Phenomenological study of the pre-mixing step of sodium-water explosive interaction

International Journal of Heat and Mass Transfer

Beauchamp

Allou

et al. 2019

Sodium-Water Reaction (SWR) is a notorious and complex interaction between two condensed phase reactants. It involves both physical and chemical processes, is fast, exothermic, and can be explosive under specific conditions. The fine-scale processes of SWR, and in particular the runaway mechanism eventually leading to explosive effects, are not yet fully understood. This paper focuses on how SWR runaway is triggered. Experiments investigating the processes of SWR with a high-speed camera are first described. These experiments suggest that sodium vaporization is responsible for provoking runaway. The main experimental observations are discussed and a scenario for SWR runaway is proposed. Finally, a semi-analytical model based on that mechanism is developed. Physical considerations and simplifying assumptions allow reducing the model to a single differential equation in the configuration of current experiments. The results of this model are consistent with experimental observations, and confirm the critical role of sodium vaporization in the onset of SWR runaway.

Section: Introductionmentioning

confidence: 99%

A small scale experiment and a simplified model to investigate the runaway of sodium-water reaction

International Journal of Heat and Mass Transfer

Beauchamp

Allou

et al. 2019

“…In this experiment, we performed high-frequency imaging and data acquisition on SWR at a small scale, in the purpose of uncovering the process of its runaway. As stated in introduction, and also identified by other authors [4], [5], the key to the onset of SWR runaway is reactant mixing, which turns SWR into a homogeneous reaction and allows for the reaction rate to jump exponentially. Two hypotheses have been proposed to explain reactant mixing: a mixing in liquid-phase [5], due to an electrostatic instability which leads to fragmentation of the sodium drop, or a mixing in gas-phase [7], [8], caused by vaporization of the reactants after their heating by the slower heterogeneous reaction.…”

Section: Discussionmentioning

confidence: 62%

“…Possible explanations for that dispersion are either the deformation of the pressure wave by the sodium-holding basket, or too low acquisition frequency (20 kHz) that might clip the signal. SWR itself is moreover known to be highly irregular in nature [4], [6]. Nevertheless, it is still clear that overpressures are globally increasing with sodium mass (Fig.…”

Section: Pressurementioning

confidence: 99%

Spectroscopic, pressure and temperature measurements of the reactant mixing process in sodium-water reaction

Nuclear Engineering and Design

Milanović

Hervé

et al. 2020

The reaction of sodium metal with water is a heterogeneous, exothermic reaction known to be prone to runaway with explosive effects when uncontrolled. The occurrence of runaways requires the reactants to be effectively mixed which is not the case initially for sodium and water. The latter are put in contact in two distinct, condensed phases, that are moreover rapidly separated by a gaseous film generated by the reaction itself. The runaway is triggered by a reactant mixing process that is not elucidated. This mixing could occur either in liquid or gas-phase. In this paper, we investigate the mixing process of sodium-water reaction in the small scale configuration of 1-4g sodium pellets with excess water in a closed vessel, using time-resolved video, optical, pressure and temperature acquisitions. The results show that sodium vaporization is implicated in the reaction and that it is generated in great quantity during runaway. However it appears from temperature measurements that boiling temperature is not reached in the sodium before runaway or only locally. It is therefore possible that reactant mixing occurs in the gas phase if an intensification of sodium vaporization takes place as a fast local transient. The possibility of reactant mixing in liquid phase is not contradicted by these results but was not identified from the available videos and data.

“…Experiments carried out by Daudin (2015), Daudin et al (2018) have highlighted the turbulent nature of the gaseous film. Many gas bubbles of various sizes separate the sodium drop from the liquid water surface (Figure 9.8) rendering the gas film highly turbulent.…”

Section: Turbulent Diffusionmentioning

confidence: 99%

“…Many gas bubbles of various sizes separate the sodium drop from the liquid water surface (Figure 9.8) rendering the gas film highly turbulent. Figure 9.8: Gas bubbles present in the gas film separating the sodium drop and the liquid water surface (time t1 before explosion) -VIPERE experiment carried out at CEA Cadarache (Daudin 2015, Daudin et al 2018. The gas film is consequently more a mixing zone than a film defined by two sharp interfaces.…”

Section: Turbulent Diffusionmentioning

confidence: 99%

Towards sodium combustion modeling with liquid water

Furfaro¹,

Saurel

Journal of Computational Physics

et al. 2020

Solid and liquid sodium combustion with liquid water occurs through a thin gas layer where exothermic reactions happen with sodium and water vapors. It thus involves multiple interfaces separating liquid and gas in the presence of surface tension, phase transition and surface reactions. The gas phase reaction involves compressible effects resulting in possible shock wave appearance in both gas and liquid phases. To understand and predict the complexity of sodium combustion with water a diffuse interface flow model is built. This formulation enables flow resolution in multidimension in the presence of complex motion, such as for example Leidenfrost-type thermo-chemical flow. More precisely sodium drop autonomous motion on the liquid surface is computed. Various modelling and numerical issues are present and addressed in the present contribution. In the author's knowledge, the first computed results of such type of combustion phenomenon in multidimensions are presented in this paper thanks to the diffuse interface approach. Explosion phenomenon is addressed as well and is reproduced at least qualitatively thanks to extra ingredients such as turbulent mixing of sodium and water vapors in the gas film and delayed ignition. Shock wave emission from the thermochemical Leidenfrost-type flow is observed as reported in related experiments. emails :