Simulation%20of%20Droplet%20Drawback%20in%20Inkjet%20Printing

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Simulation of Droplet Drawback in Inkjet Printing
Ali Jafari and Nasser Ashgriz

• Multiphase Flow Spray Systems Lab (MUSSL)

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Motivation

• Investigate the interaction between two impacting
  droplets (drawback)
• Investigate the effect of different parameters
  and liquid properties on the final droplet shapes
  (coalesced or not coalesced drops)

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Overview

• Basic assumptions
• laminar and incompressible fluid flow
• density constant
• Involved mechanisms
• fluid dynamics viscous and capillary effects
• Solidification is not considered

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Governing Equations

• Continuity and momentum equations
• Volume of Fluid (VOF)

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Interface Tracking
Procedure Surface Reconstruction Use F-field to
determine cell normal Determine case using
normal Position plane with known slope based upon
volume fraction Compute plane area and
vertices Fluid Advection Compute flux across
cell side (case dependent) Operator Split (i.e.
do for x, y and z sweeps)
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Validation comp. with Fujimotos experiments
Single water droplet impaction on a
surface D0.56 mm, V2.65
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Simulation parameters

• 20 cells per radius
• ?997 kg/m3
• µ.000891 kg/m.s
• D40 µm
• V5 m/s
• s0.073 N/m
• ?90º

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Non-coalesc., ?t30 µs, ?x58.5 µm
Times 0, 9, 25, 30, 36, 43, 49, and 60 µs
respectively
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Coalesc., ?t30 µs, ?x57.5 µm
Times 0, 9, 25, 30, 36, 43, 49, and 60 µs
respectively
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Non-coalesc., ?t25 µs, ?x56 µm
Times 0, 9, 25, 30, 36, 43, 49, and 60 µs
respectively
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Coalesc., ?t25 µs, ?x55 µm
Times 0, 9, 25, 30, 36, 43, 49, and 60 µs
respectively
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Velocity field (non-coalescence)
Velocity distribution for case 1, ?t30 µs, ?x58
µm at times 36, 40, 43, 45, 49, and 60 µs
respectively
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Velocity field (coalescence)
Velocity distribution for case 1, ?t30 µs,
?x57.5 µm at times 36, 40, 43, 45, 49, and 60 µs
respectively.
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Coalescence case 2 effect of timing
Case 2, ?t25 µs, ?x55 µm at times 30, 34, 36,
38, 49, and 60 µs respectively.
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Non-dim. Pressure contours
?t30 µs, ?x57.5 µm at times 43, 45, and 60 µs
respectively
?t30 µs, ?x58 µm at times 40, 43, and 60 µs
respectively.
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Conclusions

• Drawback is sensitive to
• Drop spacing
• Impact velocity
• Contact angle
• Inter-drop time
• Small changes in any of the above parameters may
  result in coalescing or non-coalescing drops
  e.g. for ?t25 µs, coalescence at drop spacing of
  55 ?m no coalescence at 56 ?m
• Further investigation of all important cases and
  parameters is planned and from these data,
  theoretical relations for the threshold of
  coalescence and non-coalescence would be
  developed.