الفهرس 
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Abstract
By the end of this work, we obtained the following conclusions:-
Photonic crystals are a suitable candidate for thermal water desalination by using the electromagnetic waves from the sun as the source of desalination energy.
Firstly, we have successfully designed a water desalination device based on photonic crystals. By using the design of the porous pyramids, we demonstrate Titanium nitrate (TiN) coated with titanium dioxide (TiO2) structure with the absorption of the solar energy about 95% Enable effective solar desalination. The present porous pyramids structure with inexpensive materials (TiN) and accessible fabrication procedures could offer a portable solution for water desalination based on solar energy. In addition, the purposed structure can be employed in many applications, such as photovoltaic devices and photocatalysis or any other devices based on light trapping. In the numerical results, we have used the fundamentals of the finite-element method [FEM] by using Comsol multiphysics.
Then, we illustrate the two- dimensional photonic band gap structure as a salinity sensor to measure the salinity level for the seawater with the enhancement of sensitivity. Our modeling and simulation procedure depends on the finite element method (FEM) by the COMSOL multiphysics program. We design an infinite crystal made of holes drilled inside a silicon matrix with an interpore distance (center to center) a all cylinders of radius r_1are filled with air except the middle one of different radius r_2 of the structure which contains the analyte fluid (Saline water) to be probed. Thus, the refractive index of the saline water is varies from 1.3326 to1.3505 as a function of the change in salinity level from 0 to100% at room temperature. We found that the high sensitivity is achieved at r_1= 0.25 a, r_2= 0.3 a and a= 100 nm. As (T_(n=1.35)- T_(n=1.333) )=0.4547 which is comparatively higher than other proposed sensors. The present design proved that its ability to determine the refractive index of the saline water which corresponding to the salinity level for applying the desalination process. These results strongly highlighted the suggested device properties in the field of photosensitive applications.
Although, we can found that a change in the surface morphology could affect strongly on the sensitivity, we have two cases corresponding to the last results; firstly, change the surface morphology in one-dimensional centered defect PCs are caused the decrease in sensitivity of the structure. Secondly, change the morphology (Textured and Sawtooth) in the case of Tamm resonance with a defect is caused an increase in the sensitivity of the considered structure by a remarkable ratio. Here, we noticed that the sensitivity changed from 559.7 nm/RIU (ordinary Tamm resonance) to 612.3 nm/RIU (Sawtooth Tamm resonance) at the thickness of saline water equal to 6000 nm. Thus, change the morphology of the layer surface of PCs is a promising point to research owing to its ability to photon tapping.
Finally, we try to enhance the electromagnetic heating in the thermal desalination technology to save the energy consumed in the desalination technologies. Here we success to design a two dimensional photonic crystals solar umbrella. The designed 2D- PCs solar umbrella from titanium nitrate (TiN) coated with titanium dioxide (TiO2), the thickness of the layers as d_1 (TiN)=10 μm,d_2 (TiO_2 )=5 μm and diameter of pores equal to 1 mm and the lattice parameter (a) equal to 2mm, achieve the following conditions for the desalination process Trapping almost of the incident electromagnetic wave with absorbance reached to about 90%, and reduce the power dissipation.
Convert the small wavelengths (ulti violet and visible light) to the longer wavelengths (infra-red radiation)
Localize the thermal energy close to the water surface to increase the evaporation rate.
increase the surface temperature up to 88 °C after one hour of the incident electromagnetic waves with the solar heat flux = 680 W/m2.
Also the two dimensional photonic crystals with hexagonal unit cell from TiN coated with TiO2, wherein, the thickness of TiO2 equal 50 nm, D= 50 nm, and radius equal 200 nm, at thickness of TiN equal to 1450 nm have an excellent temperature yiled as the water begain to evaporate after 20 minites from the begainaing of illumination.
Thermal desalination by using photonic umbrella has addressed the efficiency shortcomings of conventional desalination techniques, in what follow we showed the most effected shortcomings for RO, MSF and MED technologies ;
For RO technology, it required high pressure pumps which increase the operational cost.
For MSF technology, the plant requires both electrical and thermal energy in its operation. Thermal energy is employed to generate vacuum in the containers using medium-pressure steam in the ejectors; it is also employed as an external heating source, further heating the hot brine. Owing to increased energy consumption and fresh water costs, MSF appears to be less convenient than RO; nonetheless, due to large-scale production, it remains a very competitive technology. Scales and deposits are formed during flashing, mainly at the flash chamber entrances and in the heat exchanger tubes; as a result, periodic cleaning is required, resulting in greater operational expenses.
MED technology, the plant for example is highly complicated due to its various components, making it hard to achieve high efficiency. Furthermore, not all heat sources are suitable for heating the first stage due to the scaling difficulty at high temperatures. However, the most significant disadvantage of MED technology is the physical limitation imposed by the first and last temperatures in the plant sequence. Because of scalability issues, the input temperature cannot exceed70 °C.
These last shortcomings is enhanced by photonic crystals solar umbrella, because of thermal desalination by photonic umbrella is a cheap method and energy saver and easy to fabricate. Thus, from the last results and comparison with the traditional desalination technologies, we found that using photonic crystals umbrella in water desalination technology have a good yields from fresh water in addition to the time from the illumination until the water begin to evaporate by photonic crystal umbrella it take only 20 minutes Therefore, the designed 2D- PCs solar umbrella is a promising candidate in the desalination technology.