David Warsinger
MIT
Jaichander Swaminathan
Rohsenow Kendall Heat Transfer Laboratory, Department of Mechanical Engineering
Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA 02139-4307,
USA
Lucien L. Morales
Rohsenow Kendall Heat Transfer Laboratory, Department of Mechanical Engineering
Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA 02139-4307,
USA
Margaret Bertoni
Rohsenow Kendall Heat Transfer Laboratory, Department of Mechanical Engineering
Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA 02139-4307,
USA
John H. Lienhard V
Rohsenow Kendall Heat and Mass Transfer Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
Condensation performance is a key target for improving the energy efficiency of thermal desalination
technologies such as air gap membrane distillation (AGMD). This study includes the first visualization of
condensation in AGMD, through the use of a high conductivity, transparent sapphire condenser surface.
The study examines how flow patterns are affected by several novel modifications, including varied
surface hydrophobicity, module tilt angle, and gap spacer design. The experimental results were analyzed
with numerical modeling. While the orientation of the mesh spacer, which holds the air gap apart, was
found to have no substantial effect on the permeate production rate, the surface's hydrophobicity or
hydrophilicity did result in different rates. The hydrophobic surface exhibited fewer droplets bridging the
gap, more spherical droplets, and better droplet shedding. For gap sizes less than ~3 mm, the hydrophilic
surface frequently had regions of water pinned around the surface itself and the plastic spacer. While the
flow patterns observed were more complex than the film condensation typically used to model the
process, the simplified numerical modelling yielded good agreement with the data when an adjustment
factor was used to account for the gap size.