  In this paper, we present a unified scheme based on the fluid description of
the dark sector of the universe. The scheme captures models with interaction
between dark energy and dark matter, being the core of generalization the
time-varying equation-of-state parameter $\omega(a)$ and the time-dependent
interactions through the interaction function $\epsilon(a)$, where $a$ is the
scale factor. Furthermore, we propose thermodynamics constraints on this
generalized class of models using the laws of thermodynamics which are combined
with observational data. In order to test the observational viability of the
unified model, we perform a Bayesian analysis using cosmic chronometers, type
Ia supernovae, cosmic microwave background, and angular baryon acoustic
oscillation measurements.
