Flow and mixed convection heat transfer in buoyant jets from floor registers

• We experimentally analyze flow and mixed convection in building perimeter zones.
• We describe diffuser jet movement, penetration, and decay along a vertical wall.
• We identify three distinct operating regimes, which determine jet behavior.
• We find both buoyancy and momentum forces influence jet behavior in many cases.
• We provide refined models of mixed convection heat transfer in perimeter zones.

As models of energy movement in buildings and tools for load calculation become more refined, more accurate descriptions of fluid mechanics and heat transfer in perimeter zones are needed. New construction which includes glass curtain walls around perimeter zones presents a unique challenge. A mixed convection regime may be present which precludes the use of existing models developed for purely forced convection. In order to study flow and heat transfer in these situations, environmental conditions are precisely controlled in a test room to simulate situations that may occur in perimeter zones of buildings with glass curtain walls. Diffuser jets issuing from floor registers were shown to exhibit behavior not accounted for in existing heat transfer models. Results show that the movement of the jet issuing from floor registers is highly dependent on the mixed convection parameter Gr/Re2 or Richardson number. Models are put forth to predict the movement of these jets, and the resulting heat transfer at walls or windows. When the effect of buoyancy forces is accounted for, models conform to a form used previously for turbulent forced convection. Three distinct flow regimes are identified and prescriptions are put forth for ensuring proper thermal control and accurate energy models.