Design of Evaporator for Salt Water Desalination System

The ability to obtain portable drinking water is a necessity for all nations around the world and with the decline of natural fresh water sources alternative means of obtaining portable drinking water must be pursued. This project seeks to find an environmentally green method of obtaining portable water through the process of desalination, which uses a solar still system that can efficiently produce large-scale fresh water by using evaporation chambers to vaporize seawater. By using a Fresnel lens, a solar concentrating technology, can be utilized to achieve the high temperature and desalination rates for the evaporation chamber.

This work aims to design an innovative configuration of evaporator to obtain high desalination rates. The primary design of the evaporator consists of two zones, the core and the chamber. The cylindrical core is centralized within the evaporator and consists of a copper top plate in which a Fresnel lens will focus light and act as the heat source for the design. Inside this core also consists of copper piping, connecting to the heat source, which will allow for rapid increased heat exchange to lower levels of the core. The ranges of temperatures necessary for the core to function properly are between 400 K and not to exceed 1000 K. The chamber envelops the core and consists of multiple layers of fins with alternating flow direction in which salt water can drip onto and flow across. These fins are closely connected to the core in order to efficiently be heated following the start of the heating process. The configuration and arrangement of fins will be studied and optimized to significantly increase heat transfer surface area for the salt water during heating allowing for maximum evaporation rate while still allowing steam to rise and exit to the heat exchanger and remaining salt water to fall down to the bottom of the chamber. Additional considerations to be added in the future include a method for salt collection and cleaning of salt remains as well as a method to recycle any excess salt water following the end of the heating cycle and have it reused the following day. The performance of the proposed evaporation chamber is modeled and studied through CFD, heat and mass transfer simulations in COMSOL Multiphysics. With the optimized configuration, a small-scale prototype demonstration can expect results to provide a gallon of fresh water for each hour of operation throughout the daylight period.