Pressure drop in flexible ducts.
Durr-DE; Esmen-NA; Stanley-C Jr.; Weyel-DA
Appl Ind Hyg 1987 May; 2(3):99-102
A study was designed to obtain generalized semiempirical formulae for determining pressure drop in the drooping sections of flexible ducts as used in many ventilation systems. A second study was incorporated which generalized the calculation of pressure drop due to 90 degree bends in the system. Air flow and resistance measurements were made in 3, 4, and 6 inch nominal, internal diameter, industrial grade corrugated and smooth rubberized flexible ducts. Throughput velocities ranged from less than 1200 to over 8000 feet per minute. All ducts were 10 feet 6 inches in length. When the ducts were fully expanded, roughness characteristics of each were determined. The results of pressure drop due to drooping were analyzed by fitting a parametric curve to a random selection of about half of the data points and comparing the predicted pressure drop with measured values for the complete data set. The authors conclude that the results indicate that knowledge of relative roughness of flexible ducts makes it possible to estimate pressure drop for use of that duct under all reasonable conditions. Ventilation system designers can experimentally determine needed values. However, to carry out such a program a large laboratory would be needed with specialized flow measurement devices. The authors urge the manufacturers of such flexible ducts to provide needed testing and information for their products. If such information is forthcoming from manufacturers, then the equations as presented in this paper will be helpful to estimate the pressure drop through flexible hoses. If such information is not provided and cannot be obtained, the user may assume certain values given in this paper in completing the equations and doing the calculations required.
NIOSH-Publication; NIOSH-Grant; Air-pressure; Ventilation-equipment; Safety-research; Safety-engineering; Surface-properties; Air-flow; Pressure-testing; Pressure-gradients; Mathematical-models
Industrial Environ Health Scis University of Pittsburgh 130 Desoto Street Pittsburgh, PA 15261
Applied Industrial Hygiene
University of Pittsburgh at Pittsburgh, Pittsburgh, Pennsylvania