الفهرس 
Chapter ?: IntroductionOnly 14 pages are availabe for public view
 |  | from | 128 |  |  |
| | | from | 128 | | |
Abstract
Being a promising solar energy-based worldwide application, the PV cells have been extensively used and recently built in Egypt to generate electricity. The increase of its surface temperature significantly decreases its efficiency; hence many cooling techniques have been proposed and studied. In order to achieve double benefits, the heat carried out from the cells can be utilized as thermal energy to motivate another application.
The present study focuses on cooling the PV cells using a phase change material PCM enhanced by synthesizing SiC and Ag-based nano-PCM composites. Then the stored thermal energy in the composite is convected by flow water to pass through an adsorbent bed made of RD silica gel enhanced by synthesizing MOF, Mil-100 (Fe). The water vapor is then carried out through regeneration to be condensed as a water harvesting process.
The procedure of synthesizing nanomaterial-based composites, the required characterization of the novel composites, in addition to the effect of the nanomaterial type and its weight fraction on the performance are presented and analyzed. The Field Emission Scanning Electron Microscope (FE-SEM) has been utilized to display the scattering of nanoparticles in the nanocomposites being investigated. Besides, the thermal properties (e.g., melting point, latent heat, and specific heat capacity) of the nanocomposites, as well as parent materials, have been estimated based on using Differential Scanning Calorimeter (DSC-60A) developed by Shimadzu Corporation Ltd, Japan. Moreover, a Laser flash apparatus, namely NETZSCH LFA 457 is used to measure the thermal diffusivity of the studied samples and consequently estimate the thermal conductivity.
The other benefit from the thermal energy rejected by the PV cell is to be used for atmospheric water harvesting, (AWH). A Micro Flash system is utilized to determine the thermal conductivity of the synthesized nanocomposites. Regarding the AWH system, an equilibrium water vapor adsorption isotherm of RD silica gel, MIL-100(Fe), and synthesized composites of which have been measured gravimetrically using magnetic suspension adsorption measurement unit (Rubotherm: MSB-VG-S2), which is supplied by MicrotracBEL, Japan. Finally, the influence of applying the novel adsorbents on the AWH system has been estimated theoretically.
The results showed an enhancement of the thermal characteristics of the synthesized composites compared to the parent materials as the weight fraction of nanoparticles increases. This enhancement whether for nanocomposite used for cooling PV cells or that is used for AWH system.
Quantitatively, the results showed a thermal conductivity enhancement of nearly 58.2 ℅ for paraffin wax in case of adding 15 wt% SiC nanoparticles, whereas the increase is only 31.05% at the same percentage for Ag composite. Previous studies observed that adding 1wt% SiC contained composite showed 4.2% improvement in the thermal conductivity over parent paraffin wax; whereas, in this study, the composite having the same compositions shows approximately 14.11% improvement. The modification in the preparation procedure of nano-PCM shows a significant upgrade in the characteristics of synthesized composites. Considering the AWH system, the majority of pores in the composites are of sizes 1-2 nm. Furthermore, the enhancement of thermal conductivity depends on the increment of the weight fraction of MIL 100(Fe) in the composites. The composite C4, which has the highest MIL- 100 (Fe) concentration(69%), has the highest increment of 46 % compared to RD silica gel. In addition, the peak of the net uptake was registered for the C4 composite by about double the uptake in the case of RD silica gel because the efficiency of the system was enhanced by almost 1.8 times that of the silica gel-based AWH system.