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Natural convection in a cube of fluid-saturated porous medium having a constant temperature top and bottom is studied numerically. In the first of two special cases considered, the vertical sides are insulated. In this case, the numerical simulations indicate permanently unsteady regularly and irregularly fluctuating convective states at Rayleigh numbers (R*) above 550. The regularly fluctuating convective state defined by simply periodic oscillations in the Nusselt number begins at R* between 550 and 560. The frequency of the oscillations appears to depend on R* approximately as f∝ (R*)3.6. The irregularly fluctuating convective state defined by random variations in the Nusselt number begins at R* between 625 and 640. In the second case, heat is transferred through the vertical sides of the cube. Three distinct flow patterns are identified depending on the rate of heat transfer and the Rayleigh number. For all runs in the range of Rayleigh numbers studied, the transition from the first to the second flow pattern occurs abruptly.

Experiments were conducted to determine the pressure rise that results from either the combustion of a localized gas volume or the expansion of a pressurized gas volume adjacent to an inert gas in a closed vessel. The experiments consisted of either pressurized air or the combustion of stoichiometric and fuel-lean hydrogen-air mixtures compressing an inert gas. The pressure rise in the inert gas was measured as a function of either the volume fraction or the initial pressure of the expanding gas. Helium, nitrogen, air and carbon dioxide were tested to explore the effect of inert gas heat capacity on the pressure rise. The final pressure of the inert gas increased with the volume fraction and initial pressure of the expanding gas, and was influenced to a lesser extent by the heat capacity of the inert gas. A model was assessed using the experimental data, and the theoretical results were consistent with the observed trends. This model and other published models were assessed and compared using prior data for localized gas combustion surrounded by an inert gas and the partial combustion of homogeneous methane-air mixtures.

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