  We discuss a new interacting model for the cosmological dark sector in which
the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a)
is an arbitrary function of the cosmic scale factor $a$. From thermodynamic
arguments, we show that f(a) is proportional to entropy source of the particle
creation process. In order to investigate the cosmological consequences of this
kind of interacting models, we expand f(a) in a power series and viable
cosmological solutions are obtained. Finally, we use current observational data
to place constraints on the interacting function f(a).
