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TECHNICAL PAPERS: Microscale Heat Transfer

An Experimental Study of Molten Microdroplet Surface Deposition and Solidification: Transient Behavior and Wetting Angle Dynamics

[+] Author and Article Information
D. Attinger, Z. Zhao, D. Poulikakos

Laboratory of Thermodynamics in Emerging Technologies, Institute of Energy Technology, Swiss Federal Institute of Technology (ETH), 8092 Zurich, Switzerland

J. Heat Transfer 122(3), 544-556 (Apr 11, 2000) (13 pages) doi:10.1115/1.1287587 History: Received October 25, 1999; Revised April 11, 2000
Copyright © 2000 by ASME
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References

Figures

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Schematic of the picoliter size solder droplet deposition apparatus
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Flash videography technique used for recording the solder droplet deposition process
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Measured points on the droplet surface. Points A and G determine the droplet wetting area diameter. D is the highest visible point of the surface, when viewing from the side, not always at the axis of symmetry. The distance from D to segment AG determines the visible droplet height H above the surface (identified by the segment AG). The shadow below the surface and the light spot inside the droplet are optical effects. The accuracy in determining the vertical and horizontal position of A and G decreases for wetting angle values near 90 deg, and larger than 110 deg, respectively.
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Spreading, oscillations, and freezing of a solder droplet on a flat substrate. Initial conditions: v0=1.54 m/s,d0=80 μm,T1,0=210°C,T2,0=48°C.
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Spreading, oscillations, and freezing of a solder droplet on a flat substrate. Initial conditions: v0=1.49 m/s,d0=84 μm,T1,0=210°C,T2,0=135°C.
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Time evolution of the spread factor β, with the substrate temperature T2,0 as a parameter. The error is estimated in Section 2.3.
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Time evolution of the dimensionless visible droplet height over the substrate H, with the substrate temperature T2,0 as a parameter. The error is estimated in Section 2.3.
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Final, maximum and minimum droplet nondimensional visible height H as a function of T2,0. The error is estimated in Section 2.3.
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Solidification time ts as a function of T2,0. The experimental values refer to the apparent solidification time, and the order of magnitude values refer to Eqs. (5) to (8).
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Determination of the apparent dynamic wetting angles. Angle αL is determined by points (I,G,A), and angle αR by (H,A,G). The measurement incertitude δαR comes primarily from the positioning of A and H, its value is estimated +/−12 deg.
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Evolution of the wetting angle α as a function of the spread factor β for the specified initial substrate temperatures T2,0 and impact velocities v0. The angular error is estimated in Fig. 10.
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Time evolution of the spread factor β, the contact angle α, the first ripple angle γ, and the first ripple nondimensional height H11 in the case (v0=2.31 m/s,T2,0=59°C). The error is estimated in Section 2.3 and in Fig. 10.
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Contact angle measurement with atomic force microscopy. The two vertical lines determine the position of the angle measurement on the splat profile. Frames (a) and (b) show the top view of the same (previously solidified) drop before (a) and after two minutes heating (b) above its melting temperature (180°C).

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