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Figure 3.25.: The transmittance of the infrared glass for radiation of different wavelengths, provided by EdmundOptics. ing in order to avoid reflection of the surrounding infrared radiation. Likewise, the double-glass infrared window was employed for the same purpose of thermal insulation. This construction was supported by N. Kidambi in his IREP summer exchange program [67]. Figure 3.26.: Configuration of the bottom-view infrared imaging. The drop impact took place on the infrared glass, on top of which a 12 µm thick aluminium film was laid. After each impact, the slider was pulled out, warmed above the dew point, and the aluminum film was cleaned before the next drop impact. The infrared camera measured the temperature of the aluminum film, which was expected to be the temperature of the bottom of the lamella. Superhydrophobic surfaces (SHS) offer strong drop receding and even total rebounding [6]. Supercooled drop impact was conducted on such surfaces because solidification might have a noticeable influence on the receding or rebounding. 3.3. Observation Plans 73
The wettability of a surface is measured by the contact angle. The contact angles of water on both the aluminum surface and the SHS were measured. The angle measurement could be easily done by a protractor on an image, but the precision is limited and the measurement is a little bit subjective. Therefore a curve fitting method was chosen. The outline of a sessile drop on a surface was recognized and extracted from the raw image by transforming it to a binary image. One portion of the outline adjacent to the contact point was selected for the curve fitting. The contact point was defined as the point projection of the three phase contact line on the 2D image. This part outline was fitted by a polynomial curve by the “Polyfit” function provided by Matlab. After comparison, the best fit came out to be a two degree polynomial function. The first order gradient of this parabolic function at the contact point gave the value of the contact angle. Figure 3.27 shows the results of this method. More detailed information on the Matlab programming can be found in the Bachelor thesis of H. Eichhorn [40]. Figure 3.27.: Measurement of the contact angle on an aluminum surface (up) and a SHS (down). The red line at the feet of the drop are the fitted curve. The first order gradient of the curve at the contact point is the contact angle. The contact angle on the aluminum surface was measured as 40°, while the angles were respectively 151° and 137° for the left and right sides of the drop on the SHS. The static contact angle on the aluminum surface was measured as 40°. On the SHS the drop had an asymmetrical shape. 151° and 137° were obtained for the left and right contact angle respectively. An average value of 144° was chosen as a descriptive value. It must be admitted that the hydrophobicity was not perfectly 74 3. Experimental Setup
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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
Page 41 and 42: Figure 2.9.: Splash thresholds of t
Page 43 and 44: Chen and Wang [28] observed the dro
Page 45 and 46: 2.14 shows. On stainless steel, tin
Page 47 and 48: years ago [157]. Another peculiarit
Page 49 and 50: Figure 2.17.: At an ambient pressur
Page 51 and 52: The temperature needs to be found o
Page 53 and 54: The Stefan number St S completely c
Page 55 and 56: T(x, 0) = T A < T m , 0 < x < ∞ b
Page 57 and 58: Figure 2.20: Fraction of solidifica
Page 59 and 60: The mathematical description of the
Page 61 and 62: asal plane. Without all these facto
Page 64: Part I. Impact of Supercooled Water
Page 68 and 69: 3 Experimental Setup This chapter i
Page 70 and 71: drop and the tube as between such t
Page 72 and 73: of nucleation ice dendrite growth,
Page 74 and 75: The boundary condition is then 1
Page 76 and 77: 0.021 W m −1 K −1 at −165 ◦
Page 78 and 79: outlet of the liquid. There are two
Page 80 and 81: The maximum depth of water in the c
Page 82 and 83: Figure 3.11.: Pneumatic drop genera
Page 84 and 85: Figure 3.13.: Pneumatic drop genera
Page 86 and 87: Adjusting the Pulse Width Longer el
Page 88 and 89: (a) Shadowgraph imaging (b) The sid
Page 90 and 91: Figure 3.21.: The cold plate was co
Page 94 and 95: eproducible. The SHS was created by
Page 96 and 97: Figure 3.30.: Planck’s law The ot
Page 98 and 99: Figure 3.32.: Heterogeneity of the
Page 100 and 101: Figure 3.35.: The valid region afte
Page 102 and 103: Divided by dΩ, Eq. 3.33 is related
Page 104 and 105: Figure 3.39.: The wavelength depend
Page 106 and 107: Figure 3.41.: Orientation dependenc
Page 108 and 109: wavelength, so that the value for r
Page 110 and 111: Temperature Gradient In light of th
Page 112 and 113: (a) 0.00 ms (b) 1.39 ms (c) 2.79 ms
Page 114 and 115: Figure 3.48.: Synchronization syste
Page 116: Figure 3.50.: Experimental setup fo
Page 119 and 120: (a) 0 ms (b) 0 ms (c) 0.6 ms (d) 0.
Page 121 and 122: Figure 4.2.: The dynamic spreading
Page 123 and 124: Figure 4.4.: Influence envelope of
Page 125 and 126: (a) 0 ms (b) 0.4 ms (c) 0.8 ms (d)
Page 127 and 128: (a) 0 ms (b) 1.39 ms (c) 2.79 ms (d
Page 129 and 130: (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
Page 139 and 140: always after the receding reached t
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Part II reports the experimental in
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to realize a high-speed rotation of
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Figure 5.2.: Impact surface with di
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Various such devices were developed
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than the values reported in literat
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Figure 5.7.: The monodisperse drop
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This performance is a reminiscence
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Figure 5.11.: The merging distance
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signal and the excitation signal of
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The analogy with a capacitor led to
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The real situation in the applicati
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Figure 5.15.: Static electric field
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Figure 5.19.: Phase shift and pulse
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disadvantage is that the number of
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Zoom Lens Working Distance Spatial
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the impact surface was not a sharp
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5.5 Synchronization Both single pul
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The last note on these two pulse tr
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Figure 5.28.: Calculation of the im
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6 Results and Discussion This chapt
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(a) 0 µs (b) 2 µs (c) 4 µs (d) 6
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high impact velocities approaching
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(a) 32 µs (b) 84 µs (c) 100 µs F
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(a) (b) (c) Figure 6.8.: Examinatio
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Our observations show that the lame
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6.3 Velocity of the Uprising Jet In
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(a) 1 µs (b) 3 µs (c) 4 µs Figur
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(a) 0 µs (b) 8 µs (c) 32 µs Figu
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(a) 45° target (b) 75° target (c)
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Nevertheless, the drop volume was e
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was surface tension. These factors
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the motion of the impinging water,
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of the single-side splash, the latt
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(a) 0 µs (b) 2 µs (c) 4 µs (d) 6
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(a) 0 µs (b) 1 µs (c) 2 µs (d) 3
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(a) 0 µs (b) 3 µs (c) 6 µs (d) 9
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(a) 0 µs (b) 10 µs (c) 11 µs (d)
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(a) 0 µs (b) 3 µs (c) 5 µs (d) 8
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(a) 0 µs (b) 1 µs (c) 2 µs (d) 3
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(a) 0 µs (b) 6 µs (c) 10 µs (d)
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(a) 0 µs (b) 1 µs (c) 3 µs (d) 5
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(a) 0 µs (b) 8 µs (c) 24 µs (d)
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(a) 0 µs (b) 2 µs (c) 5 µs (d) 8
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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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