"The problems associated with poor thermal mixing of outside air and return air streams in air handling units equipped with conditioning coils have been recognized for many years. These problems range from nuisance cycling and frequent freeze-stat trips to more serious consequences of a frozen or ruptured conditioning coil. Typical solutions for the problem usually consist of preferred placement of outside, air and return air duct penetrations to the mixing box, manipulation of the inlet damper angles and velocity ratio between the outside air and return air streams, and the insertion of static flow mixers in the mixing box to help improve the thermal stratification.
An idealized mixing chamber, similar to those found on commercial flow-through air handling units, was modelled using computational fluid dynamics ( CFD) software. The outside air duct and return air duct penetrations were placed on adjacent walls of the chamber, each fitted with a parallel damper with four blades. A parametric study of 28 cases was then performed using CFD software to simulate the two flows converging and mixing in the chamber. The inlet flow velocities and angles of the damper blades were manipulated to produce results at a variety of conditions, and the results were analyzed at five stations downstream of the convergence of the two flows.
The results of the parametric study include quantification of the effects of the inlet damper angles and velocity ratio on the resulting temperature distribution and thermal mixing as a function of downstream distance. In addition, the flow elements in the mixing chamber which seem to have the most influence on thermal mixing are identified. A brief analysis of the apparent sensitivity of the range mixing effectiveness and statistical mixing effectiveness to the number of temperature sensors and their placement in thermal mixing experiments is also presented"--Abstract, page iii.
Sauer, Harry J., Jr., 1935-2008
Grow, David E.
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
University of Missouri--Rolla
xiv, 127 pages
© 2002 Christopher Robert Steineman, All rights reserved.
Thesis - Restricted Access
Ventilation -- Control
Air flow -- Research
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Steineman, Christopher Robert, "A numerical study of thermal mixing and flow development in a damper controlled mixing chamber" (2002). Masters Theses. 4417.
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