Variations of buoyancy-induced mass flux from single-phase to two-phase flow in a vertical porous tube with constant heat flux

This paper presents an experimental study of a buoyancy-induced flow of wat er with phase-change heal transfer in a vertical porous tribe heated at a c onstant heat flux. Experiments were carried out from subcooled liquid flow to convective boiling by varying the imposed heat fluxes. At a prescribed h eat flux the steady-state mass flux of water, as well as the temperatures a long the tube wall and along the centerline of the packed tribe, were measu red. It is shown that for both single-phase flow and the two-phase flow wit h a rather low vapor fraction, the induced mass flux increased as the heat flux was increased. However as the imposed heat flux was increased further, the induced mass flux dropped drastically, and remained relatively constan t afterwards. The influences of various parameters such as the porous tube diameter, the particle sizes, and the hydrostatic head on the induced mass flux are also examined.