Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session S24: Convection and Buoyancy Driven Flows III |
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Chair: Bakhtier Farouk, Drexel University Room: 327 |
Tuesday, November 22, 2011 3:05PM - 3:18PM |
S24.00001: Simulation of a submarine hydrothermal convection using a numerical model for a supercritical water flow Satoko Komurasaki Hydrothermal convective flows derive from geothermally heated water issued from hydrothermal vents. They are found even in deep oceans of depth over 2,000 meters where the hydrostatic pressure of water is over 200 atmospheres, and temperature of heated water is occasionally more than 300$^{\circ}$C. Under these conditions, water emerging from these vents can be supercritical. In reality, it is quickly cooled by ambient water of temperature approximately 2$^{\circ}$C and becomes liquid. It is also important to investigate of advection and diffusion of materials which are issued from hydrothermal vents accompanying heated water, in order to deepen understanding of the oceanic crust that possesses abundant resources. A flow simulation is carried out using a numerical model for a supercritical water flow where it is assumed that the pressure is high and almost constant, and the density changes only by temperature. In the computation, the modified compressible Navier-Stokes equations are solved by a method similar to an approach used in solving the incompressible equations. Computation is done employing finite difference method in 2D. Simulated flow fields are displayed using a suitable visualization technique and compared with the results of simulations based on the Boussinesq approximation. [Preview Abstract] |
Tuesday, November 22, 2011 3:18PM - 3:31PM |
S24.00002: Convective Thermal Transport in Near-Critical Fluids Nusair Hasan, Bakhtier Farouk Convective thermal transport in a pure fluid (carbon dioxide) near its gas-liquid critical point is investigated using a two-dimensional numerical model. A square enclosure is considered with bottom heating. The model considers the strong variable property effects (functions of both temperature and pressure) near the critical point, including the bulk viscosity variations. Although thermal diffusivity approaches zero near the critical point, the divergence of thermo-physical properties near the critical point gives rise to large Grashof-number flows even for very small temperature differences. The convective heat transfer coefficient near the critical point is investigated and a correlation for the Nusselt number is developed as a function of the Rayleigh number and the ratio ($p_m T_m /p_{cr} T_{cr}$) where the subscripts ``m'' and ``cr'' denote the mean and critical values respectively. As the critically diverging bulk viscosity plays a significant role on the transport processes near the critical point, effect of bulk viscosity on the flow field and heat transport induced by buoyancy in near-critical fluids is also investigated. [Preview Abstract] |
Tuesday, November 22, 2011 3:31PM - 3:44PM |
S24.00003: Thermal-hydraulic behavior of Sc-C02 in a horizontal circular straight tube Katsuyoshi Tanimizu, Reza Sadr, Davesh Ranjan Fluids above critical pressure have been practically utilized for 60 years in many applications and their use and interest is still increasing in many areas, especially power generation industries and chemical industries. Above critical pressure, very rapid changes in thermophysical properties take place near the pseudocritical temperature. In this region, the fluid transforms from liquid-like to gas-like behavior when the fluid temperature rises up and passes through the pseudocritical temperature. This allows enormous potential for energy transfer, but also alters the turbulent flow due to changes in the turbulent shear stress brought about by acceleration and buoyancy effects. However, we have not fully understood their dynamic behaviors such as turbulence yet. A supercritical CO$_{2}$ testing loop has been built at Texas A{\&}M University at Qatar to perform heat transfer and pressure drop measurements and investigate the thermo-physical and dynamic characteristics of supercritical carbon dioxide flow. The results of heat transfer measurements in a super critical fluid conducted in a horizontal pipe are reported and discussed here. [Preview Abstract] |
Tuesday, November 22, 2011 3:44PM - 3:57PM |
S24.00004: Finite-sample-width effects on chimney formation in mushy-layer convection Andrew Wells, Jin-Qiang Zhong, Anthony Fragoso, John Wettlaufer The rapid solidification of a binary alloy leads to the formation of a chemically reactive porous medium, or mushy layer, within which convection and dissolution can generate \textit{chimneys}: drainage channels devoid of solid. We combine experiment with numerical simulation to explore the influence of a finite system size on the dynamics and stability of the convective flow. For a variety of steady growth rates and cell widths, we determine conditions for chimney formation during experimental solidification of aqueous ammonium chloride in a Hele-Shaw cell. The results are compared to a two-dimensional numerical model of mushy-layer convection, providing insight into the prediction of defect formation in industrial casting processes. [Preview Abstract] |
Tuesday, November 22, 2011 3:57PM - 4:10PM |
S24.00005: A simple one-dimensional model of brine fluxes from sea-ice Grae Worster, David Rees Jones Over the winter growth season, brine within the interstices of sea-ice drains into the ocean owing predominantly to convection within the lower parts of the ice, a small-scale process difficult to model on a regional scale. Traditionally, salt loss from sea-ice has been determined using a combination of historical data and an empirical segregation law applied at the ice-ocean interface. By contrast, we apply a simple relationship between the strength of internal, small-scale convection and a mush Rayleigh number to develop a predictive, one-dimensional model of sea ice, applicable on a regional scale. This model solves the full mushy layer equations for heat and salt conservation within the ice, using a dynamically determined term for the convective transport of salt and heat. Numerical results from this model are presented, predicting the internal structure of the ice and also net salt and heat fluxes from the ice. Prospects for experimental validation and further possibilities for model development are discussed. [Preview Abstract] |
Tuesday, November 22, 2011 4:10PM - 4:23PM |
S24.00006: Fluxes through steady-state chimneys in binary alloy solidification David Rees Jones, Grae Worster Solute fluxes from mushy layers in solidifying binary alloys occur predominantly by convection through nearly vertical, straight-sided chimneys. We develop a simple, theoretical study using a patchwork of simplifying approximations that capture the essential physics while rendering the problem analytically tractable. Away from the chimney, the temperature field is horizontally uniform and vertically linear. Near the chimney, a similarity solution with linear vertical structure is found. The lubrication approximation to Stokes flow applies within the chimney itself, and the chimney is proved to be straight-sided. The melt is treated through a boundary-layer parameterization of the heat flux. A linear flux-Rayleigh number relationship is proved analytically in planar geometry, based on a criterion on chimney spacing that optimises the buoyancy flux. In three dimensions, the crucial importance of drainage area is demonstrated, and an approximately linear flux-Rayleigh number relationship is found. This constitutes a simple, physically motivated representation of solute flux, that might be used cheaply in global sea-ice models. [Preview Abstract] |
Tuesday, November 22, 2011 4:23PM - 4:36PM |
S24.00007: Mushy layer dynamics in micro and hyper gravity Joseph O'Rourke, A.J. Eldorado Riggs, Charlotte Guertler, Pearson Miller, Catherine Padhi, Madeline Popelka, Allison West, Jin-Qiang Zhong, John Wettlaufer We describe the results of experiments on mushy layers grown from aqueous ammonium chloride solution in normal, micro, and hyper gravity environments during parabolic flight.~In the fully developed chimney state, the chimney plume dynamics differ strikingly when conditions change from microgravity to hypergravity. In microgravity, we find fully arrested plume motion and suppressed varicosity. As gravity transcends Earth conditions, we observe a host of phenomena, ranging from arched plumes that undergo forced Rayleigh-Taylor instabilities to in-phase multiple plume oscillatory behavior. For the same initial solute concentrations and fixed chill temperatures, we find that, in runs of over 130 minutes, the averaged effects of hypergravity result in suppressed growth of the mushy layers, a phenomenon caused by a net enhancement of convective heat transport from the liquid to the mushy layers. These behaviors are placed in the context of the theory of convecting mushy layers as studied under normal laboratory conditions. [Preview Abstract] |
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