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Comparison of pitot traverses taken at varying distances downstream of obstructions.

Authors
Guffey-SE; Booth-DW-Sr
Source
Am Ind Hyg Assoc J 1999 Mar/Apr; 60(2):165-174
NIOSHTIC No.
20031360
Abstract
This study determined the deviations between pitot traverses taken under "ideal" conditions--at least seven duct diameter's lengths (i.e., distance = 7D) from obstructions, elbows, junction fittings, and other disturbances to flows--with those taken downstream from commonplace disturbances. Two perpendicular 10-point, log-linear velocity pressure traverses were taken at various distances downstream of tested upstream conditions. Upstream conditions included a plain duct opening, a junction fitting, a single 90 degrees elbow, and two elbows rotated 90 degrees from each other into two orthogonal planes. Airflows determined from those values were compared with the values measured more than 40D downstream of the same obstructions under ideal conditions. The ideal measurements were taken on three traverse diameters in the same plane separated by 120 degrees in honed drawn-over-mandrel tubing. In all cases the pitot tubes were held in place by devices that effectively eliminated alignment errors and insertion depth errors. Duct velocities ranged from 1500 to 4500 ft/min. Results were surprisingly good if one employed two perpendicular traverses. When the averages of two perpendicular traverses was taken, deviations from ideal value were 6% or less even for traverses taken as close as 2D distance from the upstream disturbances. At 3D distance, deviations seldom exceeded 5%. With single diameter traverses, errors seldom exceeded 5% at 6D or more downstream from the disturbance. Interestingly, percentage deviations were about the same at high and low velocities. This study demonstrated that two perpendicular pitot traverses can be taken as close as 3D from these disturbances with acceptable (< or = 5%) deviations from measurements taken under ideal conditions.
Keywords
Ventilation; Industrial-ventilation; Ventilation-systems; Exhaust-systems; Exhaust-ventilation; Air-flow; Air-contamination; Airborne-particles; Dust-analysis; Dust-collection; Dust-control-equipment; Dust-exposure; Dust-inhalation; Dust-particles; Dust-sampling; Dusts; Measurement-equipment; Author Keywords: pitot traverses; ventilation
Contact
University of Washington, School of Public Health and Community Medicine, Department of Environmental Health, Box 357234, Seattle, WA 98195-7234
CODEN
AIHAAP
Publication Date
19990301
Document Type
Journal Article
Funding Amount
205264
Funding Type
Grant
Fiscal Year
1999
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-003165
Issue of Publication
2
ISSN
0002-8894
Priority Area
Research Tools and Approaches: Intervention Effectiveness Research
Source Name
American Industrial Hygiene Association Journal
State
CA; WA; WV
Performing Organization
University of Washington, Department of Environmental Health, Seattle, WA
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