NOTE: This item is not available outside the Texas A&M University network. Texas A&M affiliated users who are off campus can access the item through NetID and password authentication or by using TAMU VPN. Non-affiliated individuals should request a copy through their local library's interlibrary loan service.
Evaluation of Mixing Downstream of Tees in Duct Systems with Respect to Single Point Representative Air Sampling
MetadataShow full item record
Air duct systems in nuclear facilities must meet the requirements of ANSI N13.1-1999 and the Environmental Protection Agency (EPA) that the exhaust airflow be monitored with continuous sampling in case of an accidental release of airborne radionuclides. The continuous air sampling in a duct system is based on the concept of single point representative sampling at the sampling location where the velocity and contaminant profiles are nearly uniform. Sampling must be at a location where there is a uniform distribution via mixing in accordance with ANSI N13.1-1999. The purpose of this work is to identify the sampling locations where the velocity, momentum and contaminant concentrations fall below the 20% coefficient of variation (COV) requirements of ANSI N13.1-1999. Four sets of experiments were conducted on a generic 'T' mixing system. Measurements were made of the velocity, tracer gas concentration, ten micrometer particles and average flow swirl angle. The generic 'T' mixing system included three different combinations of sub duct sizes (6"x6", 9"x9" and 12"x12"), one main duct size (12"x12") and five air velocities (0, 100, 200, 300, and 400 fpm). An air blender was also introduced in some of the tests to promote mixing of the air streams from the main duct and sub duct. The experimental results suggested a turbulent mixing provided the accepted velocity COVs by 6 hydraulic diameters downstream. For similar velocity in the main duct and sub duct, an air blender provided the substantial improvement in 3 hydraulic diameters needed to achieve COVs below 10%. Without an air blender, the distance downstream of the T-junction for the COVs below 20% increased as the velocity of the sub duct airflow increased. About 95% of the cases achieved COVs below 10%. With the air blender, most of the cases with the air blender had the lower COVs than without the blender. However, at an area ratio (sub duct area / main duct area) of 0.25 and above a velocity ratio (velocity in the sub duct / velocity in the main duct) of 3, the air blender proved to be less beneficial for mixing. These results can apply to other duct systems with similar geometries and, ultimately, be a basis for selecting a proper sampling location under the requirements of the single point representative sampling.
DescriptionDue to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to firstname.lastname@example.org, referencing the URI of the item.
Includes bibliographical references (leaves 117-120).
Issued also on microfiche from Lange Micrographics.
Kim, Taehong (2003). Evaluation of Mixing Downstream of Tees in Duct Systems with Respect to Single Point Representative Air Sampling. Master's thesis, Texas A&M University. Available electronically from
Request Open Access
This item and its contents are restricted. If this is your thesis or dissertation, you can make it open-access. This will allow all visitors to view the contents of the thesis.