Scaling up of nanophotonics-enabled solar direct-contact membrane desalination system under ambient condition and sun tracking: Challenges, remedies and performance report

Abstract

A direct-contact membrane desalination system is fabricated and tested. A hydrophobic PVDF membrane, coated with carbon black nano-particles, is placed between feed and permeate channels. Localized heating through absorption of solar heat by the nano-particle layer produces water vapour, which gets driven through the porous membrane by the vapour pressure gradient maintained by the temperature differential between the channels. Non-requirement of bulk feed heating enhances the photothermal efficiency of nano-particle enabled systems. It is also observed to have advantages such as low scaling and easy cleaning. The major drawback in scaling up conventional membrane desalination system is gradual loss of temperature gradient with length. Here, it is observed that for significantly longer length, temperature gradient is not reduced to a low value to set a practical limit for the system size. 99.5 % salt removal is achieved while the range of flux is 0.14–0.28 kg/m2hr under solar irradiance of 331–839 W/m2 and ambient temperature condition. Two-axis tracking is observed to produce an augmentation of flux by 23.3 %. Numerous challenges, as faced during experiments, are reported in detail along with the corresponding fixes. Thus, the present study provides a technology roadmap for scaling up a nanophotonics-enabled solar membrane desalination system.