Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D16: Drops: Evaporation |
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Chair: Deniel Anderson, George Mason University Room: D133/134 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D16.00001: Microregion model of a contact line including evaporation, kinetics and slip Daniel Anderson, Vladislav Janecek We consider the evaporation of a liquid on a uniformly heated solid substrate. In the framework of lubrication theory we consider hydrodynamics, heat conduction, phase change, evaporation kinetics, and slip. Our model focuses only on the contact line 'inner' region which allows us to quantify the impact of evaporation on the apparent contact angle and microregion heat transfer. The linearized problem with respect to the substrate overheating is solved analytically. The analytical solutions are compared with full numerical solutions and to predictions of Hocking (Physics of Fluids, 1995). [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D16.00002: Correlation for Sessile Drop Evaporation Peter Kelly-Zion, Christopher Pursell, Gregory Wassom, Brenton Mandelkorn, Chris Nkinthorn To better understand how the evaporation of sessile drops and small puddles is controlled by the vapor phase transport mechanisms of mass diffusion and buoyancy-induced convection, the evaporation rates of eight liquids evaporating under a broad range of ambient conditions were correlated with physical and geometrical properties. Examination of the correlation provides valuable insight into how the roles of diffusive and convective transport change with physical and geometrical parameters. The correlation predicts measured evaporation rates to within a root-mean-square error of 7.3{\%}. The correlation is composed of two terms, a term which provides the rate of evaporation under diffusion-only conditions, and a term which provides the influence of convection. This second term suggests the manner in which the processes of diffusion and convection are coupled. Both processes are dependent on the distribution of the vapor, through the molar concentration gradient for diffusion and through the mass density gradient for convection. The term representing the influence of convection is approximately inversely proportional to the square root of diffusivity, indicating the tendency of diffusive transport to reduce convection by making the vapor distribution more uniform. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D16.00003: Understanding thermal Marangoni flow in water sessile evaporating drops via 3D-PTV Massimiliano Rossi, Alvaro Marin, Christian J. Kaehler Understanding the flow inside sessile evaporating drops is of great interest both from a fundamental and technological point of view. Despite strong research efforts in the recent years, a complete picture on the phenomena involved in this process and a way to control them is still far to be reached. This is due to a lack of reliable experimental data on the internal flow but more dramatically on the interfacial flow. A relevant open debate concerns the role played by the Marangoni flow induced by thermal gradients. We recently show how 3D particle tracking techniques are suitable to measure the internal flow of drops and to derive quantities such as surface shear and surface tension differences (Marin et al., Soft Matter, 2016). Such experiments also indicated an increase of the thermal Marangoni flow as the droplet becomes thinner, in disagreement with current theoretical models and simulations. A possible reason for that could be a discrepancy of the imposed boundary conditions in the simulations and the experimental ones. This work follows up these observations with fully 3D time-resolved measurements of the flow inside drops evaporating on a quartz substrate, which temperature is controlled using a feedback temperature control and a microscope incubator system. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D16.00004: Experimental investigation of interfacial phenomena in evaporating sessile droplets for evaporative cooling applications Brendan MacDonald, Md. Almostasim Mahmud Evaporation of sessile droplets has applications in many fields, including evaporative cooling technology. An example from nature is human perspiration. Evaporative cooling applications typically operate at atmospheric pressure and 20 to 80$^{\circ}$C, and systems that mimic perspiration require droplets that are continuously fed fluid. A number of studies have investigated phenomena associated with evaporating sessile droplets including (1) interfacial energy transport, (2) distribution of the evaporation flux along the interface, and (3) temperature discontinuities at the liquid-vapor interface; however, many of these studies were not undertaken in the regime relevant to evaporative cooling and used low pressures and temperatures or droplets that were not continuously fed fluid and changed shape as they were depleted. We will present the results from our experimental study, which examined these phenomena in the regime relevant to evaporative cooling to determine if they are present and if they have an impact on the evaporation behavior. In this regime we found that conduction provided a majority of the energy required for evaporation, the local evaporation flux changed depending on thermocapillary convection, and interfacial temperature discontinuities were present. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D16.00005: Sharp Interface Level Set Method based Study for Evaporation of a Sessile Droplet on Hydrophilic and Hydrophobic Substrates. Javed Shaikh, Atul Sharma, Rajneesh Bhardwaj The evaporation of a sessile droplet is important in many applications like hot-spot cooling, surface patterning etc. An understanding of the droplet dynamics in terms of evaporation rate, evaporative cooling and substrate wettability is important for designing the droplet based devices. Extensive theoretical and experimental research has been conducted on evaporating droplets in recent years; however, the effect of surrounding vapors on the evaporation dynamics of a sessile droplet is not found in the literature. In this work, an in-house sharp-interface level set code based on the Ghost Fluid Method (GFM) is used. Energy, species, and momentum equations are coupled for studying the sessile droplet evaporation phenomenon on hydrophilic and hydrophobic substrates. Different modes of droplet evaporation i.e. constant contact radius (CCR), constant contact angle (CCA) are observed for the two types of substrates. The coupling of energy and species equations is used for capturing the evaporating cooling induced dip in the droplet surface temperature. The effect of surrounding vapors like fluorocarbon vapors, on the evaporative cooling, is presented for water droplet on the hydrophilic and hydrophobic substrates. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D16.00006: Geometrically-controlled drop evaporation: Dynamics and universal scaling law Khellil Sefiane, Pedro Saenz, Alexander Wray, Zhizhao Che, Omar Matar, Prashant Valluri, Jungho Kim The evaporation of a liquid drop on a solid substrate is a remarkably common phenomenon. Yet, the complexity of the underlying mechanisms has constrained previous studies to spherically-symmetric configurations. Here we present an investigation of well-defined, non-spherical evaporating drops of pure liquids and binary mixtures. We deduce a new universal scaling law for the evaporation rate valid for any shape and demonstrate that more curved regions lead to preferential localized depositions in particle-laden drops. Furthermore, geometry induces well-defined flow structures within the drop that change according to the driving mechanism and spatially-dependent thresholds for thermocapillary instabilities. In the case of binary mixtures, geometry dictates the spatial segregation of the more volatile component as it is depleted. In the light of our results, we believe that the drop geometry can be exploited to facilitate precise local control over the particle deposition and evaporative dynamics of pure drops and the mixing characteristics of multicomponent drops. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D16.00007: Influence of relative humidity and ambient temperature on hydrothermal waves (HTWs) of organic solvent volatile droplets Daniel Orejon, Yutaku Kita, Yuya Okauchi, Yuki Fukatani, Masamichi Kohno, Yasuyuki Takata, Khellil Sefiane, Jungho Kim Droplets of organic solvents undergoing evaporation have been found to display distinctive hydrothermal patterns or HTWs at the liquid-vapor interface. Since the evaporation of mentioned organic solvents in ambient conditions is ubiquitous, in this work we investigate the effect of ambient temperature and relative humidity on the self-generated HTWs by means of infrared thermography. The intensity of the HTWs was found to decrease when lowering the ambient temperature due to a reduction in droplet evaporative cooling. On other hand, the enhancement or suppression of the HTWs was also possible by controlling the relative humidity of the system. Absorption and/or condensation of water vapor onto the evaporating droplet was found to be the main cause for the differences observed on the HTWs retrieved at the liquid-vapor interface. To account for the water adsorbed or condensed we perform in-situ gas chromatography analysis at different droplet lifetimes. Experimental results showed an increase in the amount of water condensed when increasing the relative humidity of the system as expected. In addition, for the same ambient temperature ethanol evaporation was enhanced by high relative humidity. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D16.00008: Evaporation-triggered microdroplet nucleation and the four life phases of an evaporating Ouzo drop Huanshu Tan, Christian Diddens, Pengyu Lv, J. G. M. Kuerten, Xuehua Zhang, Detlef Lohse Evaporating liquid droplets are omnipresent in nature and technology, such as in inkjet printing, coating, deposition of materials, medical diagnostics, agriculture, the food industry, cosmetics, or spills of liquids. Here we show that the evaporation of such ternary mixtures can trigger a phase transition and the nucleation of microdroplets of one of the components of the mixture. As a model system, we pick a sessile Ouzo droplet (as known from daily life) and reveal and theoretically explain its four life phases: In phase I, the spherical cap-shaped droplet remains transparent while the more volatile ethanol is evaporating, preferentially at the rim of the drop because of the singularity there. This leads to a local ethanol concentration reduction and correspondingly to oil droplet nucleation there. This is the beginning of phase II, in which oil microdroplets quickly nucleate in the whole drop, leading to its milky color that typifies the so-called “Ouzo effect.” Once all ethanol has evaporated, the drop, which now has a characteristic nonspherical cap shape, has become clear again, with a water drop sitting on an oil ring (phase III), finalizing the phase inversion. Finally, in phase IV, all water has evaporated, leaving behind a tiny spherical cap-shaped oil drop. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D16.00009: A study of the evaporation of heterogeneous water droplets under active heating Maxim Piskunov, Jean Claude Legros, Pavel Strizhak Using high-speed video registration tools with a sample rate of 10$^{\mathrm{2}}$--10$^{\mathrm{4}}$ frames per second (fps), we studied the patterns in the evaporation of water droplets containing 1 and 2 mm individual metallic inclusions in a high-temperature gas environment. The materials of choice for the inclusions were steels (AISI 1080 carbon steel and AISI type 316L stainless steel) and pure nickel. We established the lifetimes $\tau_{\mathrm{h}}$ of the liquid droplets under study with a controlled increase in the gas environment temperature up to 900 K. We also considered the physical aspects behind the $\tau_{\mathrm{h\thinspace }}$distribution in the experiments conducted and specified the conditions for more effective cooling of metallic inclusions. Following the experimental research findings, a method was devised for effective reactor vessel cooling to avoid a meltdown at a nuclear power plant. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D16.00010: Fluid dynamics and deposit patterns in evaporating sessile drop containing microparticles: substrate heating and wettability effects. Nagesh D. Patil, Rajneesh Bhardwaj, Atul Sharma The evaporation of sessile water drops containing colloidal microparticles is investigated on non-heated and heated hydrophilic and hydrophobic substrates. Time-varying drop shapes and temperatures of liquid-gas interface are recorded using high-speed and infrared camera, respectively. In heated case, infrared-thermography shows larger temperature gradient across the liquid-gas interface and recorded motion of the particles confirm Marangoni flow from the contact line to apex inside the drop. On non-heated hydrophilic substrates, a ring-like pattern forms, as reported extensively in the literature; while on heated hydrophilic substrates, a thin ring with an inner-deposit forms. On non-heated hydrophobic substrates, the contact line depins to form inner-deposit without ring; while on heated hydrophobic substrates, the contact line pins to form inner-deposit with thin ring. This pinning transition occurs due to the particles self-pinning in a stagnation region developed by the Marangoni flow near the contact line. This work gives fundamental insights on the thermal and wettability effects on internal fluid dynamics of the evaporating sessile drop and associated deposit shape, with applications in ink-jet printing and biosensors. [Preview Abstract] |
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