Oscillatory extensional flow based on eccentric cylinder flow

AbstractIn an experimental procedure, a voltage rise anemometry is developed as a measurement technique for turbulent flows. Initially, fundamental investigations on a specific wind tunnel were performed for basic understanding and calibration purpose. Thus, a mathematical correlation is derived for calculating flow from measured secondary voltage of an ignition system under different thermodynamic conditions. Subsequently, the derived method was applied on a spark-ignited engine to measure in-cylinder flow. Therefore, no changes on combustion chamber were necessary avoiding any interferences of the examined flow field. Comparing four different engine configurations, a study of mean flow and turbulence was performed. Moreover, the results show a clear correlation between measured turbulence and analysed combustion parameters. Graphic abstract

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Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

Micromachines ◽

10.3390/mi12030272 ◽

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.

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A novel approach to the study of extensional flow-induced crystallization

Polymer Testing ◽

10.1016/j.polymertesting.2021.107060 ◽

2021 ◽

Vol 96 ◽

pp. 107060

Author(s):

Juliana Amirdine ◽

Thouaïba Htira ◽

Nicolas Lefevre ◽

René Fulchiron ◽

Nathalie Mathieu ◽

...

Keyword(s):

Extensional Flow ◽

Novel Approach ◽

Induced Crystallization ◽

Flow Induced Crystallization

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

ChemEngineering ◽

10.3390/chemengineering5030032 ◽

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.

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