A generalised length dimension for noncircular ducts
Abstract
A generalized length dimension is proposed for use in the determination of the friction factor in noncircular ducts. The dimension, which is applicable to ducts with a point of maximum velocity, may be regarded as the average distance of the duct boundary from the point of maximum velocity, or the cumulative effect of an infinite number of circular pipe segments of a radius equal to the length of the radial vector from the point of maximum velocity to the boundary. In friction calculations, the use of the generalized dimension in the Reynolds number and the hydraulic diameter results in better estimates than the use of the hydraulic diameter alone. The length dimension may also be used in calculations for a duct with lines of maximum velocity (rectangular duct), resulting in a 5% variation in the Blasius constant as the aspect ratio varies from zero (parallel plates) to 1.0.
 Publication:

Letters Heat Mass Transfer
 Pub Date:
 October 1980
 Bibcode:
 1980LHMT....7..323B
 Keywords:

 Diameters;
 Dimensional Analysis;
 Ducted Flow;
 Ducts;
 Friction Factor;
 Aspect Ratio;
 Flow Velocity;
 Turbulent Flow;
 Fluid Mechanics and Heat Transfer