Effects of reactant composition and nonuniformities on temperature fronts

Abstract

Stationary and spatially oscillating temperature fronts separating regions with high and low temperatures (amplitudes up to 120 K) formed during the atmospheric oxidation of carbon monoxide on a Pd on alumina ring kept in a mixed reactor. The sharp fronts bounded either one or two low temperature regions. The transition from stationary to spatially oscillating fronts occurred at a feed CO/O2 concentration ratio close to 2.0 and was independent of the reactor temperature. The net rate of local heat generation on the ring was nonuniform leading to angular variation of the temperature of the ignited state. Front motions were affected by both the nonuniformity of the system and the interaction between the catalyst and the ambient gas. The two fronts bounding a low temperature region usually moved at different velocities and their velocities increased with increasing oxygen concentration. In most cases the two fronts did not move in phase, but sometimes they moved in tandem generating a back-and-forth pulse motion. The spatial amplitude of the oscillations decreased as the slope of the net heat generation activity became steeper. The spatial variation of the standard deviation of the temperature was helpful in assessing the dynamics of the oscillating fronts.

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 .…”

“…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 . Moreover, surfaces that initially have a uniform activity will change with time and be-Ž .…”

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.…”

Optical and infrared imaging of growing polyolefin particles

“…1987 Pawlicki and Schmitz, 1987 . The Luss group published a number of articles on the use of IR thermography in different systems to study temperature profiles on the surfaces of Ž catalytic materials Annamalai et al, 1997Annamalai et al, , 1999Liauw et al, 1997;Lobban et al, 1989;Moates et al, 1996;Somani et al, . 1997 .…”