scholarly journals High-speed imaging of ice nucleation in water proves the existence of active sites

2019 ◽  
Vol 5 (2) ◽  
pp. eaav4316 ◽  
Author(s):  
Mark A. Holden ◽  
Thomas F. Whale ◽  
Mark D. Tarn ◽  
Daniel O’Sullivan ◽  
Richard D. Walshaw ◽  
...  
Keyword(s):  
High Speed ◽  
Active Sites ◽  
Complex Problem ◽  
Ice Nucleation ◽  
Crystal Formation ◽  
High Speed Imaging ◽  
Wide Range ◽  
Nanoscale Topography ◽  
Salient Factor ◽  
And Control

Understanding how surfaces direct nucleation is a complex problem that limits our ability to predict and control crystal formation. We here address this challenge using high-speed imaging to identify and quantify the sites at which ice nucleates in water droplets on the two natural cleavage faces of macroscopic feldspar substrates. Our data show that ice nucleation only occurs at a few locations, all of which are associated with micron-size surface pits. Similar behavior is observed on α-quartz substrates that lack cleavage planes. These results demonstrate that substrate heterogeneities are the salient factor in promoting nucleation and therefore prove the existence of active sites. We also provide strong evidence that the activity of these sites derives from a combination of surface chemistry and nanoscale topography. Our results have implications for the nucleation of many materials and suggest new strategies for promoting or inhibiting nucleation across a wide range of applications.

Design and control of multi-actuated atomic force microscope for large-range and high-speed imaging

2016 ◽  
Vol 160 ◽  
pp. 213-224 ◽  
Author(s):  
I. Soltani Bozchalooi ◽  
A. Careaga Houck ◽  
J.M. AlGhamdi ◽  
K. Youcef-Toumi
Keyword(s):  
Atomic Force Microscope ◽  
High Speed ◽  
Large Range ◽  
High Speed Imaging ◽  
Atomic Force ◽  
And Control

scholarly journals Experimental methodology and procedure for SAPPHIRE:a Semi-automatic APParatus for High-voltage Ice nucleation REsearch

2020 ◽  
Author(s):  
Jens-Michael Löwe ◽  
Markus Schremb ◽  
Volker Hinrichsen ◽  
Cameron Tropea
Keyword(s):  
Electric Field ◽  
High Voltage ◽  
Surface Defects ◽  
Ice Nucleation ◽  
Experimental Methodology ◽  
Cloud Formation ◽  
Crystal Formation ◽  
Strong Impact ◽  
Wide Range ◽  
Accuracy And Repeatability

Abstract. Ice nucleation is of great interest for various processes such as cloud formation in the scope of atmospheric research, and icing of airplanes, ships or structures. Ice nucleation research aims to improve the knowledge about the physical mechanisms and, therefore improve the safety and reliability of the applications affected by ice nucleation. Several influencing factors like liquid supercooling or contamination with nucleants, as well as external disturbances such as an electric field or surface defects affect ice nucleation. Especially for ice crystal formation in clouds and icing of high-voltage equipment, an external electric field may have a strong impact on ice nucleation. Although ice nucleation has been widely investigated for numerous conditions, the effect of an electric field on nucleation is not yet completely understood; results reported in literature are even contradictory. In the present study, an advanced experimental approach for the examination of ice nucleation in water droplets exposed to an electric field is demonstrated. It comprises a method for droplet ensemble preparation and an experimental setup, which allows observation of the droplet ensemble during its exposure to well-defined thermal and electric fields, which are both variable over a wide range. The entire approach aims at maximizing the accuracy and repeatability of the experiments in order to enable examination of even the most minor influences on ice nucleation. For that purpose, the boundary conditions the droplet sample is exposed to during the experiment are examined in particular detail using experimental and numerical methods. The methodological capabilities and accuracy have been demonstrated based on several test nucleation experiments without an electric field, indicating almost perfect repeatability.

Study of Flow Characteristics and Control Circuit on High-Speed Solenoid Valve

2012 ◽  
Vol 619 ◽  
pp. 107-110 ◽  
Author(s):  
Wen Hua Li ◽  
Wen Lin Shao
Keyword(s):  
High Speed ◽  
Flow Characteristics ◽  
Pulse Signal ◽  
Solenoid Valve ◽  
Control Circuit ◽  
Duty Ratio ◽  
Time Sharing ◽  
Small Current ◽  
Wide Range ◽  
And Control

Through the analysis of the flow characteristics of the high-speed solenoid valve, the conclusions that the PWM signal duty ratio is the main factor affecting the solenoid valve flow is obtained, a new available any PWM pulse signal and control circuit are proposed. Further, circuit schematic is simulated by means of SIMULINK tools in MATLAB environment and Verify its stability. A time-sharing drive circuit is design based on the PWM drive mode. The driver circuit have function which is high-current open, small current maintain. Open current and maintain current of Solenoid valve can be adjusted through this circuit. Therefore, the circuit can adapt to different parameters of the solenoid valve. A wide range of applications.

Dynamic Analysis and Control of High Speed and High Precision Active Magnetic Bearings

1992 ◽  
Vol 114 (4) ◽  
pp. 623-633 ◽  
Author(s):  
K. Youcef-Toumi ◽  
S. Reddy
Keyword(s):  
Time Delay ◽  
High Speed ◽  
Dynamic Stiffness ◽  
Magnetic Bearing ◽  
Magnetic Bearings ◽  
Successful Operation ◽  
Highly Nonlinear ◽  
Wide Range ◽  
And Control ◽  
Digital Time

The successful operation of actively controlled magnetic bearings depends greatly on the electromechanical design and control system design. The function of the controller is to maintain bearing performance in the face of system dynamic variations and unpredictable disturbances. The plant considered here is the rotor and magnetic bearing assembly of a test apparatus. The plant dynamics consisting of actuator dynamics, rigid rotor dynamics and flexibility effects are described. Various components of the system are identified and their corresponding linearized theoretical models are validated experimentally. Tests are also run to identify the coupling effects and flexibility modes. The highly nonlinear behavior of the magnetic bearings in addition to the inherent instability of such a system makes the controller design complex. A digital Time Delay Controller is designed and its effectiveness evaluated using several simulations based on linear and nonlinear models for the bearing including bending mode effects. This controller is implemented as an alternative to an existing linear analog compensator. Several experiments are conducted with each controller for spinning and nonspinning conditions. These include time responses, closed loop frequency responses and disturbance rejection responses. The experimental results and comparisons between those of a digital Time Delay Controller and an analog compensator indicate that the Time Delay Controller has impressive static and dynamic stiffness characteristics for the prototype considered. The Time Delay Controller also maintains almost the same dynamic behavior over a significantly wide range of rotor speeds.

scholarly journals Efficient SMA Actuation—Design and Control Concepts

Proceedings ◽  
2020 ◽  
Vol 64 (1) ◽  
pp. 20
Author(s):  
Paul Motzki
Keyword(s):  
High Speed ◽  
Thermal Activation ◽  
Energy Savings ◽  
Form Factors ◽  
High Energy ◽  
Innovative Design ◽  
Wide Range ◽  
Millisecond Range ◽  
And Control ◽  
High Energy Consumption

The versatility of the form factors of thermal shape memory alloys (SMA) in combination with their unique actuation and sensing abilities allow for the design and construction of innovative multifunctional systems. Despite the considerable number of advantages, such as their exceptional energy density, only a few SMA-based actuator systems are commercially available. One of the main reasons for this is their inefficient thermal activation and the resulting high energy consumption. The efficiency of SMA-based actuator systems can be improved by innovative design and control approaches. In the first part of this paper, the intelligent combination of SMA actuator wires with bi-stable, nonlinear spring elements is described. This combination eliminates the commonly quoted disadvantages of SMAs—slow actuation and energy inefficiency—for a wide range of applications. In particular, two energy-free actuator configurations are realized, which can be applied to any non-proportional actuation tasks. The second approach for the realization of high-speed actuation and energy efficiency is the activation of SMA wires with high voltage pulses, which leads to actuation times in the millisecond range and energy savings of up to 80% in comparison to the suppliers’ recommendations. It is shown that even high AC voltages such as typical mains supplies can be directly used for highly efficient SMA activation.

Learning From the Fins of Ray-Finned Fish for the Propulsors of Unmanned Undersea Vehicles

2011 ◽  
Vol 45 (4) ◽  
pp. 65-73 ◽  
Author(s):  
James L. Tangorra ◽  
Timo Gericke ◽  
George V. Lauder
Keyword(s):  
High Speed ◽  
The Body ◽  
External Disturbances ◽  
Pectoral Fins ◽  
Autonomous Regulation ◽  
Wide Range ◽  
Sensorimotor Systems ◽  
And Control ◽  
Vortex Perturbations

AbstractAdvanced propulsors are required to help unmanned undersea vehicles (UUVs) overcome major challenges associated with energy and autonomy. The fins of ray-finned fish provide an excellent model from which to develop propulsors that can create forces efficiently and drive a wide range of behaviors, from hover to low-speed maneuvers to high-speed travel. Although much is known about the mechanics of fins, little is known about the fin’s sensorimotor systems or how fins are regulated in response to external disturbances. This information is crucial for implementing propulsive and control systems that exploit the same phenomena as the biological fins for efficiency, effectiveness, and autonomous regulation. Experiments were conducted to evaluate the in vivo response of the sunfish and its pectoral fins to vortex perturbations applied directly to the fish and to the fins. The fish and the fins responded actively to perturbations that disturbed the motion of the fish body. Surprisingly, perturbations that deformed the fins extensively did not cause a reaction from either the fins or the body. These results indicate that the response of the pectoral fins to large deformations is not reflexive and that fin motions are regulated when it is necessary to correct for disturbances to the motion of the fish. The results also demonstrate a benefit of compliance in propulsors, in that external perturbations can disturb the fins without having its impact be transferred to the fish body.

scholarly journals Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers

2017 ◽  
Author(s):  
Milan Maly ◽  
Lada Janáčková ◽  
Jan Jedelský ◽  
Jaroslav Sláma ◽  
Marcel Sapík ◽  
...  
Keyword(s):  
High Speed ◽  
Laser Doppler Anemometry ◽  
Temporal Stability ◽  
Internal Flow ◽  
High Speed Imaging ◽  
Dimensionless Numbers ◽  
Swirl Chamber ◽  
Air Core ◽  
Wide Range ◽  
Pressure Swirl

It is well known that the spray characteristics of pressure-swirl atomizers are strongly linked to the internal flow andthat an unstable air core may cause instabilities in the spray. In this paper, a 10:1 scale transparent Plexiglas (PMMA) model of a pressure-swirl atomizer as used in a small gas turbine is introduced. The internal flow is examined using high-speed imaging, laser-Doppler anemometry and computational fluid dynamics tools. The experimental and numerical results were analysed and compared in terms of the air core morphology and its temporal stability. Two different liquids were used, Kerosene-type Jet A-1 represented a commonly used fuel while p-Cymene (4-Isopropyltoluene) matched the refractive index of the Plexiglas atomizer body. The internal flow characteristics were set using dimensionless numbers i.e. the Reynolds number and Froude number. The flow test conditions were limited to inlet Reynolds numbers from 750 to 1750. Two atomizers were examined to represent a simplex and spill-return (SR) geometry. In a comparative manner, the SR atomizer features a central passage in the rear wall of the swirl chamber. The main advantage of this concept is that the fuel is always supplied to the swirl chamber at a high pressure therefore providing good atomization over a wide range of the injection flow rate. However, the presence of the spill orifice strongly affects the internal flow even if the spill-line is closed. The air core in the simplex atomizer was found fully developed and stable. The SR atomizer behaved differently, the air core didnot form at all, and the spray was therefore unstable.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4995

scholarly journals Improved evaluation of granular media flows using an X-ray scanning compatible cone-plate setup

2021 ◽  
Vol 249 ◽  
pp. 03020
Author(s):  
Zohreh Farmani ◽  
Jing Wang ◽  
Ralf Stannarius ◽  
Martina Bieberle ◽  
Frank Barthel ◽  
...  
Keyword(s):  
Granular Materials ◽  
High Speed ◽  
Granular Media ◽  
Flow Behavior ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Flow Measurements ◽  
Flow Rates ◽  
X Ray ◽  
Wide Range

To understand the typically heterogeneous flowing behavior of granular materials, it is important to combine flow tests with three-dimensional imaging. To probe the flow behavior of granular materials over a wide range of flow rates, it is imperative to be able to impose such flow rates in a well controlled manner while performing imaging tests that are compatible with all imposed flow rates. Achieving both flow control and bulk imaging capacity is challenging for a number of reasons. Here, we describe the design of a setup in which we are able to do imaging while imposing a constant overall shear rate on a granular material. We characterize the setup in which flow tests will be performed, which consists of a bottom-driven cone-plate or double-cone design. We show that the setup can be integrated in x-ray microtomography devices to aid particle tracking based flow measurements. The design is also compatible with typical rheometer setups. We also perform high speed imaging of a granular flow in an ultra-fast x-ray scanner, for which we provide proof-of-principle data in a simplified shear setup. The designed flow geometry is also compatible with said high speed imaging facility, where particle image velocimetry can be employed to extract quantitative flow field data.

scholarly journals Experimental methodology and procedure for SAPPHIRE: a Semi-automatic APParatus for High-voltage Ice nucleation REsearch

2021 ◽  
Vol 14 (1) ◽  
pp. 223-238 ◽  
Author(s):  
Jens-Michael Löwe ◽  
Markus Schremb ◽  
Volker Hinrichsen ◽  
Cameron Tropea
Keyword(s):  
Electric Field ◽  
High Voltage ◽  
Surface Defects ◽  
Ice Nucleation ◽  
Experimental Methodology ◽  
Cloud Formation ◽  
Crystal Formation ◽  
Strong Impact ◽  
Wide Range ◽  
Accuracy And Repeatability

Abstract. Ice nucleation is of great interest for various processes such as cloud formation in the scope of atmospheric physics, and icing of airplanes, ships, or structures. Ice nucleation research aims to improve the knowledge about the physical mechanisms and to ensure the safety and reliability of the respective applications. Several influencing factors like liquid supercooling or contamination with nucleants, as well as external disturbances such as an electric field or surface defects, affect ice nucleation. Especially for ice crystal formation in clouds and icing of high-voltage equipment, an external electric field may also have a strong impact on ice nucleation. Although ice nucleation has been widely investigated for numerous conditions, the effect of an electric field on ice nucleation is not yet completely understood; results reported in literature are even contradictory on some issues. In the present study, an advanced experimental approach for the examination of ice nucleation in water droplets exposed to an electric field is described. It comprises a method for droplet ensemble preparation and an experimental setup, which allows observation of the droplet ensemble during its exposure to well-defined thermal and electric fields, which are both variable over a wide range. The entire approach aims at maximizing the accuracy and repeatability of the experiments in order to enable examination of even the most minor influences on ice nucleation. For that purpose, the boundary conditions the droplet sample is exposed to during the experiment are examined in particular detail using experimental and numerical methods. The methodological capabilities and accuracy have been demonstrated based on several ice nucleation experiments without an electric field, indicating almost perfect repeatability.

scholarly journals Experimental analysis of particle clustering in moderately dense gas–solid flow

2021 ◽  
Vol 933 ◽  
Author(s):  
Kee Onn Fong ◽  
Filippo Coletti
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Stokes Number ◽  
Spherical Particles ◽  
High Speed Imaging ◽  
Dense Particle ◽  
Laboratory Observation ◽  
Laboratory Setup ◽  
Wide Range

In collisional gas–solid flows, dense particle clusters are often observed that greatly affect the transport properties of the mixture. The characterisation and prediction of this phenomenon are challenging due to limited optical access, the wide range of scales involved and the interplay of different mechanisms. Here, we consider a laboratory setup in which particles fall against upward-moving air in a square vertical duct: a classic configuration in riser reactors. The use of non-cohesive, monodispersed, spherical particles and the ability to independently vary the solid volume fraction ( $\varPhi _V = 0.1\,\% - 0.8\,\%$ ) and the bulk airflow Reynolds number ( $Re_{bulk} = 300 - 1200$ ) allows us to isolate key elements of the multiphase dynamics, providing the first laboratory observation of cluster-induced turbulence. Above a threshold $\varPhi _V$ , the system exhibits intense fluctuations of concentration and velocity, as measured by high-speed imaging via a backlighting technique which returns optically depth-averaged fields. The space–time autocorrelations reveal dense and persistent mesoscale structures falling faster than the surrounding particles and trailing long wakes. These are shown to be the statistical footprints of visually observed clusters, mostly found in the vicinity of the walls. They are identified via a percolation analysis, tracked in time, and characterised in terms of size, shape, location and velocity. Larger clusters are denser, longer-lived and have greater descent velocity. At the present particle Stokes number, the threshold $\varPhi _V \sim 0.5$ % (largely independent from $Re_{bulk}$ ) is consistent with the view that clusters appear when the typical interval between successive collisions is shorter than the particle response time.

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