Boiling in a porous layer heated from below: effects of natural convection and a moving liquid/two-phase interface

Abstract

Boiling and natural-convection processes in a horizontal, fluid-saturated porous layer are investigated. The layer is heated uniformly from below and is cooled from above. Volumetric cooling is also allowed. The thermodynamic structure consists of a liquid region overlying a two-phase region. Numerical techniques are used to solve the transient, two-dimensional equations in the liquid and two-phase regions, and at the phase-change interface. A parametric study is carried out in terms of the liquid-phase Rayleigh number (Ra) and the non-dimensional bottom heat flux (Qb). Three solution regimes are observed: conduction-dominated at low Ra, convection-dominated at intermediate Ra, and oscillatory convection at high Ra. In the convection-dominated regime, transitions to multiple cell patterns are observed as Qb is increased. Oscillatory convection appears to be triggered by asymmetric disturbances in the system. The effects of initial conditions and the stability of the solutions to perturbations are also investigated. The heat transfer correlations and qualitative flow patterns are in agreement with experiments.