An Improved Modelling Approach for the Comprehensive Study of Direct Contact Membrane Distillation

Abstract

Direct Contact Membrane Distillation (DCMD) is a promising and feasible technology for water desalination. Most of the models used to simulate DCMD are one-dimensional and/or use a linear function of vapour pressure which relies on experimentally determined parameters. In this study, the model of DCMD using Nusselt correlations was improved by coupling the continuity, momentum, and energy equations to better capture the downstream alteration of flow field properties. A logarithmic function of vapour pressure, which is independent from experiments, was used. This allowed us to analyse DCMD with different membrane properties. The results of our developed model were in good agreement with the DCMD experimental results, with less than 7% deviation. System performance metrics, including water flux, temperature, and concentration polarisation coefficient and thermal efficiency, were analysed by varying inlet feed and permeate temperature, inlet velocity, inlet feed concentration, channel length. In addition, twenty-two commercial membranes were analysed to obtain a real vision on the influence of membrane characteristics on system performance metrics. The results showed that the feed temperature had the most significant effect on water flux and thermal efficiency. The increased feed temperature enhanced the water flux and thermal efficiency; however, it caused more concentration and temperature polarisation. On the other hand, the increased inlet velocity was found to provide increased water flux and reduced temperature and concertation polarisation as well. It was also found that the membrane properties, especially thickness and porosity, can affect the DCMD performance significantly. A two-fold increase of feed temperature increased the water flux and thermal efficiency, 10-fold and 27%, respectively; however, it caused an increase in temperature and concertation polarisation, at 48% and 34%, respectively. By increasing Reynolds number from 80 to 1600, the water flux, CPC, and TPC enhanced by 2.3-fold, 2%, and 21%, respectively. The increased feed concentration from 0 to 250 [g/L] caused a 26% reduction in water flux. To capture the downstream alteration of flow properties, it was shown that the ratio of inlet value to outlet value of system performance metrics decreased significantly throughout the module. Therefore, improvement over the conventional model is undeniable, as the new model can assist in achieving optimal operation conditions.

Unique Behaviors and Mechanism of Highly Soluble Salt-Induced Wetting in Membrane Distillation

“…Thus, the difference in wetting behaviors at different fluxes could be attributed to the concentration polarization (CP): the gas–liquid interface concentration ( c f,i ) on the feed side is higher than the feed bulk solution concentration ( c f,b ). The CP always enhances with the increase of flux, which can be quantified by the concentration polarization coefficient (CPC). − According to Figure c, the relationship between CPC and the induction concentration of NaCl-induced wetting was opposite under different vapor fluxes.…”

Porosity Effect of Polystyrene Membranes on Desalination Performance: A Combined Experimental and Numerical Heat and Mass Transfer Study in Direct Contact Membrane Distillation

“…The data showed good agreement with the experimental values in the literature. Additionally, Ansari et al [44] tested commercial membranes in DCMD, and their results showed a less than 7% deviation with respect to computational modeling data. The research findings showed a 2.3-fold improvement in water flux when the Reynolds number was increased from 80 to 1600, along with a 23% increase in thermal efficiency when the membrane porosity was increased from 40% to 70%.…”

A Topic Modeling Approach to Discover the Global and Local Subjects in Membrane Distillation Separation Process

“…Membrane distillation (MD), a non-isothermal separation technology, has been proposed for clean water production and treatment of high-salinity waters up to their saturation, thus allowing the management of brines discharged from other water-processing plants and seeking to achieve zero liquid discharge, which represents an important environmental benefit. The driving force in MD is the water vapor pressure difference established at both sides of a hydrophobic porous membrane [4,5]. Among the various advantages of the MD separation process, one can highlight its potential to overcome the osmotic pressure limitation of the aqueous solutions to be treated (i.e., this osmotic pressure limits the treatment of aqueous solutions with other processes such as the pressure-driven membrane separation process reverse osmosis (RO)), low temperature requirements (i.e., MD can be applied at temperatures below the boiling point of the aqueous feed solutions, thus low-temperature solar energy systems and industrial waste heat can be used), and low operating pressures (i.e., MD can be used at atmospheric pressure), among others [6][7][8][9].…”