Abstract-This paper presents a real time optimization scheme for a solar powered direct contact membrane distillation (DCMD) water desalination system. The sun and weather conditions vary and are inconsistent throughout the day. Therefore, the solar powered DCMD feed inlet temperature is never constant, which influences the distilled water flux. The problem of DCMD process optimization has not been studied enough. In this work, the response of the process under various feed inlet temperatures is investigated, which demonstrates the need for an optimal controller. To address this issue, we propose a multivariable Newton-based extremum seeking controller which optimizes the inlet feed and permeate mass flow rates as the feed inlet temperature varies. Results are presented and discussed for a realistic temperature profile.
I. INTRODUCTIONMembrane distillation (MD) is a thermal separation technique driven by a vapor pressure difference across a hydrophobic membrane. In this process, a hot feed stream is passed along one side of a porous hydrophobic membrane. Water vapor is then transferred through the membrane to the other cooler (permeate) side. The vapor then condenses at the membrane-permeate interface and clean water is produced.MD has emerged as a sustainable water desalination technique, which offers several advantages over conventional desalination methods. In contrast to reverse osmosis, MD operates at a lower water pressure, hence is less susceptible to scaling and membrane fouling. Moreover, MD water desalination can be integrated with renewable and waste energy sources, since the feed water is not heated up to boiling temperature [1]. All of these features reduce the capital and operational cost of the MD process. Over the years, new MD configurations and membrane material were the main area of research [2]. However, very limited work has been done in terms of process control and optimization [3], [4].As it is well known, the objective is always to operate any process at optimal settings, which reduces the operational costs and guaranties the performance and stability of the system. This is true for the solar-powered MD water desalination, where the objective is to maximize the water production and reduce the energy consumption at the same time through the manipulation of the feed and permeate inlet mass flow rates.In terms of process optimization, the work in [4] developed a neural network model, which was used to calculate optimal