Flow Distribution and Pressure Drop in Diffuser-Monolith Flows

Abstract

Most current automotive catalytic converters use diffusers to distribute the flow field inside the monolithic bricks where catalysis takes place. While the characteristics and performance of a simple diffuser flow are well documented, the influence of downstream brick resistance is not clear. In this paper, the trade-off between flow-uniformity and pressure drop of an axisymmetric automotive catalytic converters is studied numerically and experimentally for selected cases. The monolithic brick resistance is formulated from the pressure gradient of fully developed laminar duct-flow and corrected for the entrance effect. The monolithic brick downstream stabilizes the diffuser flows both physically and computationally. A distribution index was formulated to quantify the degree of nonuniformity in selected test cases. The test matrix covers a range of different diffuser angles and flow resistance (brick types). For simplicity, an axisymmetric geometry is chosen. Flow distribution within the monolith was found to depend strongly on diffuser performance, which is modified strongly by brick resistance. Pressure drop due to the headers and brick resistance and their relative roles is also identified. The implications of these data for converter design are discussed in terms of the trade-off between flow-uniformity and pressure drop.

Simulation of Flow Field in an SCR Converter

“…Diffusers are widely used in flow systems to convert kinetic energy to potential energy. It has been found by many experimental studies that flow distribution within a monolith depends strongly on diffuser performance [9][10][11][12]. An improper flow distribution in a catalyst could cause a decrease in convention efficiency or even a failure of the catalyst, and the resultant flow uniformity strongly affects the light-off condition and durability of converters.…”

Aerodynamics of Monolithic Matrices for Supporting Solid Reactant or Catalyst

“…Receiving particular attention in the catalytic reactor research was then the non-uniformity of temperatures in individual parallel passages. Examples are in References [9][10][11][12][13]. The temperature differences are due to the required total matrix face area F being substantially larger than the exhaust pipe cross section that brings the gas to the matrix.…”

Flow measurements across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser

“…Early studies by Wendland and Matthes [10] employed flow visualization. Kim et al [11] measured Fig. 1 Schematic diagram showing catalyst configuration comprising two monoliths in an exhaust system, catalyst channels and flow separation in a diffuser [9] the axial velocity 1 mm upstream of the leading face of a monolith using laser doppler anemometry for an axisymmetric assembly at two Reynolds numbers (Re).…”