Pressure losses in transitions between square and rectangular ducts of the same cross-sectional area

• Published in: The International journal of heat and fluid flow Vol. 6; no. 3; pp. 212 - 216
• Main Authors: Dekam, E.I., Calvert, J.R.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 1985; Elsevier Science
• Subjects: cross sectional measurement; ducts; Exact sciences and technology; Flows in ducts, channels, nozzles, and conduits; Fluid dynamics; fluid flow; friction; Fundamental areas of phenomenology (including applications); Physics; pressure measurement; transitional flow; velocity; transitional flow; fluid flow; ducts; Rectangular pipe; Transition flow; Pipe flow; Experimental study; Pressure drop; Square section
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/0142-727X(85)90014-1

Experimental results are presented for the pressure loss in transitions between square and rectangular ducts where the two ends have the same cross-sectional area. The aspect ratios at the rectangular end ranged from 0.3 to 0.625, and the transition length from 1 to 2 times the hydraulic diameter. Reynolds numbers ranged from 50 000 to 125 000. The pressure drop may be divided into components arising from friction and velocity profile distortion. The friction component, which may be evaluated by normal pipe flow methods, accounts for the observed variation with Reynolds number. The velocity profile component increases as the aspect ratio of the rectangular end falls, and is significantly higher for rectangular to square than for square to rectangular transitions. There is an optimum length to hydraulic diameter ratio, for which the pressure loss is a minimum; it has not been found exactly, but is less than 2 and probably below 1.