Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A21: Drops: Temperature and Marangoni Effects I |
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Chair: Shayandev Sinha, Harvard University Room: 603 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A21.00001: Freezing-damped drop impacts Virgile Thievenaz, Thomas Seon, Christophe Josserand We experimentally investigate the effect of freezing on the spreading of a water drop. Whenever such a drop impacts a cold surface – whose temperature is lower than 0 °C – a thin layer of ice freezes during the spreading. This freezing has a notable effect on the impact: at given Reynolds and Weber numbers, we show that lowering the surface temperature reduces the drop's maximal extent, together with the spreading duration. Using an analogy between this ice layer and the viscous boundary layer which also grows during the spreading, we are able to model the effect of freezing as an effective viscosity. The scaling laws designed for viscous drop impact can therefore be applied to such a solidification problem, avoiding the recourse to a full and complex modelling of the thermal dynamics. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A21.00002: Dynamics and temperature evolution during droplet impacts on cold surface Feng Wang, Man Hu, Daosheng Deng Droplet impacting on cold surface is significant for many practical situations in our daily life, such as anti-icing on wind turbines, aircraft and power transmission lines. By using high speed camera and thermal camera, here we report the dynamics and temperature evolution during water droplet impacts and freezes on cold metal surface. In the impact process, the maximum spread radius is found to have a 1/3 power law with the initial height, which is different from the impacting behavior at the room temperature. In the retraction process, three different morphology are indentified when changing the initial height from low to high, which is puddle, transition state and pancake. In the freezing process, the ice-water boundary and the zero degree isotherm are extracted from the high speed videos and thermal profiles. The ice-water boundary retraction speed is found to be slower than the zero degree isotherm, which indicates the subcooling freezing process. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A21.00003: Arrested dynamics of droplets impacting icy surfaces Farzad Ahmadi, Andrew Fugaro, Saurabh Nath, Hyunggon Park, Jonathan Boreyko We study the competition between the spreading and freezing dynamics of droplets impacting icy surfaces. Experiments were conducted on two different frosted surface configurations: planar or suspended cable. The dynamics of droplet impact were captured using a side-view high-speed camera, where the droplet was initially either at room temperature or close to the freezing temperature. For droplets spreading on the planar substrate, the advancing contact line was arrested significantly faster with decreasing surface temperature or initial droplet temperature. Droplets impacting the icy cable either detached and fell from the cable or were captured and frozen, depending upon the Weber number, surface temperature, droplet temperature, and the ratio of the droplet and cable diameters. A scaling model elucidated that the extent of droplet spreading is a balance between capillary-inertial effects and the specific cooling of the droplet toward its freezing temperature. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A21.00004: Coalescence dynamics of a droplet on a heated pool Pankaj Kolhe, Pavan Kumar Kirar, Kathryn Alvarenga, Kirti Sahu We experimentally investigated the coalescence dynamics of an ethanol drop in ethanol pool maintained at a higher temperature than the drop. The size of the impacting drop and the temperature difference between the pool and the drop are varied and their effect on the secondary droplet formation has been studied. It is observed that increasing the temperature of the liquid pool, has a non-monotonic effect on the partial coalescence phenomenon. Increasing the droplet size increases the size of the secondary drop for all values of the temperature differences considered in the present study. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A21.00005: Evaporation of ethanol-water sessile droplet of different compositions at an elevated substrate temperature Saravanan Balusamy, Sayak Banerjee, Pradeep Gurrala, Pallavi Katre, Kirti Sahu We experimentally investigate the evaporation dynamics of sessile droplets with different compositions of ethanol-water binary mixture at different substrate temperatures. At elevated substrate temperature, we observed an early spreading stage, an intermediate pinned stage and a late receding stage of evaporation. Increasing the substrate temperature decreases the lifetime of binary droplets rapidly. We found that the lifetime of the droplet exhibits a non-monotonic trend with the increase in ethanol concentration in the binary mixture, which can be attributed to the non-ideal behaviour of water-ethanol binary mixtures. Interestingly, the evaporation dynamics for different compositions at high substrate temperature exhibits a self-similar trend showing a constant normalised volumetric evaporation rate for the entire evaporation process. This indicates that the evaporation dynamics of a binary droplet of a given composition at high substrate temperature is equivalent to that of another pure fluid with a higher volatility at room temperature. The evaporation rates of pure and binary droplets at different substrate temperatures are compared against a theoretical model developed for pure and binary mixture droplets. The model predictions are found to be quite satisfactory. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A21.00006: Evaporation of ethanol-water sessile droplet on an inclined substrate at an elevated temperature Sayak Banerjee, Saravanan Balusamy, Pallavi Katre, Pradeep Gurrala, Kirti Sahu We experimentally investigated the evaporation dynamics of water-ethanol binary droplets of various molar compositions on an inclined heated substrate. The substrate temperature and inclination angle are varied and the droplet behaviour are observed using a combined optical and thermal imaging techniques in a custom-made goniometer-IR camera set-up. The triple line behaviour, the contact angle and the wetting diameter evolution of the droplet, as well as thermo-solutal Marangoni wave dynamics are studied. Theoretical modelling of evaporation rates for binary-droplets on heated inclined substrates has been performed and compared against the experimental results. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A21.00007: Residues formation on surface of heated wire after drop impact: correlation between solution drop impact dynamics and residues thickness Kyeongmin Kim, Sang Jun Lee, Wonjoon Choi Impact between solid structures and solutions essentially leaves residues on surfaces, such as calcite in water. While the impacting angle and velocity of the solution affect the formation of the residues, the temperature regime of the solid surface is another significant factor because it intrinsically manipulates the contact interfaces between liquids and solids, as well as the solubility. Herein, we report a systematic study of the residual nanomaterials after a drop impact containing carbon nanotubes (CNTs) on a heated metal wire in various temperature range. While a drop casting method for the individual droplet comprising CNTs induces the impact with 2-mm nichrome wires in diameter, a joule-heating method controls the wire temperature in 25-400 ºC. The phase diagram in terms of the impact velocity, wire temperature, and formation of the residues are quantitatively investigated to elucidate the correlation between the solution drop impact dynamics and the resulting CNT residue thicknesses. The fundamental understanding of the residual nanomaterials, induced by the impact between solid structures and solutions in wide temperature ranges would provide the insight for a robust design of broad engineering systems such as heat exchangers, solar power modules, and turbines. [Preview Abstract] |
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