Theoretical and experimental studies on air gap membrane distillation

Liu, G. L.; Zhu, Chao; Cheung, Chun Shun; Leung, Chun Wah

doi:10.1007/s002310050267

Cited by 107 publications

(73 citation statements)

References 14 publications

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“…In comparison with the thickness (40-250 µm) and conductivity of the membrane, the air gap is much thicker (general 2000-10,000 µm) [31,32] and has lower thermal conductivity. Therefore, more heat energy in AGMD will be used for water evaporation than in DCMD.…”

Section: Configurations Of Membrane Distillationmentioning

confidence: 99%

“…Additionally, if a low temperature feed is used as the cooling stream in this configuration, the latent heat can be recovered through the condensation of the vapor on the cooling plate. However, AGMD typically has a low flux, due to the low temperature difference [6,20,32] across the membrane and therefore larger surface areas are required.…”

Section: Configurations Of Membrane Distillationmentioning

confidence: 99%

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Advances in Membrane Distillation for Water Desalination and Purification Applications

Camacho

Dumée

Zhang

et al. 2013

Water

642

342

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Membrane distillation is a process that utilizes differences in vapor pressure to permeate water through a macro-porous membrane and reject other non-volatile constituents present in the influent water. This review considers the fundamental heat and mass transfer processes in membrane distillation, recent advances in membrane technology, module configurations, and the applications and economics of membrane distillation, and identifies areas that may lead to technological improvements in membrane distillation as well as the application characteristics required for commercial deployment. Keywordsa function of temperature, vapor pressure, and of the gas molecular mass K 0 membrane characteristic defined by Equation (9) Kn Knudsen number K(T) a function of temperature and molecular weight of the gas l mean free path of the molecules l m distance between parallel spacer fibres (m) LEP Limit Entry Pressure (kPa) M molecular mass (g/mol) M w molecular weights of water (g/mol) M a molecular weights of air (g/mol) n number of CNTs per unit cross section in bucky-paper P pressure in the air gap (kPa) half time to reach the maximum intensity-laser flash technique (s) t proportion of conductive heat (balance due to evaporative heat) loss through the membrane T mean temperature in the pores (K)

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Section: Configurations Of Membrane Distillationmentioning

confidence: 99%

Section: Configurations Of Membrane Distillationmentioning

confidence: 99%

Advances in Membrane Distillation for Water Desalination and Purification Applications

Camacho

Dumée

Zhang

et al. 2013

Water

642

342

View full text Add to dashboard Cite

show abstract

“…Traditional AGMD simply condenses distillate in the laminar film regime, an understood and well-characterized process [13,14]. With superhydrophobic surfaces, jumping droplets may occur, especially at low distillate flow rates and small air gap thicknesses.…”

Section: Condensing In Agmdmentioning

confidence: 99%

Superhydrophobic condenser surfaces for air gap membrane distillation

Warsinger

Swaminathan

Maswadeh

et al. 2015

Journal of Membrane Science

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Superhydrophobic surfaces for enhanced condensation in Air Gap Membrane Distillation (AGMD) may provide significantly improved distillate production rates and increased thermal efficiency. While AGMD is one of the most thermally efficient membrane distillation desalination configurations, large transport resistances in the air gap limit distillate production rates. AGMD experiments were performed with combinations of untreated, hydrophobic, and superhydrophobic condensation surfaces. A nanostructured copper oxide coated condensing surface produced durable 164°±4° contact angles and jumping droplet condensation. Tests were also performed on the air gap spacer, in this case a small diameter support mesh, to judge the effects of superhydrophobic treatment and conductivity on distillate production for AGMD. A novel visualization technique was implemented to see through PVDF membranes and confirm air gap behavior. The experiments were compared with numerical modeling of AGMD film-wise condensation and flooded-gap MD. The results indicate that the introduction of superhydrophobic surfaces can result in improvements in distillate production in excess of 60% over standard AGMD. However, for high distillate production condensation on the superhydrophobic plate transitions from a partially wetted droplet morphology to Wenzel flooded (wetting) conditions. Mildly hydrophobic condensing surfaces were found to provide moderate improvement in distillate production. Superhydrophobic support meshes made a negligible difference in distillate production, but high conductivity support meshes showed significant increases in flux at the expense of thermal efficiency. The results outline recommended superhydrophobic condensation conditions at varied feed and cold side temperatures for substantial improvement to distillate production rate for AGMD systems in a flat plate configuration. KEYWORDS

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“…Configurations of MD primarily differ by the design of the gap itself [26], which may be airfilled (as in the case of AGMD) [19,[27][28][29], flooded with permeate (permeate gap or PGMD) [30][31][32], or held at a partial vacuum (VMD) [33,34].…”

Section: Introductionmentioning

confidence: 99%

“…Standard AGMD modules are presumed to condense distillate in the laminar film regime, a well-characterized process [27,37]. The primary factor that can change this is the presence of the spacer which can impact the water flow.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

Warsinger

Swaminathan

Morales

et al. 2018

Journal of Membrane Science

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The thermal performance of air gap membrane distillation (AGMD) desalination is dominated by heat and mass transfer across the air gap between the membrane and the condensing surface. However, little is known about the impact of condensate flow patterns in some design variations of the air gap. In this study, air gap membrane distillation experiments were performed at various inlet temperatures, varying module inclination angle, condensing surface hydrophobicity, and gap spacer design to identify the effect of each on the permeate production rate and thermal efficiency of the system. Energy efficiency modeling was performed as well. Additionally, this study is one of the first with enhanced visualization of flow patterns within the air gap itself, by using a transparent, high thermal conductivity sapphire plate as the condenser surface. System-level numerical modeling is used to further understand the impact of these flow regimes on overall energy efficiency, including flux and GOR. A brief review of membrane distillation condensation regimes is provided as well. For tilting the AGMD flat-plate module, permeate flux was barely influenced except at extreme positive angles (>80ᵒ), and moderate negative angles (<-30ᵒ), where condensate fell onto the membrane surface. The surface with the hydrophobic coating (for dropwise condensation) was shown to have better droplet shedding (with very small nearly spherical droplets) and fewer droplets bridging the gap. Superhydrophobic surfaces (for jumping droplet condensation) were similar, with much smaller droplet sizes. Meanwhile, the hydrophilic surface for small gap sizes (< 3 mm) often had pinned regions of water around the hydrophilic surface and plastic spacer. Overall, the various results imply that the common assumption of a laminar condensate film poorly describes the flow patterns in real systems for all tilt angles and most spacer designs. Real system performance is likely to be between that of pure AGMD and permeate gap membrane distillation (PGMD) variants, and modeling shows that better condensing in air gaps may improve system energy efficiency significantly, with strong relative advantages at high salinity.

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Theoretical and experimental studies on air gap membrane distillation

Cited by 107 publications

References 14 publications

Advances in Membrane Distillation for Water Desalination and Purification Applications

Advances in Membrane Distillation for Water Desalination and Purification Applications

Superhydrophobic condenser surfaces for air gap membrane distillation

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

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