Flow and Forced Convection Heat and Mass Transfer Characteristics of Developed Laminar Flow in Channels of Relevance to Emissions Control Devices: Washcoated Monoliths and Asymmetric Particulate Filters

Tim  Watling, Johnson Matthey

The flow and forced convection heat and mass transfer characteristics for fully developed laminar flow has been investigated in two systems of relevance for automotive emissions control devices, viz. the washcoated channels of a flow-through parts, whose cross section resembles a square with rounded corners, and the octahedral channels of octo-square asymmetric particulate filters. For the former system, the full range of channel shapes from a square, via a square with rounded corners with increasing radius of curvature, to a circle is considered. For the latter system, the channel shape is varied from a square to a regular octahedron. The velocity and temperature fields have been solved using the least squares method, which gives analytical expressions for the velocity and temperature field in the form of algebraic-trigonometric series.

As the channel shape is varied from a square to a circle or regular octahedron, the velocity profile becomes slightly flatter, resulting in a small decrease in the momentum flux correction factor, kinetic energy flux correction factor and the maximum velocity; the friction factor, Sh and Nu increase, but the viscous loss coefficient (F) and the product of the channel perimeter and mass or heat transfer coefficient, which actually appear in the momentum mass and energy balance equations of a 1-dimensional model, decrease. The effect of this on along-channel pressure drop, heat and mass transfer and on the pressure changes associated with flow contraction into the part and flow expansion on leaving the part is investigated.

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