Reflooding with internal boiling of a heating model porous medium with mm-scale pores

Abstract

This paper presents a pore-scale experimental study of the reflooding of a two-dimensional model porous medium. The objective is to better understand the reflooding mechanisms in play in the context of nuclear reactor safety. The hot debris bed that forms in a nuclear reactor following a loss of coolant accident is comparable to a heat-generating porous medium. Its cooling by water reflooding involves intense boiling mechanisms that must be modeled properly to assess mitigation procedures.The experimental study presented in this paper focuses on the phenomenology of reflooding of a model porous medium composed of a bank of mm-scale heating cylinders placed between two ceramic plates. A Fluorinert TM liquid, HFE-7000, is injected at a temperature close to saturation into the dry and superheated porous medium. Each cylinder of the test section is used both as a heating element and a temperature probe, which enables to track the evolution of the three different macroscopic zones identified during cooling of the system. The reflooding dynamics, in particular the cooling fronts velocities, are thus determined thanks to pore-scale thermal measurements together with direct visualizations. The influence of the injection flow rate and of the heating power are studied in a parametric way.

Pore-scale visualization and characterization of viscous dissipation in porous media

“…Multiphase flow in porous media is important in a number of environmental and industrial subsurface applications such as the sequestration and storage of CO 2 in geological formations [1], enhanced oil recovery [2], soil remediation [3], and energy storage technologies. Interest also extends to manufactured porous materials such as nuclear safety devices [4], and distillation columns [5]. In particular, a fundamental understanding of the mechanisms of displacement of one fluid by another in porous media is crucial to predict optimal hydrocarbon recovery and subsurface storage of CO 2 .…”

Modeling of inertial multi-phase flows through high permeability porous media: Friction closure laws

“…Such assumptions are at the core of almost all published two-phase flow models. The fact that these models actually work well, at least to some degree of accuracy, lies on the existence of some ergodicity between space and time, which is partially supported by porescale experiments ( Sapin et al, 2016 ) and some macro-scale experiments . Unsteady closure and/or macro-scale equations have been proposed in the literature ( Cueto-Felgueroso and Juanes, 2009;Gray and Hassanizadeh, 1991;Hassanizadeh and Gray, 1993;Hilfer, 1998;Kalaydjian, 1987;Panfilov and Panfilova, 2005;Quintard and Whitaker, 1990; Reeves and Celia, 1996 ).…”

Experimental study of the dryout of a 2D heat-generating model porous medium

“…In fact, debris bed are known to consist of a 3D packing of particles in the millimeter size range with a high porosity (larger than 35%) and in which the flow regimes are dominated by inertial effects (high capillary and Weber numbers) [16,17]. Moreover, in the present study, the diameter of the heating elements was chosen in such a way that the ratio of the capillary length of HFE-7000 to this diameter is similar to the one obtained when considering the ratio between the capillary length of water at°100 C and a characteristic 5 mm particle size, typical of the one observed in debris bed [15]. Thus, realistic boiling conditions are obtained in the present experimental setup, as far as bubble size and confinement effects are concerned.…”

“…The main characteristics of the experimental set-up are now described. More details can be found in [14] and in [15], where the same setup is used in reflooding experiments where a liquid is injected in the heated, porous test section. Briefly, the test section is composed of 276 cylinders positioned between two ceramic plates, see Fig.…”