GRUPO DE TÉCNICAS COMPUTACIONALES
EN LA INGENIERÍA
UNIVERSIDAD de MÁLAGA
Annular liquid jets are thin sheets of liquid falling under gravity which, under certain conditions, merge in the centerline to become round liquidjets (Figure 1). The volume enclosed by annular liquid jets has been proposed as a chemical reactor for scrubbing of radioactive and non-radioactive materials, burning of toxic wastes, reduction of zirconium from zirconium tetrachloride and sodium, etc., because the liquid jet contains the reaction and the gases generated in, for example, the combustion of toxic wastes may be absorbed by the liquid which may be collected, purified and recycled so that the combustion-generated gases do not flow through the jet's outer interface and, therefore, do not pollute the environment.
Figure 1. Schematic of an annular liquid jet
Most previous studies of annular liquid jets have been concerned with the analysis of their fluid dynamics and heat/mass transfer under steady state conditions by assuming that the axial velocity component of the liquid is governed by Torricelli's free-fall formula since the geometry of the jet is curvilinear. Moreover, studies on mass transfer in annular liquid jets have taken profit of the fact that the binary diffusion coefficient of gases in liquids is much smaller than that of gases; as a consequence, mass absorption by annular liquid jets is a rather slow process, and the decrease or growth that the volume enclosed by the annular liquid jet experiences due to the mass absorbed by the liquid is mainly controlled by the mass of the gases generated by the combustion of toxic wastes.
volume enclosed by annular liquid jets is used to burn toxic wastes, in
addition to the absorption of the gaseous combustion products by the liquid,
one must account for the heat exchanges between this volume and the jet. However,
since the heat diffusion coefficient in the liquid is much larger than the mass
diffusion coefficient of the gases absorbed by the liquid, it is to be expected
that liquid jet absorb the heat at a faster rate than the gaseous combustion
products and, as a consequence, the combustion of toxic wastes in the volume
enclosed by annular liquid jets is characterized by four time scales: the
characteristic residence time which depends on the liquid volumetric flow rate,
the characteristic reaction time, and the characteristic times for heat and
mass absorption by the liquid. Since the latter is much larger than the other
three, one may assume that mass absorption is a quasi-steady phenomenon. Moreover,
if the liquid does not absorb the heat at a sufficiently large rate, the
heating of the gases enclosed by the annular jet will increase their
temperature, pressure and volume; therefore, under these conditions, the
curvilinear geometry of the annular liquid jet will be a function of time. We
are thus faced with a free-surface problem, i.e., the annular liquid jet, which
affects and is affected by the combustion of the toxic wastes that it encloses.