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The mass transfer behavior in a hollow fiber membrane module of membrane-based artificial organs (such as artificial liver or artificial kidney) were studied by numerical simulation. A new computational fluid dynamics (CFD) method coupled with K-K equation and the tortuous capillary pore diffusion model (TCPDM) was proposed for the simulations. The urea clearance rate predicted by the use of the numerical model agrees well with the experimental data, which verifies the validity of our numerical model. The distributions of concentration, pressure, and velocity in the hollow fiber membrane module were obtained to analyze the mass transfer behaviors of bilirubin and bovine serum albumin (BSA), and the effects of tube-side flow rate, shell-side flow rate, and fiber tube length on the bilirubin or BSA clearance rate were studied. The results show that the solute transport mainly occurred in the near inlet regions in the hollow fiber membrane module. Increasing the tube-side flow rate and the fiber tube length can effectively enhance the solute clearance rate, while the shell-side flow rate has less influence on the BSA clearance. The clearance of macromolecule BSA is dominated by convective solute transport, while the clearance of small molecule bilirubin is significantly affected by both convective and diffusive solute transport.

Nitrogen oxide (NOx) is one of the polluting gases harmful to humans and the environment. Nitrous oxide gas is mostly found in air, namely nitrogen monoxide (NO) and nitrogen dioxide (NO2). Nitrogen oxide gas in the air, which mostly comes from exhaust gases, needs to be reduced to minimize the threats to humans and the environment and comply with applicable regulations regarding hazards. The absorption process with a membrane contactor is an alternative to reduce NOx concentrations in the air. This study evaluates the hollow fiber membrane modules' performance in the NOx absorption process using sodium chlorate (NaClO3) and sodium hydroxide (NaOH) together as an absorbent solution. Based on the experimental results, the NOx reduction efficiency increased from 96.3 to 99.2% and from 99.4 to 99.7% with an increase in the concentration of NaClO3 from 0.02 to 0.05 M and the number of fibers in the membrane module from 50 to 150. However, the absorption efficiency declined from 99.7 to 99.2% by increasing the feed gas flow rate from 100 to 200 mL/min. The highest value of NOx reduction efficiency, the overall mass transfer coefficient, the flux, and the NOx loading obtained in the study were 99.7%, 0.01743 cm s-1, 9.510´10-8 mmole cm-2 s-1, and 0.026 mole NOx/mole NaClO3, respectively.

Understanding the mass transfer behaviors in hollow fiber membrane module of artificial liver is important for improving toxin removal efficiency. A three-dimensional numerical model was established to study the mass transfer of small molecule bilirubin and macromolecule bovine serum albumin (BSA) in the hollow fiber membrane module. Effects of tube-side flow rate, shell-side flow rate, and hollow fiber length on the mass transfer of bilirubin and BSA were discussed. The simulation results showed that the clearance of bilirubin was significantly affected by both convective and diffusive solute transport, while the clearance of macromolecule BSA was dominated by convective solute transport. The clearance rates of bilirubin and BSA increasd with the increase of tube-side flow rate and hollow fiber length. With the increase of shell-side flow rate, the clearance rate of bilirubin first rose rapidly, then slowly rose to an asymptotic value, while the clearance rate of BSA gradually decreased. The results can provide help for designing structures of hollow fiber membrane module and operation parameters of clinical treatment.

Nitrogen oxide (NOx) is one of the polluting gases harmful to humans and the environment. Nitrous oxide gas is mostly found in air, namely nitrogen monoxide (NO) and nitrogen dioxide (NO2). Nitrogen oxide gas in the air, which mostly comes from exhaust gases, needs to be reduced to minimize the threats to humans and the environment and comply with applicable regulations regarding hazards. The absorption process with a membrane contactor is an alternative to reduce NOx concentrations in the air. This study evaluates the hollow fiber membrane modules' performance in the NOx absorption process using sodium chlorate (NaClO3) and sodium hydroxide (NaOH) together as an absorbent solution. Based on the experimental results, the NOx reduction efficiency increased from 96.3 to 99.2% and from 99.4 to 99.7% with an increase in the concentration of NaClO3 from 0.02 to 0.05 M and the number of fibers in the membrane module from 50 to 150. However, the absorption efficiency declined from 99.7 to 99.2% by increasing the feed gas flow rate from 100 to 200 mL/min. The highest value of NOx reduction efficiency, the overall mass transfer coefficient, the flux, and the NOx loading obtained in the study were 99.7%, 0.01743 cm s-1, 9.510*10-8 mmole cm-2 s -1, and 0.026 mole NOx/mole NaClO3, respectively. [ABSTRACT FROM AUTHOR]

Cell-assisted lipotransfer (CAL) is an advanced lipoinjection method that uses autologous lipotransfer with addition of a stromal vascular fraction (SVF) containing adipose-derived stromal stem cells (ASCs). The CAL procedure of manual isolation of cells from fat requires cell processing to be performed in clean environment. To isolate cells from fat without the need for a cell processing center, such as in a procedure in an operation theater, we developed a novel method for processing SVF using a closed cell washing concentration device (CCD) with a hollow fiber membrane module. The CCD consists of a sterilized closed circuit, bags and hollow fiber, semi-automatic device and the device allows removal of >99.97% of collagenase from SVF while maintaining sterility. The number of nucleated cells, ASCs and viability in SVF processed by this method were equivalent to those in SVF processed using conventional manual isolation. Our results suggest that the CCD system is as reliable as manual isolation and may also be useful for CAL. This approach will help in the development of regenerative medicine at clinics without a cell processing center. [ABSTRACT FROM AUTHOR]

The mass transfer behavior in a hollow fiber membrane module of membrane-based artificial organs (such as artificial liver or artificial kidney) were studied by numerical simulation. A new computational fluid dynamics (CFD) method coupled with K-K equation and the tortuous capillary pore diffusion model (TCPDM) was proposed for the simulations. The urea clearance rate predicted by the use of the numerical model agrees well with the experimental data, which verifies the validity of our numerical model. The distributions of concentration, pressure, and velocity in the hollow fiber membrane module were obtained to analyze the mass transfer behaviors of bilirubin and bovine serum albumin (BSA), and the effects of tube-side flow rate, shell-side flow rate, and fiber tube length on the bilirubin or BSA clearance rate were studied. The results show that the solute transport mainly occurred in the near inlet regions in the hollow fiber membrane module. Increasing the tube-side flow rate and the fiber tube length can effectively enhance the solute clearance rate, while the shell-side flow rate has less influence on the BSA clearance. The clearance of macromolecule BSA is dominated by convective solute transport, while the clearance of small molecule bilirubin is significantly affected by both convective and diffusive solute transport.

• Solution concentration using multistage osmotically assisted reverse osmosis (OARO) system was performed. • Two types of hollow fiber (HF) membrane modules with different numbers of HFs were used. • Feed solution was concentrated by the OARO process even using highly concentrated NaCl solutions and low applied pressures. • A multistage system produced a higher degree of concentration as compared with a single stage system. • Water flux and concentration ratio were influenced by the internal concentration polarization in the modules. Reverse osmosis (RO) is commonly used to concentrate solutions in food preparation and environmental applications among others. Limitations on the applied pressure, which must be higher than the osmotic pressure of the feed solution, determine the concentration that can be achieved by RO. Recently, an osmotically assisted reverse osmosis (OARO) system that can be operated even with low applied pressure has been suggested as a new concentration process. In this study, we performed concentration tests on a multistage OARO system that used two types of hollow fiber (HF) membrane modules made from cellulose triacetate with different numbers of HFs. Water permeated through the membrane and the concentration increased as it progressed through the modules, even when using concentrated NaCl solutions (1.0 and 2.0 M) with low applied pressures (10 and 15 bar). The concentration increased in each of ten stages in a multistage concentration test. Water flux and concentration ratio were strongly influenced by the internal concentration polarization in the modules. [ABSTRACT FROM AUTHOR]

Effect of fiber arrangement on the performance of hollow fiber ultrafiltration membrane modules has been studied using computational fluid dynamics (CFD) method. Four fiber arrangement modes, namely sparse to dense radially, dense to sparse radially, random and uniform, have been considered in the present study by developing dedicated CFD models. The fluid flow and fouling behavior inside the hollow fiber membrane modules have been simulated. The time-dependent velocity and pressure distributions have been presented for each module. The proportion of energy consumed by the inlet manifold decreased while the one by fiber bundle increased. The module with fiber arrangement sparse to dense radially had higher energy efficiency than the other three modules. In each module, the region where fibers had extreme fiber average flux tended to migrate with time. At the end of filtration, the fibers with highest fiber average flux were the ones with originally lowest fiber average flux and vice versa. However, the overall distribution of fiber average cake mass, which had the similar profile of original flux distribution, underwent little change. The mathematical model, consisting of geometrical and operating parameters, can be applicable to describe the water productivity of hollow fiber membrane modules with different fiber arrangement. [ABSTRACT FROM AUTHOR]

Steam methane reforming (SMR) is widely used in the hydrogen production industry; however, a significant amount of CO 2 is released during this process. Several efforts have been made to produce low-CO 2 hydrogen (blue hydrogen) via SMR; however, the proposed solutions are not applicable to small-scale plants. Therefore, this study proposes an on-site SMR process combined with a hollow fiber membrane module (HFMM) for CO 2 capture in small-scale plants. First, mathematical models for the on-site SMR process and HFMMs were developed, and their accuracy was validated with real-world data. Second, we designed and implemented the SMR–HFMM model based on different operating conditions and gas compositions at three potential CO 2 capture locations (dry syngas, PSA tail gas, and flue gas). The CO 2 capture performances at these three locations were compared using five performance indicators: stage cut, separation factor, CO 2 recovery rate, permeate composition, and retentate composition. Finally, to evaluate the integrated processes for each CO 2 capture location, feasible ranges of the number of HFMMs and the levelized cost of hydrogen (LCOH) were calculated. In the case of CO 2 captured in dry syngas, the number of HFMMs required to achieve a CO 2 purity of over 90% was calculated to be 10–25. Furthermore, despite additional HFMM installation, the LCOH was 0.8%–1.5% lower than that of the conventional on-site SMR process that is 7.07–7.13 USD/kgH 2. The proposed integrated SMR–HFMM process is a potential solution to the problem of CO 2 emissions in on-site SMR processes with a lower LCOH. Therefore, the findings of this study could be of significant importance in improving the environmental sustainability of hydrogen production in small-scale plants. [Display omitted] • Steam methane reforming (SMR) emits CO 2. • Conventional blue hydrogen production methods are not appropriate for on-site SMR plant. • Integration of on-site SMR with a hollow fiber membrane module (HFMM) for hydrogen production was proposed. • HFMM could capture CO 2 with high efficiency in a real on-site SMR plant. [ABSTRACT FROM AUTHOR]

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The potential use of air-gap membrane distillation (AGMD) process for the removal of copper sulfate (CuSO4) from aqueous solution was examined. A series of experiments were conducted to investigate the effects of both operation parameters and module parameters, including hot feed temperature(T3), coolant temperature (T1), feed flow rate (F), feed salt concentration (cf), vacuum pressure (P), the rate of hollow fiber membranes and heat-exchange hollow fibers (Nm/Nd) and the length of the modules (L) on permeate water flux (J), gained output ratio (GOR), water productivity (PV), and salt rejection rate (R) in AGMD process. It was found that the performance of AGMD process could be enhanced, but permeate water quality was deteriorated by adding vacuum pressure. Moreover, J declined, but PV and GOR increased as L increased. With the increment of Nm/Nd, J decreased when operation parameters keep constant, PV and GOR showed different variation trends with different T1 values due to the insufficient cold energy. The highest CuSO4 rejection rate exceeded 99.95%, so AGMD process has potential for CuSO4 separation from aqueous solution. [ABSTRACT FROM AUTHOR]

Abstract This study experimentally and theoretically analyzed the performance of two types of large-scale hollow fiber (HF) forward osmosis (FO) modules for pressure retarded osmosis (PRO). The effects of operating conditions on the module performance of the 5-inch scale HF modules with a cross-wound HF configuration were investigated. A modified analytical model, based on the friction-concentration polarization (FCP) model, which combined the PRO theory with water flux and salt leakage, was proposed for PRO performance estimation. The theoretical results agreed within 9.7% deviation with the experimental results under all conditions. The energy efficiency of the HF PRO module was also theoretically derived. The power generation estimation for the 5-inch membrane module revealed that 10 to 15% of the energy could be recovered from the reverse osmosis seawater desalination process. However, some parts of the membrane could not be used efficiently inside the modules because of the non-optimal dimensions. Therefore, new types of modules, having shorter lengths and larger module diameters, were proposed and provided greater net energy output, as compared with the original module, due to the reduction of both the region where the water was not sufficiently permeated and the pressure drop inside the HF membrane. Graphical abstract Unlabelled Image Highlights • A pilot-scale PRO test was performed using 2 types of 5-inch scale CTA HF modules. • The proposed FCP-based analytical model agreed well with all experimental data. • The positive net energy and energy efficiency of the PRO system were estimated. • A precise analytical model helped propose preferable HF module dimensions for PRO. • Wide and short HF module dimensions were better for positive power generation. [ABSTRACT FROM AUTHOR]

The counter-flow hollow fiber membrane-based direct evaporative cooler (MDEC) was proposed as an energy-efficient and hygienic air cooling solution. The random sequential addition algorithm was used to simulate the randomness of fiber distribution within the MDEC in engineering practice. 3D numerical models were developed with a computational domain determined as a hexagonal prism containing multiple fibers. The experimentally validated model depicted the air state variation along the path under regular and random fiber distributions. The differences in wet-bulb effectiveness (ε wb) and coefficient of performance (COP) of MDEC with two configurations, regular and random fiber distributions, were compared for different packing fractions and air flow rates. Furthermore, dimensionless correlations for the shell-side friction factor (f), Nusselt number (Nu), and Sherwood number (Sh) were derived to generalize the results to other hollow fiber membrane modules employed in liquid/gas systems. The results showed that the channel flow effect and dead zone under the random configuration worsened the heat and moisture handling performance of MDEC. Compared with the regular configuration, both Nu and Sh were degraded by 11.6–55.6%, but f was desirably reduced by 28.8–49.8%. Balancing cooling capability and energy efficiency, a regular configuration with moderate packing fraction was more beneficial for engineering practice. • The counter-flow hollow fiber membrane module is proposed for evaporative cooling. • Random sequential addition algorithm is used to represent the randomness of fiber distribution. • 3D models with different fiber configurations and packing fractions are developed. • Regular fiber distribution with moderate packing fraction enables efficient cooling and energy saving. • Compared to regular distribution, shell-side Nu , Sh , and f are all reduced in random distribution. [ABSTRACT FROM AUTHOR]

• Microfluidics allowed the synthesis of polyamide (PA) thin films on polysulfone hollow fibers (HFs). • Control of the synthesis conditions made possible 1–25 numbers and 10–50 cm lengths of HFs. • The study of the PA monomer concentration and residence and reaction times allowed synthesis optimization. • Water nanofiltration demonstrated high separation performance in terms of rose Bengal and MgSO 4 rejections. • PA/MOF bilayered HFs increased the water permeance while maintaining high solute rejection. The commercialization of thin film composite (TFC) hollow fiber (HF) membranes remains challenging owing to issues associated with membrane manufacturing. TFC membranes were synthesized by microfluidic interfacial polymerization of polyamide (PA) on polysulfone hollow fiber (HF) membrane modules. A total of 33 HF membrane modules were prepared with different number of HFs (from 1 to 25) and different lengths (from 10 to 50 cm). They were evaluated in a nanofiltration operation in terms of water permeance and rose Bengal (RB) and MgSO 4 rejections. Among the 33 modules, 73% showed RB rejections higher than 95%, while 36% of the modules reached rejections above 99%. During the membrane synthesis, different parameters, such as PA monomer concentration, residence time and reaction time, were studied. As a result, the amount of monomer was reduced by ca. 80%. The versatility of microfluidics allowed incorporating hydrophilic metal-organic framework (MOF) ZIF-93 to produce HF modules with PA/MOF bilayered membranes (a continuous layer of MOF between the support and the PA film) which led to an important enhancement of the water permeance from 1.3 (bare PA membrane) to 5.3 L·m−2·h−1·bar−1 (PA/ZIF-93 HF membrane), maintaining RB rejection above 95%. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper investigated the streamline, velocity vector, and velocity and pressure profiles of fluid to find out the potential of cleaning by backwashing and channel washing at membrane pores and inner surface of inside-out filtration pressurized hollow fiber membrane using computational fluid dynamics simulation. The results of streamline in the module and membrane showed that foulants accumulated on the membrane inner surface is difficult to completely eliminate by backwashing, however, channel washing successfully performed due to the strong velocity streamline. Channel washing showed more than 42 times of an average velocity at membrane inner surface and pores compared with backwashing. The applied pressure on module and membrane in channel washing was much lower than that of backwashing because most injected fluid flows directly from module inlet to outlet without penetrating membrane. The velocity and pressure profiles at pores and inner surface of membrane fiber by backwashing and channel washing showed that the velocity within the membrane pores at channel washing maintained at much higher range and the pressure on the membrane at channel washing was a lot of fluctuation due to better filtration performance. [ABSTRACT FROM AUTHOR]

A novel three‐dimensional CFD model has been developed on the basis of fluid flow in the shell and lumen sides, and permeation and fouling behavior in the porous membrane zone. The simulated 25‐min dead‐end outside‐in filtration process showed that the energy consumed by the inlet manifold decreases during the constant pressure filtration. The velocity and pressure distributions in the module change with time. Flux distribution both in the axial and radial directions becomes increasingly more uniform, so does the cake distribution. Flux distribution and cake distribution inter‐adjust each other in different modes. A correlation equation has been developed to describe the relationship between the volumetric flow rate and accumulated water production. The correlation equation with simple experiment enables the dynamic evolution of energy consumed by shell inlet manifold to be presented, which can be the criterion of how well the shell inlet manifold or module has been designed. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2655–2669, 2018 [ABSTRACT FROM AUTHOR]

In this research, an approximated technique is proposed for predicting the performance of membrane gas separation using an asymmetric membrane-based gas separator. The permeation behavior of the high-flux asymmetric membrane varies from that of the traditional symmetric membrane. The advanced mathematical model has been applied in this study for the separation of a binary gas mixture. In the present work, a shell-fed hollow fiber module like counter-current flow pattern is modeled mathematically for CO2 separation from CH4. Finite Difference method (FDM) is applied to solving the equations numerically. The models offered separation for a membrane module, for given gas conditions, simulating permeate and residue composition and the stage cut. The different parameters are investigating like a change in the pressure ratio, stage cut and feed flow rates. The numerical approach is helpful as it entails the least effort and computational time due to the fact algebraic equations are used instead of differential equations. The obtained model's data also verified with numerical and experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Air gap membrane distillation (AGMD) and permeate gap membrane distillation (PGMD) were investigated and compared through self-developed hollow fiber membrane modules with internal energy recovery. The effects of the feed temperature, the coolant temperature, the flow rate, the gap thermal conductivity, and the gap width on the flux and the gained output ratio (GOR) were evaluated experimentally. The gap between the membrane and the condensing surface was a key factor affecting the flux and the GOR in both AGMD and PGMD. It was found that the improvement of gap thermal conductivity using brass net was useless in improving flux and GOR. The permeate water filled in the gap changed the process of mass and heat transfer in the gap which gave rise to the increase in the flux and thermal recovery. The flux and GOR in PGMD increased by 7.9% and 59.82% in the gap of 0.5 mm compared to the AGMD. The salt rejection of all experiments was greater than 99.8%. [ABSTRACT FROM AUTHOR]

The new sustainable power generation technique which can convert the salinity gradient energy to the hydroelectric energy is expected. This technique is called Pressure Retarded Osmosis (PRO). Clarification of the relationship between the performance of the PRO module and permeation characteristics is important. It’s already known that increase of salt concentration can increase the permeation flux through the membrane. As the conventional researches, the effects of increase of fresh water concentration and concentration polarization have evaluated. In this research, relationship between the salt concentration and membrane module is focused. The effects of fresh water dissipation and flow state of salt water in hollow fiber membrane module as new factors are researched with experiment and numerical simulation. As result, in the case of low salt concentration, permeation is not caused sufficiently in module. On the other hand, in the case of high salt concentration, very low permeation flux area exists extensively, and the effects of concentration polarization and fresh water dissipation are relatively large. Therefore salt water flow rate and module shape should be changed for each salt concentration.

Recently developed crosslinked-thermally rearranged (XTR) polymeric membranes, which show enhanced gas separation, are applicable for CO 2 separation from post-combustion gases. Moreover, the resulting thermally rearranged polybenzoxazole (TR-PBO) structure that is thermally induced from hydroxyl-polyimides (HPI) provides high thermal and chemical resistance, which is favorable for gas separation applications containing condensable gases such as water vapor. Herein, the influence of water vapor on the CO 2 capture efficiency was evaluated using XTR poly(benzoxazole- co -imide) (XTR-PBOI) hollow fiber membrane modules which were compared with crosslinked HPI (XHPI) in mixture gas and single gases for CO 2 and N 2 . The results revealed that the permeate CO 2 flow rate in the hydrophobic XTR-PBOI module showed enhanced separation performance, whereas the flow rate severely decreased in the relatively hydrophilic XHPI module, reflecting more significant capillary condensation effect in the XHPI membranes. Both membrane modules showed excellent plasticization resistance, and the XTR-PBOI hollow fiber membrane module presented reasonable long-term stability over 240 h. [ABSTRACT FROM AUTHOR]

A novel frost-free air source heat pump (ASHP) combined with membrane-based liquid desiccant dehumidification and humidification is proposed and investigated in this paper. Liquid-to-air membrane dehumidifier (LAMD) is employed to dehumidify the air before entering the outdoor coils in the proposed system so that frosting can be prevented. Diluted solution is regenerated to humidify the supply air via the liquid-to-air membrane regenerator (LAMR), which can overcome the droplets carry-over problem in the liquid-to-air energy exchanger. Model simulations are carried out to study the system performance under various operating parameters and climatic conditions, meanwhile the comparison between the proposed system and conventional defrosting system is performed. Results demonstrate that the COP sen and the COP tot of the novel system are at least 37.7% and 64.3% higher than that of the COP reverse of conventional reverse-cycle defrosting ASHP system in the variation ranges of the analyzed parameters,respectively.Humidification effects on the supply air depend on the ambient air properties. And air humidification by the regenerator can meet the needs of the air-conditioning room comfort when the ambient air is above 0 °C and 70% RH. [ABSTRACT FROM AUTHOR]

Non-uniform flow in the hollow fiber membrane modules is believed to cause non-ideal performance of the module. To investigate the relationship between the module design and performance, a novel CFD model was developed to analyze numerically the effect of inlet manifold on the energy consumption and flow distribution for the module. The CFD results were compared with the experimental data and a good agreement between them was obtained. Eight manifolds were chosen as cases in the CFD simulation. The flow field in the shell and lumen sides and the flux distribution in the porous membrane zone were revealed by the CFD simulation. An adapted model has been proposed to account for the energy consumption distribution between the manifold and the fiber bundle. The manifold can consume a considerable portion of the overall energy with an improper structure design. When the fractional hole area of the inlet are 0.64%, 43.42%, and 100%, the proportion of the energy consumed by the manifold are 95%, 51%, and 7%, respectively. The non-uniform flow from the shell manifold to the module results in uneven velocity and pressure distributions in the shell side. However, the effect of the manifold structure on the flow distribution in the lumen side appears to be negligible. The flux distribution has a three-dimensional non-uniformity. The high velocity from the manifold opening to the module causes a high local flux at the beginning of the fiber, whereas the flow impingement on the dead end and the pressure drop in the lumen side results in a high local flux at the end of the fiber. The uniformity of the flux distribution depends on the flow distribution in the shell side with given fiber properties. For the specific hollow fiber membrane module in the present study, the inlet holes should be evenly distributed at the cross section to achieve uniform flow distribution in the module. To reduce the energy consumption, the fractional hole area should be as high as possible. The CFD model and the mechanism of how the inlet manifold affects the performance of the module will be beneficial to the structure design and optimization of the hollow fiber membrane modules. [ABSTRACT FROM AUTHOR]

Pressure Retarded Osmosis (PRO) is expected to the new power generation system. The performance of the PRO module is closely relating to the permeation characteristics. In this paper, when fresh water flow rate is changed, 4 factors related to the reduction of permeation flow rate are researched with experiment. These 4 factors are concentration of solute in fresh water, salt leakage, concentration polarization, and dissipation of fresh water. The characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in PRO system. It is cleared that the dissipation of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of solute in fresh water, salt leakage influence to the reduction of permeation flow rate in the case of high fresh water flow rate.

Ammoniacal nitrogen is a commonly encountered nitrogenous pollutant produced by industrial processes present in wastewater. In this work, model wastewater containing ammoniacal nitrogen (in the form of NH 4 Cl) was used as a feed solution in the demonstration of osmotically assisted reverse osmosis (OARO) using a multi-stage hollow fiber membrane module setup. The OARO process aimed to dewater the model wastewater and effectively concentrate the ammoniacal nitrogen in solution for easier recovery. Split feed OARO, wherein the feed stream is split either into the concentrated retentate or refluxed back into the permeate side flowing counter-current with the feed, was conducted and the influence of several operational parameters, such as applied pressure, feed flow rate, reflux ratio, on the concentration process was investigated. Also, the properties of the feed solution, i.e. initial feed concentration and presence of other ionic species, such as NaCl, were also tested. Higher concentration efficiency was observed at the following conditions: higher applied pressure, lower flow rate, and higher reflux ratio. The use of low concentrated feed solutions might be useful to decrease the applied pressure and the occurrence of internal concentration polarization was also avoided. The results in this work show that OARO could be a practical membrane-based process for enrichment and recovery of ammoniacal nitrogen from wastewater to further realize a circular economy, in which waste materials such as ammoniacal nitrogen are recovered and reused to produce valuable products. [Display omitted] • Osmotically assisted reverse osmosis (OARO) was conducted for NH 4 Cl concentration. • Split feed OARO was performed using multi-stage hollow fiber membrane module setup. • The influence of applied pressure, feed flow rate, and reflux ratio was investigated. • Initial feed concentration and presence of NaCl in the feed also affected OARO process. • OARO is a practical membrane process for enrichment of recovery of ammoniacal nitrogen. [ABSTRACT FROM AUTHOR]

The use of membrane contactor technology is well-known in the process industry and can be employed in many important fields; such as separation and absorption processes, membrane distillation, pervaporation, biotechnology, food industries etc. In recent years, research has been carried out regarding the use of membrane contactors in the components of absorption refrigeration systems. The use of membrane contactors makes it realizable to design compact components with improved heat and mass transfer. Heat and mass transfer performance of the components is significantly enhanced due to the higher area to volume ratio available. Membrane based absorber and desorber allow the reduction in size of the absorption refrigeration systems to a great extent and thus absorption refrigeration technology can be used in transport and small scale applications. In this paper, the applications of membrane contactors in absorption refrigeration systems are reviewed. The application of membrane contactors in the components of absorption refrigeration systems, the configurations of refrigeration cycles that employ membrane contactors and the characteristics of the membrane contactors used in absorption refrigeration systems are all reviewed in detail. Information is collected on the choice of working fluid mixture to be used in absorption refrigeration systems that use membrane based components and the compatibility of working fluid mixtures with the membrane contactor material is discussed. The significance and limitations of using membrane contactors in absorption refrigeration systems is included in this paper. [ABSTRACT FROM AUTHOR]

In this study the effects of shear stress distribution and pressure loss on two different hollow fiber module types through have been investigated. The CFD simulations are based on the numerical solutions of the Reynolds averaged Navier–Stokes equations on three dimensional module geometries. The fluid flow inside modules is modeled using a realizable k-ε turbulence model. Module geometries consist two different types of inlet and outlet. One of the modules has normal and the other has tangential inlet and outlet. These two module types are investigated by CFD simulations and results are verified with experimental studies. Based on the simulation results, it has been observed that tangential inlet and outlet create rotational flow inside the module and this causes higher shear stress when compared to normal module geometry. The velocity profiles inside the modules and average pressure drop between inlet and outlet ports are presented. For tangential module configuration, the distribution of velocity inside the module is more homogeneous than the normal module configuration. Average pressure drop between inlet and outlet ports for both module configurations is nearly the same in steady state simulations. The results of the experimental studies are in accordance with the simulation results. [ABSTRACT FROM AUTHOR]

Abstract: A new air-gap membrane distillation (AGMD) module for desalination with internal latent-heat-recovery which consisted of parallel hollow fiber membranes and heat exchange hollow fibers was successfully developed. The influences of feed flow rate, feed temperature and feed initial concentration on AGMD process were investigated. The vapor pressure polarization coefficient (η) was introduced to measure the reduction in the effective driving force for mass transfer with regard to the driving force imposed. Among all AGMD experiments, the maximum water vapor permeate flux (JD ) of 5.30kg/m2 h and the gained output ratio (GOR) of 5.70 were obtained. A theoretical model based on the mass and energy balances of the hot feed side was established to calculate the temperature and the local water vapor permeate flux distributions along the hollow fiber membrane, which showed that the temperature drop and local water vapor permeate flux drop were much larger at the upper part than those at the lower part of the membrane module in the hot feed side. [Copyright &y& Elsevier]

Abstract: In this study, an innovative food storage system based on green membrane technology is evaluated for food preservation. This is the first study of hollow fiber membrane modules in a controlled atmosphere storage (CAS) system to maintain an environment that prolongs the lifespan of fruits and vegetables during transportation and storage. Compared to conventional CAS systems that utilize nitrogen flushing, the proposed membrane controlled atmosphere storage (MCAS) system provides a nitrogen-enriched air stream to control the concentration of both oxygen and carbon dioxide in the storage container. Detailed mathematical models to describe mixed gas permeation in a hollow fiber membrane module and guide system design are developed. The performance of MCAS systems under on–off and continuous operation modes is evaluated and a case study of the newly developed MCAS system in food transportation presented. [Copyright &y& Elsevier]

Abstract: This work aimed to study the enhancement of oxygen transfer rates in hollow fiber membrane contactors by applying Dean vortices. Systematic investigations of how the geometric parameters, like curve diameter, helical pitch or geometric shape, and flow rates affect the mass transport were done to assess the potential for membrane contactors. The membrane was a hydrophobic microfiltration hollow fiber (polypropylene). Helical, meander and twisted formed hollow fibers with fiber lengths from 5 to 30cm and curvature diameters between 5 and 19mm were constructed. The oxygen transfer rates per membrane area were investigated. The curved hollow fibers show a linear dependence between Dean number and enhancement factor and an increase of transfer rates up to an enhancement factor of 2.4. For the meander shaped fibers a critical Dean number/range between 10–20 was found, where the mass transport enhancement is adjusted rapidly to those of helical hollow fibers. Also the mass transfer in packed membrane modules was investigated, taking into account the theoretical packing densities of the different fiber geometries. It was found that a volumetric enhancement of gas transfer rates for helical and meander formed fibers can only be improved applying very small curvature diameters less than 4mm. [Copyright &y& Elsevier]

Abstract: Conjugate heat and mass transfer in a hollow fiber membrane module used for liquid desiccant air dehumidification is investigated. The module is like a shell-and-tube heat exchanger where the liquid desiccant stream flows in the tube side, while the air stream flows in the shell side in a counter flow arrangement. Due to the numerous fibers in the shell, a direct modeling of the whole module is difficult. This research takes a new approach. A representative cell comprising of a single fiber, the liquid desiccant flowing inside the fiber and the air stream flowing outside the fiber, is considered. The air stream outside the fiber has an outer free surface (Happel’s free surface model). Further, the equations governing the fluid flow and heat and mass transfer in the two streams are combined together with the heat and mass diffusion equations in membranes. The conjugate problem is then solved to obtain the velocity, temperature and concentration distributions in the two fluids and in the membrane. The local and mean Nusselt and Sherwood numbers in the cell are then obtained and experimentally validated. [Copyright &y& Elsevier]

Abstract: Hollow fiber membrane modules are widely used in various industries. The disordered nature of hollow fiber distributions in the module exhibits the existence of a fractal structure formed by the voids between the fibers. The area fractal dimension of the voids on the module cross section is obtained. Then the shell side flow distribution and convective heat and mass transfer are investigated based on the fractal theory developed. An experimental work where an air flow in the shell side is humidified by a water flow in the tube side is performed to validate the model. It is found that the model predicts the flow distribution and the heat and mass transfer deteriorations well with local data for a triangular array. With the model, friction factor and Sherwood number deteriorations which take into account of the degree of irregularity, in terms of fractal dimension, are analyzed. The results show that the higher the packing density is, the less the fractal dimension is, and the less the non-uniformity of the flow distribution is. The Sherwood and Nusselt numbers of a randomly distributed fiber module are only 1–5% of a uniformly spaced tube array. Correlations are proposed for the estimation of friction factor and Sherwood numbers considering the degree of irregularity. The predictions are also compared to the available mass transfer correlations in the literature. [Copyright &y& Elsevier]

Abstract: Hollow fiber membrane based air humidification offers great advantages over the traditional methods because the liquid water droplets are prevented from mixing with the process air, while water vapor can permeate through the membranes effectively. The novelty in this research is that the coupled heat and moisture transport in a hollow fiber membrane module for air humidification is investigated, both numerically and experimentally. The air stream and the water stream flow in a counter flow arrangement. It is found that the membranes play a key role in humidification performances. For sensible heat transfer, both the liquid side and the membrane side resistance can be neglected, while the total heat transfer coefficients are determined by the air side heat transfer coefficients. In contrast, in mass transfer, only the liquid side resistance can be neglected, while the total mass transfer coefficients are co-determined by membrane properties and the air side convective mass transfer coefficients. [Copyright &y& Elsevier]

Abstract: The absorption of carbon dioxide from a carbon dioxide/nitrogen mixture into an aqueous diethanolamine solution (as an example of a typical amine solution) using a hollow fiber contactor is simulated to obtain the effect of several operational variables (liquid velocity, fiber length, lean carbon dioxide loading, and amine concentration) on productivity and amine solution to carbon dioxide ratio. The model employed is based on the ones commonly used in the literature for this process, but it was significantly improved as some simplifications usually considered (irreversible reaction, low carbon dioxide loading, constant partition coefficient of molecular carbon dioxide between liquid and gas phases, absence of bicarbonate and carbonate anions) have been removed. The effect of these simplifications on the simulated results is quite important. A simple performance parameter study is proposed to evaluate the contactor''s performance, keeping the feed gas concentration and the fraction of carbon dioxide removal constant. This procedure leads to optimum values of the liquid velocity and lean carbon dioxide loading, while the performance parameter improves with amine concentration. [Copyright &y& Elsevier]

Abstract: In this work, separation of hydrogen from carbon monoxide by a polyimide hollow fiber membrane module was investigated. Polyimide showed high selectivity for hydrogen relative to carbon monoxide at different operational conditions. Effects of temperature, pressure and stage-cut on permeability of gases and membrane selectivity were experimentally studied. The experiments were carried out employing mixtures containing: 0, 10, 25, 40 and 50% carbon monoxide. Feed temperatures and pressures were varied between 20 and 80°C and 5–9bar, respectively. Pure gas permeances through the membrane were found to be nearly constant at different pressures. Also, the results confirmed the plasticization effect of carbon monoxide on the membrane and showed reduction of hydrogen permeance in mixed gas experiments due to competitive sorption and concentration polarization effects. Also, membrane area for a specific separation was calculated using a new developed model. The optimum condition which results in minimum required area for the membrane can be determined in this way. [Copyright &y& Elsevier]

Abstract: A membrane adsorption–extraction process to recover di-(2-ethylhexyl) phosphate (D2EHPA) from the raffinate is developed, i.e. a hollow fiber membrane extraction module, in which raffinate flows in the tube side and n-heptane used as the “extractant” flows in the shell side. The emulsion with D2EHPA, n-heptane and Triton X-114 was used as the simulated raffinate, and it was proved that both the affinity of membrane for oil droplets and the extraction of D2EHPA by n-heptane contribute to the method. Via recycling the feed, the final recovery efficiency of D2EHPA could be as high as 90%. The effects of two main operating conditions, tube side velocity and shell side velocity, were investigated. The tube side velocity was found to be an essential operation factor, while the shell side velocity had a slight influence. [Copyright &y& Elsevier]

Abstract: The absorption behavior of carbon dioxide using a hollow fiber membrane contactor was numerically analyzed. In this analysis, the absorbent solution is flowing in the inner side of the fiber bore and the pure gas in the shell and the module operated in a non-wetted mode. The derived coupled non-linear governing partial differential equations were numerically solved by the orthogonal collocation technique. Three typical alkanolamines of industrial use, the diethanolamine (DEA), the 2-amino-2-methyl-1-propanol (AMP), and the diisopropanolamine (DIPA) were used as absorbents in this work. One important feature of this study was building the mathematical model based on the two-step carbamate formation model instead of the one-step model used by previous investigators. The outlet absorbed dioxide concentration was simulated and studied with respect to the liquid velocity, initial amine concentration and external mass transfer coefficient. The analysis includes the effects of the diameter and length of the fibers on the liquid outlet gas concentration as a function of the liquid velocity in the fiber. Simulation results show that AMP solutions present a much higher absorption capacity compared to the other two amine solutions. [Copyright &y& Elsevier]

Abstract: Whereas the structure of the flow field generated in the hollow fiber membrane modules operating as liquid–liquid or gas–liquid contactors has been studied extensively theoretically, this is not the case for the much more complex flow field generated during the filtration operation of the same type of modules. The present work is a first approach to analyze and understand the particular flow field. The mathematical problem is formulated and then geometrical and physical simplifications are introduced in order to decompose the full problem in a series of simpler sub-problems. In addition to the presentation of the general structure and the features of the problem, the focus of the present work is to derive all possible analytical solutions of the sub-problems. Several results based on analytical or simple numerical approaches are also presented. [Copyright &y& Elsevier]

Abstract: Polysulfone (PSf) asymmetric hollow fiber membranes with molecular weight cut-off (MWCO) of 13,000Da have been prepared and employed for removal of the triphenylmethane dyes including malachite green (MG), brilliant green (BG) and new fuchsin (NF) from aqueous solutions. Several water-soluble polymers such as poly(diallydimethyl ammonium chloride) (PDADMAC), poly(sodium-4-styrenesulfonate) (PSS) and polyvinyl alcohol (PVA) have been examined for the polyelectrolyte-enhanced ultrafiltration (PEUF). The experimental results indicate that all the three triphenylmethane-type dyes can be removed effectively using the PSf hollow fiber ultrafiltration membrane with the aid of the anionic PSS polymer. The enhancement is primarily due to the formation of complexes between the anionic polymer and the cationic dye molecules through electrostatic attraction. The cationic and nonionic polymers such as PDADMAC and PVA are not suitable for the decolorization of MG, BG and NF aqueous solutions. The decolorization performances of the PSf membrane module can be fully restored by the back-washing operation using alcohol after each experiment. [Copyright &y& Elsevier]

A dual-tube dense-phase silicone rubber membrane bioreactor was investigated for control of cyclohexane-contaminated air as part of a jet propulsion (JP-8) fuel remediation investigation strategy. The reactor was seeded with a mixed bacterial consortium isolated from the water/fuel interface of a JP-8 jet fuel sample and activated sludge, capable of aromatic and cyclic compound biodegradation. Cyclohexane removal ranged from 1.1 to 28.6 mg L -1 , with removal percentages ranging from 4.6% to 37.6%. Removal in the bioreactor ranged from 29.4 to 596.6 mg min -1 m -2 and measured elimination capacities ranged from 46.7 to 947.9 g m -3 h -1 . Removal rates and elimination capacity increased with increasing biofilm growth and with increasing loading rates of cyclohexane. Loading rates ranged from 395.9 to 2189.5 mg min -1 m -2 . Results of this study showed effective removal of cyclohexane using the membrane bioreactor, suggesting that this technology may have applicability for treating vapors contaminated with cyclic hydrocarbons. [ABSTRACT FROM AUTHOR]