Effects Of Membrane Parameters Research Articles

Modeling study of the effects of intrinsic membrane parameters on dilutive external concentration polarization occurring during forward and pressure-retarded osmosis

In membrane-based desalination systems, the mass transfer coefficient is a critical determinant when estimating changes within the boundary layers. However, it is pivotal to recognize the substantial role of intrinsic membrane parameters that can significantly influence the formation of boundary layers by modulating the water and salt fluxes. In this context, we investigated the effects of intrinsic membrane parameters on dilutive external concentration polarization (dECP) during forward osmosis (FO) and pressure-retarded osmosis (PRO). In particular, the Péclet number is utilized to evaluate the degree of dECP. The results revealed that the effects of the membrane parameters on dECP differ completely in accordance with the membrane orientations or magnitude of hydraulic pressure. Moreover, this study emphasizes that the reduction of solute permeability, i.e., improving the selectivity, should be the priority of FO/PRO membrane optimization because solute permeability is the only parameter that simultaneously suppresses both the internal concentration polarization and dECP. Hence, the results of the current study are expected to serve as valuable guidelines for future FO/PRO membrane optimization research.

Effect of membrane parameters and filter structure on the efficiency of leukocyte removal by electrospun poly(ethylene-co-vinyl alcohol) membranes

Electrospinning technology is an experimentally verified tool for the generation of membranes with competing efficiency useful for leukodepletion filter, customarily used in blood banks to lessen the risks with blood transfusions. Even though a few electrospun polymers have been reported to be efficient leukodepletion filter membranes, poly(ethylene-co-vinyl alcohol) (EVAL) being one among, owe to their exceptional advantage of being electrospun from a non-toxic solvent like rubbing alcohol. Besides their excellent blood compatibility, EVAL membranes proffer a leukodepletion performance nearly as same as that of commercial leukodepletion filters. However, the role of various membrane parameters on the leukodepletion efficiency of electrospun EVAL membranes need to be disclosed in advance to their commercialization. Hence this study is an attempt to disclose the ability of electrospinning to being tuned towards the fabrication of filters with different membrane parameters including fiber diameter and pore diameter, with a typical example of EVAL. In addition, the impact of filter design upon the leukodepletion performance was also unveiled by comparing a symmetric filter where all the membranes were of uniform pores with that of an asymmetric filter where the pore sizes of upper and lower layer in the filter was different. The results of blood filtration experiments through the developed prototype filters underline the superiority of asymmetric filters over to symmetric one and, the asymmetric filters wherever the fiber diameter was 1.8 and 3 μm, offered rapid and excellent leukodepletion. Membranes with thinner fibers showed an increased flow resistance. The pore sizes of the membranes being 9 − 29 μm, larger than the size of blood cells, alludes to the direct adhesion of leukocytes to filter membranes as the major mechanism of leukocyte removal. Hence it is concluded that despite the suitability of electrospinning for fabrication of leukodepletion filter media, the use of nano-dimension fibers is not preferred for leukocyte adhesion filter when the material of choice is such a polymer with ideal surface chemistry, wettability and inherent ability for leukocyte binding.

Effects of graphene membrane parameters on diaphragm-type optical fibre pressure sensing characteristics

Considering the potential application of graphene in optical fibre Fabry–Perot pressure-sensitive membrane, a constitutive model for strain-induced deformation characteristics of graphene membrane was established based on the large deflection elastic theory of circular membrane. The effects of membrane parameters, including pre-stressing force, Young's modulus and membrane layer number on deflection mechanical behaviours were studied by using finite element method. The simulation results demonstrated that the pre-stressing force had a significant impact on the deflection deformation and natural frequency with small loads. And the values of Young's modulus should also be considered with large applied loads, because of the imperfect high-quality and uniform graphene preparation methods. Then we carried out a computational study of the effects of membrane thickness on its reflectivity with Fresnel's equations. It was shown that a single-layered graphene membrane with 25 μm diameter can achieve an approximate sensitivity of 80 nm/kPa for a 40 μm Fabry–Perot cavity.

Interference characteristics in a Fabry–Perot cavity with graphene membrane for optical fiber pressure sensors

Due to higher mechanical strength and ultra-thin thickness, graphene is used as a sensitive diaphragm in a Fabry---Perot cavity to improve the sensitivity of pressure sensors. In accordance with the working principle of Fabry---Perot interferometer, a load---deflection mathematical model of fiber-tip pressure sensor with graphene membrane is established based on the large deflection elastic theory of circular membrane. The effects of membrane parameters, including prestressing force and membrane layer number, on deflection mechanical behaviors are studied by using finite element method. Also, the effects of graphene membrane layer and incident light angle on the film reflectivity are obtained according to the refractive index characteristics of the membrane. The simulation results show that an approximate linear relation between loads and deflections exists in the simulated pressure range from 0 to 3.5 kPa, and a theoretical pressure sensitivity of 1,096 nm/kPa for a single-layered graphene membrane can be achieved. To estimate the performance of multi-layered graphene membrane as the diaphragm, an extremely thin 13-layered 125-μm diameter graphene diaphragm is fabricated on the tip of the fiber end, which forms a low finesse Fabry---Perot interferometer. The Fabry---Perot cavity with a length of 40 μm can exhibit a fringe visibility of approximate 0.56 with a measured membrane reflectivity of 1.49 %. The experimental results demonstrate that the use of graphene as diaphragm material would allow highly sensitive and miniature fiber-tip sensors.

Concentration of olive mill wastewater by membrane distillation for polyphenols recovery

The possibility of olive mill wastewaters (OMW) treatment and concentration by membrane distillation has been investigated. The objective is to obtain pure water and a concentrate containing high amounts of polyphenols, which can be extracted later. Two types of commercial membranes, polytetrafluoroethylene (TF200) and polyvinilydene fluoride (GVHP), were tested and the effects of membrane parameters on direct contact membrane distillation (DCMD) performance (i.e. permeate flux and polyphenols retention) were studied. The effects of different DCMD operating parameters were also investigated. The obtained results demonstrated the efficiency of DCMD for OMW treatment and concentration. The membrane TF200 showed a better separation coefficient (99%) after 9 h of DCMD operation than the membrane GVHP (89%) and the corresponding OMW concentration factor was found to be 1.72 for the membrane TF200, whereas it was only 1.4 for the GVHP membrane after 9 h operating time.

Effect of membrane parameters on the size and uniformity in preparing agarose beads by premix membrane emulsification

Agarose microbeads were prepared by premix membrane emulsification with Shirasu-Porous Glass (SPG) membrane and Polyethylene (PE) membrane. The effects of membrane parameters, including pore size, pore size distribution, contact angle between membrane surface and the water phase, shape of pore opening and membrane thickness on size and uniformity of agarose beads were investigated in this study. The results showed that pore size distribution and shape of pore opening did not affect the emulsification results apparently within a wide range in premix membrane emulsification, not as the result in general emulsification. The contact angle between the water phase and the membrane surface must be large enough to obtain uniform-sized agarose beads in both direct membrane emulsification and premix membrane emulsification. The results also showed that the membrane pore size and thickness affected the size distribution of emulsion. Thicker membrane resulted in more uniform and smaller emulsion when the number of pass through membrane is controlled. There was a linear relationship between the number average diameter of agarose beads and membranes pores size in premix membrane emulsification. Agarose beads with diameters from 3.06 to 9.02 μm were prepared by controlling membranes pore size. The ratio of the number average diameter of agarose beads to membrane pore diameters was found to be 0.486.

Effects of Membrane Parameters on Performance of Vapor Permeation through a Composite Supported Liquid Membrane

Support liquid membranes have been used in air dehumidification due to their inherent high mass transfer rates. In this study, the effects of membrane structural parameters on vapor permeation through a LiCl solution based supported liquid membrane are investigated. To aid in the analysis, a mass transfer model has been proposed for moisture transfer through the membrane, which is composed of a supported liquid layer sandwiched by two hydrophobic protective layers. The model takes into account of the resistance in boundary layers, in the protective hydrophobic layers, and in the supported liquid layer. It is a transient model. It also reflects the distributed nature of moisture permeation through the membrane. The results found that the emission rate exhibits a non‐uniform distribution nature on the membrane surface. The structural parameters of the support and the protective layers, such as thickness, pore diameters, and porosity, have great effects on vapor permeation.

Status of cross-flow membrane emulsification and outlook for industrial application

Cross-flow membrane emulsification has great potential to produce monodisperse emulsions and emulsions with shear sensitive components. However, until now, only low disperse phase fluxes were obtained. A low flux may be a limiting factor for emulsion production on a commercial scale. Therefore, the effects of membrane parameters on the disperse phase flux are estimated. Besides, the effects of these parameters on the droplet size and droplet size distribution are qualitatively described. Wetting properties, pore size and porosity mainly determine the droplet size (distribution). Membrane morphology largely determines the disperse phase flux. As an example, industrial-scale production of culinary cream was chosen to evaluate the required membrane area of different types of membranes: an SPG membrane, an α-Al 2O 3 membrane and a microsieve. Due to the totally different morphologies of these membranes, the fraction of active pores is 1 for a microsieve and is very low for the other membranes. The choice of the optimal membrane did not depend on the production strategy: either to produce large quantities or to produce monodisperse emulsions, the best suitable was a microsieve with an area requirement of around 1 m 2. In general, the total membrane resistance should be low to obtain a large disperse phase flux. In contrast, the membrane resistance should be high to obtain monodisperse emulsions when using membranes with a high porosity.

Phenomenological Theory of Electro‐osmotic Effect and Water Management in Polymer Electrolyte Proton‐Conducting Membranes

Partial dehydration of the proton‐conducting membrane under working conditions is one of the major problems in low‐temperature fuel cell technology. In this paper a model, which accounts for the electro‐osmotically induced drag of water from anode to cathode and the counterflow in a hydraulic pressure gradient is proposed. A balance of these flows determines a gradient of water content across the membrane, which causes a decline of the current‐voltage performance. Phenomenological transport equations coupled with the capillary pressure isotherm are used, involving the conductivity, permeability, and electro‐osmotic drag coefficients dependent on the local water content. The effects of membrane parameters on current‐voltage performance are investigated. A universal feature of the obtained current‐voltage plots is the existence of a critical current at which the potential drop across the membrane increases dramatically due to the dehydration of membrane layers close to the anode. For a membrane with zero residual conductivity in its dry parts, the critical current is a limiting current. Well below the critical current the effect of dehydration is negligible and the current‐voltage plot obeys Ohm's law. The shape of the capillary pressure isotherm determines the nonohmic corrections. A comparison of the results of this study to those of the pertinent diffusion‐type models reveals qualitatively different features, the convection model is found to be closer to experimental observations.

The Effect of Membrane Parameters on the Properties of the Nerve Impulse

The effect of varying membrane capacitance, conductance, and rate constants on the properties of the nerve impulse is considered in terms of the degree of regeneration in the Hodgkin-Huxley model for the squid giant axon. It is shown through computer simulation that reducing regeneration generally increases the duration of the action potential and decreases its amplitude, rate of rise, and conduction velocity. The threshold becomes much less sharp and the amplitude of the response of a patch of membrane grades with stimulus strength. A second stimulus, applied shortly after a first stimulus, considerably perturbs the membrane potential from its original time-course. Under certain conditions, the nerve signal can propagate with a small decrement.