TEMPERATURE PATTERNS ON A CATALYTIC RIBBON HEATED BY A CONSTANT VOLTAGE

Chemical reactions were carried out on a thin Pt ribbon heated electrically at constant voltage. A thermal imager revealed that symmetry breaking can cause the formation of a stationary high-temperature pulse during the oxidation of ammonia in air. Chaotic variations in the overall reaction rate during the oxidation of propylene in air are caused by a back-and-forth movement of a temperature front emanating from either one of the supports. The average front velocity is of the order of 0.1 cm/s. The probability density function of the time interval between two successive oscillations in the reaction rate is usually widely spread around two modes. The power spectrum of the overall reaction rate decays exponentially, while that of a local temperature decays as a power law. The behavioral features during constant-voltage electrical heating are intermediate between those under constant-average-resistance (temperature) and constant-current electrical heating.