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• The mechanism of " in-situ heat transfer" was put forward for the first time. • The jacketed structure can reduce the consumption of energy and cooling water. • Analyzed the novel VMD process from the perspective of mass and heat transfer. Thermal driven membrane distillation (MD) technology is a promising method for purifying & recovering various salty (especially high salty) or contaminated wastewaters with low-grade heat sources. However, the drawbacks of "high energy consumption" and "high cooling water consumption" pose special challenges for the future development of this technology. In this article, we report an innovative strategy called " in-situ heat transfer", which is based on the jacketed structure composed of hollow fiber membranes and capillary heat exchange tubes, to simplify the migration steps of condensation latent heat in MD heat recovery process. The results indicate that the novel heat recovery strategy exhibits higher growth rates both in the flux and gained output ratio (47.4 % and 173.1 %, respectively), and further reduces the system′s dependence on cooling water. In sum, under the control of the " in-situ heat transfer" mechanism, the functional coupling of "vapor condensation (exothermic)" and "feed evaporation (endothermic)" in limited-domain space is an attractive alternative solution, because it eliminates the disadvantages of the imbalance between heat supply and demand in traditional heat recovery methods. Our research may facilitate the development of MD heat recovery modules for industrial applications, which will help to further achieve the goal of energy saving and emission reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

Polymer hollow fiber membranes (HFMs) are the core or base membranes of various membrane processes (e.g., ultrafiltration and membrane distillation). Preparing polymer HFMs with higher water flux helps improve the efficiency of the membrane processes. Using pore‐forming additives is the commonly used and efficient method to improve the water flux. The current dilemma is that the conventional methods that increase the amounts or the molecular weight of the additives to improve the water flux usually lead to the decrease in membrane mechanical strength. Herein, different from the conventional research strategy, increasing the surfactant surface activity (SA) is first found to deeply promote the core of nonsolvent‐induced phase separation (NIPS) that of the mutual diffusion between water and dopes. As a result, this method distinctly improves the surface porosity (from 0.8% to 9.7%) and optimizes the pore size distribution of polyvinylidene fluoride (PVDF) HFMs. Benefit from these, the water flux of ultrafiltration (3.1‐fold increase, maximally) and direct contact membrane distillation (2.3‐fold increase, maximally) are increased greatly. Moreover, the mechanical strength is not negatively affected due to the additive amount of small molecule surfactants is constant and small (2.0 wt%). [ABSTRACT FROM AUTHOR]

Abstract Pore channel wetting in hydrophobic membranes is one of the most significant challenges in hydrophobic membrane applications, including membrane distillation (MD), membrane absorption (MA), and membrane deaeration (MDA). Surface active substances (SAS) present in the feed solution have been commonly considered as the "accelerator" of such wetting processes. In this work, a gas-liquid interface extraction method was employed as a pretreatment process to remove the SAS before commencing hydrophobic membrane application. The effects of hydraulic retention time (HRT), bubble intensity (BI), and gas-liquid interface extraction height (h) on the pore channel hydrophilic wetting were investigated using response surface methodology (RSM). The experimental results indicated that the order of the single- factor impact strength was the HRT , followed by BI , then h. The optimal conditions were an HRT of 30 min, BI of 0.5 NL/min, and h of 15 cm; thereafter, the time before hydrophilic leakage time (HLT) could be prolonged from 15 min to 590 min, which meant that the stable running time was increased forty-fold. The results indicated that completing gas-liquid interface extraction pretreatment before commencing the membrane application process can effectively retard pore channel wetting in hydrophobic membrane applications. Highlights • Gas-liquid interfacial extraction method can effectively retard pore channel wetting. • The order of the single factor impact strength was HRT > BI > h. • The optimized conditions were: HRT = 30 min; BI = 0.50 NL/min; h = 15 cm. • The time to reach the HLT was extended to 590 min from the original 15 min. [ABSTRACT FROM AUTHOR]

In this paper, the low-temperature thermally induced phase separation (L-TIPS) method was adopted to prepare a high-performance polyvinylidene fluoride (PVDF) hydrophobic membrane for membrane distillation (MD) with non-solvent polyethylene glycol-400 (PEG400) and solvent triethyl phosphate as a fully water-soluble mixed diluent. In the process of L-TIPS membrane formation, the unidirectional regulatory role of coagulation bath temperature on cross-section radius of the PVDF hollow-fiber membrane was analyzed. The results show that the tensile strength of the membrane increases with the increase of the external coagulation bath water temperature, which is the opposite of the general rule. PEG400 is employed to regulate the membrane structure, and more specifically to increase the cellular structure (a positive impact on tensile strength) and reduce the sphere-packed aggregation structure (a negative impact on tensile strength). When the coagulation bath temperature is 60 °C, the tensile strength of the membrane reaches 6.21 MPa (more than 2–4 times higher than the hydrophobic membranes reported). Meanwhile, the PVDF hollow-fiber hydrophobic membrane also has a high flux, the vacuum membrane distillation flux reaches 30.6 kg m −2 h −1 , which is 14.6 times higher than that at the coagulation bath temperature of 15 °C. [ABSTRACT FROM AUTHOR]

During the process of membrane distillation (MD) heat recovery, due to the adverse effects of the heat exchange boundary layer and membrane surface boundary layer, the latent heat is hindered in its transfer and ultimately leading to the loss of heat recovery and mass transfer capacity of the system. In this study, a novel type of jacketed hollow fiber vacuum membrane distillation module (J-HF-VMD-M) has been successfully developed. It has the dual functions of "feed evaporation" and "vapor condensation", which is helpful in reducing the volume and complexity of the system. Based on the structural characteristics of the jacketed module, a "Synergistic heat transfer model of double boundary layers" (SHT-DBL Model) is proposed for the first time. Compared with the previous "independent heat transfer" method between boundary layers, the "synergistic heat transfer" can overcome the above challenges more effectively. Compared with the non-heat recovery process in experimental range, the equivalent membrane distillation flux of the jacketed-type heat recovery process increased by 246.1 %, especially the gain output ratio increased by 145.1 %, and the corresponding increment is more significant than that of the traditional heat recovery process. • A novel type of jacketed vacuum membrane distillation module was successfully developed. • Module enabled the online real-time recovery of condensation latent heat. • The "synergistic heat transfer model of double boundary layers" was proposed for the first time. • The heat recovery performance of the VMD process was significantly improved. • The packing density has a unique influence on the jacketed module. [ABSTRACT FROM AUTHOR]

The feed flow state affects temperature polarization (TP), concentration polarization (CP), and membrane fouling during the membrane distillation process. A novel braided structure for AGMD was proposed in this paper, in which hollow fiber membranes and heat exchange tubes are braided together. The braided structure can alter feed flow direction and reduces the membrane's contact area. Theoretical calculations show that the braided structure reduces the critical Reynolds number for the feed's unstable flow, and improves the feed flow state by forming Dean vortices. Comparative experiments of the braided module and parallel module were carried out. The results show that the braided module performs better than the parallel module. The braided module has a higher flux (J) and gained output ratio (GOR) when treating the tap water with significant TP; a lower decline rate in J and GOR besides a smaller concentration polarization coefficient (CPC) when treating 3.5 wt% NaCl aqueous solution; a slower formation of membrane fouling and a lower reduction in J and GOR when treating a humic acid/calcium carbonate mixed solution. It is proved that the braided structure can improve the performance of AGMD by enhancing the feed flow state to mitigate the TP, CP, and membrane fouling. • A novel braided structure for the hollow fiber AGMD module was proposed. • The effect of braided structure on the critical Reynolds number value of the feed flow state was analyzed. • The effects of braided structure on polarization effect and membrane fouling were investigated. [ABSTRACT FROM AUTHOR]

Vacuum membrane distillation was applied in the treatment of high ammonia content wastewater for the recovery of ammonia. Hydrophobic poly(vinylidene fluoride) hollow fiber membranes were used as the separation media. The initial ammonia concentration and pH value of the feed solution were destined owing to the composition of the wastewater. The effects of feed temperature, velocity, and operation time on the ammonia removal efficiency, separation factor, and water content in produced ammonia vapor were studied. The results showed that feed temperature was the most important factor affecting ammonia removal efficiency, which was improved from 78 to 99% as the temperature enhanced from 30 to 60°C. The feed velocity and operation time also affected the ammonia removal efficiency and separation factor obviously. A pilot-scale experiment was carried out using a membrane module of 20 m2membrane area. Preliminary results showed that proper ammonia removal efficiency and product property were obtained. [ABSTRACT FROM AUTHOR]

In this work, a novel air-bubbling vacuum membrane distillation (AVMD) process was constructed on the basis of traditional vacuum membrane distillation (VMD) process. Compressed air was pressed into the lumen side of the hollow fiber membranes together with the hot feed solution just at the inlet of membrane module. So gas/liquid two-phase flow was formed in membrane lumen. Hydrophobic polyvinylidene fluoride (PVDF) hollow fiber microporous membranes were employed in this work. The effects of operating conditions, such as the feed air flow rate, the feed temperature and concentration on the performance of AVMD process were studied. The surface morphology of the PVDF membranes used in the VMD and AVMD process was characterized by scanning electronic micrograph (SEM). The results showed that the permeate flux increased as the air flow rate and/or feed temperature enhanced. The permeate flux of VMD process was 22 kg/m²h when tested at 75°C with a feed flow rate of 120 l/h and a vacuum pressure of 0.085 MPa. While, the flux of AVMD process reach 40 kg/m²h with the aid of a gas flow rate of 60 l/h. The flux of the two processes both declined gradually as the feed concentration increased from 3.5 g/l to 300 g/l, but that of AVMD was much slower. The conductivity of the product water was kept lower than 3 µS/cm. SEM paragraphs showed that there's much more salt deposition on the surface of the membrane used in VMD process than that used in AVMD process. [ABSTRACT FROM AUTHOR]

Three membrane distillation (MD) configurations, vacuum membrane distillation (VMD), sweeping gas membrane distillation (SGMD) and direct contact membrane distillation (DCMD), have been experimentally studied in a shell-and-tube capillary membrane module using sodium chloride aqueous solutions as feed. The flux, fresh water conductivity and desalination rate were compared. Preliminary experiments by VMD were carried out using seawater and sodium chloride aqueous solutions with the same salinity as seawater as feed. The influences of operating parameters: the flow rate, feed temperature, concentration, and permeate vacuum, have been investigated. The saline solution had higher flux than seawater since the membrane fouling. The membrane fouling was analyzed by SEM and the results indicate that embrane fouling is very serious in seawater desalination by VMD which resulting that the flux decreases obviously with operating time. [ABSTRACT FROM AUTHOR]

An integrated membrane process was constructed, which composed of immersing ultrafiltration(UF) cell as pretreatment step and vacuum membrane distillation (VMD) cell for both pure water reclamation from reverse osmosis (RO) drained wastewater and discharge reduction. The effect of feed temperature, velocity, and vacuum pressure at the pump side on the membrane performance in VMD process was studied. The performance of VMD process in the concentration of pretreated and untreated RO drained wastewater was compared. The surface morphology of the hydrophobic polyvinylidene fluoride hollow fiber membrane was observed by scanning electronic micrograph. Energy Dispersed Spectroscopy was also adopted to analyze the composition of the deposition on the membrane surface. Using un-pretreated RO drained water as the feed, the initial flux of VMD was 22.6 kg/m²h, and declined to 15.6 kg/m²h as the concentration multiple reached four. The composition of contamination on membrane surface contains 32% calcium, 1.92% magnesium, and 1.41% sodium. Whereas the RO drained water was pretreated by hardness removal and UF, the VMD initial flux reached 25.6 kg/m²h, and declined to 17.8 kg/m²h as the concentration multiple got 10. The flux decreased to 11.8 kg/m²h as the concentration multiple enhanced to 20. The contamination contains 26% sodium, 37% chlorine, and 2% calcium. [ABSTRACT FROM AUTHOR]

Abstract In this study, activated carbon (AC) enhanced hydrophobic/hydrophilic dual-layer nanofiber composite membranes were prepared for direct contact membrane distillation (DCMD) by incorporating different concentrations (0–3.0 wt%) of AC nanoparticles into the polyvinylidene fluoride- co -hexafluoropropylene (PVDF-HFP) hydrophobic active layer. The membranes were composed of two layers, a thin hydrophobic PVDF-HFP/AC electrospun active layer and a thick hydrophilic support layer. Results indicated that the incorporation of AC nanoparticles have greatly increased the membrane properties and performance. The membrane containing 1.5 wt% AC nanoparticles (M3) showed the best flux performance (45.6 L/m2 h) compared to other membranes fabricated in this study and a commercial PTFE benchmark membrane (41.8 L/m2 h) without compromising the salt rejection. A two-dimensional model was developed to investigate the flux profile of the PVDF-HFP/AC membranes. The present study suggests that the incorporation of AC nanoparticles into PVDF-HFP active layer can impart additional functionalities to the composite membranes that would enhance the membranes DCMD performance. The fabricated PVDF-HFP/AC composite membranes present great potential in the application of DCMD desalination. Graphical abstract Unlabelled Image Highlights • Dual-layer nanofiber membranes were fabricated by electrospinning for DCMD. • The membranes were composed of PVDF-HFP/AC active layer and Nylon 6,6 substrate. • The incorporation of AC nanoparticles enhanced the flux performance in DCMD process. • M3 composite membrane presented excellent permeability and performance stability. • A two-dimensional model was developed to explain the effect of AC particle on flux. [ABSTRACT FROM AUTHOR]

Zero-brine discharge technology is being closely followed because it can help address water scarcity. Crystallizers show the promise of zero discharge because of their ability to recover resources from concentrated brine. However, traditional industrial metal crystallizers corrode easily and are bulky. Membrane distillation is favored because of its large evaporation area and high efficiency. However, membrane fouling is an inevitable problem in membrane distillation. To address these issues, this study designed a new type of membrane crystallization process, namely bubble membrane crystallization (BMC). In this process, a hollow fiber hydrophobic membrane was used to aerate a feed solution to accelerate the evaporation of the feed solution, which helped crystallize the concentrated brine, and avoided corrosion and membrane fouling. In this study, NaCl crystals with uniform distribution (80.0–110.0 µm) were produced. The results showed that the membrane aeration treatment made BMC possesses excellent anti-pollution and long-term stability. This process advances all-plastic crystallizer technology to achieve zero-brine discharge. [ABSTRACT FROM AUTHOR]

In this study, a vacuum assisted air gap membrane distillation process was designed to weaken the negative influence of non-condensable gases and improve the process performance. It was found that the applied vacuum (within a certain range of vacuum pressure) could remove the non-condensable gases and effectively improve the process performance. It was also found that water vapor cannot condense at the cooling surface in the module when the vacuum pressure is too high. Hence, the concept of optimal vacuum pressure was introduced and studied. The OVP was considered a critical factor to ensure that the VA-AGMD process was dominated by AGMD rather than by vacuum membrane distillation. The effect of some parameters on the optimal vacuum pressure was examined and is discussed in this paper. [ABSTRACT FROM AUTHOR]

Air gap width has an important influence on the performance of air gap membrane distillation (AGMD) process. In this study, a novel double-pipe AGMD module (DP-AGMD-M) consisted of PVDF hollow fiber membrane and heat exchange capillary copper tubes was successfully developed. The evenly distribute and easily control of the air gap width in DP-AGMD-M can be implemented. The effect of the air gap width ( d a ), hot feed temperature ( T 1 ), hot feed flow rate ( Q ), temperature difference (Δ T ) between the hot feed outlet temperature and the cold feed inlet temperature, and the effective membrane module length ( L ) on the performance of DP-AGMD-M were experimental studied. The concept of the equivalent membrane distillation flux ( J AGMD ) was firstly introduced in this paper and used to evaluate the comprehensive performance of DP-AGMD-M. The optimal performances, including membrane distillation flux ( J ), gained output ratio ( GOR ) and J AGMD were obtained. Within the experimental range, the maximum J arrived at 11.4 kg/(m 2 · h), the maximum GOR reached 6.6 and the maximum J AGMD was 29.6 kg/(m 2 · h). [ABSTRACT FROM AUTHOR]

Electrospun nanofiber membranes (ENMs) have garnered significant attention among researchers for membrane distillation (MD) in treating high-salinity wastewater due to their high water flux and low mass transfer resistance. However, a significant challenge in using ENMs for MD is membrane wetting, which results from the deformation of their weakly randomly overlaid nanofibers structure due to water flow shear forces. Herein, we focused on the membrane's structure and successfully prepared superhydrophobic nanofiber membranes with 3D-network reinforced pore structure by immersing PVDF ENMs in a mixed solution of polydimethylsiloxane (PDMS) and titanium dioxide nanoparticles (TNPs) after a hot-pressing treatment for impregnation and coating. The resulting membrane exhibits exceptional properties, including a high water contact angle (WCA) of 160.3°, a high liquid entry pressure (LEP) of 1.57 bar, and sustained structural integrity with an unchanged pore size distribution even after 5 h of water scouring. These characteristics contribute to a water flux of 39.3 kg·m−2·h−1 and an unexpectedly long durability of up to 102 h, along with an outstanding salt rejection exceeding 99.99 %. Moreover, the membrane demonstrates stable water flux and resistance to wetting when processing a 3.5 wt% NaCl solution containing 0.1 mM sodium dodecyl sulfate (SDS), underscoring its significant potential for MD applications. [ABSTRACT FROM AUTHOR]

In this paper, a kind of poly(vinylidene fluoride) (PVDF) porous heat exchange tube (HET) was prepared via non-solvent induced phase separation (NIPS) method. This porous HET possessed an ultra-thin dense skin layer of 2 μm. Since the thermal conductivity of water is higher than that of PVDF, filling the pores with water can significantly improve the heat performance of the porous HET. A full plastic double-pipe air gap membrane distillation (AGMD) module was fabricated with the porous HETs and PVDF hollow fiber membranes. In the AGMD process, the wetting treatment can make the membrane distillation flux (J) and the gained output ratio (GOR) increased by 30%. During the long-term stability test, the maximum conductivity of distillate water was only 17.2 μS/cm. The experimental results demonstrated that the porous HET can be applied for the AGMD process to treat high saline brine, and the ultra-thin dense layer can prevent the leakage of saltwater. • A porous heat exchange tube for AGMD process was prepared by NIPS method. • This porous heat exchange tube possesses an ultra-thin dense skin layer of 2 μm. • Wet the porous heat exchange tube can improve the performance of the AGMD process. • In the AGMD process, the maximum J and GOR can reach 9.73 kg/(m2·h) and 10.93, respectively. [ABSTRACT FROM AUTHOR]

In this study, a new simultaneous heat and mass transfer theoretical model of the membrane distillation process operating under direct contact membrane distillation (DCMD) mode has been developed for the hydrophobic/hydrophilic dual-layer composite membranes. Using the proposed model, a criterion parameter (β) was derived to determine whether the flux will be increased for the prepared hydrophobic/hydrophilic composite membranes. A flux ratio ( γ DL/SL M ) of dual-layer to single-layer membrane was also developed to predict the DCMD flux performance of the composite membranes. To validate the theoretical model, three sets of dual-layer hydrophobic/hydrophilic composite membranes and single-layer hydrophobic membranes with defined total thicknesses (240 μm, 260 μm, and 285 μm) and different thickness ratios (δ / δ o = 3.69, 2.48 and 2.19) were purposefully fabricated using electrospinning technique. Theoretical modelling results were compared with the experimental data in terms of DCMD flux ratio. The experimental data of flux ratios for the three sets of fabricated membranes at 60 °C, γ DL/SL E , are 2.75, 1.97 and 1.80, respectively, which fit well with the model prediction values ( γ DL/SL M = 2.96, 2.18, and 1.97) within high agreement level at a relative standard deviation of 9.6%. Furthermore, the flux ratio of DL2 to SL2 membranes (dual-layer and single-layer membranes with 260 μm total thicknesses and δ / δ o = 2.48 thickness ratio) at different feed inlet temperatures still maintain a high degree of consistency with model values. Overall, the results show the experimental data agree well with the theoretical model prediction for the flux ratio within relative standard deviation of 10.1%, thereby confirming the validity of the proposed model. Additionally, a critical value of the thickness ratio (χ) was calculated χ = 1 + 1 β , this value could provide useful guidance to design a highly efficient hydrophobic/hydrophilic dual-layer composite membrane for DCMD applications in the future work. Image 1 • Dual-layer nanofiber membranes were fabricated by electrospinning for DCMD. • The membrane was composed of PVDF-HFP nanofibers and Nylon 6,6 membrane substrate. • A mathematical model was developed to predict the flux of dual-layer membranes. • The theoretical model was tested and validated by the experimental results. • The experimental data resemble well with the theoretically calculated values. [ABSTRACT FROM AUTHOR]

This study presents the design and fabrication of a new adsorptive nanofibrous membrane incorporating metal-organic framework (MOF) by electrospinning technique for removing ammonia-nitrogen from wastewater via direct contact membrane distillation (DCMD) process. Three types of MOF particles (HKUST-1, AlFu, and UiO-66-NH 2) were used as functional nanoadditives and incorporated into the nanofibrous membrane matrix. The ammonia removal performance of these nanocomposite membranes was comprehensively investigated and compared with an activated carbon (AC) incorporated nanofibrous membrane. Various parameters such as ammonia removal efficiency, ammonia separation factor, overall ammonia mass transfer coefficient, ammonia flux, and membrane stability were evaluated. Among the tested MOFs, UiO-66-NH 2 demonstrated excellent performance and was selected for further optimization. The 5.0 wt.% UiO-66-NH 2 incorporated membrane exhibited the best performance for ammonia removal. Additionally, the mechanism of MOF incorporated nanofibrous membranes for ammonia removal from aqueous solution by DCMD was schematically analyzed. In overall, this study confirmed the feasibility of fabricating MOF incorporated electrospun adsorptive nanofibrous membranes with outstanding ammonia removal performance, demonstrating the potential of membrane distillation to remove ammonia-nitrogen from the aquatic environment. • MOF incorporated mixed-matrix membranes were fabricated by electrospinning. • Three types of MOFs with different properties were used as the nanoadditives. • MOF incorporated adsorptive membranes showed enhanced ammonia removal performance. • The MOF incorporated membranes have great potential in DCMD for ammonia removal. [ABSTRACT FROM AUTHOR]

This study aimed to develop an effective method to fabricate super-hydrophobic polyvinylidene fluoride (PVDF) membrane for direct contact membrane distillation (DCMD). Hydroxyl rich silica particle was prepared and added into PVDF dope solution, which was used to prepare super-hydrophobic PVDF membrane via phase inversion method. The influence of the particle on the membrane structure and performance were studied, and the micro-structure forming mechanism of the membranes was researched. It was found that the special spherical micro-structure was formed due to the addition of the hydroxyl rich silica. The spherical micro-structure is mainly composed of γ type crystal, and the transition of PVDF chains from α to γ was induced by the hydroxyl group of the silica particle. Furthermore, the silica particle also acted as the nuclei for crystallization, and the hydrogen bond formed between hydroxyl groups and PVDF chains could facilitate the three-dimensional growth of polymeric spherulites. The pure water contact angle (CA) on the membrane surface reached 153° at the optimum addition (1.5 wt%) of hydroxyl rich silica. The MD flux was also enhanced up to 2.7 times of the unmodified membrane. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the mechanism of membrane fouling during the membrane distillation (MD) process by using humic acid (HA) and calcium carbonate (CaCO 3) as the model organic and inorganic foulants respectively. The aggregation induced crystallization theory was introduced to analyze the fouling process. Field emission scanning electron microscopy (FESEM) images and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and variation of foulants on membrane surfaces that treated different feeds at different concentration factors. The interface free energies of the membranes surfaces were calculated based on contact angles and surface tensions between the testing solutions and the membrane surfaces. The results indicated that the aggregations of HA onto the hydrophobic polyvinylidene fluoride (PVDF) membrane surface altered membrane surface properties, which reduced critical nucleus radius (R ⁎ ) and facilitated the heterogeneous nucleation of CaCO 3. Furthermore, the presence of calcium ion enhanced the aggregation of HA, which further promoted the crystallization of CaCO 3. • Mechanism of synergistic effect of organic and inorganic foulants is studied. • XPS was used to analyze the progress of fouling. • Critical nucleus radius determined the synergistic effect of fouling. [ABSTRACT FROM AUTHOR]

Highly porous polyvinylidene fluoride (PVDF) hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux of the process. For the first time in this paper, porous hydrophobic PVDF asymmetric hollow fiber membranes with a high outer surface porosity for use in vacuum membrane distillation (VMD) were successfully fabricated by applying a simultaneous co-extrusion spinning process through the non-solvent induced phase separation (NIPS) method. In this approach, five kinds of dual-layer composite membranes were prepared by employing different inner and outer polymer dopes. Single-layer membrane was also fabricated through the conventional dry-jet wet phase inversion method. Results revealed that the introduction of the simultaneous co-extrusion spinning process greatly increased the outer surface porosity of the dual-layer composite membranes. It was also observed that the VMD flux of the dual-layer membranes spun through the simultaneous co-extrusion spinning process was 54% higher than the single-layer membrane fabricated by the conventional dry-jet wet phase inversion method. A VMD flux as high as 61.8 kg/(m 2 h) at 70 °C was obtained for the novel dual-layer composite membranes. [ABSTRACT FROM AUTHOR]

Air-bubbling vacuum membrane distillation (AVMD) process was designed to boost the heat and mass transfer in membrane distillation (MD). Both effect of flow pattern on the performance of AVMD process and the heat and mass transfer mechanism in this process were studied in this paper. The results showed that the performance of VMD was improved obviously by air-bubbling method. The flux was doubled at certain feed velocity and gas/liquid proportion. The study showed that flow pattern was the key factor affecting the mass and heat transfer efficiencies. The heat transfer coefficients, corresponding to the two main flow patterns in AVMD process, bubbly flow h f b u b = 1.7527 R e t p 0.4215 P r 1 3 μ b / μ w 0.14 λ / d and slug flow h f s l u = 0.0632 R e t p 1.0420 P r 1 3 μ b / μ w 0.14 λ / d , were obtained and employed in the modeling of AVMD process. The modeling results showed that the theoretical prediction of flux aligned with experimental results well, in which the error was within ± 5%. Both variations of Temperature Polarization Coefficient ( TPC ) and Concentration Polarization Coefficient ( CPC ) in AVMD process were studied based on the obtained correlations. And the result showed that both TPC and CPC were significantly influenced by the flow patterns. [ABSTRACT FROM AUTHOR]

• Inter-connected channel superhydrophobic PVDF membrane was prepared by NIPS method. • Saturated NaCl-H 2 O induced the pre-gelation and crystallization of polymer chains. • Membrane with CA of 155.3°, good DCMD performance and stability was obtained. In-situ construction of superhydrophobic polyvinylidene fluoride (PVDF) membrane was prepared through nonsolvent induced phase inversion process for direct contact membrane distillation (DCMD). Saturated sodium chloride aqueous solution (NaCl-H 2 O) was added to the casting solution as a green phase inversion inducing agent. The variation of polymer crystal and the formation mechanism of micro-nano structure on membrane surface were studied. The results showed that NaCl crystals could act as nucleus for the pre-gelation and crystallization of PVDF chains. The "harsh" nonsolvent, water, accelerated the gelation process. When the optimum amount of NaCl-H 2 O was added, superhydrophobic membrane with lotus leaf like micro-nano spherical structure and interconnected channels was obtained. The pure water contact angle reached 155.3° with DCMD flux of 54.5 L/m2∙h, which was about 1.6 times for the membrane without NaCl-H 2 O addition. The stability was also improved owing to the superhydrophobic structure. [ABSTRACT FROM AUTHOR]