Title Page
Abstract
Contents
1. INTRODUCTION 13
1.1. Background of spray cooling 13
1.2. Surface texturing methods 19
1.2.1. Supersonic cold-spraying 19
1.2.2. Aerosol deposition 24
1.2.3. Electrospinning & Electroplating 28
1.3. Research objective 32
2. EXPERIMENTAL SETUP 34
2.1. Materials 34
2.2. Experimental setup and fabrication 35
2.2.1. Supersonic cold-spraying cases: AgNW, Teflon, Copper pyramid 35
2.2.2. Aerosol deposition case: TiO₂ 40
2.2.3. Electrospraying, Electrospinning, and Electroplating cases: ZnO NW, Ni NC, and Thorny devil 42
2.2.4. Characterizations 50
3. RESULTS AND DISCUSSION 54
3.1. Various nanotexturing morphologies and water contact angles 54
3.2. Drop impact on the various nanotextured surfaces 59
3.3. Advanced surface texturing: macro- (copper pyrimid) and nano-texturing (ZnO NW) 81
4. CONCLUSIONS 104
5. REFERENCES 107
Table 1.1. The geometry parameters of supersonic cold-spraying nozzle 23
Table 2.1. Specification of inline heater 39
Table 2.2. Specification of syringe pump 39
Table 2.3. Specification of atomizers 39
Table 2.4. Specification of vacuum pump 41
Table 2.5. Specification of booster pump 41
Table 2.6. Specification of hot-plate 47
Table 2.7. Specification of syringe pump 48
Table 2.8. Specification of high voltage power supplier 49
Table 2.9. Specification of SEM equipment 51
Table 2.10. Specification of surface profiler 51
Table 2.11. Specification of a high-speed camera 51
Table 2.12. Specification of an infrared camera 52
Table 2.13. Specification of the thermocouple 52
Table 2.14. Specification of data logger 52
Table 2.15. Specification of XRD 53
Table 3.1. Drop impact velocity at various drop release heights (H) and the corresponding values of the Reynolds and Weber numbers. The initial drop diameter was D₀ = 4.2 mm. 74
Table 3.2. Heat flux (j) at various substrate temperatures (Tsub) and drop release heights (H).[이미지참조] 75
Table 3.3. Effective heat transfer coefficient of the nanotextured surfaces during air and spray cooling. The percentage increase (%) represents the difference in the effective... 80
Table 3.4. Total surface area of the coarse and fine samples without ZnO NW decoration. 90
Table 3.5. Effective heat transfer coefficient of the textured surfaces during air and spray cooling. The percentage increase (%) represents the difference in the effective... 103
Figure 1.1. The schematic of supersonic cold-spraying technology. 22
Figure 1.2. The cross-sectional image of supersonic cold-spraying nozzle inside geometry. 23
Figure 1.3. Spraying coating technologies according to particle size and velocity. 26
Figure 1.4. The schematic of aerosol deposition. (a) TiO₂ powder SEM images dispersed in powder feeder, (b) the side view and (c) the top view of SEM image for TiO₂ coating layer. 27
Figure 1.5. Schematic of (a) the electrospinning and (b) electroplating process. 31
Figure 2.1. Schematic of supersonic cold-spraying components 38
Figure 2.2. Schematic of electrospraying 46
Figure 2.3. Hot-plate device 47
Figure 2.4. Syringe pump of Legato 100 48
Figure 2.5. High voltage power supplier 49
Figure 3.1.1. (a) Spray cooling on the textured surface for high-power density electronics, which were supplied the heat from heat source. Schematics illustrating (b)... 54
Figure 3.1.2. (a-f) The surface SEM images for all cases. (g-n) The illustration of water contact angle (WCA) and captured images for all cases. Note that the release height... 56
Figure 3.2.1. (a) The visualization image of leidenfrost effect on the surface of bare case at 150 ℃. The measured evaporation front view images for each cases: (b) Teflon, (c)... 59
Figure 3.2.2. Surface roughness for (a) Bare, (b) ZnO NW, (c) TiO₂, and (d) thorny-devil cases. 62
Figure 3.2.3. The tilted snapshots of the spreading drop on the (a) Bare, (b) ZnO NW, (c) TiO₂, and (d) thorny-devil surfaces. (The initial drop diameter, D₀ = 4.2 mm) 64
Figure 3.2.4. Single drop impact on the surface of ZnO NW, TiO₂, and thorny-devil cases according to release heights H = 1, 4, 8, and 16 cm. Note that the substrate... 66
Figure 3.2.5. Single drop impact on the surface of ZnO NW, TiO₂, and thorny-devil cases according to release heights H = 1, 4, 8, and 16 cm. Note that the substrate... 67
Figure 3.2.6. Single drop impact on the surface of ZnO NW, TiO₂, and thorny-devil cases according to release heights H = 1, 4, 8, and 16 cm. Note that the substrate... 68
Figure 3.2.7. (a) The electronic kit schematic and photograph of setup shows the water spray cooling and drop evaporation. (b) Air (△Tair) and spray (△Tspray) cooling cycles...[이미지참조] 76
Figure 3.3.1. (a) Supersonically sprayed copper microparticles passing through a mesh for constructing pyramids. Zinc acetate dihydrate (ZnAc) seeding by electrospraying... 81
Figure 3.3.2. SEM images with the low and high magnification, water contact angles for each case, and XRD peak patterns of (a) bare, (b) pyramid, and (c) pyramid/ZnO... 84
Figure 3.3.3. Tilted snaphots on (a) bare, (b) fine pyramid, (c) coarse pyramid, (d) fine/ZnO NW, and (e) coarse/ZnO NW case at 140 ℃ during spreading drop. Note that... 87
Figure 3.3.4. Tilted snapshots of (a) coarse resolution pyramids at 200 ℃ (delayed Leidenfrost state) during spreading drop. (b) fine pyramid, (c) coarse pyramis, (d)... 91
Figure 3.3.5. Comparing the evaporation time △t (a, b), and (c, d) estimated heat flux, j during single drop impact on the surface of all cases. The experiment substrate... 94
Figure 3.3.6. The measured top surface temperature (Ttop) on the electronic kit according to various texturing case. (a) Ttop profile and (b) the difference values (△T or...[이미지참조] 98