Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session T12: Drops: Heat Transfer, Evaporation and Buoyancy Effects II & Multiple Drop Interactions |
Hide Abstracts |
Chair: Andrew Dickerson, University of Tennessee Room: North 126 ABC |
Tuesday, November 23, 2021 12:40PM - 12:53PM |
T12.00001: Ultrasonically-Enhanced Condensation Heat Transfer using Droplet Ejection Thomas R Boziuk, Marc K Smith, Ari Glezer Ultrasonic actuation of the liquid-vapor interface between co-flowing layers of vapor and slow-moving sub-cooled liquid which exploits the difference in acoustic impedance to form a multi-scale train of droplets ejected into the vapor flow is investigated experimentally. The increased interfacial surface area of the ejected droplets results in increased heat transfer between the vapor and the liquid and a significant increase in vapor condensation rate. A two-stream liquid-vapor experimental setup was designed to assess the effects of the acoustic actuation on the formation and ejection of the subcooled liquid droplets and the enhanced condensation over a range of flow rates and liquid subcooling. The present measurements yield the increases in the sensible heat of the liquid stream and the increased rate of mass transfer from the vapor to liquid stream. Comparisons of temperature distributions in the absence and presence of actuation are used to assess the enhanced heat transfer between the vapor and liquid phase at both steady-state and transient conditions and indicate applications to tube heat exchangers. |
Tuesday, November 23, 2021 12:53PM - 1:06PM |
T12.00002: Low Weber number droplet impact on heated hydrophobic surfaces Junhui Li, Patricia B Weisensee Using synchronized high-speed optical and infrared (IR) imaging, we correlate droplet dynamics during low-We impact on heated hydrophobic surfaces to the spatial distribution of the solid-liquid interfacial temperature, heat flux, and the total heat transfer to the droplet. Denoting the droplet diameter and impact velocity as D and v, respectively, based on scaling arguments we find that the total transferred heat Q scales as D1.25v, which is validated experimentally. A unique feature of low-We droplet impact on non-wetting surfaces is the formation of a sub-millimetric entrapped bubble that forms during receding. The substrate temperature underneath the bubble is significantly higher than for the surrounding droplet due to the low thermal conductivity of air. The local heat flux at the inner droplet-bubble contact line becomes increasingly important as the droplet recedes. Nonetheless, the overall heat transfer is reduced by 5.6% and 7.1% at surface temperatures of 50°C and 65°C, respectively, as the bubble reduces the liquid-solid interface area. On a rough hydrophobic surface, the average heat flux is lower compared to the smooth surface, indicating a larger interfacial thermal resistance on the rough surface. |
Tuesday, November 23, 2021 1:06PM - 1:19PM |
T12.00003: Freezing splashes Christophe F Josserand, Rodolphe Grivet, Thomas Seon, Axel Huerre The splashing of impacting drops is a key feature of multiphase flows with important applications from combustion to printing, or disease spreading for instance. |
Tuesday, November 23, 2021 1:19PM - 1:32PM |
T12.00004: Anisotropic Heat Transfer Induced by Microscale Hydrodynamics of a Single Droplet under Shear Yanxing Wang, Dominick Nevares, Fangjun Shu The heat transfer characteristics of a single droplet in a simple shear flow have been numerically studied over a wide range of parameters. The heat transfer in the vertical and lateral directions, and heat exchange between the carrier flow and the droplet have been considered. In the presence of surface tension, the interaction between the carrier flow and the droplet generates a microscale recirculating flow inside the droplet, which drives the surrounding fluid to recirculate through viscous effect. The recirculating flows demonstrate obvious three-dimensional features, and causes anisotropic heat transfer enhancement through advection. The enhancement is stronger at larger Peclet numbers. The droplet behaviors are governed by two nondimensional parameters, the capillary number and viscosity ratio. Below a critical capillary number, which depends on viscosity ratio, the droplet extends in the streamwise direction at a certain inclination angle. Above the critical capillary number, the droplet breaks up into several smaller droplets. When viscosity ratio is greater than a critical value, the droplet tumbles until an elliptical shape is obtained. The droplet motility and deformation make the heat transfer characteristics more complicated. The effect of each of the known parameters (including Reynolds, capillary, and Prandtl numbers) on the heat transfer processes has been examined. This research offers promising potential for the accurate control of the heat and mass transfer in emulsions. |
Tuesday, November 23, 2021 1:32PM - 1:45PM Not Participating |
T12.00005: Wetting Behaviors of Liquid Nitrogen on Micro-textured Surfaces at Ultra-Low Temperatures Nischal Maharjan, Meng Shi, Himanshu Mishra Liquid Nitrogen (LN2) is used for facilitating heat transfer in numerous precision equipment, such as cryopumps, superconducting magnets, and cryosurgical guns. Due to the ultralow boiling point of LN2 (77 K at 1 atm), as it comes into contact with surfaces at normal temperature and pressure (NTP – 293 K and 1 atm), a vapor cushion is formed underneath and the drops start levitating. This is the well-known Leidenfrost phenomenon. Due to the complex heat transfer and phase change associated with this process, the present understanding of wetting of LN2 on structural surfaces remains unsatisfactory. In response, we have investigated the fate of LN2 drops placed on the following precisely temperature-controlled silica surfaces: smooth silica, surfaces with mushroom-shaped doubly reentrant pillars (DRPs), and those with cylindrical pillars. Specifically, we measured the lifetimes of LN2 drops on these surfaces as a function of ultralow temperatures. This allowed us to find out how/when LN2 transitions from a wetting liquid to the Leidenfrost state. We will also shed light on the effects of the surface wettability, liquid surface tension, and the interfacial heat transfer on the fate of LN2 drops. These findings should prove to be helpful in the rational design of LN2 applications. |
Tuesday, November 23, 2021 1:45PM - 1:58PM |
T12.00006: Characteristics and dynamics of levitating millimetre-sized drops on surfaces maintained above the Leidenfrost temperature Mohamed Maher, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Damir Juric, Omar K Matar Evaporation of liquids plays a decisive role in many engineering and industrial applications, such as spray cooling, microfluidics, and coatings. Particularly when a liquid drop is dispensed over a surface above the Leidenfrost temperature TLF, it exhibits a vigorous phase-change behaviour coupled with deteriorating heat transfer from the surface to the drop due to the formation of a thin-isolating vapour layer. We present a numerical study of the evaporation of a millimetric drop surrounded by dry air at a temperature above TLF. The dynamics and characteristics of the Leidenfrost drop and the interfacial heat transfer are investigated under various flow and thermal properties. A high-fidelity solver is used for a fully-resolved direct numerical simulation, employing the Level Contour Reconstruction Method to accurately capture the highly deforming liquid-gas interface. The model's capability for simulating evaporation is validated against several classical evaporation models, including the Stefan-Maxwell model. |
Tuesday, November 23, 2021 1:58PM - 2:11PM |
T12.00007: Numerical modeling of interfacial two-phase flows with phase change Bradley Boyd, Yue Ling We developed a numerical model to simulate two-phase flow with phase change at the interface. The sharp liquid-gas interface is tracked using the geometric Volume-of-Fluid (VOF) method. The bulk fluids are considered to be viscous, conducting, and incompressible with significant surface tension at the interface. The model is developed based on the open-source Basilisk framework, using adaptive-mesh refinement (AMR) to fully resolve the region near the interface. The model is validated using the 1D Stefan problem and 1D sucking problem. The validated approach is then used to simulate an evaporating droplet falling in a high-temperature environment. |
Tuesday, November 23, 2021 2:11PM - 2:24PM |
T12.00008: Linear stability of thermocapillary convection in non-volatile sessile droplets on a heated substrate Lukas Babor, Hendrik C Kuhlmann The linear stability of the incompressible steady axisymmetric thermocapillary flow in spherical sessile droplets is calculated numerically. The governing equations are discretized on Taylor-Hood finite elements using FEniCS. A combination of Newton's law of cooling and radiative heat transfer is imposed on the free surface. We compute the dependence of the critical Marangoni number on the contact angle for a range of Prandtl and convective and radiative Biot numbers. As the contact angle is increased from small values the basic flow is destabilized and the critical Marangoni number reaches a minimum. The minimum is followed by a very strong stabilization which is associated with a frequent change of the critical mode and a partial re-stabilization when the neutral curves turn backward. We find a range of intermediate contact angles where the basic flow is stable up to high Marangoni numbers. When the contact angle is increased even further, the basic flow is destabilized again. |
Tuesday, November 23, 2021 2:24PM - 2:37PM |
T12.00009: Twin drop impact on a deep liquid Andrew Dickerson, Madison Artman-Breitung, Daren A Watson We take the enduring topic of drop impact on a deep pool of similar liquid a step further by allowing twin drops to impact simultaneously. Impacts are sufficiently proximal that impact crown and craters interact, distorting craters, merging craters, and creating previously undocumented super-surface interactions. The unique features of twin impacts occur when crowns collide to create a central veil that bifurcates the two cavities and the expulsion of jet-like features atop colliding crowns. The emergence of a plethora of splash features is dependent on Froude number (Fr=30-200) and drop separation distance. We analyze crater evolution using theory developed for singular drops. Crater and jet energies are compared for various impact velocities and drop separation distances. We find that craters close enough to merge produce thicker, but not higher, rebound jets. |
Tuesday, November 23, 2021 2:37PM - 2:50PM |
T12.00010: Bifurcations in droplet collisions Anshuman Dubey, Bernhard Mehlig Collision rates of droplets in straining and vortical flows exhibit closed trajectories which start and end on the collision spheres. These closed trajectories reduce collision rates by reducing the collision sphere area at which trajectories approaching from large separations can collide. Further, neutral droplet dynamics in the presence of flow gradients, and charged droplet dynamics in a quiescent flow exhibit trajectories where the large droplet overtakes the smaller one before collision. Yet, the mechanisms describing the appearance of such closed trajectories and overtaking trajectories are not understood. We use dynamical systems theory to explain that closed trajectories appear due to the presence of fixed points in the relative droplet dynamics. Finally, we explain the appearance of overtaking trajectories using bifurcation theory. |
Tuesday, November 23, 2021 2:50PM - 3:03PM |
T12.00011: Drops within drops within drops Monika Nitsche We consider a nested set of viscous drops in Stokes flow. We derive the system of equations governing the motion of the drops and of the fluid within them. We then present numerical simulations on the evolution of (a) a set of n initially concentric drops in a strainfield and (b) double drops moving through a constriction. Of interest in particular is the effect of the fluid viscosities on the internal strain rates and on the breaking of constrained drops. |
Tuesday, November 23, 2021 3:03PM - 3:16PM |
T12.00012: Spontaneous drop interactions on swellable fibres Pierre Van de Velde, Julien Dervaux, Suzie Protière, Camille Duprat Swelling of individual fibers when exposed to a favourable solvent is very common for most natural fibrous materials. In this study, we analyze experimentally the absorption dynamics of two drops placed on a swellable fiber. We observe that for some configurations, a local oversaturation of the polymer may occur between the two drops, causing some solvent to escape the elastomeric network leading to the creation of a new drop at the fiber surface that may coalesce with the two initial drops. We rationalize these observations using a linear poroelastic model that can quantitatively predict the absorption dynamics of the drops and the configurations for which fluid escaping the fibre (deswelling) may be observed.
|
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700