A Novel Zero-Discharge Desalination System with Two state-of-the-art Solar Collectors for Fresh Water Production and Brine Management Powered by Solar Energy

Author(s): Hassanzadeh Naeini, Ali | Advisor(s): Winston, Roland; Palko, James | Abstract: Drinking Water plays an important role in human society and its consumption is increasing significantly due to growth in population and living standards. More than 97% of the water on earth is saline and undrinkable. Desalination is an engineering solution to produce drinking water from saline water. Although desalination is a prac- tical solution that could solve the water scarcity challenge around world, there are two major challenges associated with desalination: energy-intensity and brine disposal. Desalination is an energy-intensive process that requires large amounts of electricity and/or heat. Therefore, desalination plants prefer to use cheap energy sources mostly powered by fossil fuels. However, solving the water scarcity challenge should not ex- acerbate global warming, which will have catastrophic effects on our planet. Also, desalination produces a concentrated brine which must be discharged back to the en- vironment. Brine disposal from inland desalination is very problematic. Brine is also often discharged to the ocean, which can threaten the health of marine ecosystems. In this thesis, I present research on two solar collector systems that can be used as an energy source to drive desalination, and one desalination system that can reduce brine discharge to the environment. The first system is a novel medium-temperature solar collector with pentagon absorber called the External Compounds Parabolic Concentrated (XCPC). The collector, with 6 evacuated tubes, CPC reflector and manifold, is designed in SolidWorks. Then the collector is simulated using the finite element method implemented in COMSOL Multiphysics with coupled optical-thermal multiphysics to predict optical and thermal efficiency of the system. The proposed medium-temperature collector is tested with a selective-coated pentagon absorber un- der real-world conditions at the University of California, Merced. The experimental and numerical results show close similarity; the optical efficiency of 64% and thermal efficiency of 50% at working temperature of 200 ◦C are achieved both numerically and experimentally. Secondly, a low-cost concentrated hybrid Photovoltaic-Thermal (PV/T) collector is designed, simulated, and experimentally tested. The proposed PV/T collector simultaneously generates both electricity and thermal energy for low temperature application (60-90 ◦C) such as residential and/or commercial hot wa- ter and small-scale desalination. The collector itself consists of a glass tube with a reflective coating applied on the bottom half which directs incoming rays to strings of solar cells applied over a flat minichannel absorber. Performance is simulated us- ing COMSOL Multiphysics to guide the collector design. Afterwards, multiple tubes are manufactured and tested in both direct-flow minichannel and heat pipe absorber configurations. The assembled PVT collector demonstrated a thermal, electrical and combined efficiency of 60% and 10-15% , 70-75%. The third system presented uses a novel zero liquid discharge desalination approach called Immiscible Liquid Medi- ated Humidification Dehumidification (ILM-HDH). This system introduces a second liquid, mineral oil, to provide heat for evaporation to separate the salt and contam- ination from fresh water in a feedwater stream. ILM-HDH reuses the condensation energy of water which makes it potentially 3-4 times more efficient than state-of-art evaporators while still achieving maximum water recovery. In addition, ILM-HDH address the issue of corrosion in thermal desalination systems since it uses mineral oil instead of saline water as the Heat transfer Fluid(HTF). This feature also makes ILM-HDH highly compatible with the two solar collectors proposed in this study, since the HTF can be directly pumped into the solar collectors with no corrosion issues or need for a heat exchanger.