Onset Of Transient Convection Research Articles

Onset of transient convection in a porous medium with an embedded low-permeability layer

Deep saline aquifers used for CO2 sequestration are commonly made of sedimentary formations consisting of several layers of distinguishable permeability. In this work, the effect of a non-monotonic, vertically varying permeability profile on the onset of convective instability is studied theoretically using linear stability analyses. The onset time depends on the interaction between the permeability profile and the location of the concentration perturbation peak beyond which the concentration of CO2 decays. A thin low-permeability layer can either accelerate or delay the onset time of the convective instability depending on the nature of the permeability variation – whether the permeability transition is smooth or layered, the Rayleigh number (Ra), and the location of the permeability change (a^) relative to the perturbation peak (a^c*), which scales as a^c*≈14Ra−1 for homogeneous systems. However, the low permeable layer has no effect on the onset time when it is near the lower boundary of a medium with sufficiently large Ra (a^c*≪a^). This nontrivial dependence highlights the implication of ignoring geological features of a small spatial extent, indicating the importance of a detailed characterization of CO2 storage sites.

3D Time-Dependent Simulations of Onset of Transient Convection in Evaporative Cooling of Liquids

The onset of transient convection in deep fluids caused by unsteady-state top-cooling was simulated under constant heat flux (CHF) boundary conditions. The 2D and 3D time-dependent simulations using a computational fluid dynamics (CFD) package have been successfully performed for several experiments. They provided the detailed mechanism of the onset of convection that began from the point of instability to the evolution of the mushroom plumes very similar to those observed in experiments. The critical times, critical depths, critical wavelengths, and heat transfer coefficients were computed accurately, and were found to be in good agreement with experimental and theoretical values. The average Nusselt number for the evaporative cooling of water was about 2.2.

Effects of Combined Horizontal and Vertical Heterogeneity on the Onset of Transient Convection in a Porous Medium

Effects of Combined Horizontal and Vertical Heterogeneity on the Onset of Transient Convection in a Porous Medium

The onset of transient convection in fluid-saturated porous layer heated uniformly from below

A theoretical analysis of convective instability is conducted in an initially quiescent, fluid-saturated, horizontal porous layer heated from below with constant heat flux. Darcy's law is used to model the fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven convective motion. Under the principle of exchange of stabilities, the stability analysis is performed on the basis of the propagation theory which adopts the thermal penetration depth as a characteristic length scaling factor. The result predicts the critical condition of onset of buoyancy-driven convection which is governed by the Darcy-Rayleigh number