In this work, we used a recycled low-density polyethylene (LDPE) in order to prepare flat sheet membranes with different polymer concentrations (5 and 10%). The used chemical method for the membrane's preparation is the phase inversion. After obtaining the membranes, we characterized them by atomic force microscopy (AFM) and scanning electron microscopy (SEM) to study their structure and surface characteristics. Based on the SEM images, our membranes have a dense skin layer. In addition, we observed a decrease in the porosity with the increase in the polymer concentration. When the polymer concentration increases from 5 to 10% the porosity decreases from 35.54% to 20.28%. Furthermore, we remarked significant changes in the contact angle and the surface roughness with the increase of the polymer concentration. The roughness increases from 363 to 577 nm for the same evolution of the polymer concentration. These high values of roughness imply obtaining values of contact angles greater than 90° and hydrophobic membranes, which is beneficial for the membrane distillation. Furthermore, the use of our membranes in vacuum membrane distillation (VMD) experiments showed a permeate flux up to 1.503 kg/hm2; for the membrane with 35.54% of porosity and 5% of polymer concentration.
The aim of this work was to evaluate the effect of solar irradiation on the permeate flow rate produced by vacuum membrane distillation installation. The used membrane module, in our case, is composed of two hollow fibers membrane wound in helically coiled shape. These fibers were placed in parabolic through concentrator absorber. The relatively hot solution (brine) in the absorber was used as a feed for our fibers. After the establishment of the model governing equations, a resolution was done with the finite element method. The sensitivity of the permeate flow rate to the solar irradiation and feed salt concentration were all investigated. According to the results, when the solar irradiation growth from 200 to 800 W/m², the permeate flow rate roses from 0.1377 to 0.3633 kg/h. In the case of a solar irradiation of 800 W/m², a marginal effect of the feed salt concentration on the permeate flow rate was remarked. For the evolution of the feed salt concentration between 10 and 300 g/l, a drop by 12% of the permeate flux was reported.
A comprehensive comparison was performed between helical and straight hollow fibers. Applications of helical hollow fibers membrane were studied. The use of helical fibers minimizes fouling and concentration polarization. Helical configuration promotes turbulence.The production of straight and helical hollow fibers plays an important role in developing hollow fiber membrane technology that encompasses a broad range of designs. During the last two decades, scientific studies devoted to straight hollow fibers were more abundant than those focused on helical fibers. Several major applications considering side-by-side testing of these two geometries are discussed in this review. For membrane extraction, desalination, and membrane contactor processes, it is observed that permeability rates are 10%-400 % higher for helical fibers compared to straight fibers. This outcome is justified by the presence of Dean-vortices-induced flow turbulences inherent to the geometry of helical membranes. These conditions give rise to an uptake of mass and heat transfer coefficients and a reduction of temperature and concentration polarization phenomena. Aside from enhanced flow properties, helical hollow fiber bundles tend to be more robust by design, thus exhibiting better resiliency over long service operations than straight bundles. One persistent shortcoming of the helical fibers seems to be an increase in pressure drop. However, this does not always translate into a higher energy consumptioni.e., versus straight bundles. Given the performance advantage, product robustness, and adaptiveness to a broad range of applications, the adoption of helical hollow fiber technology deserves growing support from the membrane community in academic and industrial settings.
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