Pressure Loss Characteristics in Catalytic Converters

A technique has been developed to study the axial static pressure profile through the channels of a 400 cells per square inch (cpsi) catalytic converter monolith. The shape of the profile proved different from the accepted laminar flow profile, although the flow conditions are clearly laminar within the channels of the converter. The fact that the inner surfaces of the channels are extremely rough, and that this roughness is highly irregular, is thought to have an effect on the developed pressure profile.

The measured profile was compared against the pressure profiles predicted by the most popular models in the published literature. A two-point criterion was developed to distinguish among those models. It was observed that Shah's model [1]* for the pressure drop along a square duct is the most appropriate.

Additional static pressure measurements were taken both before and after the catalyst element and used to calculate the entrance and exit total pressure loss coefficients. A dependence on the channels Reynolds number was proven to exist. It was noticed that, as the length of the sample increased, the experimental results were much more repeatable with less scatter. Combined laminar-turbulent flow characteristics were observed on the trends of the total pressure loss coefficients.