Investigation on a Fresnel Lens Assisted Heater for Seawater Desalination System

One of the most precious resources in the world, nowadays and specially in the future, is fresh water. This resource is not equally distributed around the world; there are places where water is even scarce. However, there is a large amount of seawater on the earth. Seawater can be converted into fresh water, using a desalination method. Several technologies of desalination process have been created applying physics concepts; some of them are more suitable, convenient, economic and non-contaminant for the purpose requirements than others. The use of solar energy has become an easy, suitable and green solution method to obtain heat for seawater desalination. It is possible to concentrate the heat flux from the sunlight into one small focal area by using a Fresnel lens. When the focal area is correctly located to an evaporation chamber, the obtained heat from the sun can significantly elevate the temperature of the chamber, and therefore, evaporate the water while setting the salt aside. This vapor can be condensed to produce fresh water for human consumption. 

This project is about to develop an efficient solar desalination portable technology to obtain drinking water. A Fresnel lens is used to heat the core of a water heater with the purpose to significantly increase the evaporation rate of seawater, to separate the salt. Depending of the size (diameter) and the focal length (distance from the lens to the focal area), the obtained heat varies significantly. Therefore, different sizes of flat and curved Fresnel lens were tested and optimized in this project using COMSOL Multiphysics, with the purpose to compare the results and find the best option. 

The heater system has an internal core to act as a heat supplier for the chamber. The design and size of the core is related with the amount of heat that it can transport and distribute to the chamber, where a uniform distribution of the heat is an important aspect. This project includes the study of different internal designs of the core and their testing in order to find the best option to achieve efficient heat distribution for maximizing fresh water production. At this point, each option of design has been tested and the results compared. On one of the tested designs, the temperature obtained was up to 1000 K on the top of the core receiver. These designs can be used in groups in a large-scale device, for example, or in portable or small-scale desalination system.