Frictional and Heat Transfer Characteristics of Flow in Triangle and Hexagon Channels of Wall-Flow Monoliths

摘要

In the 1D modeling of flow and heat/mass transfer of wall flow monoliths (WFMs), it is common to use a friction factor and Nusselt number generated from an idealized 2D/3D solution. The results are usually expressed as functions of wall Reynolds number and Peclet number, and they have been derived for circular tubes and parallel plates with porous walls decades ago. Recently, the 3D solution has been generated for fully developed laminar flow in square channels with porous walls and uniform wall velocity, and the general functions for friction factor and Nusselt number were derived for 1D modeling. In this work, we extend the study to the 3D geometry of additional regular polygons, particularly hexagons and triangles, since they are also used for wall flow monoliths to filter exhaust emissions. In order to extend the life span of the monolith, asymmetric channel designs with different inlet-to-outlet channel ratio or different sizes have become an important approach. The main idea is to increase the soot or ash capacity in the inlet channels. For the hexagonal channel design, two inlet channels per outlet channel are common. Due to the different inlet/outlet channel ratio, the flow and heat transfer characteristics are significantly different compared to traditional design with the same inlet/outlet channel ratio. The difference between the asymmetric design and symmetric design is studied, and the implication for 1D modeling is discussed.