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An Experimental Study of the Pressure Losses in Converging Flow Fittings Used in Exhaust Systems.

Sepsy CF; Pies DB
College of Engineering, Ohio State University, Columbus, Ohio 1972 Dec:234 pages
A study was conducted to correlate pressure losses for all fittings normally used in industrial ventilation exhaust systems. The project was divided into two parts. In the first part an experimental investigation was made of pressure losses in 16 converging flow fittings with 8 inch common seam diameters which covered a wide range of branch tap and main fitting body styles. The second part of the study correlated pressure losses on a generalized basis which would be valid for all converging flow fittings normally used in industry. Fittings with take/off diameters from 3 to 16 inches were studied. Flow conditions most commonly used in industrial ventilation systems were used; branch to main upstream velocity ratios varied from 0.75 to 6. Branch entry angles of 30, 45, and 90 degrees were studied. Branch and main loss coefficients were found to correlate with good agreement when plotted against the ratio of branch to upstream volume flow rate. Branch and main loss coefficients were found to be significantly affected by the three types of branch tap entrance (sharp, rolled, and round edge). A simple energy/mass balance model was found to be unreliable, due to heat transfer from the fitting to the ambient due to viscous dissipation of turbulent eddies as the branch flow enters the mainstream flow. A negative loss coefficient was seen when the upstream flow rate was high enough compared to the branch flow rate; the upstream flow added sufficient energy to the flow between the branch and downstream to cause an increase in total pressure.
NIOSH-Contract; Contract-099-71-0028; Ventilation-systems; Ventilation-equipment; Exhaust-ventilation; Exhaust-systems; Air-flow; Industrial-ventilation;
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College of Engineering, Ohio State University, Columbus, Ohio
Page last reviewed: February 18, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division