Purdue University Graduate School

File(s) under embargo


posted on 2023-04-29, 01:10 authored by Yashwant S YogiYashwant S Yogi

The water crisis is increasing with every passing day due to climate change and increase in demand. Different desalination methods have been developed over the years to overcome this shortage of water. Reverse Osmosis is the most widely used desalination technology, but cannot treat many fouling-prone and high salinity water sources. A new desalination technology, Membrane distillation (MD), has the potential to purify wastewater as well as highly saline water up to a very high purity. It is a thermal energy-driven desalination method, which can operate on low temperature waste heat sources from industries, powerplants and renewable sources like solar power. Among the different configurations of MD, Air Gap Membrane Distillation (AGMD) is the most versatile and flexible. However, the issue that all MD technology, including AGMD face, is the low energy efficiency. Different sections of AGMD system have been modified and improved over the years through consistent research to improve its energy efficiency, but one section that is still new and unexplored, and has a very high potential to improve the energy efficiency of AGMD, is the ‘air gap’.

The aim of this research is to tap into the potential of the air gap and increase the energy efficiency of the AGMD system. It is known that decreasing the air gap thickness improves the energy efficiency parameter called Gained output ratio (GOR) to a great extent, especially at very small air gap thickness. The minimum gap thickness that maximizes the performance is smaller than the current gap thicknesses used. But it is difficult to attain such smaller air gap thickness (< 2mm) without the constant risk of flooding. Flooding can be prevented, and smaller air gap thickness can be achieved if instead of film wise condensation on the condensing surface, a different condensation flow regime is formed. This study tests different novel condensing surfaces like Slippery liquid infused porous surfaces (SLIPS) and Superhydrophobic surfaces (fabricated with different methods) inside the AGMD system with a goal of attaining smaller air gap thickness and improve the performance of AGMD system for the first time. The performance of these surfaces is compared with plain copper surface as well as with each other. Finally, numerical models are developed using the experimental data for these surfaces.


Degree Type

  • Master of Science


  • Mechanical Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

David M. Warsinger

Additional Committee Member 2

Justin Weibel

Additional Committee Member 3

Nenad Miljkovic