  Solar still is an eco-friendly and convenient desalination system that can
provide fresh water for remote areas and emergencies. The energy efficiency and
productivity of conventional solar still are unsatisfying and need improvement,
which requires a deep understanding of the heat and mass transfer process in
solar still. In this work, the effect of the inner air circulation on the
system's heat and mass transfer performance and energy efficiency are studied
theoretically and experimentally. The theoretical results reveal that a weak
acceleration of the air circulation inside the SS will significantly increase
its performance, due to the improved mass transfer process. By enhancing the
inner air circulation, the evaporation and condensation in the solar still can
reach up to the limit, and the theoretical energy efficiency reaches up to 87%,
91.5%, and 94.5%, for the input power density at 300 W/m2, 500 W/m2, and 700
W/m2, respectively. Besides, lower ambient temperature and higher ambient
convective heat transfer coefficient will decrease the energy efficiency. Given
the heat loss, the experimental energy efficiencies are only 3% to 6% lower
than the theoretical results, which indicates that the great performance
predicted by the theory can be realized in practical application. This work
provides a new understanding and strategy for improving the performance of the
solar still.
