A Dynamic Flash Evaporation and Vapor Separation System for Seawater Desalination

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

There is a worldwide scarcity of potable water. Desalination of abundantly available seawater especially in coastal areas offers a viable option for conversion of seawater into fresh water. A number of schemes for desalination of water in the past have been developed. However, these schemes are either energy intensive or capital intensive. As a result, the cost of production of potable water is relatively high. The project will develop, analyze, and optimize a novel high-throughput desalination technique that is compact, modular, and relatively inexpensive to build and operate. In this technique solar-heated sea water from a solar pond flows through a set of injector passages, where the water becomes superheated leading to formation of vapor bubbles. Formation of bubbles accelerates the pressure drop allowing more thermal energy to be converted into vapor. The vapor-liquid mixture exits the injector passages into a larger tube tangentially. Centrifugal force generated as a result of swirl causes liquid to move outward while vapor forms a core in the middle of the separator tube. Vapor leaves the vapor core via a retrieval tube to a condenser to create potable water. Separated liquid is pumped back to the solar pond to be reheated. Having demonstrated the viability of the concept in the laboratory, the team is proposing to expand the experimental work to demonstrate the applicability of the concept over a broad range of operational parameters. Data for thermal conversion efficiency, vapor separation effectiveness and temperature and pressure profiles in the injector passages and separator tube are to be obtained. The data will be used to support analytical and numerical modeling of the process. Void fraction in the separator tube is to be measured and stability of vapor core in the separator tube will be investigated under a variety of mass and momentum flux conditions. This is an area unexplored before and represents a significant intellectual challenge with respect to meaningful experiments and analytical/numerical modeling. Gained knowledge will be used to optimize thermal conversion efficiency and vapor separation effectiveness under a range of flow conditions and temperatures of water exiting the solar pond. Lastly experimental effort will be used to develop an operational map that could be of great value for practical implementation of this novel concept at atmospheric and sub-atmospheric pressures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.