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Chemically reacting plumes, gas hydrate dissociation and dendrite solidification


Chemical transport by natural convection is a common occurrence in environmental and industrial settings, and in many cases a reaction occurs between the source fluid and the fluid entrained by the ambient. This process is particularly important in the case of ventilated spaces, especially when the chemical is hazardous to the occupants. We explore analytically, numerically and experimentally the physics involved when a chemically reacting plume enters a ventilated space in order to determine the species distribution in time. We compare our results to traditional ventilation strategies that rely on well-mixed spaces and discuss the main differences. Furthermore, there are many case in which the chemical reaction is endothermic or exothermic, such as in dilution reactions, pool fires and others. In this case the buoyancy force depends on the heat of reaction as well as the ambient density distribution and we develop a model to take into account this extra source/sink applying methods based on traditional plume models. This thesis also presents a separate investigation on gas hydrate decomposition in porous media due to an increase in ocean water temperature. The problem is essentially broken up into two parts, depending on the system conditions in relation to the phase diagram. In the first case the hydrate dissolves at warmer temperatures at a rate that scales with species diffusion. In the second case the hydrate dissociates into water and gas, which requires a special treatment for the two-phase flow through the sediment. Here we determine methane gas flow rates into the ocean from the sea bed as a function of thermal forcing and sediment properties. Finally, we present a related project on dendrite solidification in super-cooled binary liquids (e.g. hydrate and alloys). Slender body theory is applied to a steady state dendrite and solved analytically using the Wiener-Hopf technique. We examine the interface shape as a function of temperature, concentration, and kinetic under-cooling and compare this to the classic similarity solution

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