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6 Results and Discussion This chapter is dedicated to the experimental results on the drop splash phenomena. Section 6.1 introduces graphically the four types of splash as well as the aerodynamic breakup observed in the experiment. Section 6.2 discusses on the modeling of the splash threshold after examining the previous models with our experimental results. Section 6.3 comprises the measurement of the velocity of the uprising jet. It is found out that the velocity of the uprising jet was multiple times higher than the impact velocity, and it had a strong dependency on the impact angle. Section 6.4 introduces the measurement of the spreading radii, which clearly exhibits the discrepancy from the normal impact. Drop impact on the 0° target layer led to generation of singular secondary droplets. Mass-loss was hence measurable in this special case. Section 6.5 introduces the mass-loss coefficient of this special case. This chapter emphasizes the reliability of the measurements, and therefore only representative graphic data are exhibited. Comprehensive graphic data and diagrams are listed in the appendixes. 6.1 Outcomes of the Oblique Drop Impact Single drop impact on dry surfaces were conducted under various conditions. The impact surface was always dry. The drop diameter was of a narrow range from 181 µm to 204 µm. Variation of the impact speed and the impact angle were accomplished by incrementing the rotational frequency of the target and the target angle, respectively. The target angles included 0°, 5°, 10°, 15°, 30°, 45°, 60° and 75°. The rotational frequency of the target was from 5 Hz to 30 Hz, corresponding to 10m/s to 63m/s. Both the deposition and the splash were observed. Aerodynamic breakup of the spreading lamella was discovered. 6.1.1 Morphologies of the Drop Splash Four types of drop splash were identified in the oblique impact as Figure 6.1 to Figure 6.4 represent. With larger impact angles, prompt splash emerged ahead of the corona splash as the impact velocity incremented. Secondary droplets emerged spontaneously upon impact, and flew away from the spreading lamella quickly. This observation provides a side-view of the prompt splash observed by 163
Mehdizadeh et al. [83] and Pan et al. [103], which is shown in Figure 2.14 in Chapter 2. (a) 0 µs (b) 2 µs (c) 4 µs (d) 7 µs (e) 10 µs (f) 14 µs Figure 6.1.: Prompt splash. Target angle: 75°, drop diameter: 188 µm, impact velocity: 34m/s, impact angle: 82°. Spatial resolution: 7.07µm/pixel, field of view: 2.21 mm × 1.84 mm, fps: 1 MHz. With sufficiently high velocities, a thin uprising jet emerged at the edge of the spreading lamella, and the secondary droplets formed at the tip of the uprising jet. This is a typical corona splash, although one side was significantly weaker than the other side because of the oblique impact, as shown in Figure 6.2. A pixelwise scrutiny of these images reveals that no single drops were visible in the cloud composed of liquid jets and secondary droplets. The reason lies at their rapid motion. The secondary droplets had a larger velocity than the rotating target, as they flew away from the impact surface. Motion blur happened unanimously to these secondary droplets and consequently denied the diameter measurement. At lower impact angles the uprising jet was formed only on one side as shown by Figure 6.3, while the other side was in the regime of the prompt splash. The two types of splash are named as corona-corona splash and corona-prompt splash, respectively. At sufficiently small impact angles, one side of the asymmetric spreading lamella ended up in deposition, while the other side rose up, forming an uprising jet, which 164 6. Results and Discussion
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Drop Impact on Dry Surfaces with Ph
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Hiermit versichere ich, die vorlieg
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Fachgebiet Reaktive Strömungslehre
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to non-monotonic threshold impact v
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Splash, einseitiger Splash sowie de
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3.4.2. Calibration of the Infrared
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Nomenclature Latin capitals Unit A
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k angular wavenumber rad m −1 k R
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F G ge i K L lam m max min n opt r
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1 Introduction 1.1 Motivation Aircr
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of the WCE acquired experimentally
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passage was cooled down to −196
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SLD icing conditions have been defi
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−9 ◦ C and layers of freezing r
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adjacent downstream control volume,
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conventional methods. Papadakis et
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Figure 2.5.: Ice horn and clear ice
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This model showed good agreement un
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Xu et al. proposed the following sc
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Figure 2.9.: Splash thresholds of t
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Chen and Wang [28] observed the dro
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2.14 shows. On stainless steel, tin
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years ago [157]. Another peculiarit
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Figure 2.17.: At an ambient pressur
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The temperature needs to be found o
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The Stefan number St S completely c
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T(x, 0) = T A < T m , 0 < x < ∞ b
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Figure 2.20: Fraction of solidifica
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The mathematical description of the
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asal plane. Without all these facto
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Part I. Impact of Supercooled Water
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3 Experimental Setup This chapter i
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drop and the tube as between such t
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of nucleation ice dendrite growth,
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The boundary condition is then 1
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0.021 W m −1 K −1 at −165 ◦
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outlet of the liquid. There are two
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The maximum depth of water in the c
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Figure 3.11.: Pneumatic drop genera
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Figure 3.13.: Pneumatic drop genera
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Adjusting the Pulse Width Longer el
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(a) Shadowgraph imaging (b) The sid
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Figure 3.21.: The cold plate was co
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Figure 3.25.: The transmittance of
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eproducible. The SHS was created by
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Figure 3.30.: Planck’s law The ot
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Figure 3.32.: Heterogeneity of the
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Figure 3.35.: The valid region afte
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Divided by dΩ, Eq. 3.33 is related
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Figure 3.39.: The wavelength depend
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Figure 3.41.: Orientation dependenc
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wavelength, so that the value for r
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Temperature Gradient In light of th
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(a) 0.00 ms (b) 1.39 ms (c) 2.79 ms
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Figure 3.48.: Synchronization syste
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Figure 3.50.: Experimental setup fo
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(a) 0 ms (b) 0 ms (c) 0.6 ms (d) 0.
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Figure 4.2.: The dynamic spreading
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Figure 4.4.: Influence envelope of
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(a) 0 ms (b) 0.4 ms (c) 0.8 ms (d)
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(a) 0 ms (b) 1.39 ms (c) 2.79 ms (d
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(a) 0 ms (b) 0.05 ms (c) 0.1 ms (d)
Page 131 and 132: (a) −4 ◦ C, at 6.8 ms. (b) −1
Page 133 and 134: The contact temperature is closer t
Page 135 and 136: Obviously, the contact temperature
Page 137 and 138: Figure 4.13.: The dimensionless min
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Page 142: Part II reports the experimental in
Page 145 and 146: to realize a high-speed rotation of
Page 147 and 148: Figure 5.2.: Impact surface with di
Page 149 and 150: Various such devices were developed
Page 151 and 152: than the values reported in literat
Page 153 and 154: Figure 5.7.: The monodisperse drop
Page 155 and 156: This performance is a reminiscence
Page 157 and 158: Figure 5.11.: The merging distance
Page 159 and 160: signal and the excitation signal of
Page 161 and 162: The analogy with a capacitor led to
Page 163 and 164: The real situation in the applicati
Page 165 and 166: Figure 5.15.: Static electric field
Page 167 and 168: Figure 5.19.: Phase shift and pulse
Page 169 and 170: disadvantage is that the number of
Page 171 and 172: Zoom Lens Working Distance Spatial
Page 173 and 174: the impact surface was not a sharp
Page 175 and 176: 5.5 Synchronization Both single pul
Page 177 and 178: The last note on these two pulse tr
Page 179 and 180: Figure 5.28.: Calculation of the im
Page 184 and 185: (a) 0 µs (b) 2 µs (c) 4 µs (d) 6
Page 186 and 187: high impact velocities approaching
Page 188 and 189: (a) 32 µs (b) 84 µs (c) 100 µs F
Page 190 and 191: (a) (b) (c) Figure 6.8.: Examinatio
Page 192 and 193: Our observations show that the lame
Page 194 and 195: 6.3 Velocity of the Uprising Jet In
Page 196 and 197: (a) 1 µs (b) 3 µs (c) 4 µs Figur
Page 198 and 199: (a) 0 µs (b) 8 µs (c) 32 µs Figu
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Page 202 and 203: Nevertheless, the drop volume was e
Page 204: was surface tension. These factors
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(a) 0 µs (b) 16 µs (c) 32 µs (d)
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(a) 0 µs (b) 8 µs (c) 20 µs (d)
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A.7 5° target (a) 0 µs (b) 24 µs
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(a) 0 µs (b) 20 µs (c) 36 µs (d)
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(a) 0 µs (b) 8 µs (c) 16 µs (d)
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(a) 0 µs (b) 24 µs (c) 52 µs (d)
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(a) 0 µs (b) 16 µs (c) 32 µs (d)
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(a) 0 µs (b) 20 µs (c) 40 µs (d)
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(a) 0 µs (b) 10 µs (c) 22 µs (d)
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(a) 0 µs (b) 36 µs (c) 68 µs (d)
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(a) 0 µs (b) 36 µs (c) 72 µs (d)
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(a) 0 µs (b) 8 µs (c) 16 µs (d)
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(a) (b) (c) (d) (e) (f) Figure B.4.
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(a) 0 ms (b) 0.4 ms (c) 0.5 ms (d)
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(a) 0 ms (b) 0.35 ms (c) 1 ms (d) 1
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2.15.Prompt splash (left) was docum
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3.12.Time t =0 corresponds to the s
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3.31.The extension ring (left) betw
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4.7. Infrared imaging: total reboun
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5.5. The custom made vibrating orif
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5.14.Static electric field between
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6.6. Capillary wave created by the
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A.5. Drop diameter: 189 µm, impact
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A.29.Drop diameter: 203 µm, impact
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List of Tables 2.1. MVD of Freezing
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Imaging and Computer Simulations. T
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[42] GENT, R. W., N. P. DART and J.
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[70] KOROLEV, ALEXEI V., GEORGE A.
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[99] MUNDO, CHR., M. SOMMERFELD and
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[125] RYERSON, CHARLES C., GEORGE G
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[153] ŠIKALO Š., C. TROPEA and E.
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Curriculum Vitae Personal Informati
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