The fluid mechanics of horizontal exchange flows in naturally ventilated buildings
Author(s)
Higton, Thomas David
Type
Thesis
Abstract
The research in this thesis concerns the mathematical and physical modelling of natural ventilation flows involving buoyancy-driven horizontal exchange flows (the simultaneous movement of air in both directions through an opening in the vertical plane). Exchange flows are commonplace through any open window or doorway, and therefore our understanding of them is of significant importance in the design of natural ventilation systems. Previous research has been limited to the study of exchange flows in isolation and their effect on steady airflows in a few special cases of building ventilation, for example, mixing ventilation (Linden1990). The primary aim of this thesis is to improve our understanding of how exchange flows affect ventilation dynamics and temperature stratifications within rooms and to develop new theoretical models that thus facilitate the efficient design of natural ventilation systems.
Two exchange flows are focused on; unbalanced doorway exchange flows (non-zero net flux) and balanced window} exchange flows (zero net flux). Unbalanced doorway exchange flows driven by a localised or distributed heat source are studied by investigating the steady ventilation flow in a room with a doorway and a high-level vent. When the neutral pressure level is below the top of the doorway, a steady ventilation regime is observed that includes an unbalanced exchange flow through the doorway (and classical displacement ventilation when the neutral pressure level is above the doorway). The ventilating flow is found to depend on the aspect ratio of the doorway, the height of the doorway relative to the height of the room, the area of the high-level vent and the properties of the heat source. Complementary small-scale experiments using the salt-bath modelling technique show excellent agreement with the predictions of the theoretical modelling…
Two exchange flows are focused on; unbalanced doorway exchange flows (non-zero net flux) and balanced window} exchange flows (zero net flux). Unbalanced doorway exchange flows driven by a localised or distributed heat source are studied by investigating the steady ventilation flow in a room with a doorway and a high-level vent. When the neutral pressure level is below the top of the doorway, a steady ventilation regime is observed that includes an unbalanced exchange flow through the doorway (and classical displacement ventilation when the neutral pressure level is above the doorway). The ventilating flow is found to depend on the aspect ratio of the doorway, the height of the doorway relative to the height of the room, the area of the high-level vent and the properties of the heat source. Complementary small-scale experiments using the salt-bath modelling technique show excellent agreement with the predictions of the theoretical modelling…
Version
Open Access
Date Issued
2022-07-09
Date Awarded
01/12/2022
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Burridge, Henry
Hughes, Graham
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/R512540/1
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)