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You searched for subject:(Droplet Splashing). Showing records 1 – 3 of 3 total matches.

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University of California – Riverside

1. Vu, Henry. Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts.

Degree: Mechanical Engineering, 2010, University of California – Riverside

Spray atomization and droplet dynamics are research topics that have existed for many decades. Their prevalence in manufacturing, energy generation and other practical applications is undeniable, though researchers have often overlooked the importance of understanding the physics of atomization or droplet impact characteristics in the ongoing effort to improve efficiency. In this talk, I will address the atomization of thermodynamically unstable "flashing" sprays and the splashing mechanisms of single droplets impinging on flat, smooth surfaces. The related heat transfer phenomena for cooling applications are also addressed. These topics are motivated by efforts to improve the thermal protection provided by cryogenic spray cooling in laser dermatological procedures, increasing the throughput of the spray production of nano and micro-scale particulates used as dyes and catalysts, and in modeling of the release and dispersion of flammable or hazardous chemicals through large-scale collisions with storage containers. Through the use of high-speed video imaging, phase Doppler interferometric measurements and numerical modeling of the two-phase flow taking place within spray nozzles, a detailed picture of the processes involved in flash atomization are attained. Results reveal that flashing fluid jets under low superheats undergo many dynamic processes leading to eventual droplet formation, including the nucleation of vapor bubbles within the nozzle interior and their subsequent expansion and explosion. At high superheats, a stable "flare flashing" regime is attained resulting in very fine atomization. These insights may lead to improved nozzle designs to better control the atomization process.High-speed imaging of droplet impacts also reveals new insights into the mechanisms of splashing. The surrounding ambient air pressure, fluid viscosity, and fluid-surface affinity are found to profoundly influence the initiation and characteristics of splashing. A new analytical model explaining the mechanisms of crown splashing is developed along with correlations predicting the threshold of splashing.

Subjects/Keywords: Engineering, Mechanical; atomization; droplet splashing; droplets; flashing sprays; multiphase flows; spray cooling

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Vu, H. (2010). Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts. (Thesis). University of California – Riverside. Retrieved from http://www.escholarship.org/uc/item/5tp0c3h3

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Vu, Henry. “Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts.” 2010. Thesis, University of California – Riverside. Accessed April 14, 2021. http://www.escholarship.org/uc/item/5tp0c3h3.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Vu, Henry. “Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts.” 2010. Web. 14 Apr 2021.

Vancouver:

Vu H. Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts. [Internet] [Thesis]. University of California – Riverside; 2010. [cited 2021 Apr 14]. Available from: http://www.escholarship.org/uc/item/5tp0c3h3.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Vu H. Thermo-fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts. [Thesis]. University of California – Riverside; 2010. Available from: http://www.escholarship.org/uc/item/5tp0c3h3

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University of Illinois – Urbana-Champaign

2. Weisensee, Patricia Barbara. Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications.

Degree: PhD, Mechanical Engineering, 2016, University of Illinois – Urbana-Champaign

Droplets. Droplets are omnipresent: from rain droplets, over ink-jet printers, to advanced heat exchangers and thermal management systems. But in order to use droplets to our advantage, we need to study and understand how they interact with surfaces. Throughout this dissertation, I use optical photography and high speed imaging to characterize droplet-solid interactions. When liquid water comes into contact with a hydrophobic surface, such as Teflon, it forms individual droplets. The contact angle that the droplet develops with the surface is well understood in an air environment. However, when placed in a pure water vapor environment, I show that contact angles can decrease by up to 10% as compared to those in air. At the same time, on micro- and nanostructured surfaces, the vapor environment has little effect on the static contact angles. Based on Young’s equation and Fowke’s concept of the additivity of surface tensions, I propose that the decrease in contact angle on flat hydrophobic Teflon arises from molecular water vapor adsorption to the Teflon surface. In many engineering applications, the use of metals, as opposed to silicon and polymers, is desired to render surfaces water and oil repellent. I introduce micro electrical discharge machining (mEDM) as a viable tool to fabricate scalable micro-mushrooms (~ 100 µm) on steel blocks (~ 1 cm). I show that narrow micro-mushrooms with wide spacing give the highest contact angles (θA/θR = 170°/151°) and droplet mobility with water, while microstructures with flat tops, strong re-entrant curvature and smaller gap widths are necessary to support non-wetting droplets with liquids with a low surface tension, such as oils and alcohols (θA/θR = 148°/74° with isopropanol). After studying static and quasi-static droplet-surface interactions, I continued characterizing droplet dynamics during impact on micro- and nanostructured surfaces. Contact times during impact on rigid surfaces are constant over a wide range of impact speeds, and are thus difficult to control. I show that contact times of water droplets impacting elastic superhydrophobic surfaces can be reduced by up to 50% when compared to impact on rigid surfaces due to a springboard effect, during which droplet lifts off the surface prior to fully recoiling. Upon impact, the droplet excites the substrate to oscillate, while during liquid retraction, the substrate imparts vertical momentum back to the droplet, causing early droplet lift-off with reduced contact time. Through detailed experimental and theoretical analysis, I show that this novel springboarding phenomenon is achieved for a specific range of Weber numbers (We > 40) and droplet Froude numbers during spreading (Fr > 1). For droplets impacting vibrating superhydrophobic surfaces (60-320 Hz), I show that vibration frequency and phase at impact strongly influence the contact time of the bouncing droplets. I introduce the concept of a frequency-dependent critical impact phase at which contact times transition from a minimum (tc ≈ 0.5 tc,th) to a maximum… Advisors/Committee Members: King, William P (advisor), King, William P (Committee Chair), Miljkovic, Nenad (committee member), Jacobi, Anthony (committee member), Cahill, David (committee member).

Subjects/Keywords: Wettability; Surface Engineering; Phase Change Heat Transfer; Droplet Impact; Dropwise Condensation; Lubricant-Infused Surface (LIS); Slippery liquid-infused porous surface (SLIPS); Splashing; Contact Time

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Weisensee, P. B. (2016). Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/95580

Chicago Manual of Style (16th Edition):

Weisensee, Patricia Barbara. “Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications.” 2016. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed April 14, 2021. http://hdl.handle.net/2142/95580.

MLA Handbook (7th Edition):

Weisensee, Patricia Barbara. “Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications.” 2016. Web. 14 Apr 2021.

Vancouver:

Weisensee PB. Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2016. [cited 2021 Apr 14]. Available from: http://hdl.handle.net/2142/95580.

Council of Science Editors:

Weisensee PB. Droplet interactions with micro- and nanostructured surfaces for advanced heat transfer applications. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2016. Available from: http://hdl.handle.net/2142/95580

3. Dhiman, Rajeev. Splashing and Breakup of Droplets Impacting on a Solid Surface.

Degree: 2009, University of Toronto

Two new mechanisms of droplet splashing and breakup during impact have been identified and analyzed. One is the internal rupture of spreading droplet film through formation of holes, and the other is the splashing of droplet due to its freezing during spreading. The mechanism of film rupture was investigated by two different methods. In the first method, circular water films were produced by directing a 1 mm diameter water jet onto a flat, horizontal plate for 10 ms. In the second method, films were produced by making 0.6 mm water droplets impact a solid surface mounted on the rim of a rotating flywheel. Substrate wettability was varied over a wide range, including superhydrophobic. In both cases, the tendency to film rupture first increased and then decreased with contact angle. A thermodynamic stability analysis predicted this behavior by showing that films would be stable at very small or very large contact angle, but unstable in between. Film rupture was also found to be promoted by increasing surface roughness or decreasing film thickness. To study the effect of solidification, the impact of molten tin droplets (0.6 mm diameter) on solid surfaces was observed for a range of impact velocities (10 to 30 m/s), substrate temperatures (25 to 200°C) and substrate materials (stainless steel, aluminum and glass) using the rotating flywheel apparatus. Droplets splashed extensively on a cold surface but on a hot surface there was no splashing. Splashing could be completely suppressed by either increasing the substrate temperature or reducing its thermal diffusivity. An analytical model was developed to predict this splashing behavior. The above two theories of freezing-induced splashing and film rupture were combined to predict the morphology of splats typically observed in a thermal spray process. A dimensionless solidification parameter, which takes into account factors such as the droplet diameter and velocity, substrate temperature, splat and substrate thermophysical properties, and thermal contact resistance between the two, was developed. Predictions from the model were compared with a wide range of experimental data and found to agree well.

PhD

Advisors/Committee Members: Chandra, Sanjeev, Mechanical and Industrial Engineering.

Subjects/Keywords: Fluid Dynamics; Heat Transfer; Droplet Impact; Droplet Splashing; Thermal Spray Coating; Water Jet Impact; 0548

…investigate the effect of droplet solidification on the splashing and breakup of droplets. By… …water droplet on a mirror-polished stainless steel surface at 40 m/s [5]: (a… …molten tin droplet generator ...26 Figure 2.10: Photograph of the water droplet… …generator .27 Figure 2.11: A schematic diagram of the droplet impact apparatus… …30 Figure 2.13: A typical sequence of droplet impact, Do =600 μm, Vo =10 m/s .32… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Dhiman, R. (2009). Splashing and Breakup of Droplets Impacting on a Solid Surface. (Doctoral Dissertation). University of Toronto. Retrieved from http://hdl.handle.net/1807/17753

Chicago Manual of Style (16th Edition):

Dhiman, Rajeev. “Splashing and Breakup of Droplets Impacting on a Solid Surface.” 2009. Doctoral Dissertation, University of Toronto. Accessed April 14, 2021. http://hdl.handle.net/1807/17753.

MLA Handbook (7th Edition):

Dhiman, Rajeev. “Splashing and Breakup of Droplets Impacting on a Solid Surface.” 2009. Web. 14 Apr 2021.

Vancouver:

Dhiman R. Splashing and Breakup of Droplets Impacting on a Solid Surface. [Internet] [Doctoral dissertation]. University of Toronto; 2009. [cited 2021 Apr 14]. Available from: http://hdl.handle.net/1807/17753.

Council of Science Editors:

Dhiman R. Splashing and Breakup of Droplets Impacting on a Solid Surface. [Doctoral Dissertation]. University of Toronto; 2009. Available from: http://hdl.handle.net/1807/17753

.