
Professore Ordinario
Dipartimento di Ingegneria Chimica, Chimica
Industriale e Scienza dei Materiali (DICCISM)
Università degli Studi di Pisa
Via Dotisalvi 2
 56126 Pisa  Italy
Tel. ++390502217848; Fax: ++390502217866;
Email: r.mauri@ing.unipi.it
See
the Publication List.
In the
first part of this research effort, the transport of heat, mass and momentum in
two phase, macroscopically homogeneous systems is studied, both experimentally
and theoretically. Familiar examples include the flow of suspensions through
pipes and the heat and mass conduction through composite materials. In general,
the systems that we study consist typically of two phases, in which one is
finely divided; thus, on the macroscale, the
composite can be viewed as an effective continuum, having a set of welldefined
effective properties, such as an effective diffusivity for the transport of
solutes through porous media, or an effective viscosity, for the flow of
suspensions. Since, in principle, the theoretical determination of a given
effective parameter requires the solution of a corresponding problem on a microscale, which from a practical standpoint is very
difficult to implement, our approach is instead to determine these effective
parameters using some sort of statistical averaging. In this way, we have
determined the effective viscosity of neutrally buoyant suspensions, the
effective reactivity, velocity and diffusivity of solutes in porous media, the
mean thermocapillary velocity of polydisperse
suspensions of bubbles, and the shearinduced diffusivity of suspensions of
rigid spheres.
In another
research effort, the phase separation of deeply quenched liquid mixtures into
two phases is studied. Since the phase transition process can be triggered by
changing either the temperature or the composition of the system, separation
can be achieved either by heating and cooling the solvent mixtures across their
miscibility curve, or by adding a solubility modifier. Two main topics are
being currently investigated. First, the morphology of phase separation of
liquid mixtures is studied from a fundamental point of view, both
experimentally and theoretically, showing that it does not correspond to that
of traditional nucleationandgrowth processes. Second, from a more
technological viewpoint, we have developed a new process of solvent extraction,
which a) is much faster than conventional approaches at extracting solutes from
porous materials, and b) is rapid and emulsionfree even when surface active
compounds are added to the system. The first result is due to the fact that in
our process the pores are more effectively wetted, while the explanation of the
second effect is that phase separation of critical liquid mixtures occurs
without the appearance of moving interfaces. The new process has been applied
in bioengineering to extract antibiotics from fermentation broths, and in
remediation, to extract heavy metals from contaminated soils and sludge.
Finally, we have developed a
general approach to simulate multiphase flow processes in confined geometries
using the diffuse interface method. Multiphase flows are generally modeled assuming
that the different phases are separated by an interface, that is a surface of
zero thickness; imposing that the condition of local equilibrium is satisfied,
all physical properties are allowed to change discontinuously across the
interface. Naturally, that results in a free boundary problem, which means that
one of the main problems of this approach is to determine the position of the
interface. In microdevices, an additional difficulty
is encountered, as most lengthscales of the systems
are comparable to the real interface thickness; this problem arises also in
modeling drop coalescence and break up and moving contact angles. In these
cases, it is more reasonable to use a different approach, proposed at the end
of the 19^{th} century by Rayleigh and Van der Waals, where interfaces
have a nonzero thickness, i.e. they are "diffuse", so that all
quantities, such as density or composition, vary continuously. This approach
was later generalized by Landau and Ginzburg, who
developed the mean field theory of phase transition. In particular, when the
equations of motion are derived, an additional stress, so called Korteweg stress, arise naturally as reversible body forces,
that tends to minimize the free energy of the system. This approach has been
applied to simulate several processes, such as a) mixing, spinodal
decomposition and nucleation of macroscopically quiescent regular mixtures; b)
deformation, coalescence and breakup of fluid volumes under shear flows; c)
heat transfer enhancement due to phase change.