, number of screens, inter-screen spacing, and operating conditions were considered. Mixing was addressed from a distributive and dispersive perspectives using both qualitative and quantitative descriptions. The distributive mixing indicated that a central injection of a single fluid should be coupled with a short inter-screen spacing to better spread the particles and enhance mixing as opposed to a larger inter-screen spacing. On the contrary, the mixing of two immiscible fluids of similar properties reveal that a large inter-screen spacing is recommended. From a dispersive mixing perspective, extensional efficiency contours revealed that the fluid would undergo all three modes of flow behavior, each of which dominating a certain region depending on the location with respect to the screen. Finally, it was interesting to find that a coarser screen geometry consistently outperformed finer screens in spreading and mixing the particles.

DI-CNG Injector Characterization at Small Energizing Times by Means of Numerical Simulation

2012 ◽  
Author(s):  
Mirko Baratta ◽  
Andrea E. Catania ◽  
Nicola Rapetto ◽  
Alois Fuerhapter ◽  
Matthias Gerlich ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Research Effort ◽  
Flow Behavior ◽  
Direct Injection ◽  
Time History ◽  
Operating Conditions ◽  
Flow Measurements ◽  
Injection Duration

In the last few years, a significant research effort has been made for developing and enhancing Direct Injection (DI) for compressed natural gas (CNG) engines. Several research projects have been promoted by the European Community (EC) in this field with the objective of finding new solutions for the automotive market and also of encouraging a fruitful knowledge exchange among car manufacturers, suppliers and technical universities. This paper concerns part of the research activity that has been carried out by the Politecnico di Torino, AVL List GmbH and Siemens AG within the EC VII Framework Program (FP) InGAS Collaborative Project (CP), aimed at optimizing the control phase of a new injector for CNG direct injection, paying specific attention to its behavior at small injected-fuel amounts, i.e., small energizing times. The CNG injector which was developed within the research project proved to be suitable to be used in a DI SI engine, featuring a pent-roof combustion chamber head and a bowl in piston, with reference to both homogeneous and stratified charge formation. Fuel flow measurements made by AVL on the four-cylinder engine revealed a good linearity between injection duration and fuel mass-flow rate for injection durations above a reference value. In order to improve the injector characterization at short injection durations, an experimental and numerical activity was designed. More specifically, a multidimensional CFD model of the actual injector geometry was built by Politecnico di Torino, and purposely-designed simulation cases were carried out, in which the needle-lift time-history was defined on the basis of experimental measurements made by Siemens. The numerical model was validated on the basis of experimental data concerning the total injected-fuel amount under different conditions. Then, the model was applied in order to evaluate the dynamic flow characteristic by taking also the inner geometry of the injector valve group into account, so as to establish a correlation to the needle lift measurements done by Siemens for injector characterization. In the paper this dynamic behavior of the injector is analyzed, under actual operating conditions, and its impact on the nozzle injection capability is discussed. The simulation results did not show significant oscillations of the stagnation pressure upstream of the nozzle throat section, and thus the resultant mass-flow rate profile is almost proportional to the needle-lift one. As a consequence, in order to characterize the injector flow behavior in the nonlinear region (short injection duration), the measurement of needle lift is sufficient.

Heat Coupling of Gasoline Upgrading and Fluid Catalytic Cracking Processes

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Xingying Lan ◽  
Chunming Xu ◽  
Gang Wang ◽  
Jian Chang ◽  
Chunxi Lu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Balance ◽  
Cfd Simulation ◽  
Flow Behavior ◽  
Operating Conditions ◽  
Energy Utilization ◽  
Regeneration System ◽  
Fcc Gasoline ◽  
Fcc Catalysts ◽  
The Heat Balance

Heat supplement is necessary for FCC gasoline upgrading processes to keep the heat balance of reaction-regeneration system, while excess heat would be removed in FCC process due to the processing of heavy feedstock. Combining gasoline upgrading processes with FCC process can realize the heat coupling so as to achieve the maximum energy utilization. In this paper, the heat balance calculations of a commercial FCC unit and a FCC gasoline aromatization process were carried out, and the feasibility as well as the way to accomplish the heat coupling for the two processes was investigated. The results showed that the coked aromatization catalysts could be heated to the desired temperature by the direct contact with the hot regenerated FCC catalysts. The pilot experiment and CFD simulation was carried out to investigate the flow behavior and heat transfer of the direct coupling system of FCC process and FCC gasoline aromatization process. The results indicated that the well-mixing and efficient heat transfer between FCC catalysts and aromatization catalysts, as well as the sufficient regeneration of aromatization catalysts, could be achieved at appropriate operating conditions.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

Zero Dimensional Quasi-Predictive Thermodynamic Simulation for Establishing Initial Cylinder Conditions for CFD Simulation of Diesel Combustion

2015 ◽  
Author(s):  
Ryan A. Bandura ◽  
Timothy J. Jacobs
Keyword(s):  
Experimental Data ◽  
Heat Release ◽  
Cfd Simulation ◽  
Fuel Injection ◽  
Initial Conditions ◽  
Thermodynamic Simulation ◽  
Operating Conditions ◽  
Gas Composition ◽  
Gas Temperature ◽  
Rate Of Heat Release

Computational fluid dynamics (CFD) is now a ubiquitous computational tool for engine design and diagnosis. It is often necessary to provide well-known initial cycle conditions to commence the CFD computations. Such initial conditions can be provided by experimental data. To create an opportunity to computationally study engine conditions where experimental data are not available, a zero-dimensional quasi-predictive thermodynamic simulation is developed that uses well-established spray model to predict rate of heat release and calculated burned gas composition and temperature to predict nitric oxide (NO) concentration. This simulation could in turn be used in reverse to solve for initial cylinder conditions for a targeted NO concentration. This paper details the thermodynamic simulation for diesel engine operating conditions. The goal is to produce a code that is capable of predicting NO emissions as well as performance characteristics such as mean effective pressure (MEP) and brake specific fuel consumption (BSFC). The simulation uses general conservation of mass and energy approaches to model intake, compression, and exhaust. Rate of heat release prediction is based on an existing spray model to predict how fuel concentrations within the spray jet change with penetration. Rate of heat release provides predicted cylinder pressure, which is then validated against experimental pressure data under known operating conditions. An equilibrium mechanism is used to determine burned gas composition which, along with burned gas temperature, can be used for prediction of NO in the cylinder. NO is predicted using the extended Zeldovich mechanism. This mechanism is highly sensitive to temperature, and it is therefore important to accurately predict cylinder gas temperature to obtain correct NO values. Additionally, MEP and BSFC are determined. The simulation focuses on single fuel injection events, but insights are provided to expand the simulation to model multiple injection events.

scholarly journals Experimental Study of a Cavitating Centrifugal Pump During Fast Startups

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
S. Duplaa ◽  
O. Coutier-Delgosha ◽  
A. Dazin ◽  
O. Roussette ◽  
G. Bois ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Transient Flow ◽  
Flow Behavior ◽  
Rocket Engine ◽  
Rotation Velocity ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Physical Analysis ◽  
Different Types

The startup of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behavior is reached. The pump transient behavior induces significant pressure fluctuations, which may result in partial flow vaporization, i.e., cavitation. An existing experimental test rig has been updated in the LML Laboratory (Lille, France) for the startups of a centrifugal pump. The study focuses on the cavitation induced during the pump startup. Instantaneous measurement of torque, flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behavior during rapid starting periods. Three different types of fast startup behaviors have been identified. According to the final operating point, the startup is characterized either by a single drop of the delivery static pressure, by several low-frequency drops, or by a water hammer phenomenon that can be observed in both the inlet and outlet of the pump. A physical analysis is proposed to explain these three different types of transient flow behavior.

Numerical Simulation of Inner Flow in a Double Blades Pump Based on OpenFOAM and its PIV Verification

2012 ◽  
Author(s):  
Yun Ren ◽  
Houlin Liu ◽  
Kai Wang ◽  
Minggao Tan ◽  
Denghao Wu ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Flow Behavior ◽  
Energy Performance ◽  
Operating Conditions ◽  
Centrifugal Pumps ◽  
Complex Flow ◽  
Unstable Flow ◽  
Software Packages ◽  
Flow Phenomena ◽  
Particle Imaging

The presence of unstable flow phenomena may significantly alter the flow pattern and characteristics of centrifugal pumps; that is, the unstable flows may seriously deteriorate the pumps performance. In this paper, considering the high cost of running license fees and not available with all the computing resources, a high quality Open Source CFD simulation platform like OpenFOAM instead of commercial software packages is adopted. Furthermore, the required capability such as GGI is added and boundary conditions are specialized to better simulate complex flow behavior through rotor-stator components in a double blades pump, whose specific speed is 115.6. In order to disclose the characteristics completely, six research schemes are developed and are now presented in this paper. The ratios (Q/Qd) of the flow rate are 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, respectively. The task mainly focuses on the comparison of energy performance under different operating conditions between numerical calculations and experiments, the analysis of the inner flow in the impeller and the comparison of the velocity field in the impeller mid-height between simulation data and the Particle Imaging Velocimetry (PIV) experimental data. The results show that good agreements are found both in terms of the energy performance with experimental results and computed velocities with the PIV data, but improvements can be made.

EXPERIMENTAL AND CFD INVESTIGATION OF R410A DISTRIBUTORS FOR AIR CONDITIONER

2014 ◽  
Vol 22 (02) ◽  
pp. 1440002 ◽  
Author(s):  
QING HAN ◽  
CHI ZHANG ◽  
JIANGPING CHEN
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Present Model ◽  
Cfd Simulation ◽  
Operating Conditions ◽  
Maximum Deviation ◽  
Two Phase ◽  
Performance Reduction

In order to obtain a higher heat transfer coefficient of refrigerant flow, the diameter of tubes tends to be smaller and smaller, which leads to large pressure drop of the refrigerant flow. Therefore, multiple numbers of parallel refrigerant passages are employed by using distributors. It is very important to distribute the two-phase refrigerant evenly into each tube, otherwise the thermal performance is significantly deteriorated. The performance reduction by flow mal-distribution could be as large as 20–25%. The goal of this paper is to investigate the influence of different configurations to the performance of refrigerant distributors by experiments and computational fluid dynamic code. The effects of mass flow rate and quality of distributor inlet on the characteristics were also quantitatively considered. In this study, an experiment test rig was built to measure the mass flow rate and quality of four circuits after using distributors under different conditions respectively. Refrigerant R410A was used as working fluids. Three classic types (jet, cyclone and reservoir) of distributors with four paths were manufactured and tested under relevant operating conditions. The inlet temperature was 4°C, mass flow rate range was 50–100 kg/h and the quality range was 0.1–0.3. Experimental results show that the maximum deviation of mass flow rate for jet, cyclone and reservoir type is 13.0%, 21.6% and 10.9%, respectively; the maximum deviation of quality was 0.08, 0.10 and 0.05, respectively. In addition, the standard deviation of mass flow rate and quality over four paths were selected to evaluate the performance of different type distributors. The results show that the performance of jet and reservoir are better than cyclone. The flow behavior of two-phase refrigerant such as phase distribution and separation phenomena was studied by Computational Fluid Dynamics (CFD). The flow pattern of inlet for R410A was investigated and used in the present model. The results in the present model show good and reasonable approximation with experimental data which validate the CFD simulation. CFD simulation analysis elucidates the mechanics which shows how the configuration and operation conditions affect the refrigerant distribution.

scholarly journals CFD Simulation for Separation of Carbon Dioxide-Methane Mixture by Pressure Swing Adsorption

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
K. Rambabu ◽  
L. Muruganandam ◽  
S. Velu
Keyword(s):  
Carbon Dioxide ◽  
Flow Rate ◽  
Pressure Swing Adsorption ◽  
Cfd Simulation ◽  
Separation Efficiency ◽  
Carbon Dioxide Concentration ◽  
Operating Conditions ◽  
Analytical Models ◽  
Feed Mixture ◽  
Pressure Swing

A developing technology for gas separations is pressure swing adsorption, which has been proven to be more economical and energy efficient compared to other separation methods like cryogenic distillation and membrane separation. A pressure swing adsorption (PSA) column, with carbon dioxide-methane as feed mixture and 6-FDA based polyimides as the adsorbent, was modeled and simulated in this work. Ansys Fluent 12.1, along with supplementary user defined functions, was used to develop a 2D transient Eulerian laminar viscous flow model for the PSA column. The model was validated by comparing the simulated results with established analytical models for PSA. The developed numerical model was used to determine the carbon dioxide concentration in the column as a function of time based on different operating conditions. Effect of various operating parameters like pressure, temperature, and flow rate on the separation efficiency has been studied and reported. Optimization studies were carried out to obtain suitable operating conditions for the feed gases separation. Simulation studies were carried out to determine the separation length required for complete separation of the feed mixture corresponding to different inlet feed concentrations which were entering the column at a given flow rate.

CFD Simulation of Hydrogen Separation in Pd Hollow Fiber Membrane

2016 ◽  
Vol 11 (1) ◽  
pp. 83-88 ◽  
Author(s):  
Zahra Mansourpour ◽  
Hooman Ziaei-Halimejani ◽  
Seyed Morteza Sadeghnejad ◽  
Mohammadreza Boskabadi
Keyword(s):  
Experimental Data ◽  
Hollow Fiber ◽  
Cfd Simulation ◽  
Hydrogen Adsorption ◽  
Separation Efficiency ◽  
Hollow Fiber Membrane ◽  
Hydrogen Separation ◽  
Operating Conditions ◽  
Fiber Membrane ◽  
Membrane Modeling

Abstract In this article, hydrogen adsorption from gas mixture involve nitrogen and hydrogen by palladium hollow fiber membrane investigated and two dimensional model proposed for hydrogen adsorption in this model. This model has been evaluated based on equations (momentum and mass transfer) in all three parts (shell, membrane and tube) for existing gaseous compounds with using finite element method. The results of simulation validated by experimental data of hydrogen adsorption by palladium hollow fiber membrane. Modeling predictions shows good agreement with experimental data at different operating conditions such as different gas flows, temperature, pressure and etc. the result of simulation shows hydrogen separation efficiency increases with increasing temperature and pressure and decreases with increasing inlet rate. Also with using this model better performance of hollow fiber membranes can be obtained. In fact, hollow fiber membrane can be designed at different conditions and for different rates that it can save cost of various tests.

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