Buoyancy and velocity field synergy principle for enhancing buoyancy-driven ventilation and natural smoke venting

Buoyancy-driven ventilation is a zero-energy measure for removing residual heat and gaseous contaminant from building interior space, and buoyancy-driven natural smoke venting is prevalent in smoke control for guaranteeing human evacuation. This paper establishes a mechanical energy conservation equation, describing the non-isothermal fluid delivery and the associated mechanical energy transport along with natural convection. A field synergy principle regarding buoyancy and velocity fields is proposed based on the conservation equation. The multi-field synergetic relations among pressure gradient, velocity, and buoyancy are derived. The mechanical energy input resulted from the work done by thermal buoyancy in the buoyancy-driven non-isothermal flow is correlated with both Ra and the field synergy degree between buoyancy and velocity, which is characterized by a field synergy number, FsU,g. The proposed new field synergy principle has been verified with natural convection occurred in vertical channels bounded with parallel plates, and it is applied in typical buoyancy-driven ventilation or smoke venting scenarios. The buoyancy-driven ventilation or smoke venting capability can be enhanced through improving the degree of synergy between buoyancy and velocity in the flow domain, even though the indoor air or smoke temperature is decreased. This principle helps to further understand the physical essence and role of thermal force in buoyancy-driven ventilation and smoke flows, and it provides a new route for enhancing natural ventilation and smoke control effectiveness in buildings.