Buoyancy-Driven Exchange Flow with Applications to Architectural Fluid Mechanics

• Author / Creator

  Nabi, Saleh

• Buoyancy driven flow between two finite zones containing fluid of slightly different density is investigated. Two zones separated by (i) a single common doorway, and, (ii) top and bottom vents.
  In the former case, a two-layer exchange flow develops once the barrier is removed. In the zone that initially contained dense fluid, a buoyant plume of light fluid mixes with the dense fluid leading, over time, to the development of non-trivial ambient density stratification. Meanwhile, dense fluid flows as a gravity current into the zone that initially contained light fluid. This gravity current reflects from the end wall and propagates back toward the opening in the form of an internal bore. When the bore reaches the opening the dynamics of the exchange flow are substantially altered. Such coupled dynamics of the two zones are modeled using elements of gravity current, internal bore and plume theory. Depending on the geometric parameters two scenarios are possible. Either the terminal position of the first front lies above the bottom of the barrier, or it lies below. In the latter case, the associated complications are (i) the nature of the exchange flow changes once the downward-propagating first front surpasses the bottom of the barrier, and, (ii) the terminal stratification in the zone that initially contains the light fluid now includes an intermediate layer. We also present a model that presumes that both zones remain well-mixed.
  When the two zones are separated by top and bottom vents, two oppositely directed exchange flows are generated. The transient evolution of the interface, stratification and buoyancy in each zone are estimated both for the case where the light zone does and does not contain a source of buoyancy. Attention is focused on the influence of the effective area, source buoyancy flux and the time during which the source is switched on.
  Similitude experiments help to identify the limitations of the analytical models for each scenario. The implications of our results on the design of multi-zone buildings that exploit passive heat gains are also discussed.

• Subjects / Keywords

  • Gravity current
  • Adjacent building zones
  • Natural ventilation
  • Plumes
  • Buoyancy-driven exchange flow
  • Internal bore

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3RJ49318

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.