Study on Terminal Velocity of Continuously Ejected Micro Inkjet Droplet

Abstract It is important to make the droplet formation in the printable area for a design of an inkjet device. One of the important variables for the inkjet is an ejecting velocity which can be controlled by the inkjet device. When the drop-on-demand inkjet nozzle is used, unless the ejecting velocity exceeds the minimum velocity, the droplet may not be ejected or the nozzle surface can be wet, thus the next droplet formation may fail. On the other hand, if the droplet velocity is too fast, splashing may happen when the drop impacts on a substrate, which makes the undesirable printing error. The falling velocity of the inkjet droplet changes by the drag force of air along the falling distance. Therefore, it is required to estimate the exact ejecting, falling and terminal velocity of the inkjet droplet. We measured the inkjet droplet velocity ejecting from the nozzle of a piezoelectric drop-on-demand inkjet device with a push mode. The nozzle diameter was 70 μm and polyethylene glycol aqueous solution was used as ink. The inkjet droplets were generated within a range of 500 to 10,000 Hz of frequencies at a reference piezoelectric input voltage. The successive inkjet droplets were captured by the high-speed camera with 100,000 fps, then the inkjet droplet velocities were analyzed visually at each falling location. The initial to terminal velocity changes of the droplets were calculated theoretically to be compared with the experimental results according to the diameter of the droplet, the drag coefficient, and the Reynolds number. The general terminal velocity of the droplet is determined by the density and diameter of the droplet. However, this study confirmed that the terminal velocity of the continuously ejected droplets by the drop-on-demand inkjet was determined by the interval of the droplets which depended on the frequency. The inkjet droplet in the low frequency has the long interval that is enough to consider as an independent droplet so that it can follow the terminal velocity curve of the general droplet. However, with increasing the frequency, the inkjet droplets are generated frequently and its interval gets shorter, and then its terminal velocity is relatively high not following the general terminal velocity curve. It is considered that each droplet gets into the wake field of the former droplet so that its drag force can decrease and the velocity can increase. We analyzed the velocity change of the inkjet droplet according to its diameter and frequency based on the experimental and numerical results.

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Additive manufacturing of high loading concentration zirconia using high-speed drop-on-demand material jetting

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-020-05829-2 ◽

2020 ◽

Vol 109 (9-12) ◽

pp. 2733-2746

Author(s):

Haniyeh Fayazfar ◽

Farzad Liravi ◽

Usman Ali ◽

Ehsan Toyserkani

Keyword(s):

Additive Manufacturing ◽

High Speed ◽

High Loading ◽

On Demand ◽

Drop On Demand

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High Speed Roll-to-Roll Printable Transistor Enabled by a Pulsed Light Curable CNT Ink

Journal of Manufacturing and Materials Processing ◽

10.3390/jmmp3020033 ◽

2019 ◽

Vol 3 (2) ◽

pp. 33

Author(s):

Peter Mack Grubb ◽

Farzad Mokhtari Koushyar ◽

Travis Lenz ◽

Aref Asghari ◽

Gongwen Gan ◽

...

Keyword(s):

High Speed ◽

Flash Lamp ◽

Pulsed Light ◽

Production Methods ◽

On Demand ◽

Roll To Roll ◽

Drop On Demand ◽

Visible Light Range ◽

Strong Energy ◽

Triton X

This paper reports the first high speed roll-to-roll printable transistor using a carbon nanotube (CNT) semiconducting layer. The transistor is made possible through the development of a pulsed light curable CNT ink compatible with typical drop on demand inkjet cartridges. This CNT ink uses a xylene based solvent with methanol, glycerin, and Triton X-100 modifiers to create an evaporable solution with appropriate absorption spectra for a mercury or xenon flash lamp with strong energy transmission in the UVB to mid visible light range, allowing the solution to absorb the energy from the flash lamp and evaporate. Transistor dimensions were defined by the capabilities of a typical roll-to-roll drop on demand cartridge. The final device demonstrated an on/off ratio of 104, representing performance similar to gravure printed devices. This represents the first CNT ink which can be used in high speed production methods without long thermal curing steps in the workflow.

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Droplet Formation Under the Effect of a Flexible Nozzle Plate

Volume 11: Micro and Nano Systems, Parts A and B ◽

10.1115/imece2007-41598 ◽

2007 ◽

Author(s):

S. Sangplung ◽

J. A. Liburdy

Keyword(s):

Surface Tension ◽

Droplet Formation ◽

Step Function ◽

Droplet Velocity ◽

Viscous Force ◽

Flexible Plate ◽

Computational Domain ◽

Cfd Model ◽

Drop On Demand ◽

Nozzle Plate

Droplet formation from a flexible nozzle plate driven by a prescribed-waveform excitation of a piezoelectric is numerically investigated using a computational fluid dynamics (CFD) model with the VOF method. The droplet generator with a flexible nozzle plate, which is free to vibrate due to the pressure acting on the plate, is modeled in a CFD computational domain. The CFD analysis includes the fluid-structure interaction between fluid and a flexible plate using large deflection theory. The problem is characterized by the nondimensional variables based on the capillary parameters of time, velocity, and pressure. The CFD model is validated with the experiment results. This study examines the characteristics of the applied waveforms and nozzle plate material properties to change the vibrational characteristics of the nozzle plate. The effect of fluid properties on the droplet formation process is also investigated focusing on surface tension and viscous forces. The mechanism of the droplet formation excited by a drop-on-demand piezoelectric waveform is investigated using a step-function and a pulse waveform. The piezoelectric displacement plays an important role in generating either forward-driven momentum or a suction pressure inside the chamber. For the step-function waveform, the nondimensional applied impulse is defined and used to characterize the post-breakoff droplet volume. Increasing the impulse of the piezoelectric can be used to cause a faster droplet velocity and it is shown that the vibration of the nozzle plate has a strong effect on the droplet velocity, shape, and volume. Surface tension has strong influence to the droplet formation characteristics which is contrast to a viscous force that makes no difference on the droplet formation for different viscosities. For the combination of a fluid with high surface tension and the most flexible nozzle plate, this system can not cause the droplet ejected out of the nozzle.

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Numerical study on the effects of non-dimensional parameters on drop-on-demand droplet formation dynamics and printability range in the up-scaled model

Physics of Fluids ◽

10.1063/1.4742913 ◽

2012 ◽

Vol 24 (8) ◽

pp. 082103 ◽

Cited By ~ 26

Author(s):

Eunjeong Kim ◽

Jehyun Baek

Keyword(s):

Numerical Study ◽

Droplet Formation ◽

Scaled Model ◽

On Demand ◽

Drop On Demand ◽

Formation Dynamics ◽

Dimensional Parameters

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High-speed laser speckle imaging to unravel picoliter drop-on-demand to substrate interaction

Review of Scientific Instruments ◽

10.1063/5.0011167 ◽

2021 ◽

Vol 92 (8) ◽

pp. 083906

Author(s):

R. Antonelli ◽

R. Fokkink ◽

N. Tomozeiu ◽

J. Sprakel ◽

T. E. Kodger

Keyword(s):

High Speed ◽

Laser Speckle ◽

Laser Speckle Imaging ◽

Speckle Imaging ◽

On Demand ◽

Substrate Interaction ◽

Drop On Demand

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On-demand Ferrofluid Droplet Formation With Non-linear Magnetic Permeability in the Presence of a Non-uniform Magnetic Field

10.21203/rs.3.rs-1075479/v1 ◽

2021 ◽

Author(s):

Mohamad Ali Bijarchi ◽

Mohammad Yaghoobi ◽

Amirhossein Favakeh ◽

Mohammad Behshad Shafii

Keyword(s):

Magnetic Field ◽

Magnetic Susceptibility ◽

Uniform Magnetic Field ◽

Maxwell Equations ◽

Droplet Diameter ◽

Droplet Formation ◽

Bond Number ◽

On Demand ◽

Drop On Demand ◽

The Magnetic Field

Abstract The magnetic actuation of ferrofluid droplets offers an inspiring tool in widespread engineering and biological applications. In this study, the dynamics of ferrofluid droplet generation with a Drop-on-Demand feature under a non-uniform magnetic field is investigated by multiscale numerical modeling. Langevin equation is assumed for ferrofluid magnetic susceptibility due to the strong applied magnetic field. Large and small computational domains are considered. In the larger domain, the magnetic field is obtained by solving Maxwell equations. In the smaller domain, a coupling of continuity, Navier Stokes, two-phase flow, and Maxwell equations are solved by utilizing the magnetic field achieved by the larger domain for the boundary condition. The Finite volume method and coupling of level-set and Volume of Fluid methods are used for solving equations. The droplet formation is simulated in a two-dimensional axisymmetric domain. The method of solving fluid and magnetic equations is validated using a benchmark. Then, ferrofluid droplet formation is investigated experimentally and the numerical results are in good agreement with the experimental data. The effect of 12 dimensionless parameters including the ratio of magnetic, gravitational, and surface tension forces, the ratio of the nozzle and magnetic coil dimensions, and ferrofluid to continuous-phase properties ratios are studied. The results showed that by increasing the magnetic Bond number, gravitational Bond number, Ohnesorge number, dimensionless saturation magnetization, initial magnetic susceptibility of ferrofluid, the generated droplet diameter reduces, whereas the formation frequency increases. The same results were observed when decreasing the ferrite core diameter to outer nozzle diameter, density, and viscosity ratios.

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A High Temperature Drop-On-Demand Droplet Generator for Metallic Melts

Micromachines ◽

10.3390/mi10070477 ◽

2019 ◽

Vol 10 (7) ◽

pp. 477 ◽

Cited By ~ 6

Author(s):

Saeedeh Imani Moqadam ◽

Lutz Mädler ◽

Nils Ellendt

Keyword(s):

High Speed ◽

Temperature Drop ◽

Pressure Oscillation ◽

Ex Situ ◽

Droplet Generator ◽

On Demand ◽

Micro Particles ◽

Drop On Demand ◽

Aisi 52100 Steel ◽

Size And Morphology

In this study we present the design and functionality of a pneumatic drop-on-demand droplet generator that produces metallic micro particles with a size range of 300 µm to 1350 µm at high temperatures of up to 1600 °C. Molten metal droplets were generated from an EN 1.3505 (AISI 52100) steel which solidified during a falling distance of 6.5 m. We analyzed the resulting particle size and morphology using static image analysis. Furthermore, the droplet formation mode was analyzed using high-speed recordings and the pressure oscillation was measured in the crucible. The system is meant to be reproducible in all aspects and therefore the in-situ measurements are set to control the droplet size and trajectory during the run. Additionally, the ex-situ measurements are done on the particles in order to characterize them in size and morphology aspects.

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