Downstream variations of air-gap membrane distillation and comparative study with direct contact membrane distillation : A modelling approach

Air-Gap Membrane Distillation (AGMD) promises to reduce heat loss in membrane distillation. Most AGMD models are one-dimensional and do not consider the downstream variations. In addition, a linear function of vapour pressure is used, which either relies on experimentally determined parameters or a simplified mass transfer resistance to model the water permeate flux. This study introduces a new, improved model that simultaneously considers both heat and mass transfer in the AGMD process by coupling the continuity, momentum, and energy equations. A novel precise logarithmic function of vapour pressure was derived to model the water permeate flux, independent of experimentally determined parameters. By varying the inlet temperature, Reynolds number, inlet concentration, and air-gap thickness, the performance of AGMD was evaluated. The results revealed that our model improved the water flux prediction from more than 10% to less than 4% deviation from experimental results. Among the operating conditions, only increasing the Reynolds number improved all the system performance metrics, including higher water flux and lower temperature and concentration polarisation effects. Results were compared with Direct Contact Membrane Distillation (DCMD) outcomes and showed that unlike AGMD, DCMD suffers from a substantial decrease in water flux along the module. For DCMD, the exit water flux value decreased by 50% in comparison with the inlet value, while the water flux decreased by only 2% for AGMD, using a 1 mm air gap thickness.</p

Computational fluid dynamics modelling of air-gap membrane distillation : Spacer-filled and solar-assisted modules

Air-gap membrane distillation (AGMD) is a novel method of water purification and promises to reduce heat requirements. However, AGMD is characterized by low water permeate flux and a significant downstream performance reduction including temperature, concentration polarisations and membrane fouling. These challenges are difficult to explore both experimentally and numerically. To date, computational fluid dynamics (CFD) of AGMD focuses on temperature polarisation without considering solute transport. In addition, they lacked an accurate calculation of water flux affecting the distributed flow properties, especially close to the membrane. A 2D comprehensive study using CFD simulation of the AGMD was developed to determine the effectiveness of solar absorbers and spacer filaments on these challenges. A precise logarithmic function of vapour pressure was used to model the mass transfer within the membrane. The simulation was in excellent agreement with previously published experimental results. Results showed that using solar absorbers can slightly increase the water flux and decrease both the temperature and concentration polarisation effects. Additionally, the results were more sensitive to the air-gap thickness compared to using solar absorbers. Results also proved that cylindrical detached spacers provided higher water flux when compared to semicircular and rectangular attached spacers. The proposed spacer-filled module improved the AGMD performance and resulted in the uniform water flux from the inlet to the outlet. The water flux increased by 15 %, and the downstream performance variation of the developed module was <3 % throughout the module, compared to 21 % for the module with no spacer. This is a very encouraging development for low-energy water purification systems.</p

Computational fluid dynamics simulations of solar-assisted, spacer-filled direct contact membrane distillation : Seeking performance improvement

Significant downstream performance reduction and concentration polarisation reduce direct contact membrane distillation (DCMD) efficiency. These challenges are not well researched since they are difficult to implement experimentally and numerically. Hence, this study examined the impact of solar absorbers and different spacer filaments upon DCMD performance. A 2D computational fluid dynamics model that considered simultaneous mass and heat transfer across the membrane and throughout the channels was developed to simulate water flux in DCMD modules under the use of solar absorbers and spacer filaments of various designs. The simulation outcomes were in excellent agreement with experimental results provided by two different studies, with the assisted solar absorber module and the spacer-filled module deviating <5 % and 3 % from the experimental results, respectively. A module equipped with the solar absorber membrane enhanced the DCMD performance better than a module with a solar absorber plate. The results also illustrated that a module with cylindrical detached spacer filaments improved DCMD performance more than a module with rectangular and semicircular attached spacers. Finally, it was shown that a module equipped with an integrated developed spacer and solar absorber membrane significantly enhanced water flux and both concentration and temperature polarisations, specifically when the inlet velocity was increased. Water flux and the temperature polarisation coefficient increased by 220 % in the integrated module, and the concentration polarisation coefficient decreased by 10 %. Moreover, the developed module resulted in a substantial increase in downstream performance.</p

Core-shell particles: from fabrication methods to diverse manipulation techniques

Core-shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core-shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core-shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core-shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core-shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail.Published versionThis research was funded by Australian Research Council (DP220100261)