A comprehensive review of air gap membrane distillation process

Abstract

a b s t r a c tMembrane distillation (MD) is a promising thermally driven membrane separation technique. In MD, water vapor is being separated from the hot feed water solution using a microporous hydrophobic membrane, due to the difference in temperature, and hence vapor pressure, across the membrane. Air gap membrane distillation (AGMD) process is one of the common configurations of applying the MD process for water desalination and other applications. In AGMD, a stagnant air gap is introduced between the membrane and a condensation surface within the membrane module to reduce the conduction heat loss through the membrane. In this review article, design characteristics and operating conditions of AGMD and its modified designs to enhance the productivity and reduce the energy consumption are surveyed and discussed. Previous work on pilot AGMD systems and multi-stage or multi-effect systems with energy saving modules is highlighted. Membrane materials and developments used with the AGMD modules are presented with discussion of membrane fouling and scaling problems. In addition, modeling techniques based on the heat and mass transfer equations and simulation approaches of the AGMD process are presented. The merits of operating the AGMD systems with solar and other renewable energies are discussed along with the economic aspects. The future research directions of AGMD are highlighted in this review. This will help researchers to direct their research without repetition of previous known studies.

Plasma-Induced Superhydrophobicity as a Green Technology for Enhanced Air Gap Membrane Distillation

“…Mass transfer coefficient is proportional to porosity and the fact that O 2 plasma etching increases porosity suggests that it plays a dominant role in the permeate flux increase of all plasma treated membranes. 62 Due to its largest pore size, the plasma treated PTFE 1 membrane yields, as expected, the highest flux at 10.9 L/(m 2 h) when compared to the other plasma treated PTFE membranes (Figure 5C). However, in addition to wetting control, plasma treatment enables the permeate water fluxes of the plasma treated PTFE 0.1 and PTFE 0.2 membranes to exceed that of the untreated PTFE 1 membrane.…”

“…Plasma treated membranes exhibit lower tortuosity (improved pore shape) and increased porosity values compared to untreated ones (Table ). Mass transfer coefficient is proportional to porosity and the fact that O 2 plasma etching increases porosity suggests that it plays a dominant role in the permeate flux increase of all plasma treated membranes …”

Desalination by Membrane Distillation

“…However, due to high mass transfer resistance at permeate side, the flux is less as compared with other configurations. The air gap reduces the conduction heat loss from feed to permeate [8][9][10].…”

“…The heat transfer coefficients h f and h p can be calculated using Nusselt number relation as shown in Eq. (10), while the h m can be calculated from Eq. (3).…”

Recent Progress in the Membrane Distillation and Impact of Track-Etched Membranes

“…As shown in Figure 2 , there are four known and well-studied membrane distillation configurations: DCMD, AGMD, SGMD and VMD [ 31 , 32 , 33 , 34 ]. There are also known three supplemental configurations: liquid or water gap membrane distillation (LGMD/WGMD), thermostatic sweeping gas membrane distillation (TSGMD) and vacuum-assisted air gap membrane distillation (VA-AGMD) [ 35 , 36 , 37 ].…”