Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A19: Convection and Buoyancy-Driven Flows: Phase Changes |
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Chair: Eduardo Ramos, Universidad Nacional Autonoma de Mexico Room: 2006 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A19.00001: Solidification and natural convection in a Hele-Shaw cell Eduardo Ramos, Guillermo Ramirez, Jonathan Cisneros, Guillermo Hernandez-Cruz Water solidification in presence of natural convection has been experimentally observed in a Hele-Shaw cell. Initially, the cell is filled with liquid water, and the upper and lower horizontal walls are kept at -10 $^{\circ}$C and 25 $^{\circ}$C respectively. The water starts to solidify near the upper wall and a solidification front advances downwards. The unstable temperature gradient triggers natural convection in the liquid filled region of the cell (where thermal and geometrical conditions lead a Rayleigh number larger tan critical). As the solidification front moves and its distance to the lower wall reduces, the Rayleigh number diminishes below the critical value and natural convection stops. The motion of the front and the natural convection motion are recorded with a video camera and measured with image processing and PIV respectively. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A19.00002: Rotating ice blocks Stephane Dorbolo, Nicolas Adami The motion of ice discs released at the surface of a thermalized bath was investigated. As observed in some rare events in the Nature, the discs start spinning spontaneously. The motor of this motion is the cooling of the water close to the ice disc. As the density of water is maximum at 4$^{\circ}$C, a downwards flow is generated from the surface of the ice block to the bottom. This flow generates the rotation of the disc. The speed of rotation depends on the mass of the ice disc and on the temperature of the bath. A model has been constructed to study the influence of the temperature of the bath. Finally, ice discs were put on a metallic plate. Again, a spontaneous rotation was observed. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A19.00003: The convective dynamics of a suspension of ice crystals David Rees Jones, Andrew Wells The formation of solid crystals from a liquid cooled beneath its freezing temperature occurs in a wide range of environmental and industrial situations, such as in the formation of so-called ``frazil ice'' in rivers and the polar oceans. Eddies in the fluid flow act to keep the crystals suspended, while the relative buoyancy of the crystals causes them to rise, eventually sedimenting to form a layer of ice, called grease ice in the oceans. Here, we consider the interaction between the fluid dynamics of a suspension of crystals and the thermodynamics of phase change governing the growth and melting of the crystals. The crystals grow when the local temperature lies below the freezing temperature and melt when it lies above. We explore simplified scenarios that illustrate the important features of this multiphase flow and the effect of this ``active suspension'' on heat transfer. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A19.00004: Influence of phase changes on Rayleigh-Benard convection Michael Adler, Kelken Chang, Raymond Shaw How does a condensing trace species influence the convection of an inert carrier gas? The question is relevant to cloud formation at typical atmospheric conditions. We simulate Rayleigh-Benard convection in a cylindrical geometry over a range of Rayleigh numbers for which the flow remains laminar. The top and bottom boundaries are fixed at the equilibrium vapor pressure of the condensable species. The buoyancy is influenced by temperature, vapor, and condensate concentrations. The temperature and vapor fields combine via the Clausius-Clapeyron equation to yield a spatially complex supersaturation field; this, in turn, drives condensation. The temperature field is coupled to the condensation process through latent heating. The resulting volume heat source affects the convection and leads to a height dependent Nusselt number. For fixed Rayleigh number, increasing the temperature difference alters the buoyancy and Nusselt number height profiles. An analytical model for the latent heating profile for the purely diffusive case is shown to predict the correct magnitude of heating. This study sets the stage for experiments that will be carried out in the Michigan Tech Pi-Chamber, an aspect ratio 2 chamber with volume 3.14 m$^3$ and controlled temperature and water vapor boundaries. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A19.00005: Natural convection during a phase change of sodium acetate trihydrate Yasunori Ouchi, Satoshi Someya, Tetsuo Munakata A latent heat storage system has higher storage capacity than a sensible heat storage system. Sodium acetate trihydrate has large latent heat at the temperature, 58$^{\circ}$C, suitable for a hot-water supply system. The present study focused on convection in a phase change process to understand the heat transfer from the phase change material(PCM). The convection occurred only in certain conditions of supercooling temperature and PCM concentration. A spicular crystal grew quickly and the thermal convection couldn't be detected at large supercooling temperature with high concentration of PCM. In the range of 5 $\sim$ 13$^{\circ}$C of supercooling temperature, the buoyancy driven convection due to the latent heat of PCM was measured using the PIV. It was also observed that a part of CH$_{3}$COONa-3H$_{2}$O solution was sucked into the growing spicular crystals to supply CH$_{3}$COONa at the condition with small concentration and at 5 $\sim$ 13$^{\circ}$C of supercooling temperature. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A19.00006: Investigation of Thermal Stratification by Direct Contact Condensation in a Suppression Pool Koji Okamoto, Daehun Song, Nejdet Erkan Thermal stratification in the suppression pool of Boiling Water Reactor were investigated using simple slab-type experimental facilities. The steam direct condensation causes the vibration of bubble interface, resulting in the mixing enhancement at the nozzle. Using the bubble motion model, the Richardson number had been estimated which is a ratio of buoyancy to interface fluctuation momentum. The thermal stratification occurrence had been strong relation to the Richardson number. The flow pattern inside the chamber had also affected by the Richardson number. The flow pattern were measured by PIV. The velocity distribution were compared with the numerical simulation, showing the good agreement. In small Ri, i.e., lower fluctuation condition, the thermal stratification does occur. Thus, the momentum caused by the direct condensation determined the occurrence of the thermal stratification. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A19.00007: Growth of mushy layers with temperature modulations Guang-Yu Ding, Chao Wu, Jin-Qiang Zhong Directional solidification of aqueous solutions produces a solid-melt coexisting zone whose growth rate can be predicted by the mushy-layer theory. We present measurements of mushy-layer growth when solidifying aqueous ammonium chloride with the cooling temperature modulated periodically $T_B(t)=T_0+Acos({\omega}t)$. The mush-liquid interface $h(t)$ evolves as the square root of time for a constant $T_B$, but exhibits periodical humps in the present of modulations. The growth rate $\dot{h}(t)$ is best approximate to $\dot{h}(t)={\dot{h}_0}e^{-{\gamma}{\omega}t/2{\pi}}cos({\omega}t+\pi+{\phi}(t))$, with a decay rate $\gamma=0.82{\pm}0.05$ independent on the modulation amplitude $A$ and frequency $\omega$, and a phase-shift ${\phi}(t)$ increasingly lag behind $T_B$ as a function of time. We discuss a mushy-layer growth model based on the Neumann solution of the Stefan problem with periodical boundary conditions, and show that the numerical results are in agreement with the experimental observations. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A19.00008: Convective instabilities in a ternary alloy mushy layer Daniel Anderson, Peter Guba We investigate a mathematical model of convection, thermal and solutal diffusion in a primary mushy layer during the solidification of a ternary alloy. In particular, we explore the influence of phase-change effects, such as solute rejection, latent heat and background solidification, in a linear stability analysis of a non-convecting base state solution. We identify how different rates of diffusion (e.g.~double diffusion) as well as how different rates of solute rejection (double solute rejection) play a role in this system. Novel modes of instability that can be present under statically stable conditions are identified. Parcel arguments are proposed to explain the physical mechanisms that give rise to the instabilities. [Preview Abstract] |
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