simulation of droplet drawback in inkjet printing multiphase flow & spray systems lab (mussl)...
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Simulation of Droplet Drawback in Inkjet Printing
Multiphase Flow & Spray Systems Lab (MUSSL)
Ali Jafari and Nasser Ashgriz
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)
Overview
Basic assumptions laminar and incompressible fluid flow density constant
Involved mechanisms fluid dynamics: viscous and capillary effects Solidification is not considered
Governing Equations
Continuity and momentum equations
Volume of Fluid (VOF)
])([
111
0
T
b
VV
FgpVVt
V
V
0)(
FVt
F
Interface Tracking
Procedure:Surface Reconstruction
Use F-field to determine cell “normal” Determine “case” using normalPosition plane with known slope based upon volume fraction Compute plane area and vertices
Fluid AdvectionCompute flux across cell side (case dependent)Operator Split (i.e. do for x, y and z sweeps)
A sample “F” field
1
1
1 1
1 1
1 1
1
0 0 00
0 00
0
0 0
0
0
0
.85
.92
.68
.35
.09.31
.09
.42Two-fluid VOF method based on Piecewise Linear Interface Calculation (PLIC) algorithm.
Validation: comp. with Fujimoto’s experiments
Non-Dim Time
D/D
0
0 1 2 3 4 50
0.5
1
1.5
2
2.5
3
ExperimentNum. V=2.65Num. V=2.55
Single water droplet impaction on a surface
D=0.56 mm, V=2.65 60,30 era
Simulation parameters
20 cells per radius
ρ=997 kg/m3
μ=.000891 kg/m.s
D=40 μm
V=5 m/s
σ=0.073 N/m
Ө=90º
Non-coalesc., Δt=30 μs, Δx=58.5 μm
Times: 0, 9, 25, 30, 36, 43, 49, and 60 μs respectively
Times: 0, 9, 25, 30, 36, 43, 49, and 60 μs respectively
Coalesc., Δt=30 μs, Δx=57.5 μm
Non-coalesc., Δt=25 μs, Δx=56 μm
Times: 0, 9, 25, 30, 36, 43, 49, and 60 μs respectively
Coalesc., Δt=25 μs, Δx=55 μm
Times: 0, 9, 25, 30, 36, 43, 49, and 60 μs respectively
Velocity field (non-coalescence)
Velocity distribution for case 1, Δt=30 μs, Δx=58 μm at times 36, 40, 43, 45, 49, and 60 μs respectively
Velocity field (coalescence)
Velocity distribution for case 1, Δt=30 μs, Δx=57.5 μm at times 36, 40, 43, 45, 49, and 60 μs respectively.
Case 2, Δt=25 μs, Δx=55 μm at times 30, 34, 36, 38, 49, and 60 μs respectively.
Coalescence case 2: effect of timing
Non-dim. Pressure contours
Δt=30 μs, Δx=57.5 μm at times 43, 45, and 60 μs respectively
Δt=30 μs, Δx=58 μm at times 40, 43, and 60 μs respectively.
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 Δt=25 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.