  Viscoelastic fluids are a subclass of complex fluids used in widespread
applications ranging from biological to large-scale industrial settings. These
fluids are often associated with various complex flow phenomena due to the
presence of non-linear elastic stresses, originating due to the stretching and
relaxation phenomena of microstructure (such as polymer molecules in the case
of a viscoelastic polymer solution) in a deformed flow field. One such
phenomenon is elastic instability (EI) which emerges due to the interaction
between elastic stresses and streamline curvature present in a flow system at
small values of the Renolds number (ratio of the inertial to that of the
viscous forces) when the Weissenberg number (ratio of the microstructure
relaxation time to that of the rate of flow deformation) exceeds a critical
value. On further increasing this Weissenberg number to higher values, the
unstable flow field caused due to this elastic instability transits to a more
chaotic and turbulent-like flow structure called elastic turbulence (ET). Over
the last two decades or so, an extensive investigation has been performed on
this particular topic in the complex fluids research community. Some excellent
articles recently present this ET phenomenon's development, understanding, and
progress in the literature. This article focuses on the application
perspectives of this phenomenon. In particular, this article aims to provide a
comprehensive review of the investigations conducted so far in the literature
to demonstrate the potential of these EI and ET phenomena in three main
application areas, namely, microfluidic mixing, microscale heat transfer, and
chemically enhanced oil recovery (EOR) process. Additionally, a detailed
discussion of the limitations and future directions of these EI and ET
phenomena from an application point of view is also presented in this article.
