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Convection Cells (convection + cell)

Distribution by Scientific Domains

Engineering	33%

Selected Abstracts

A simulation of the hydrothermal response to the Chesapeake Bay bolide impact

GEOFLUIDS (ELECTRONIC), Issue 3 2005
W. E. SANFORD
Abstract Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10,16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10,15 m2) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10,14 m2) results in a system dominated by warm-water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine. [source]

Solute and Heat Transport Model of the Henry and Hilleke Laboratory Experiment

GROUND WATER, Issue 5 2010
Christian D. Langevin
SEAWAT is a coupled version of MODFLOW and MT3DMS designed to simulate variable-density ground water flow and solute transport. The most recent version of SEAWAT, called SEAWAT Version 4, includes new capabilities to represent simultaneous multispecies solute and heat transport. To test the new features in SEAWAT, the laboratory experiment of Henry and Hilleke (1972) was simulated. Henry and Hilleke used warm fresh water to recharge a large sand-filled glass tank. A cold salt water boundary was represented on one side. Adjustable heating pads were used to heat the bottom and left sides of the tank. In the laboratory experiment, Henry and Hilleke observed both salt water and fresh water flow systems separated by a narrow transition zone. After minor tuning of several input parameters with a parameter estimation program, results from the SEAWAT simulation show good agreement with the experiment. SEAWAT results suggest that heat loss to the room was more than expected by Henry and Hilleke, and that multiple thermal convection cells are the likely cause of the widened transition zone near the hot end of the tank. Other computer programs with similar capabilities may benefit from benchmark testing with the Henry and Hilleke laboratory experiment. [source]

Density-dependent surface water,groundwater interaction and nutrient discharge in the Swan,Canning Estuary

HYDROLOGICAL PROCESSES, Issue 13 2001
Anthony J. Smith
Abstract Salinity in the Swan,Canning Estuary, Western Australia, varies seasonally from freshwater conditions in winter up to the salinity of seawater in summer. Field observations show that the resulting seasonal density contrasts between the estuary and the adjacent fresh groundwater system are sufficient to drive mixed-convection cells that give rise to circulation of river water in the aquifer. In this study, we examine the role of steady density-driven convection as a mechanism that contributes to the exchange of dissolved nutrients, particularly ammonium, between the Swan,Canning Estuary and the local groundwater system. We present results from two-dimensional (section) and three-dimensional density-coupled flow and mass transport modelling, in comparison with Glover's abrupt-interface solution for saltwater intrusion. The modelling is focused on developing an understanding of the physical processes that influence the long-term or mean convective behaviour of groundwater beneath the estuary. It is shown that the convective stability depends fundamentally on the interplay between two factors: (1) the downward destabilizing buoyancy effect of density contrasts between the estuary and aquifer; and (2) the upward stabilizing influence of regional groundwater discharge. The structure of convection cells beneath the estuary and recirculation rates of estuary water within the groundwater system are shown to be related to a flow-modified Rayleigh number that depends critically on the aquifer anisotropy and estuary meander pattern. The recirculation of estuary water by these mechanisms is responsible for transport of high concentrations of ammonium, observed in pore fluids in the estuary bed sediments, into groundwater and its eventual return to the estuary. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Flow visualization and solute transport in evaporating droplets

AICHE JOURNAL, Issue 7 2010
Pallippadan Johny Jaijus
Abstract We have investigated the velocity field and associated particle transport in an evaporating water droplet using the tool of particle image velocimetry. Experiments were performed where single droplets containing polystyrene particles were exposed to evaporation. Our method applicable to droplets confined between two parallel surfaces differs from the conventional PIV techniques on the 3D droplets and removes many of the limitations associated with mapping of velocity field. To avoid refraction of light at the droplet surface we have studied the motion in a disc-shaped droplet which was prepared by confining the drop between two nonwetting surfaces and its base is pinned to a wetting surface. Experiments were carried out under the conditions where Marangoni flow creates convection cells and finally leading to deposition of particles toward the pinned edge. The contact angle, height of the droplet, velocity field, and the particle concentration inside the evaporating droplet was measured and its time evolution was recorded. © 2009 American Institute of Chemical Engineers AIChE J, 56: 1674,1683, 2010 [source]

Variability in red supergiant stars: pulsations, long secondary periods and convection noise

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
L. L. Kiss
ABSTRACT We study the brightness variations of galactic red supergiant stars using long-term visual light curves collected by the American Association of Variable Star Observers over the last century. The full sample contains 48 red semiregular or irregular variable stars, with a mean time-span of observations of 61 yr. We determine periods and period variability from analyses of power density spectra and time,frequency distributions. We find two significant periods in 18 stars. Most of these periods fall into two distinct groups, ranging from a few hundred to a few thousand days. Theoretical models imply fundamental, first and possibly second overtone mode pulsations for the shorter periods. Periods greater than 1000 d form a parallel period,luminosity relation that is similar to the long secondary periods of the asymptotic giant branch stars. A number of individual power spectra shows a single mode resolved into multiple peaks under a Lorentzian envelope, which we interpret as evidence for stochastic oscillations, presumably caused by the interplay of convection and pulsations. We find a strong 1/f noise component in the power spectra that is remarkably similar in almost all stars of the sample. This behaviour fits the picture of irregular photometric variability caused by large convection cells, analogous to the granulation background seen in the Sun. [source]

A semiquantitative analysis of the dynamics of a Goldman-type vaporiser

ANAESTHESIA, Issue 6 2000
D. A. Young
When a turbulent flow of a carrier gas is passed over a liquid anaesthetic agent contained in a vaporiser of Goldman design, evaporation from the cooled surface leads rapidly to a succession of fluid instabilities which set in at characteristic critical conditions. An initially quiescent boundary layer at the surface is sequentially replaced by a thin layer of toroidal (Bénard,Marangoni) convection cells which are driven by surface tension gradients. These are then augmented by Rayleigh,Bénard convection driven by gravity, the whole process terminating in intermittent columnar plunging of cold fluid from a chaotic surface layer of pulsating thickness to the base of the liquid pool. Residual striations from these plunging columns persist throughout the bulk of the liquid so long as evaporation continues. The ultimate state is then one in which turbulence occurs throughout both liquid and vapour phases. In this paper, a semiquantitative analysis of the system dynamics is given with supportive experimental evidence where possible. [source]