Describes work examining factors affecting flow resistance in rectangular ducts. Summarises the experimental results and discusses them. Test ducts included 14 x 6in. and 22 x 8in. ducts constructed of galvanised sheet metal and several sizes constructed using 3/4in. plywood, providing aspect ratios ranging from 1 to 4. Specific data points are portrayed on the traditional Moody diagram, and each data set is represented by an 'effective' relative roughness based on hydraulic diameters. Discusses the contribution to flow resistance caused by joints, cross-breaks and beaded construction. States the complete set of data shows the effect of joints clearly. Explores an alternative scheme of representing total pressure drop for ducts that may more clearly convey the separate contributions to total pressure drop in ducts than is conveyed when the resistance is associated only with the duct surface condition.

KEYWORDS: Air flow, ducts, research, flow resistance, testing, pressure drop, rectangular