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Design of automotive catalytic converters is a complex process involving the optimization of many physical and chemical variables. Often, simple characteristics such as geometric surface area and space velocity are used to compare alternative designs. Unfortunately, these parameters do not account for all of the relative variables affecting emissions performance. The effectiveness-Ntu methodology, developed for heat exchanger design, can be extended to catalytic converter design through the heat and mass transfer analogy. This technique allows comparisons to include all physical variables affecting emissions performance. This paper presents Ntu-based, catalyst performance criteria for steady state and transient emissions and exhaust flow restriction. The theoretical analysis includes the effects of washcoat on cell geometry and, subsequently, on heat/mass-transfer performance.

Consistent optimization of low emissions catalyst systems will require appropriate use of alternative substrate geometries. Fundamental heat transfer, mass transfer and friction characteristics provide a solid foundation for evaluating the benefits of these geometries. The purpose of this report is to validate a bench test, based on a previously reported technique, for measuring the fundamental characteristics of catalyst substrates. The sample matrix is subjected to a periodically varying inlet temperature and convective transport properties, reported as Colburn factors, are found by matching the phase shift and amplitude attenuation of the inlet and outlet temperature waves in a finite difference computer program. Flow friction attributes, reported as Fanning friction factors, are found through reduction of measured pressure loss at constant flow rate.