Penetrative convection of a plane turbulent wall jet in a two-layer thermally stable environment: a problem in enclosure fires

Abstract

An experimental investigation has been carried out on the penetrative characteristics of a heated, two-dimensional, turbulent wall jet discharged downward into a two-layer thermally stable environment. Such flows, with opposing buoyancy effects, are frequently encountered in heat rejection processes and in enclosure fires. The discharge temperature of the jet is taken as higher than the upper layer temperature so that the jet is negatively buoyant in both layers. Of particular interest is the penetration of the jet into the lower layer. The conditions for which it fails to penetrate the interface between the two layers are also determined. The penetration distance of the jet is measured and related to the inflow conditions, particularly to the temperature and the velocity at the discharge. The thermal field is studied in detail to determine the basic characteristics of such flows. The mass flow rate penetrating downward as well as that rising upward due to thermal buoyancy are obtained and compared with the jet inlet mass flow rate. The heat transfer to the surface is measured for several wall temperatures and considered in terms of the penetrative flow. Flow visualization with smoke is also undertaken in order to obtain further insight into the basic nature of the flow.