Computaional study of seawater desalination using hollow fiber vacuum membrane distillation

Abstract

Computational fluid dynamics simulations were conducted to study the performance of the vacuum membrane distillation on hollow fiber membrane module to serve the seawater desalination sector. The membrane thickness of the hollow fiber membrane is seen in a wide range in the published studies which brings the research attention to address its effect. Therefore, a study was conducted to test the different membrane thickness of the hollow fiber membrane on the module performance. Two different configurations of a single hollow fiber membrane module were investigated. The study was carried out at different feed temperature 60 °C and 70 °C while the flow rate of the feed solution is fixed where its Reynolds number is set at 500. The study showed how the membrane thickness affects strongly on the module performance. It is seen that the permeate flux dropped correspondingly as the membrane thickness increases. The temperature and concentration polarization were addressed along the membrane surface and its distribution around the fiber membrane at different cross sections of the module. Moreover, the study gives insights to the performance of the two different configurations of the hollow fiber membrane modules. A highly packed hollow fiber membrane module was studied. Three-dimensional hollow fiber module contains of 150 fibers in 60-degree module was designed to represent the real module where the fibers packed in the module reaches 900 fibers. The symmetrical feature applied to the computational module which allows to reduce the expense of the computational study. To frame the module performance, the study was conducted at different feed temperature where it is set at 60 °C, 70 °C and 80 °C while the feed solution flow rate is set at two different Reynolds number 250 and 500. 2 The study shows how packed fibers in the module influences the module performance. It is noticed that the low permeate flux obtained out of the module is due to the packed fibers which results in low feed flow rate. The different feed temperatures affect the obtained permeate flux and it is found that the low permeate flux obtained at lowest feed temperature. The highly temperature and concentration polarization created along the membrane surface found at the high permeate flux produced. The module length influence on the hollow fiber membrane module was studied. The two different module length was designed. The module lengths were set at 50 mm and 100 mm. The module contains of 60 fibers where the feed solution flows in the shell. The study shows the module length influence on the module performance. The permeate flux produced in the module was found decreased as the module length increases. The behavior of the temperature and concentration polarization corresponding to the permeate flux and it is found their worst scenario at the longest module.