Temperature patterns on a hollow cylindrical catalytic pellet

Abstract

The atmospheric oxidation of a mixture containing 6 vol % carbon monoxide was carried out on a hollow cylindrical catalytic pellet. The catalyst was held in a conical reactor which enabled simultaneous measurement of the temperature patterns on the top and side of the pellet by an IR imager. Upon a decrease in the reactor temperature the fully ignited, high temperature state of the pellet is transformed to a nonuniform one with temperature fronts separating high and low temperature regions. The transition and the resulting states are rather intricate and are strongly influenced by the nonuniformity of the catalyst and the transport to and from it, as well as the global coupling, which stabilizes temperature fronts and patterns, which would not exist in its absence. Intricate pulse splitting and extinction were observed both on the top and the side of the pellet. Highly irregular motions and conversions were obtained following a decrease in the reactor temperature. (c) 1999 American Institute of Physics.

Pattern Formation in Globally Coupled Electrochemical Systems with an S-Shaped Current-Potential Curve

“…This illustrative explanation of the emergence and properties of the patterns is not really new. It is similar to the ones given in literature in order to explain the formation of hot and cold domains in heterogeneous catalytic reactions where the global constraint stems from the control of the catalyst temperature ,,,,, or the formation of stationary potential domains in electrochemical N-NDR systems . It should hold as given here also for the formation of current filaments in semiconductors with an S-NDR in the current−voltage relation ,− and is most likely also discussed in connection with patterns in gas-discharge tubes .…”

“…Global coupling can change the system's spatiotemporal behavior qualitatively, and its influence on pattern formation has been an active area of research primarily during the last decade. − The impact of global coupling on pattern formation depends on the local dynamics of the system (whether the medium is bistable, excitable, oscillatory, or chaotic) as well as on the way it enters into the equations, and it manifests itself in diverse responses of the system, such as the formation of stationary domains 2,7,8,12 or standing waves, , the creation of pulses, ,,, the synchronization of oscillations, , or the suppression of turbulence. , In physical systems, it comes into play whenever a spatially extended physical or chemical system is electrically controlled, as it is often the case for semiconductor devices, , gas discharge lamps or a heterogeneously reacting system with an electrically controlled catalyst temperature. ,,,,, But it is also present if the local change in a variable induces a transport process that is much faster than any other time scale of the system. Then, the fast spread of a local change acts effectively as a global coupling.…”

Formation and dynamics of a hot zone in radial flow reactor

“…Any nonuniformity in the flow field caused by the flow distributor or quartz sleeve would not have shifted the front location upon turning the reactor around between the two supports. Inhomogeneities in the catalytic activity are inherent features of heterogeneous catalytic sys-Ž tems Philippou et al, 1991;Pawlicki and Schmitz, 1987;Kellow and Wolf, 1991;Annamalai et al, 1997Annamalai et al, , 1999Liauw et . al., 1996;Somani et al, 1997 .…”

Dynamics of hot zones on top of packed-bed reactors

“…Middya et al (1994) pointed out that global coupling can affect the dynamic features of spatio-temporal temperature patterns on catalytic surfaces and stabilize patterns that would not exist in its absence. Such patterns were observed on catalytic wires and ribbons (Lobban et al, 1989;Philippou et al, 1991), catalytic rings (Graham et al, 1993;Annamalai et al, 1997), hollow cylindrical catalytic pellets (Annamalai et al, 1999) and in a radial-flow packed-bed reactor (Marwaha et al, 2001). One of our objectives was to investigate if the transverse hot zone on the top of a packed bed are affected by global coupling.…”