Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A12: Drops: Heat Transfer and Evaporation IDrops
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Chair: Tuan Tran, Nanyang Technological University Room: 505 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A12.00001: Spray visualization of alternative fuels at hot ambient conditions Kumaran Kannaiyan, Reza Sadr Gas-to-Liquid (GTL) has gained significant interest as drop-in alternative jet fuel owing to its cleaner combustion characteristics. The physical and evaporation properties of GTL fuels are different from those of the conventional jet fuels. Those differences will have an effect on the spray, and in turn, the combustion performance. In this study, the non-reacting near nozzle spray dynamics such as spray cone angle, liquid sheet breakup and liquid velocity of GTL fuel will be investigated and compared with those of the conventional jet fuel. This work is a follow up of the preliminary study performed at atmospheric ambient conditions where differences were observed in the near nozzle spray characteristics between the fuels. Whereas, in this study the spray visualization will be performed in a hot and inert environment to account for the difference in evaporation characteristics of the fuels. The spray visualization images will be captured using the shadowgraph technique. A rigorous statistical analysis of the images will be performed to compare the spray dynamics between the fuels. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A12.00002: Thermal imaging of levitated fresh and salt water drops during laser irradiation. Cody Brownell, Harrison Biggs Simulation of high energy laser propagation and scattering in the maritime environment is problematic, due to the high likelihood of turbulence, fog, and rain or sea spray within the beam path. Considering large water drops (diameters of approximately 1-mm), such as those found in a light rain, an incident high energy laser will lead to rapid evaporation of the water drop as it traverses the beam path. In this work we present surface temperature measurements of a water drop obtained using a FLIR IR camera. The drop is acoustically levitated, and subject to a continuous wave laser with a wavelength of 1070-nm and a mean irradiance of approximately 800 W/cm$^{\mathrm{2}}$. These measurements show that the steady-state surface temperature of the drop is well below the saturation temperature, and for pure substances the equilibrium temperature decreases with decreasing drop volume similar to observations with smaller aqueous aerosols. Temperature non-uniformity within the drop is also assessed from statistics of the surface temperature fluctuations. Preliminary results from irradiated salt water drops show notably different behavior from fresh water drops, including temperature spikes as the drop volume decreases and occasional nucleate boiling. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A12.00003: Out of the frying pan: Explosive droplet dynamics Jeremy Marston, Chao Li, Tadd Truscott, Mohammad Mansoor Regardless of culinary skills, most people who have used a stove top have encountered the result of water interacting with hot oil. The phenomenon is particularly memorable if the result is impingement of hot fluid on one's skin. Whilst ubiquitous, a deeper probing of this phenomenon reveals a vastly rich dynamical process. We use high-speed imaging to investigate the idealized case of a single water droplet impacting onto a hot oil film. At a qualitative level, we have observed three regimes of fluid ejection -- jets, cones and explosive vaporization. The latter of these results in the spectacular creation of aerosol with sizes down to the sub-micrometer range. We present our experimental findings based upon control parameters such as temperature, film thickness and oil type. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A12.00004: High-Speed Imaging of Explosive Droplet Boiling at the Superheat Limit F. Robert Ferris, Jim Hermanson, Arash Asadollahi, Asghar Esmaeeli The explosive boiling processes of droplets of diethyl ether (1-2 mm in diameter) at the superheat limit were examined both experimentally and computationally. Experimentally, droplet explosion was studied using a heated bubble column to bring the test droplet to the superheat limit. The droplet fluid was diethyl ether (superheat limit 147 C at 1 bar) with immiscible glycerol employed as the heated host fluid. Tests were carried out at pressures between 0.5 and 4 bar absolute. The pressure rise associated with the explosive boiling event was captured using a piezoelectric quartz pressure transducer with a 1 MHz DAQ system. High-speed imaging of the interfacial behavior during explosive boiling was performed using a Phantom v12.1 camera at a frame rate of up to one million frames per second with the droplets illuminated by diffuse back-lighting. The imaging reveals features of the Rayleigh-Taylor instability at the vapor-liquid interface resulting from the unstable boiling process. Computationally, Direct Numerical Simulations are performed at Southern Illinois University Carbondale to compliment the experimental tests. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A12.00005: Enhanced Condensation Heat Transfer On Patterned Surfaces Elaheh Alizadeh-Birjandi, H.Pirouz Kavehpour Transition from film to drop wise condensation can improve the efficiency of thermal management applications and result in considerable savings in investments and operating costs by millions of dollars every year. The current methods available are either hydrophobic coating or nanostructured surfaces. The former has little adhesion to the structure which tends to detach easily under working conditions, the fabrication techniques of the latter are neither cost-effective nor scalable, and both are made with low thermal conductivity materials that would negate the heat transfer enhancement by drop wise condensation. Therefore, the existing technologies have limitations in enhancing vapor-to-liquid condensation. This work focuses on development of surfaces with wettability contrast to boost drop wise condensation, which its overall heat transfer efficiency is 2-3 times film wise condensation, while maintaining high conduction rate through the surface at low manufacturing costs. The variation in interfacial energy is achieved through crafting hydrophobic patterns to the surface of the metal via scalable fabrication techniques. The results of experimental and surface optimization studies are also presented. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A12.00006: Fine structure of the vapor field in evaporating dense sprays Emmanuel Villermaux, Alexandre Moutte, Muriel Amielh, Patrice Meunier Making use of an original technique which permits the simultaneous measurement of both the displacement field of evaporating droplets in a spray, and of their vapor, we investigate the relevance of a scenario introduced earlier to describe the evaporation dynamics of dense sprays [{\it Phys. Rev. Fluids} 1, 014201 (2016)]. A plume of dense acetone droplets evaporating in air is studied, for which the stirring field is measured by particle image velocimetry of the droplets, and the vapor field is imaged quantitatively by laser-induced fluorescence. We show, thanks to these unique in situ measurements, that the spray boundary with the diluting environment is slaved to the dynamics of its saturating vapor concentration field, whose structure is analyzed for different well defined local flow topologies. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A12.00007: Thermal antibubble Stephane Dorbolo, Benoit Scheid, Baptiste Darbois-Texier, Laurent Maquet The impact of a droplet on a pool, again... Droplets of a volatile liquid are dropped on a hot pool of oil. The temperature of the pool is beyond the boiling temperature of the liquid that the droplet is made of. For a given set of parameters (impact height, droplet size, temperature of the bath), the droplet penetrates below the surface of the bath being protected by a thin film of vapor. This object reminds the antibubble case that is the opposite picture of a bubble: instead of having a spherical thin film of a liquid in a gas, the antibubble is a thin film of gas in a liquid. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A12.00008: Anti-iridescent colloidal photonic nanostructure from thermal gradients and polymeric brush effects. Seung Yeol Lee, Hyoungsoo Kim, Shin-Hyun Kim, Howard Stone Colloidal nanostructures induced by self-assembly are important in reflective displays, plasmonic or photonic sensors, and color pigments. During the evaporation of droplets of colloidal suspension, due to the non-uniform evaporation rate along the droplet interface, a radially outward flow is created and it carries colloidal particles to the pinned contact line of the droplet. We document that the packing at the contact line is a face-center-cubic (fcc) colloidal nanostructure in a ring shape. The fcc structure of the colloidal nanoparticles exhibits angle-dependent color. In particular, we introduce a novel method to suppress the familiar coffee-ring effect and modify colloidal nanostructures to exhibit angle-independent optical properties. A suspension of polyethylene oxide (PEO)-coated silica nanoparticles dispersed in ethanol-water mixture is prepared. The droplet containing the nanoparticles dries on a heated substrate, which creates a thermal gradient along the interface of the droplet. This thermal gradient induces thermal-Marangoni stresses that suppress the coffee-ring effects. PEO adsorbed on the surface of silica nanoparticles produces an additional interaction between colloidal nanoparticles, which makes the final structure disordered. The disordered photonic nanostructures in our experiments exhibit angle-independent structural color. This technique can be applied to printing or optical filtering systems. [Preview Abstract] |
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