Effects of kinetic and transport phenomena on thermal explosion and oscillatory behaviour in a spherical reactor with mixed convection

Abstract

Thermal explosions are often influenced by the complex interaction between transport and reaction phenomena. In particular, reactant consumption can promote safer, non-explosive operation conditions of combustion systems. However, in liquids or gases, the presence of forced convection can affect the behaviour of a system, instigating oscillations in the temperature, reactant concentration and velocity fields. This work describes the effect of reactant consumption on a simple, one-step, exothermic reaction occurring in a spherical reactor with both forced and natural convection, by means of numerical simulations. Regime diagrams characterised by ratios of timescales for each transport and reaction phenomena are presented and the explosion boundary is represented for several forced convection and reaction consumption intensities. Special attention is given to the oscillatory behaviour observed for moderate forced convection and oscillatory regions are represented on the regime diagrams. Parametric conditions for this new oscillatory regime are identified by extending the criticality condition developed by Frank-Kamenetskii for the effect of reactant consumption in diffusive systems to include the effects of both natural and forced convection.

Advances in rapid compression machine studies of low- and intermediate-temperature autoignition phenomena

“…The evolution of various phenomena and their demarcation boundaries will shift accordingly. Nevertheless, analogous diagrams have been created for other experimental devices, e.g., [258,259], and are useful since they can aid experimental design, for both machine arrangement as well as selecting operating conditions. Modern RCMs used to study autoignition chemistry are configured to minimize non-uniformities and other physical effects such as boundary layer growth, and thus tend to operate within the region labeled in Fig.…”

The critical condition for thermal explosion in an isoperibolic system

“…34,35 A realistic model should take into account reactant consumption and finite values of the activation energy. 36,37 Frank-Kamenetskii and other authors improved the analysis by taking into account reactant consumption 31,[34][35][36][38][39][40][41][42][43] and finite values of the activation energy. 36,42 Analytical solutions are limited to idealized geometries that allow the system to be reduced to a one-dimensional (1D) model.…”

“…As we will see, the first assumption is accurate in some instances where thermal explosion arises at the very early stages of the reaction but for relatively low enthalpy reactions, such as the decomposition of oxide precursor salts, this may be a poor approximation . A realistic model should take into account reactant consumption and finite values of the activation energy . Frank‐Kamenetskii and other authors improved the analysis by taking into account reactant consumption and finite values of the activation energy …”

Exploding Chemical Gardens: A Phase‐Change Clock Reaction

“…[9,10] Thep recise definition of ac hemical clock is am atter of debate.S ome have argued for ad efinition that restricts ac lock reaction to an abrupt increase in the concentration of one or more products owing to the total consumption of alimiting reagent, [11] while others argue that it is not the details of the kinetics but the phenomenology that is important. [15,16] In the case of our scenario,t he concept of ac hemical clock is based upon the chemicalgarden reaction acting as atimer, the period of which we can control. [13,14] But it is inarguable that the classic clock reactions are timers:they have an induction period that may be very long followed by asharp change,often acolor change, at agiven moment, and this induction time can be controlled and predicted by altering the quantities of reagents.Examples in gaseous combustion have shown the dependence of the induction time before explosion on the transport rates of chemicals and heat.…”