Numerical Modelling of Droplet Deformation in a High-Pressure Homogeniser

2002 ◽  
Author(s):  
David S. Whyte ◽  
Steven Carnie ◽  
Malcolm Davidson
Keyword(s):  
High Pressure ◽  
Numerical Modelling ◽  
Numerical Study ◽  
Extensional Flow ◽  
Operating Conditions ◽  
Droplet Deformation ◽  
Photographic Paper ◽  
Turbulent Fluctuations ◽  
Fluid Properties ◽  
Break Up

A numerical study of droplet deformation in a high-pressure homogeniser is presented. This work is an attempt to identify flow criteria responsible for droplet break-up in a homogeniser used to produce dispersions for the manufacture of photographic paper. The main goal of this study is to recommend changes to homogeniser flow & geometry, operating conditions or fluid properties that will enhance droplet break-up. Laminar elongation, turbulent stresses within the orifice and downstream turbulence and cavitation have been suggested as possible mechanisms within the homogeniser for droplet rupture. Results for simulations, using a combination of homogeniser and droplet scale computation indicate that droplets are unaffected by local extensional flow or turbulent fluctuations and that other mechanisms must be responsible for droplet break-up.

scholarly journals Comparison of Experimental and Numerical Transient Drop Deformation during Transition through Orifices in High-Pressure Homogenizers

2021 ◽  
Vol 5 (3) ◽  
pp. 32
Author(s):  
Benedikt Mutsch ◽  
Peter Walzel ◽  
Christian J. Kähler
Keyword(s):  
High Pressure ◽  
Visual Analysis ◽  
Imaging Technique ◽  
Extensional Flow ◽  
Droplet Breakup ◽  
Experimental Results ◽  
Drop Deformation ◽  
Droplet Deformation ◽  
Shadow Imaging ◽  
Good Agreement

The droplet deformation in dispersing units of high-pressure homogenizers (HPH) is examined experimentally and numerically. Due to the small size of common homogenizer nozzles, the visual analysis of the transient droplet generation is usually not possible. Therefore, a scaled setup was used. The droplet deformation was determined quantitatively by using a shadow imaging technique. It is shown that the influence of transient stresses on the droplets caused by laminar extensional flow upstream the orifice is highly relevant for the droplet breakup behind the nozzle. Classical approaches based on an equilibrium assumption on the other side are not adequate to explain the observed droplet distributions. Based on the experimental results, a relationship from the literature with numerical simulations adopting different models are used to determine the transient droplet deformation during transition through orifices. It is shown that numerical and experimental results are in fairly good agreement at limited settings. It can be concluded that a scaled apparatus is well suited to estimate the transient droplet formation up to the outlet of the orifice.

scholarly journals An Experimental and Numerical Study of CO2–Brine-Synthetic Sandstone Interactions under High-Pressure (P)–Temperature (T) Reservoir Conditions

2019 ◽  
Vol 9 (16) ◽  
pp. 3354
Author(s):  
Zhichao Yu ◽  
Siyu Yang ◽  
Keyu Liu ◽  
Qingong Zhuo ◽  
Leilei Yang
Keyword(s):  
High Pressure ◽  
Numerical Modelling ◽  
Numerical Study ◽  
Mineral Dissolution ◽  
Co2 Injection ◽  
High Pressure And Temperature ◽  
Reservoir Conditions ◽  
Stainless Steel Reactor ◽  
Geochemical Reactions ◽  
And Storage

The interaction between CO2 and rock during the process of CO2 capture and storage was investigated via reactions of CO2, formation water, and synthetic sandstone cores in a stainless-steel reactor under high pressure and temperature. Numerical modelling was also undertaken, with results consistent with experimental outcomes. Both methods indicate that carbonates such as calcite and dolomite readily dissolve, whereas silicates such as quartz, K-feldspar, and albite do not. Core porosity did not change significantly after CO2 injection. No new minerals associated with CO2 injection were observed experimentally, although some quartz and kaolinite precipitated in the numerical modelling. Mineral dissolution is the dominant reaction at the beginning of CO2 injection. Results of experiments have verified the numerical outcomes, with experimentally derived kinetic parameters making the numerical modelling more reliable. The combination of experimental simulations and numerical modelling provides new insights into CO2 dissolution mechanisms in high-pressure/temperature reservoirs and improves understanding of geochemical reactions in CO2-brine-rock systems, with particular relevance to CO2 entry of the reservoir.

Considerations on the Numerical Modelling and Performance of Axial Swirlers Under Relight Conditions

2012 ◽  
Author(s):  
Charlie Koupper ◽  
Nicholas Grech ◽  
Pavlos K. Zachos ◽  
Vassilios Pachidis ◽  
Riti Singh
Keyword(s):  
Numerical Modelling ◽  
Boundary Conditions ◽  
Numerical Study ◽  
Selection Process ◽  
Linear Trend ◽  
Tangential Velocity ◽  
Velocity Profiles ◽  
Sensitivity Study ◽  
Operating Conditions ◽  
Lower Velocity

Numerical modelling of aero engine combustors under relight conditions is a matter of continuously increasing importance due to the demanding engine certification regulations. In order to reduce the complexity and the cost of the numerical modelling, common practice is to replace the atomizer’s swirlers with velocity profiles boundary conditions, very often scaled down from nominal operating conditions assuming similarity of the swirler flowfield. The current numerical study focuses on the flowfield characteristics of an axially swirled atomizer operating within a windmilling engine environment. The scalability of the velocity profile from higher power settings is examined. Observations on the performance of the axial swirler under relight conditions are also made. Experimental data was used as a validation platform for the numerical solver, after a grid sensitivity study and a turbulence model selection process. Boundary conditions for simulating the windmilling environment were extracted from experimental work. The swirler axial and tangential velocity profiles were normalised using the swirler inlet velocity. Results showed that both profiles are only scalable for windmilling conditions of high flight Mach number (≥ 0.5). At low flight Mach numbers, the actual profile had a lower velocity than that predicted through scaling. The swirl number was found to deteriorate significantly with the flight velocity following a linear trend, reducing significantly the expected flame quality. As a consequence the burner is forced to operate at the edge of its stability loop with low certainty regarding its successful relight.

Generalized Model for the Approximation of Coupled Acousto-Mechanical Natural Frequencies in High-Pressure Centrifugal Compressors

2020 ◽  
Author(s):  
Christoph Rocky Heinrich ◽  
Arnold Kühhorn ◽  
Klaus Steff ◽  
Nico Petry
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Natural Frequencies ◽  
Numerical Study ◽  
Operating Conditions ◽  
Centrifugal Compressors ◽  
Element Analysis ◽  
Generalized Model ◽  
Wide Range ◽  
The Impact

Abstract The oil and gas, chemical, and process industries employ centrifugal compressors for a wide range of applications. Due to this, the conditions under which centrifugal compressors have to operate, vary significantly from case to case. Gas pipeline compressors, for example, may feature discharge pressures well over 100 bar. During the last decades, comprehensive research was conducted on the impact of high pressure operating conditions on the vibrational behavior of centrifugal compressors. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced interaction between the side cavities and the impeller, which results in a frequency shift of the acoustic and structural modes. For the safe operation of compressors, it is necessary to predict these coupled natural frequencies accurately. The state-of-the-art approach to achieve this objective is the finite element method. While this technique provides high-quality results, it incurs high computational costs and is, therefore, time-consuming. The authors of the current paper propose a generalized model to overcome this challenge. It uses the uncoupled modes of the impeller and side cavities in a modal superposition to approximate the coupled system's natural frequencies. In this way, the intended design geometries are considered while reducing the computational effort significantly. In a numerical study, the generalized model is applied to different systems of increasing complexity, and the results are compared to a finite element analysis. Finally, the paper concludes with a discussion of the limitations and benefits of all employed numerical methods.

scholarly journals Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 272
Author(s):  
Doojin Lee ◽  
Amy Q. Shen
Keyword(s):  
Interfacial Tension ◽  
Microfluidic Device ◽  
Extensional Flow ◽  
Immiscible Fluids ◽  
Droplet Microfluidics ◽  
Channel Height ◽  
Deformation Model ◽  
Droplet Deformation ◽  
Extensional Flows ◽  
2D Model

Droplet microfluidics provides a versatile tool for measuring interfacial tensions between two immiscible fluids owing to its abilities of fast response, enhanced throughput, portability and easy manipulations of fluid compositions, comparing to conventional techniques. Purely homogeneous extension in the microfluidic device is desirable to measure the interfacial tension because the flow field enables symmetric droplet deformation along the outflow direction. To do so, we designed a microfluidic device consisting of a droplet production region to first generate emulsion droplets at a flow-focusing area. The droplets are then trapped at a stagnation point in the cross junction area, subsequently being stretched along the outflow direction under the extensional flow. These droplets in the device are either confined or unconfined in the channel walls depending on the channel height, which yields different droplet deformations. To calculate the interfacial tension for confined and unconfined droplet cases, quasi-static 2D Darcy approximation model and quasi-static 3D small deformation model are used. For the confined droplet case under the extensional flow, an effective viscosity of the two immiscible fluids, accounting for the viscosity ratio of continuous and dispersed phases, captures the droplet deformation well. However, the 2D model is limited to the case where the droplet is confined in the channel walls and deforms two-dimensionally. For the unconfined droplet case, the 3D model provides more robust estimates than the 2D model. We demonstrate that both 2D and 3D models provide good interfacial tension measurements under quasi-static extensional flows in comparison with the conventional pendant drop method.

scholarly journals Designs of InGaN Micro-LED Structure for Improving Quantum Efficiency at Low Current Density

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Shiqiang Lu ◽  
Jinchai Li ◽  
Kai Huang ◽  
Guozhen Liu ◽  
Yinghui Zhou ◽  
...  
Keyword(s):  
Quantum Efficiency ◽  
Current Density ◽  
Carrier Transport ◽  
Defect Density ◽  
Numerical Study ◽  
Structure Design ◽  
Operating Conditions ◽  
Hole Injection ◽  
Electron Blocking Layer ◽  
Recombination Processes

AbstractHere we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

Numerical Simulation of Gas Flow and Heat Transfer in Cross-Wavy Primary Surface Channel for Microtubine Recuperators

2005 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang ◽  
L. Q. Luo ◽  
Z. P. Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Numerical Study ◽  
High Reliability ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
The Cross

Three-dimensional numerical simulation was conducted to investigate the flow field and heat transfer performance of the Cross-Wavy Primary Surface (CWPS) recuperators for microturbines. Using high-effective compact recuperators to achieve high thermal efficiency is one of the key techniques in the development of microturbine in recent years. Recuperators need to have minimum volume and weight, high reliability and durability. Most important of all, they need to have high thermal-effectiveness and low pressure-losses so that the gas turbine system can achieve high thermal performances. These requirements have attracted some research efforts in designing and implementing low-cost and compact recuperators for gas turbine engines recently. One of the promising techniques to achieve this goal is the so-called primary surface channels with small hydraulic dimensions. In this paper, we conducted a three-dimensional numerical study of flow and heat transfer for the Cross-Wavy Primary Surface (CWPS) channels with two different geometries. In the CWPS configurations the secondary flow is created by means of curved and interrupted surfaces, which may disturb the thermal boundary layers and thus improve the thermal performances of the channels. To facilitate comparison, we chose the identical hydraulic diameters for the above four CWPS channels. Since our experiments on real recuperators showed that the Reynolds number ranges from 150 to 500 under the operating conditions, we implemented all the simulations under laminar flow situations. By analyzing the correlations of Nusselt numbers and friction factors vs. Reynolds numbers of the four CWPS channels, we found that the CWPS channels have superior and comprehensive thermal performance with high compactness, i.e., high heat transfer area to volume ratio, indicating excellent commercialized application in the compact recuperators.

A Study of the Lateral Stability of Railroad Vehicles Using a Nonlinear Constrained Multibody Formulation

2001 ◽  
Author(s):  
Davide Valtorta ◽  
Khaled E. Zaazaa ◽  
Ahmed A. Shabana ◽  
Jalil R. Sany
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Theory ◽  
Linear Stability Analysis ◽  
Numerical Study ◽  
Operating Conditions ◽  
Lateral Stability ◽  
Railroad Vehicles ◽  
Contact Formulation ◽  
The Stability

Abstract The lateral stability of railroad vehicles travelling on tangent tracks is one of the important problems that has been the subject of extensive research since the nineteenth century. Early detailed studies of this problem in the twentieth century are the work of Carter and Rocard on the stability of locomotives. The linear theory for the lateral stability analysis has been extensively used in the past and can give good results under certain operating conditions. In this paper, the results obtained using a linear stability analysis are compared with the results obtained using a general nonlinear multibody methodology. In the linear stability analysis, the sources of the instability are investigated using Liapunov’s linear theory and the eigenvalue analysis for a simple wheelset model on a tangent track. The effects of the stiffness of the primary and secondary suspensions on the stability results are investigated. The results obtained for the simple model using the linear approach are compared with the results obtained using a new nonlinear multibody based constrained wheel/rail contact formulation. This comparative numerical study can be used to validate the use of the constrained wheel/rail contact formulation in the study of lateral stability. Similar studies can be used in the future to define the limitations of the linear theory under general operating conditions.

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