On one hand, this work presents the reactor design impact on the thermal performance and energy storage during the dehydration of salt hydrate of the thermochemical material; magnesium chloride hexahydrate (MgCl2.6H2O). The dehydration process is performed by flowing hot air through the material. A transient 2D axisymmetric mathematical model for the open thermochemical long-term heat storage reactor by using COMSOL Multiphysics software is presented. Two configurations of the reactor design are considered; cylinder and truncated cone having the same height and volume of seven designs; cylindrical (base design), convergent truncated cones of outlet to inlet area ratio (AR) 1.4, 4 and 5.8 and divergent truncated cones of AR 0.71, 0.25 and 0.17. Results show that the reactor of lower AR has a lower charging time and higher pressure drop and temperature difference. However, the reactor design hasn’t a great impact on the maximum value of water content concentration inside the thermochemical material. The maximum variation of the energy storage of the thermochemical material is about 25.5% and the dehydration time more than three times due to the design reactor changing. Maximum stored energy is achieved for the reactor truncated cone of AR of 1.4 while the minimum desorption time is obtained for the cone of AR 0.17%. A lab-scale for a closed thermochemical heat storage system is carried out in Tokyo tech for the aim of seasonal storage, using magnesium chloride hexahydrate. It based on thermochemical reactions (dehydration and hydration of salt hydrate) and works with the temperature range suitable with solar collector applications. A cross reactor and plate heat exchanger are designed and examined. A ten dehydration and hydration tests are studied for different designs and salt hydrate with alone salt hydrate and mixture under low-temperature range (95 ˚C) for charging. The pressure inside the reactor and temperature at most positions at different times are analyzed for selected cycles. During hydration, the plate's temperature range is from 20˚C to 30˚C which suitable for heating space and demotic water in the winter season. The heat exchanger plates should have not any gaps as the salt hydrate leaked after overhydration. The evaporator position (the connection between the evaporator and the reactor) should develop the vapor distribution through all porous material. The addition of zeolite 13X to magnesium chloride hexahydrate with a mass ration of 1:4 develop the hydration process and increase its efficiency. Though promising results have been obtained, ameliorations need to be made, in order to make the closed thermochemical heat storage system competitive for space heating.

Egypt is facing energy crisis due to the rapid development of every consumption sector. This situation makes the search for efficient application and utilization of renewable energy such as solar energy extremely urgent. By 2010, hydropower and the wind were the main renewable energy, contributed for 12 % of Egypt’s electricity generation. Recently, petroleum and dry natural gas consumption became higher than the production. The flat-plate solar collectors (FPSC) are the most common collectors for domestic water heating systems in many countries today, according to the Renewable Policy Network report (REN21, 2015). Due to the convection and radiation losses, these types of solar thermal collectors have comparatively low efficiency and outlet temperatures. To improve the FPSC performance, a large number of studies on solar thermal collectors used high-thermal-conductivity fluid instead of base fluid water were carried on. The objective of this study is to improve the thermal efficiency of FPSC. To achieve these goals, firstly, this study aims to present an experimental and comparative computational study on the performance of FPSC as the working medium is nanofluid. A stable suspension of Alumina nanofluid with 0.15% weight concentration was prepared. A surfactant TX-100 was used to raise the suspension stability of Al2O3-H2O nanofluid. The experiment has been conducted outdoors in New Borg El-Arab City, Alexandria, Egypt. The volume flow rate is 5.5 l/min. A combined analytical and Computational model was developed by using Microsoft Excel, and ANSYS17 software. The numerical results were in good agreement with the experimental results. The results show that the time constant for water in the FPSC is 3.8 min. An 18% increase in efficiency at the high-temperature difference, while the improvement at the low-temperature difference is 3% when the 0.15%wt Alumina nanofluid is the heat transfer medium. The simulation results show that the outlet temperature decreases with increasing in volumetric flow rate. The best volumetric flow rate is 5.5 l/min at summer season. The pressure drop through FPSC increase with increasing in nanoparticles concentration in the nanofluid. The pressure drop was at the lowest value during the noon time, as the viscosity decreased. At low concentrations, the thermal efficiency increased with increasing volume fraction for both Alumina and Copper oxide nanofluids. The maximum enhancement in efficiency was 2.32% at 1% volume fraction of Alumina nanofluid, but the better performance was brought about 0.5% Copper oxide.