WATER FILTRATION BY SEQUENTIAL EVAPORATION AND CONDENSATION: A MOLECULAR DYNAMICS APPROACH

Abstract

In the present study an effort has been made to get an insight into the thermal mode of water filtration by sequential boiling and condensation from molecular perspective. Understanding the physics behind the heat and mass transfer during phase change occurring at molecular level may help in developing better filtration systems. Micro or nano level filters can be multiplexed to get macro filters. In addition to water filtration, molecular level understanding of the phase change phenomena can greatly help in improving the design of nano and micro sized electronic devices for efficient removal of thermal loads for their smooth operation. Molecular level numerical simulations have been carried out to study the boiling and condensation of water on a copper substrate under the framework of classical Molecular Dynamics (MD). Performed simulations can be broadly classified into three cases namely (1) Rapid boiling (2) Sequential occurrences of boiling and condensation and (3) Water filtration in the process of boiling and condensation. In the first type of cases, rapid boiling of thin water film on a hot copper substrate maintained at 800 K was studied and results were compared for two different geometries of the copper plate namely (1.1) Smooth (1.2) Nanostructured with a rectangular groove. Results showed that the presence of rectangular groove led to advancement in the bubble nucleation time. Also, the bubble initiation and growth commenced at the nanostructure itself making it an active nucleation site while it was almost probabilistic for flat surface. The rate of mass transfer was also high in the presence of nano rectangular groove. In the second case sequential occurrences of boiling and condensation of thin liquid water film within a hydrophobic molecular confinement formed by two solid copper walls one maintained at 560 K (heat source) and another at 300 K (heat sink) was studied and results were compared for three different geometries of the copper plates namely (2.1) Both hot and cold plates as smooth and flat. (2.2) Hot plate smooth while cold plate nanostructured having a semicylindrical protrusion (2.3) Hot plate smooth while cold plate nanostructured having two semicylindrical protrusions. Results showed that the performance of the condensing plate with two semicylindrical humps was highest owing to its maximum surface area followed by single hump and smooth surface structure.